nym_http_api_client/

lib.rs

// Copyright 2023 - Nym Technologies SA <contact@nymtech.net>
// SPDX-License-Identifier: Apache-2.0

#![allow(deprecated)]
// silences clippy warning: use of deprecated tuple variant `HttpClientError::GenericRequestFailure`: use another more strongly typed variant - this variant is only left for compatibility reasons - TODO

//! Nym HTTP API Client
//!
//! Centralizes and implements the core API client functionality. This crate provides custom,
//! configurable middleware for a re-usable HTTP client that takes advantage of connection pooling
//! and other benefits provided by the [`reqwest`] `Client`.
//!
//! ## Making GET requests
//!
//! Create an HTTP `Client` and use it to make a GET request.
//!
//! ```rust
//! # use url::Url;
//! # use nym_http_api_client::{ApiClient, NO_PARAMS, HttpClientError};
//!
//! # type Err = HttpClientError;
//! # async fn run() -> Result<(), Err> {
//! let url: Url = "https://nymvpn.com".parse()?;
//! let client = nym_http_api_client::Client::new(url, None);
//!
//! // Send a get request to the `/v1/status` path with no query parameters.
//! let resp = client.send_get_request(&["v1", "status"], NO_PARAMS).await?;
//! let body = resp.text().await?;
//!
//! println!("body = {body:?}");
//! # Ok(())
//! # }
//! ```
//!
//! ## JSON
//!
//! There are also json helper methods that assist in executing requests that send or receive json.
//! It can take any value that can be serialized into JSON.
//!
//! ```rust
//! # use std::collections::HashMap;
//! # use std::time::Duration;
//! use nym_http_api_client::{ApiClient, HttpClientError, NO_PARAMS};
//!
//! # use serde::{Serialize, Deserialize};
//! #[derive(Clone, Copy, Debug, Serialize, Deserialize)]
//! pub struct ApiHealthResponse {
//!     pub status: ApiStatus,
//!     pub uptime: u64,
//! }
//!
//! #[derive(Clone, Copy, Debug, Serialize, Deserialize)]
//! pub enum ApiStatus {
//!     Up,
//! }
//!
//! # type Err = HttpClientError;
//! # async fn run() -> Result<(), Err> {
//! // This will POST a body of `{"lang":"rust","body":"json"}`
//! let mut map = HashMap::new();
//! map.insert("lang", "rust");
//! map.insert("body", "json");
//!
//! // Create a client using the ClientBuilder and set a custom timeout.
//! let client = nym_http_api_client::Client::builder("https://nymvpn.com")?
//!     .with_timeout(Duration::from_secs(10))
//!     .build()?;
//!
//! // Send a POST request with our json `map` as the body and attempt to parse the body
//! // of the response as an ApiHealthResponse from json.
//! let res: ApiHealthResponse = client.post_json(&["v1", "status"], NO_PARAMS, &map)
//!     .await?;
//! # Ok(())
//! # }
//! ```
//!
//! ## Creating an ApiClient Wrapper
//!
//! An example API implementation that relies on this crate for managing the HTTP client.
//!
//! ```rust
//! # use async_trait::async_trait;
//! use nym_http_api_client::{ApiClient, HttpClientError, NO_PARAMS};
//!
//! mod routes {
//!     pub const API_VERSION: &str = "v1";
//!     pub const API_STATUS_ROUTES: &str = "api-status";
//!     pub const HEALTH: &str = "health";
//! }
//!
//! mod responses {
//!     # use serde::{Serialize, Deserialize};
//!     #[derive(Clone, Copy, Debug, Serialize, Deserialize)]
//!     pub struct ApiHealthResponse {
//!         pub status: ApiStatus,
//!         pub uptime: u64,
//!     }
//!
//!     #[derive(Clone, Copy, Debug, Serialize, Deserialize)]
//!     pub enum ApiStatus {
//!         Up,
//!     }
//! }
//!
//! mod error {
//!     # use serde::{Serialize, Deserialize};
//!     # use core::fmt::{Display, Formatter, Result as FmtResult};
//!     #[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq)]
//!     pub struct RequestError {
//!         message: String,
//!     }
//!
//!     impl Display for RequestError {
//!         fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
//!             Display::fmt(&self.message, f)
//!         }
//!     }
//! }
//!
//! pub type SpecificAPIError = HttpClientError;
//!
//! #[cfg_attr(target_arch = "wasm32", async_trait(?Send))]
//! #[cfg_attr(not(target_arch = "wasm32"), async_trait)]
//! pub trait SpecificApi: ApiClient {
//!     async fn health(&self) -> Result<responses::ApiHealthResponse, SpecificAPIError> {
//!         self.get_json(
//!             &[
//!                 routes::API_VERSION,
//!                 routes::API_STATUS_ROUTES,
//!                 routes::HEALTH,
//!             ],
//!             NO_PARAMS,
//!         )
//!         .await
//!     }
//! }
//!
//! impl<T: ApiClient> SpecificApi for T {}
//! ```
#![warn(missing_docs)]

pub use inventory;
pub use reqwest::{self, ClientBuilder as ReqwestClientBuilder, StatusCode};
use std::error::Error;
use std::sync::Mutex;
#[cfg(not(target_arch = "wasm32"))]
use std::time::Instant;
#[cfg(target_arch = "wasm32")]
use wasmtimer::std::Instant;

pub mod registry;

// re-exported (not merely `use`d) because it appears as a bound on the public
// `ApiClientCore::create_request`, so external crates cannot implement that public trait
// without being able to name it (e.g. to provide a test double).
pub use crate::path::RequestPath;
use async_trait::async_trait;
use bytes::Bytes;
use cfg_if::cfg_if;
use http::{
    HeaderMap,
    header::{ACCEPT, CONTENT_TYPE, RETRY_AFTER, USER_AGENT},
};
use itertools::Itertools;
use mime::Mime;
use reqwest::{RequestBuilder, Response, header::HeaderValue};
use serde::{Deserialize, Serialize, de::DeserializeOwned};
#[cfg(not(target_arch = "wasm32"))]
use std::io::ErrorKind;
use std::{
    fmt::Display,
    sync::atomic::{AtomicUsize, Ordering},
    time::Duration,
};
use thiserror::Error;
use tracing::{debug, instrument, warn};

use std::sync::{Arc, LazyLock};

#[cfg(feature = "tunneling")]
mod fronted;
#[cfg(feature = "tunneling")]
pub use fronted::{FrontPolicy, FrontingConfig};
#[cfg(feature = "tunneling")]
mod rotation;
#[cfg(feature = "tunneling")]
use rotation::RotationManager;
mod host_header;
mod url;
pub use url::{IntoUrl, Url};
mod user_agent;
pub use user_agent::UserAgent;

#[cfg(not(target_arch = "wasm32"))]
pub mod dns;
mod path;
#[cfg(not(target_arch = "wasm32"))]
pub mod tls;

#[cfg(not(target_arch = "wasm32"))]
pub use dns::{HickoryDnsResolver, ResolveError};

// helper for generating user agent based on binary information
#[cfg(not(target_arch = "wasm32"))]
use crate::registry::default_builder;
#[doc(hidden)]
pub use nym_bin_common::bin_info;
#[cfg(not(target_arch = "wasm32"))]
use nym_http_api_client_macro::client_defaults;

/// Default HTTP request connection timeout.
///
/// The timeout is relatively high as we are often making requests over the mixnet, where latency is
/// high and chatty protocols take a while to complete.
pub const DEFAULT_TIMEOUT: Duration = Duration::from_secs(30);

const NYM_OUTER_SNI_HEADER: &str = "NYM-ORIGINAL-OUTER-SNI";

#[cfg(not(target_arch = "wasm32"))]
client_defaults!(
    priority = -100;
    gzip = true,
    deflate = true,
    brotli = true,
    zstd = true,
    timeout = DEFAULT_TIMEOUT,
    user_agent = format!("nym-http-api-client/{}", env!("CARGO_PKG_VERSION"))
);

static SHARED_CLIENT: LazyLock<reqwest::Client> = LazyLock::new(|| {
    tracing::info!("Initializing shared HTTP client");
    cfg_if! {
        if #[cfg(target_arch = "wasm32")] {
            reqwest::ClientBuilder::new().build()
                .expect("failed to initialize shared http client")
        } else {
            let mut builder = default_builder();

            builder = builder.dns_resolver(Arc::new(HickoryDnsResolver::new()));

            builder
                .build()
                .expect("failed to initialize shared http client")
        }
    }
});

pub(crate) static SHARED_NETWORK_RECONFIGURATION: LazyLock<Arc<Mutex<Option<Instant>>>> =
    LazyLock::new(|| Arc::new(Mutex::new(None)));

/// Indicate to the shared marker that a network reconfiguration happened.
pub fn network_reconfigured() {
    *SHARED_NETWORK_RECONFIGURATION.lock().unwrap() = Some(Instant::now());
}

/// Collection of URL Path Segments
pub type PathSegments<'a> = &'a [&'a str];
/// Collection of HTTP Request Parameters
pub type Params<'a, K, V> = &'a [(K, V)];

/// Empty collection of HTTP Request Parameters.
pub const NO_PARAMS: Params<'_, &'_ str, &'_ str> = &[];

/// Serialization format for API requests and responses
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SerializationFormat {
    /// Use JSON serialization (default, always works)
    Json,
    /// Use bincode serialization (must be explicitly opted into)
    Bincode,
    /// Use YAML serialization
    Yaml,
    /// Use Text serialization
    Text,
}

impl Display for SerializationFormat {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            SerializationFormat::Json => write!(f, "json"),
            SerializationFormat::Bincode => write!(f, "bincode"),
            SerializationFormat::Yaml => write!(f, "yaml"),
            SerializationFormat::Text => write!(f, "text"),
        }
    }
}

impl SerializationFormat {
    #[allow(missing_docs)]
    pub fn content_type(&self) -> String {
        match self {
            SerializationFormat::Json => "application/json".to_string(),
            SerializationFormat::Bincode => "application/bincode".to_string(),
            SerializationFormat::Yaml => "application/yaml".to_string(),
            SerializationFormat::Text => "text/plain".to_string(),
        }
    }
}

#[allow(missing_docs)]
#[derive(Debug)]
pub struct ReqwestErrorWrapper(reqwest::Error);

impl Display for ReqwestErrorWrapper {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        cfg_if::cfg_if! {
            if #[cfg(not(target_arch = "wasm32"))] {
                if self.0.is_connect() {
                    write!(f, "failed to connect: ")?;
                }
            }
        }

        if self.0.is_timeout() {
            write!(f, "timed out: ")?;
        }
        if self.0.is_redirect()
            && let Some(final_stop) = self.0.url()
        {
            write!(f, "redirect loop at {final_stop}: ")?;
        }

        self.0.fmt(f)?;
        if let Some(status_code) = self.0.status() {
            write!(f, " status: {status_code}")?;
        } else {
            write!(f, " unknown status code")?;
        }

        if let Some(source) = self.0.source() {
            write!(f, " source: {source:?}")?;
        } else {
            write!(f, " unknown lower-level error source")?;
        }

        Ok(())
    }
}

impl std::error::Error for ReqwestErrorWrapper {}

/// The Errors that may occur when creating or using an HTTP client.
#[derive(Debug, Error)]
#[allow(missing_docs)]
pub enum HttpClientError {
    #[error("did not provide any valid client URLs")]
    NoUrlsProvided,

    #[error("failed to construct inner reqwest client: {source}")]
    ReqwestBuildError {
        #[source]
        source: reqwest::Error,
    },

    #[deprecated(
        note = "use another more strongly typed variant - this variant is only left for compatibility reasons"
    )]
    #[error("request failed with error message: {0}")]
    GenericRequestFailure(String),

    #[deprecated(
        note = "use another more strongly typed variant - this variant is only left for compatibility reasons"
    )]
    #[error("there was an issue with the REST request: {source}")]
    ReqwestClientError {
        #[from]
        source: reqwest::Error,
    },

    #[error("failed to parse {raw} as a valid URL: {source}")]
    MalformedUrl {
        raw: String,
        #[source]
        source: reqwest::Error,
    },

    #[error("failed to parse header value: {source}")]
    InvalidHeaderValue {
        #[source]
        source: http::Error,
    },

    #[error("failed to send request for {url}: {source}")]
    RequestSendFailure {
        url: Box<reqwest::Url>,
        #[source]
        source: ReqwestErrorWrapper,
    },

    #[error("failed to read response body from {url}: {source}")]
    ResponseReadFailure {
        url: Box<reqwest::Url>,
        headers: Box<HeaderMap>,
        status: StatusCode,
        #[source]
        source: ReqwestErrorWrapper,
    },

    #[error("failed to deserialize received response: {source}")]
    ResponseDeserialisationFailure { source: serde_json::Error },

    #[error("provided url is malformed: {source}")]
    UrlParseFailure {
        #[from]
        source: url::ParseError,
    },

    #[error("the requested resource could not be found at {url}")]
    NotFound { url: Box<reqwest::Url> },

    #[error("attempted to use domain fronting and clone a request containing stream data")]
    AttemptedToCloneStreamRequest,

    // #[error("request failed with error message: {0}")]
    // GenericRequestFailure(String),
    //
    #[error(
        "the request for {url} failed with status '{status}'. no additional error message provided. response headers: {headers:?}"
    )]
    RequestFailure {
        url: Box<reqwest::Url>,
        status: StatusCode,
        headers: Box<HeaderMap>,
    },

    #[error(
        "the returned response from {url} was empty. status: '{status}'. response headers: {headers:?}"
    )]
    EmptyResponse {
        url: Box<reqwest::Url>,
        status: StatusCode,
        headers: Box<HeaderMap>,
    },

    #[error(
        "failed to resolve request for {url}. status: '{status}'. response headers: {headers:?}. additional error message: {error}"
    )]
    EndpointFailure {
        url: Box<reqwest::Url>,
        status: StatusCode,
        headers: Box<HeaderMap>,
        error: String,
    },

    #[error("failed to decode response body: {message} from {content}")]
    ResponseDecodeFailure { message: String, content: String },

    #[error("failed to resolve request to {url} due to data inconsistency: {details}")]
    InternalResponseInconsistency { url: ::url::Url, details: String },

    #[cfg(not(target_arch = "wasm32"))]
    #[error("encountered dns failure: {inner}")]
    DnsLookupFailure {
        #[from]
        inner: ResolveError,
    },

    #[error("Failed to encode bincode: {0}")]
    Bincode(#[from] bincode::Error),

    #[error("Failed to json: {0}")]
    Json(#[from] serde_json::Error),

    #[error("Failed to yaml: {0}")]
    Yaml(#[from] serde_yaml::Error),

    #[error("Failed to plain: {0}")]
    Plain(#[from] serde_plain::Error),

    #[cfg(target_arch = "wasm32")]
    #[error("the request has timed out")]
    RequestTimeout,
}

#[allow(missing_docs)]
#[allow(deprecated)]
impl HttpClientError {
    /// Returns true if the error is a timeout.
    pub fn is_timeout(&self) -> bool {
        match self {
            HttpClientError::ReqwestClientError { source } => source.is_timeout(),
            HttpClientError::RequestSendFailure { source, .. } => source.0.is_timeout(),
            HttpClientError::ResponseReadFailure { source, .. } => source.0.is_timeout(),
            #[cfg(not(target_arch = "wasm32"))]
            HttpClientError::DnsLookupFailure { inner } => inner.is_timeout(),
            #[cfg(target_arch = "wasm32")]
            HttpClientError::RequestTimeout => true,
            _ => false,
        }
    }

    /// Returns the HTTP status code if available.
    pub fn status_code(&self) -> Option<StatusCode> {
        match self {
            HttpClientError::ResponseReadFailure { status, .. } => Some(*status),
            HttpClientError::RequestFailure { status, .. } => Some(*status),
            HttpClientError::EmptyResponse { status, .. } => Some(*status),
            HttpClientError::EndpointFailure { status, .. } => Some(*status),
            _ => None,
        }
    }

    pub fn reqwest_client_build_error(source: reqwest::Error) -> Self {
        HttpClientError::ReqwestBuildError { source }
    }

    pub fn request_send_error(url: reqwest::Url, source: reqwest::Error) -> Self {
        HttpClientError::RequestSendFailure {
            url: Box::new(url),
            source: ReqwestErrorWrapper(source),
        }
    }

    pub fn is_data_inconsistency(&self) -> bool {
        matches!(self, HttpClientError::InternalResponseInconsistency { .. })
    }
}

/// Core functionality required for types acting as API clients.
///
/// This trait defines the "skinny waist" of behaviors that are required by an API client. More
/// likely downstream libraries should use functions from the [`ApiClient`] interface which provide
/// a more ergonomic set of functionalities.
#[cfg_attr(target_arch = "wasm32", async_trait(?Send))]
#[cfg_attr(not(target_arch = "wasm32"), async_trait)]
pub trait ApiClientCore {
    /// Create an HTTP request using the host configured in this client.
    fn create_request<P, B, K, V>(
        &self,
        method: reqwest::Method,
        path: P,
        params: Params<'_, K, V>,
        body: Option<&B>,
    ) -> Result<RequestBuilder, HttpClientError>
    where
        P: RequestPath,
        B: Serialize + ?Sized,
        K: AsRef<str>,
        V: AsRef<str>;

    /// Create an HTTP request using the host configured in this client and an API endpoint (i.e.
    /// `"/api/v1/mixnodes?since=12345"`). If the provided endpoint fails to parse as path (and
    /// optionally query parameters).
    ///
    /// Endpoint Examples
    /// - `"/api/v1/mixnodes?since=12345"`
    /// - `"/api/v1/mixnodes"`
    /// - `"/api/v1/mixnodes/img.png"`
    /// - `"/api/v1/mixnodes/img.png?since=12345"`
    /// - `"/"`
    /// - `"/?since=12345"`
    /// - `""`
    /// - `"?since=12345"`
    ///
    /// for more information about URL percent encodings see [`url::Url::set_path()`]
    fn create_request_endpoint<B, S>(
        &self,
        method: reqwest::Method,
        endpoint: S,
        body: Option<&B>,
    ) -> Result<RequestBuilder, HttpClientError>
    where
        B: Serialize + ?Sized,
        S: AsRef<str>,
    {
        // Use a stand-in url to extract the path and queries from the provided endpoint string
        // which could potentially fail.
        //
        // This parse cannot fail
        let mut standin_url: Url = "http://example.com".parse().unwrap();

        match endpoint.as_ref().split_once("?") {
            Some((path, query)) => {
                standin_url.set_path(path);
                standin_url.set_query(Some(query));
            }
            // There is no query in the provided endpoint
            None => standin_url.set_path(endpoint.as_ref()),
        }

        let path: Vec<&str> = match standin_url.path_segments() {
            Some(segments) => segments.collect(),
            None => Vec::new(),
        };
        let params: Vec<(String, String)> = standin_url.query_pairs().into_owned().collect();

        self.create_request(method, path.as_slice(), &params, body)
    }

    /// Send a created HTTP request.
    ///
    /// A [`RequestBuilder`] can be created with [`ApiClientCore::create_request`] or
    /// [`ApiClientCore::create_request_endpoint`] or if absolutely necessary, using reqwest
    /// tooling directly.
    async fn send(&self, request: RequestBuilder) -> Result<Response, HttpClientError>;

    /// Create and send a created HTTP request.
    async fn send_request<P, B, K, V>(
        &self,
        method: reqwest::Method,
        path: P,
        params: Params<'_, K, V>,
        json_body: Option<&B>,
    ) -> Result<Response, HttpClientError>
    where
        P: RequestPath + Send + Sync,
        B: Serialize + ?Sized + Sync,
        K: AsRef<str> + Sync,
        V: AsRef<str> + Sync,
    {
        let req = self.create_request(method, path, params, json_body)?;
        self.send(req).await
    }

    /// If multiple base urls are available rotate to next (e.g. when the current one resulted in an error)
    ///
    /// Takes an optional URL argument. If this is none, the current host will be updated automatically.
    /// If a url is provided first check that the CURRENT host matches the hostname in the URL before
    /// triggering a rotation. This is meant to prevent parallel requests that fail from rotating the host
    /// multiple times.
    fn maybe_rotate_hosts(&self, offending_url: Option<Url>);

    /// If the fronting policy for the client is set to `OnRetry` or `ConfiguredRetry` this
    /// function will enable fronting if not already enabled. `domain` should be the host of the
    /// URL that triggered the failure, and is used by `ConfiguredRetry` to track failures per
    /// domain.
    #[cfg(feature = "tunneling")]
    fn maybe_enable_fronting(&self, domain: Option<&str>, context: impl std::fmt::Debug);
}

/// A `ClientBuilder` can be used to create a [`Client`] with custom configuration applied consistently
/// and state tracked across subsequent requests.
pub struct ClientBuilder {
    urls: Vec<Url>,

    timeout: Option<Duration>,
    custom_user_agent: Option<HeaderValue>,
    reqwest_client_builder: Option<reqwest::ClientBuilder>,
    #[allow(dead_code)] // not dead code, just unused in wasm
    use_secure_dns: bool,

    #[cfg(feature = "tunneling")]
    front: fronted::Front,

    retry_limit: usize,
    serialization: SerializationFormat,

    error: Option<HttpClientError>,
}

impl ClientBuilder {
    /// Constructs a new `ClientBuilder`.
    ///
    /// This is the same as `Client::builder()`.
    pub fn new<U>(url: U) -> Result<Self, HttpClientError>
    where
        U: IntoUrl,
    {
        let str_url = url.as_str();

        // a naive check: if the provided URL does not start with http(s), add that scheme
        if !str_url.starts_with("http") {
            let alt = format!("http://{str_url}");
            warn!(
                "the provided url ('{str_url}') does not contain scheme information. Changing it to '{alt}' ..."
            );
            // TODO: or should we maybe default to https?
            Self::new(alt)
        } else {
            let url = url.to_url()?;
            Self::new_with_urls(vec![url])
        }
    }

    /// Create a client builder from network details with sensible defaults
    #[cfg(feature = "network-defaults")]
    // deprecating function since it's not clear from its signature whether the client
    // would be constructed using `nym_api_urls` or `nym_vpn_api_urls`
    #[deprecated(note = "use explicit Self::new_with_fronted_urls instead")]
    pub fn from_network(
        network: &nym_network_defaults::v2::NymNetworkDetails,
    ) -> Result<Self, HttpClientError> {
        let urls = network.nym_api_urls();
        Self::new_with_fronted_urls(urls.clone())
    }

    /// Create a client builder using the provided set of domain-fronted URLs
    #[cfg(feature = "network-defaults")]
    pub fn new_with_fronted_urls(
        urls: Vec<nym_network_defaults::ApiUrl>,
    ) -> Result<Self, HttpClientError> {
        let urls = urls
            .into_iter()
            .map(|api_url| {
                // Convert ApiUrl to our Url type with fronting support
                let mut url = Url::parse(&api_url.url)?;

                // Add fronting domains if available
                #[cfg(feature = "tunneling")]
                if let Some(ref front_hosts) = api_url.front_hosts {
                    let fronts: Vec<String> = front_hosts
                        .iter()
                        .map(|host| format!("https://{}", host))
                        .collect();
                    url = Url::new(api_url.url.clone(), Some(fronts)).map_err(|source| {
                        HttpClientError::MalformedUrl {
                            raw: api_url.url.clone(),
                            source,
                        }
                    })?;
                }

                Ok(url)
            })
            .collect::<Result<Vec<_>, HttpClientError>>()?;

        let mut builder = Self::new_with_urls(urls)?;

        // Enable domain fronting using the shared fronting policy
        #[cfg(feature = "tunneling")]
        {
            builder = builder.with_fronting(None);
        }

        Ok(builder)
    }

    /// Constructs a new http `ClientBuilder` from a valid url.
    pub fn new_with_urls(urls: Vec<Url>) -> Result<Self, HttpClientError> {
        if urls.is_empty() {
            return Err(HttpClientError::NoUrlsProvided);
        }

        let urls = Self::check_urls(urls);

        Ok(ClientBuilder {
            urls,
            timeout: None,
            custom_user_agent: None,
            reqwest_client_builder: None,
            use_secure_dns: true,
            #[cfg(feature = "tunneling")]
            front: fronted::Front::off(),

            retry_limit: 0,
            serialization: SerializationFormat::Json,
            error: None,
        })
    }

    /// Configure use of an independent HTTP request executor. This prevents use of beneficial
    /// features like connection pooling under the hood.
    #[cfg(not(target_arch = "wasm32"))]
    pub fn non_shared(mut self) -> Self {
        if self.reqwest_client_builder.is_none() {
            self.reqwest_client_builder = Some(default_builder());
        }
        self
    }

    /// Add an additional URL to the set usable by this constructed `Client`
    pub fn add_url(mut self, url: Url) -> Self {
        self.urls.push(url);
        self
    }

    fn check_urls(mut urls: Vec<Url>) -> Vec<Url> {
        // remove any duplicate URLs
        urls = urls.into_iter().unique().collect();

        // warn about any invalid URLs
        urls.iter()
            .filter(|url| !url.scheme().contains("http") && !url.scheme().contains("https"))
            .for_each(|url| {
                warn!("the provided url ('{url}') does not use HTTP / HTTPS scheme");
            });

        urls
    }

    /// Enables a total request timeout other than the default.
    ///
    /// The timeout is applied from when the request starts connecting until the response body has finished. Also considered a total deadline.
    ///
    /// Default is [`DEFAULT_TIMEOUT`].
    #[must_use]
    pub fn with_timeout(mut self, timeout: Duration) -> Self {
        self.timeout = Some(timeout);
        self
    }

    /// Sets the maximum number of retries for a request. This defaults to 0, indicating no retries.
    ///
    /// Note that setting a retry limit of 3 (for example) will result in 4 attempts to send the
    /// request in the case that all are unsuccessful.
    ///
    /// If multiple urls (or fronting configurations if enabled) are available, retried requests
    /// will be sent to the next URL in the list.
    #[must_use]
    pub fn with_retries(mut self, retry_limit: usize) -> Self {
        self.retry_limit = retry_limit;
        self
    }

    /// Provide a pre-configured [`reqwest::ClientBuilder`]
    #[must_use]
    pub fn with_reqwest_builder(mut self, reqwest_builder: reqwest::ClientBuilder) -> Self {
        self.reqwest_client_builder = Some(reqwest_builder);
        self
    }

    /// Sets the `User-Agent` header to be used by this client.
    #[must_use]
    pub fn with_user_agent<V>(mut self, value: V) -> Self
    where
        V: TryInto<HeaderValue>,
        V::Error: Into<http::Error>,
    {
        match value.try_into() {
            Ok(v) => self.custom_user_agent = Some(v),
            Err(err) => {
                self.error = Some(HttpClientError::InvalidHeaderValue { source: err.into() })
            }
        }
        self
    }

    /// Set the serialization format for API requests and responses
    #[must_use]
    pub fn with_serialization(mut self, format: SerializationFormat) -> Self {
        self.serialization = format;
        self
    }

    /// Configure the client to use bincode serialization
    #[must_use]
    pub fn with_bincode(self) -> Self {
        self.with_serialization(SerializationFormat::Bincode)
    }

    /// Returns a Client that uses this ClientBuilder configuration.
    pub fn build(self) -> Result<Client, HttpClientError> {
        if let Some(err) = self.error {
            return Err(err);
        }

        #[cfg(target_arch = "wasm32")]
        let reqwest_client = Some(reqwest::ClientBuilder::new().build()?);

        #[cfg(not(target_arch = "wasm32"))]
        let reqwest_client = self
            .reqwest_client_builder
            .map(|mut builder| {
                // unless explicitly disabled use the DoT/DoH enabled resolver
                if self.use_secure_dns {
                    builder = builder.dns_resolver(Arc::new(HickoryDnsResolver::new()));
                }

                // reqwest builds its TLS config from the process-wide default provider
                tls::install_default_crypto_provider();
                builder
                    .build()
                    .map_err(HttpClientError::reqwest_client_build_error)
            })
            .transpose()?;

        #[cfg(feature = "tunneling")]
        let rotation = RotationManager::new(self.urls.len());

        let client = Client {
            base_urls: self.urls,
            current_idx: Arc::new(AtomicUsize::new(0)),
            reqwest_client,
            custom_user_agent: self.custom_user_agent,

            #[cfg(feature = "tunneling")]
            front: self.front,
            #[cfg(feature = "tunneling")]
            rotation,

            #[cfg(target_arch = "wasm32")]
            request_timeout: self.timeout.unwrap_or(DEFAULT_TIMEOUT),
            retry_limit: self.retry_limit,
            serialization: self.serialization,
        };

        Ok(client)
    }
}

/// A simple extendable client wrapper for http request with extra url sanitization.
#[derive(Debug, Clone)]
pub struct Client {
    base_urls: Vec<Url>,
    current_idx: Arc<AtomicUsize>,
    reqwest_client: Option<reqwest::Client>,
    custom_user_agent: Option<HeaderValue>,

    #[cfg(feature = "tunneling")]
    front: fronted::Front,
    /// Per-host front-rotation state for `base_urls`, kept out of `FrontedUrl` itself so that
    /// type stays a plain value. Shared across clones like `current_idx`.
    #[cfg(feature = "tunneling")]
    rotation: RotationManager,

    #[cfg(target_arch = "wasm32")]
    request_timeout: Duration,

    retry_limit: usize,
    serialization: SerializationFormat,
}

impl Client {
    /// Create a new http `Client`
    // no timeout until https://github.com/seanmonstar/reqwest/issues/1135 is fixed
    //
    // In order to prevent interference in API requests at the DNS phase we default to a resolver
    // that uses DoT and DoH.
    pub fn new(base_url: ::url::Url, timeout: Option<Duration>) -> Self {
        Self::new_url(base_url, timeout).expect(
            "we provided valid url and we were unwrapping previous construction errors anyway",
        )
    }

    /// Attempt to create a new http client from a something that can be converted to a URL
    pub fn new_url<U>(url: U, timeout: Option<Duration>) -> Result<Self, HttpClientError>
    where
        U: IntoUrl,
    {
        let builder = Self::builder(url)?;
        match timeout {
            Some(timeout) => builder.with_timeout(timeout).build(),
            None => builder.build(),
        }
    }

    /// Creates a [`ClientBuilder`] to configure a [`Client`].
    ///
    /// This is the same as [`ClientBuilder::new()`].
    pub fn builder<U>(url: U) -> Result<ClientBuilder, HttpClientError>
    where
        U: IntoUrl,
    {
        ClientBuilder::new(url)
    }

    /// Update the set of hosts that this client uses when sending API requests.
    pub fn change_base_urls(&mut self, new_urls: Vec<Url>) {
        self.current_idx.store(0, Ordering::Relaxed);
        #[cfg(feature = "tunneling")]
        {
            self.rotation = RotationManager::new(new_urls.len());
            // failures recorded against the old hosts must not count towards the new set
            self.front.reset_failures();
        }
        self.base_urls = new_urls
    }

    /// Create new instance of `Client` using the provided base url and existing client config
    pub fn clone_with_new_url(&self, new_url: Url) -> Self {
        Client {
            base_urls: vec![new_url],
            current_idx: Arc::new(Default::default()),
            reqwest_client: None,
            custom_user_agent: None,

            #[cfg(feature = "tunneling")]
            front: self.front.clone(),
            #[cfg(feature = "tunneling")]
            rotation: RotationManager::new(1),
            retry_limit: self.retry_limit,

            #[cfg(target_arch = "wasm32")]
            request_timeout: self.request_timeout,
            serialization: self.serialization,
        }
    }

    /// Get the currently configured host that this client uses when sending API requests.
    pub fn current_url(&self) -> &Url {
        &self.base_urls[self.current_idx.load(std::sync::atomic::Ordering::Relaxed)]
    }

    /// The wire-level request target this client is currently pointed at: the active host's own
    /// URL, or - while fronting has selected one - that front's URL instead. See
    /// [`Self::current_front_host`] for just the front's host.
    #[cfg(feature = "tunneling")]
    pub fn current_url_str(&self) -> &str {
        let idx = self.current_idx.load(Ordering::Relaxed);
        let url = &self.base_urls[idx];
        if self.front.is_enabled() {
            self.rotation
                .as_str(idx, url, self.front.include_non_fronted_in_rotation())
        } else {
            url.inner_url().as_str()
        }
    }

    /// The front host (domain or IP) currently selected for the active base url, if fronting has
    /// selected one for it.
    #[cfg(feature = "tunneling")]
    pub fn current_front_host(&self) -> Option<&str> {
        let idx = self.current_idx.load(Ordering::Relaxed);
        self.dynamic_front_str(idx, &self.base_urls[idx])
    }

    /// Get the currently configured host that this client uses when sending API requests.
    pub fn base_urls(&self) -> &[Url] {
        &self.base_urls
    }

    /// Get a mutable reference to the hosts that this client uses when sending API requests.
    pub fn base_urls_mut(&mut self) -> &mut [Url] {
        &mut self.base_urls
    }

    /// Change the currently configured limit on the number of retries for a request.
    pub fn change_retry_limit(&mut self, limit: usize) {
        self.retry_limit = limit;
    }

    /// The front host currently selected for host `idx`, according to whichever of
    /// [`RotationManager::front_str`] / [`RotationManager::active_rotation_front_str`] applies
    /// under the configured fronting policy, or `None` if fronting is currently disabled.
    ///
    /// The `None`-when-disabled check happens here rather than relying on every caller to check
    /// [`Front::is_enabled`] first: the rotation slot is only reset by [`Self::update_host`]
    /// while fronting is enabled, so once fronting is turned off it keeps pointing at whatever
    /// front was last selected until the next successful rotation - callers must not mistake
    /// that stale slot for an active front.
    ///
    /// Takes `idx`/`url` explicitly (rather than re-reading `current_idx`) so that callers can
    /// pin a single consistent snapshot of the active host - see the comment on
    /// [`Self::apply_hosts_to_req`] about avoiding TOCTOU races across rotations.
    #[cfg(feature = "tunneling")]
    fn dynamic_front_str<'a>(&self, idx: usize, url: &'a Url) -> Option<&'a str> {
        if !self.front.is_enabled() {
            return None;
        }
        if self.front.include_non_fronted_in_rotation() {
            self.rotation.active_rotation_front_str(idx, url)
        } else {
            self.rotation.front_str(idx, url)
        }
    }

    #[cfg(feature = "tunneling")]
    fn matches_current_host(&self, url: &Url) -> bool {
        let idx = self.current_idx.load(Ordering::Relaxed);
        let current = &self.base_urls[idx];

        // Only compare against the front host if the current url actually has one configured -
        // otherwise requests to it go out unfronted, so the offending host will be the real one.
        if self.front.is_enabled() && current.has_front() {
            let active_front = self.dynamic_front_str(idx, current);

            match active_front {
                Some(_) => url.host_str() == active_front,
                None => url.host_str() == current.host_str(),
            }
        } else {
            url.host_str() == current.host_str()
        }
    }

    #[cfg(not(feature = "tunneling"))]
    fn matches_current_host(&self, url: &Url) -> bool {
        url.host_str() == self.current_url().host_str()
    }

    /// If multiple base urls are available rotate to next (e.g. when the current one resulted in an error)
    ///
    /// Takes an optional URL argument. If this is none, the current host will be updated automatically.
    /// If a url is provided first check that the CURRENT host matches the hostname in the URL before
    /// triggering a rotation. This is meant to prevent parallel requests that fail from rotating the host
    /// multiple times.
    fn update_host(&self, maybe_url: Option<Url>) {
        // If a causal url is provided and it doesn't match the hostname currently in use, skip update.
        if let Some(err_url) = maybe_url
            && !self.matches_current_host(&err_url)
        {
            return;
        }

        #[cfg(feature = "tunneling")]
        if self.front.is_enabled() {
            let idx = self.current_idx.load(Ordering::Relaxed);
            let url = &self.base_urls[idx];

            if self.front.include_non_fronted_in_rotation() {
                // each host gets a turn shown directly before cycling through its fronts one at
                // a time - only rotate away once the direct turn and every front are exhausted.
                if url.has_front() && self.rotation.take_rotation_turn(idx, url) {
                    return;
                }
            } else if url.has_front() && !self.rotation.update(idx, url) {
                // if we are using fronting, try updating to the next front. If one is available
                // we swapped to it for the current host, otherwise we move on and try the next
                // base url (if one is available)
                return;
            }
        }

        if self.base_urls.len() > 1 {
            let orig = self.current_idx.load(Ordering::Relaxed);

            #[allow(unused_mut)]
            let mut next = (orig + 1) % self.base_urls.len();

            // if fronting is enabled we want to update to a host that has fronts configured,
            // unless the policy explicitly allows non-fronted domains into the rotation.
            #[cfg(feature = "tunneling")]
            if self.front.is_enabled() && !self.front.include_non_fronted_in_rotation() {
                while next != orig {
                    if self.base_urls[next].has_front() {
                        // we have a front for the next host, so we can use it
                        break;
                    }

                    next = (next + 1) % self.base_urls.len();
                }
            }

            self.current_idx.store(next, Ordering::Relaxed);
            debug!(
                "http client rotating host {} -> {}",
                self.base_urls[orig], self.base_urls[next]
            );
        }
    }

    /// Make modifications to the request to apply the current state of this client i.e. the
    /// currently configured host. This is required as a caller may use this client to create a
    /// request, but then have the state of the client change before the caller uses the client to
    /// send their request.
    ///
    /// This enures that the outgoing requests benefit from the configured fallback mechanisms, even
    /// for requests that were created before the state of the client changed.
    ///
    /// This method assumes that any updates to the state of the client are made before the call to
    /// this method. For example, if the client is configured to rotate hosts after each error, this
    /// method should be called after the host has been updated -- i.e. as part of the subsequent
    /// send.
    pub(crate) fn apply_hosts_to_req(
        &self,
        r: &mut reqwest::Request,
    ) -> (Option<&str>, Option<&str>) {
        // Read `current_idx` exactly once and derive everything below - including any rotation
        // state lookups - from this pinned `(idx, url)` snapshot. Reading it again later could
        // observe a different host if a rotation is interleaved in between.
        let idx = self.current_idx.load(Ordering::Relaxed);
        let url = &self.base_urls[idx];
        let domain = url.host_str();
        r.url_mut().set_host(domain).unwrap();

        // A caller-supplied `Host` header takes priority: we must not clobber it, nor simply
        // strip it (that would just let the underlying HTTP client fall back to a `Host` header
        // of its own choosing, derived from the request URL -- which may be the front's host).
        let caller_overrode_host = host_header::overridden_by_caller(r);

        #[cfg(feature = "tunneling")]
        if self.front.is_enabled() {
            let front_host = self.dynamic_front_str(idx, url);

            if let Some(front_host) = front_host {
                if let Some(actual_host) = url.host_str() {
                    tracing::debug!(
                        "Domain fronting enabled: routing via CDN {} to actual host {}",
                        front_host,
                        actual_host
                    );

                    // this should never fail as we are transplanting the host from one url to another
                    r.url_mut().set_host(Some(front_host)).unwrap();

                    if caller_overrode_host {
                        warn!(
                            front = front_host,
                            actual_host,
                            "caller supplied a Host header on a fronted request; domain fronting \
                             relies on the Host header matching the actual backend host, so this \
                             request will likely fail to route through the CDN",
                        );
                        host_header::collapse_override(r);
                    } else {
                        host_header::set(r, Some(actual_host));
                    }

                    // Set a custom header to capture the outer host (used in the SNI) of the request
                    let front_host_header: HeaderValue =
                        front_host.parse().unwrap_or(HeaderValue::from_static(""));
                    _ = r
                        .headers_mut()
                        .insert(NYM_OUTER_SNI_HEADER, front_host_header);

                    return (domain, Some(front_host));
                } else {
                    tracing::debug!(
                        "Domain fronting is enabled, but no host_url is defined for current URL"
                    )
                }
            } else {
                tracing::debug!(
                    "Domain fronting is enabled, but current URL has no front_hosts configured"
                )
            }
        }

        // Ensure no stale fronting headers survive from a prior fronted attempt on this
        // (possibly cloned/retried) request -- e.g. after a host rotation or a recovery to
        // fronting-disabled. The caller's own `Host` header is left untouched.
        if caller_overrode_host {
            host_header::collapse_override(r);
        } else {
            host_header::set(r, None);
        }
        r.headers_mut().remove(NYM_OUTER_SNI_HEADER);

        (domain, None)
    }
}

#[cfg_attr(target_arch = "wasm32", async_trait(?Send))]
#[cfg_attr(not(target_arch = "wasm32"), async_trait)]
impl ApiClientCore for Client {
    #[instrument(level = "debug", skip_all, fields(path=?path))]
    fn create_request<P, B, K, V>(
        &self,
        method: reqwest::Method,
        path: P,
        params: Params<'_, K, V>,
        body: Option<&B>,
    ) -> Result<RequestBuilder, HttpClientError>
    where
        P: RequestPath,
        B: Serialize + ?Sized,
        K: AsRef<str>,
        V: AsRef<str>,
    {
        let url = self.current_url();
        let url = sanitize_url(url, path, params);

        let mut req = reqwest::Request::new(method, url.into());

        self.apply_hosts_to_req(&mut req);

        let client = if let Some(client) = &self.reqwest_client {
            client.clone()
        } else {
            SHARED_CLIENT.clone()
        };
        let mut rb = RequestBuilder::from_parts(client, req);

        rb = rb
            .header(ACCEPT, self.serialization.content_type())
            .header(CONTENT_TYPE, self.serialization.content_type());

        if let Some(user_agent) = &self.custom_user_agent {
            rb = rb.header(USER_AGENT, user_agent.clone());
        }

        if let Some(body) = body {
            match self.serialization {
                SerializationFormat::Json => {
                    rb = rb.json(body);
                }
                SerializationFormat::Bincode => {
                    let body = bincode::serialize(body)?;
                    rb = rb.body(body);
                }
                SerializationFormat::Yaml => {
                    let mut body_bytes = Vec::new();
                    serde_yaml::to_writer(&mut body_bytes, &body)?;
                    rb = rb.body(body_bytes);
                }
                SerializationFormat::Text => {
                    let body = serde_plain::to_string(&body)?.as_bytes().to_vec();
                    rb = rb.body(body);
                }
            }
        }

        Ok(rb)
    }

    async fn send(&self, request: RequestBuilder) -> Result<Response, HttpClientError> {
        let mut attempts = 0;
        loop {
            // try_clone may fail if the body is a stream in which case using retries is not advised.
            let r = request
                .try_clone()
                .ok_or(HttpClientError::AttemptedToCloneStreamRequest)?;

            // apply any changes based on the current state of the client wrt. hosts,
            // fronting domains, etc.
            let mut req = r
                .build()
                .map_err(HttpClientError::reqwest_client_build_error)?;
            let (domain, _front_used) = self.apply_hosts_to_req(&mut req);
            let domain = domain.map(str::to_owned);
            let url: Url = req.url().clone().into();
            // internal bookkeeping only -- never sent on the wire.
            req.headers_mut().remove(host_header::MANAGED_MARKER_HEADER);

            let request_start = Instant::now();

            #[cfg(target_arch = "wasm32")]
            let response: Result<Response, HttpClientError> = {
                let client = self
                    .reqwest_client
                    .as_ref()
                    .unwrap_or_else(|| &*SHARED_CLIENT);
                Ok(
                    wasmtimer::tokio::timeout(self.request_timeout, client.execute(req))
                        .await
                        .map_err(|_timeout| HttpClientError::RequestTimeout)??,
                )
            };

            #[cfg(not(target_arch = "wasm32"))]
            let response = {
                let client = self
                    .reqwest_client
                    .as_ref()
                    .unwrap_or_else(|| &*SHARED_CLIENT);
                client.execute(req).await
            };

            match response {
                Ok(resp) => {
                    // Check if the response indicates that we are being rate limited
                    if is_http_rate_limit_err(&resp) {
                        warn!("encountered rate limit error for {}", url.as_str());
                        // if we have multiple urls, update to the next
                        self.maybe_rotate_hosts(Some(url.clone()));
                    } else {
                        // If fronting is enabled and we rotate through a non-fronted SNI that
                        // succeeds it means that an API endpoint is working when accessed directly.
                        // We then reset counters for fronting enable and begin state tracking anew.
                        //
                        // While HTTP failures (e.g. 400 404, 502, etc.) to non-fronted API calls
                        // still indicate that the request "succeeded" from the point of view of
                        // domain fronting this check requires that the HTTP request itself
                        // succeeded (e.g. 2XX response).
                        #[cfg(feature = "tunneling")]
                        if _front_used.is_none()
                            && self.front.is_enabled()
                            && self.front.should_recover_on_non_fronted_success()
                            && resp.status().is_success()
                        {
                            debug!(
                                "non-fronted request to {} succeeded while fronting was enabled; disabling fronting and resetting retry counters",
                                url.as_str()
                            );
                            self.front.recover();
                        }
                    }

                    return Ok(resp);
                }
                Err(err) => {
                    let last_network_reconfiguration =
                        *SHARED_NETWORK_RECONFIGURATION.lock().unwrap();
                    let network_reconfigured =
                        last_network_reconfiguration.is_some_and(|last| last > request_start);

                    #[cfg(target_arch = "wasm32")]
                    let is_network_err = err.is_timeout();
                    #[cfg(not(target_arch = "wasm32"))]
                    let is_network_err = might_be_network_interference(&err);

                    if is_network_err & !network_reconfigured {
                        // if we have multiple urls, update to the next
                        self.maybe_rotate_hosts(Some(url.clone()));

                        #[cfg(feature = "tunneling")]
                        self.maybe_enable_fronting(
                            domain.as_deref(),
                            ("network", url.as_str(), &err),
                        );
                    }

                    if attempts < self.retry_limit {
                        attempts += 1;
                        warn!(
                            "Retrying request due to http error on attempt ({attempts}/{}): {err}",
                            self.retry_limit
                        );
                        continue;
                    }

                    // if we have exhausted our attempts, return the error
                    cfg_if::cfg_if! {
                        if #[cfg(target_arch = "wasm32")] {
                            return Err(err);
                        } else {
                            return Err(HttpClientError::request_send_error(url.into(), err));
                        }
                    }
                }
            }
        }
    }

    fn maybe_rotate_hosts(&self, offending: Option<Url>) {
        self.update_host(offending);
    }

    #[cfg(feature = "tunneling")]
    fn maybe_enable_fronting(&self, domain: Option<&str>, context: impl std::fmt::Debug) {
        // If fronting is set to be OnRetry or ConfiguredRetry, enable domain fronting as we
        // have encountered an error.
        let was_enabled = self.front.is_enabled();
        self.front.retry_enable(domain);
        if !was_enabled && self.front.is_enabled() {
            tracing::debug!("Domain fronting activated after failure: {context:?}",);
        }
    }
}

/// Check for a rate limit response: a plain HTTP 429, a 503 with a `Retry-After` header, or a
/// rate limit challenge response from the vercel API.
pub(crate) fn is_http_rate_limit_err(resp: &Response) -> bool {
    is_rate_limit_response(resp.status(), resp.headers())
}

fn is_rate_limit_response(status: StatusCode, headers: &HeaderMap) -> bool {
    let too_many_reqs = status == StatusCode::TOO_MANY_REQUESTS;
    let rate_limit_503 = is_throttled_service_unavailable(status, headers);
    let vercel_backoff = is_vercel_rate_limit_challenge(status, headers);

    too_many_reqs || rate_limit_503 || vercel_backoff
}

/// A 503 accompanied by `Retry-After` indicates the server is asking us to back off, as opposed
/// to a plain 503 which may just mean the service is down.
// One of the hosts that we use implements rate-limiting by sending responses with 429 status-code
// initially, but then uses 503 with a `Retry-After` header. Using this check allows us to pivot
// away from those API endpoints and hopefully escape the rate-limit related error state.
//
// This is not meant to handle the `Retry-After` and is only checked to determine if we might
// benefit from rotating hosts (if there is more than one available).
fn is_throttled_service_unavailable(status: StatusCode, headers: &HeaderMap) -> bool {
    status == StatusCode::SERVICE_UNAVAILABLE && headers.contains_key(RETRY_AFTER)
}

const VERCEL_CHALLENGE_HEADER: &str = "x-vercel-mitigated";
const VERCEL_CHALLENGE_VALUE: &[u8] = b"challenge";

/// Check for a Rate Limit challenge response from the vercel API
fn is_vercel_rate_limit_challenge(status: StatusCode, headers: &HeaderMap) -> bool {
    let status = status == StatusCode::FORBIDDEN;
    let header = headers
        .get(VERCEL_CHALLENGE_HEADER)
        .is_some_and(|v| v.as_bytes() == VERCEL_CHALLENGE_VALUE);
    let content_type = headers
        .get(CONTENT_TYPE)
        .and_then(|value| value.to_str().ok())
        .and_then(|value| value.parse::<Mime>().ok())
        .is_some_and(|mime_type| {
            mime_type.type_() == mime::TEXT && mime_type.subtype() == mime::HTML
        });

    status && header && content_type
}

#[cfg(not(target_arch = "wasm32"))]
const MAX_ERR_SOURCE_ITERATIONS: usize = 6;

/// This functions attempts to check the error returned by reqwest to see if rotating host
/// information (for clients with multiple hosts defined) could be helpful. This looks for
/// situations where the error could plausibly be caused by a network adversary, or where rotating
/// to an equivalent hostname might help.
///
/// For example --> NetworkUnreachable will not be helped by rotating domains, but ConnectionReset
/// might be caused by a network adversary blocking by SNI which could possibly benefit from
/// rotating domains.
#[cfg(not(target_arch = "wasm32"))]
pub(crate) fn might_be_network_interference(err: &reqwest::Error) -> bool {
    if err.is_timeout() {
        return true;
    }

    if !(err.is_connect() || err.is_request()) {
        return false;
    }

    // The io::Error source is several layers deep, for clarity this is done as a loop
    // * reqwest::Error -> hyper_util::Error
    // * hyper_util::Error -> hyper_util::ClientError
    // * hyper_util::ClientError -> io::Error
    let mut inner = err.source();
    for _ in 0..MAX_ERR_SOURCE_ITERATIONS {
        if let Some(e) = inner {
            if let Some(io_err) = e.downcast_ref::<std::io::Error>() {
                // try downcast to io::Error from <dyn std::error:Error>
                match io_err.kind() {
                    // device not connected to the internet
                    ErrorKind::NetworkUnreachable | ErrorKind::NetworkDown => return false,
                    // connection errors can indicate connection interference
                    ErrorKind::ConnectionReset
                    | ErrorKind::HostUnreachable
                    | ErrorKind::ConnectionRefused => return true,
                    // TLS errors get wrapped in custom io::Errors
                    ErrorKind::Other | ErrorKind::InvalidData => {
                        // io::Error get_ref works while source doesn't here -_-
                        //   if you don't like it take it up with the rust devs https://users.rust-lang.org/t/question-about-implementation-of-std-source/121117
                        inner = io_err.get_ref().map(|e| e as &dyn std::error::Error);
                    }
                    _ => return false,
                }
            } else if let Some(_tls_err) = e.downcast_ref::<rustls::Error>() {
                // try downcast to TLS error
                return true;
            } else if let Some(resolve_err) = e.downcast_ref::<hickory_resolver::net::NetError>() {
                // try downcast to DNS error. NXDOMAIN means the domain doesn't exist, SERVFAIL
                // indicates a recurive lookup failure and is likely ephemeral but given that it is
                // a failure within (expected reliable DoH/DoT) we rotate the domain.
                return resolve_err.is_nx_domain()
                    || matches!(
                        resolve_err,
                        hickory_resolver::net::NetError::Dns(
                            hickory_resolver::net::DnsError::ResponseCode(
                                hickory_resolver::proto::op::ResponseCode::ServFail
                            )
                        )
                    );
            } else if let Some(h2_err) = e.downcast_ref::<h2::Error>() {
                // try downcast to a h2 (HTTP/2) error. hyper only wraps these as io::Error
                // when they are actually backed by one (see `hyper::Error::new_h2`), so if we
                // get here it's a protocol-level RST_STREAM or GOAWAY. TLS integrity protection
                // means this can only have been sent by whichever party actually terminates the
                // TLS connection - for a fronted request that's the front's CDN edge. So it
                // indicates that host/front may have actively rejected the connection (e.g.
                // detected fronting, rate limiting, or its own backend failing). This has enough
                // potentially to continue breaking things that we should rotate hosts if we can.
                return h2_err.is_remote() && (h2_err.is_reset() || h2_err.is_go_away());
            } else {
                inner = e.source();
            }
        } else {
            break;
        }
    }

    false
}

/// Common usage functionality for the http client.
///
/// These functions allow for cleaner downstream usage free of type parameters and unneeded imports.
#[cfg_attr(target_arch = "wasm32", async_trait(?Send))]
#[cfg_attr(not(target_arch = "wasm32"), async_trait)]
pub trait ApiClient: ApiClientCore {
    /// Create an HTTP GET Request with the provided path and parameters
    fn create_get_request<P, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
    ) -> Result<RequestBuilder, HttpClientError>
    where
        P: RequestPath,
        K: AsRef<str>,
        V: AsRef<str>,
    {
        self.create_request(reqwest::Method::GET, path, params, None::<&()>)
    }

    /// Create an HTTP POST Request with the provided path, parameters, and json body
    fn create_post_request<P, B, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
        json_body: &B,
    ) -> Result<RequestBuilder, HttpClientError>
    where
        P: RequestPath,
        B: Serialize + ?Sized,
        K: AsRef<str>,
        V: AsRef<str>,
    {
        self.create_request(reqwest::Method::POST, path, params, Some(json_body))
    }

    /// Create an HTTP DELETE Request with the provided path and parameters
    fn create_delete_request<P, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
    ) -> Result<RequestBuilder, HttpClientError>
    where
        P: RequestPath,
        K: AsRef<str>,
        V: AsRef<str>,
    {
        self.create_request(reqwest::Method::DELETE, path, params, None::<&()>)
    }

    /// Create an HTTP PATCH Request with the provided path, parameters, and json body
    fn create_patch_request<P, B, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
        json_body: &B,
    ) -> Result<RequestBuilder, HttpClientError>
    where
        P: RequestPath,
        B: Serialize + ?Sized,
        K: AsRef<str>,
        V: AsRef<str>,
    {
        self.create_request(reqwest::Method::PATCH, path, params, Some(json_body))
    }

    /// Create and send an HTTP GET Request with the provided path and parameters
    #[instrument(level = "debug", skip_all, fields(path=?path))]
    async fn send_get_request<P, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
    ) -> Result<Response, HttpClientError>
    where
        P: RequestPath + Send + Sync,
        K: AsRef<str> + Sync,
        V: AsRef<str> + Sync,
    {
        self.send_request(reqwest::Method::GET, path, params, None::<&()>)
            .await
    }

    /// Create and send an HTTP POST Request with the provided path, parameters, and json data
    async fn send_post_request<P, B, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
        json_body: &B,
    ) -> Result<Response, HttpClientError>
    where
        P: RequestPath + Send + Sync,
        B: Serialize + ?Sized + Sync,
        K: AsRef<str> + Sync,
        V: AsRef<str> + Sync,
    {
        self.send_request(reqwest::Method::POST, path, params, Some(json_body))
            .await
    }

    /// Create and send an HTTP DELETE Request with the provided path and parameters
    async fn send_delete_request<P, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
    ) -> Result<Response, HttpClientError>
    where
        P: RequestPath + Send + Sync,
        K: AsRef<str> + Sync,
        V: AsRef<str> + Sync,
    {
        self.send_request(reqwest::Method::DELETE, path, params, None::<&()>)
            .await
    }

    /// Create and send an HTTP PATCH Request with the provided path, parameters, and json data
    async fn send_patch_request<P, B, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
        json_body: &B,
    ) -> Result<Response, HttpClientError>
    where
        P: RequestPath + Send + Sync,
        B: Serialize + ?Sized + Sync,
        K: AsRef<str> + Sync,
        V: AsRef<str> + Sync,
    {
        self.send_request(reqwest::Method::PATCH, path, params, Some(json_body))
            .await
    }

    /// 'get' json data from the segment-defined path, e.g. `["api", "v1", "mixnodes"]`, with tuple
    /// defined key-value parameters, e.g. `[("since", "12345")]`. Attempt to parse the response
    /// into the provided type `T`.
    #[instrument(level = "debug", skip_all, fields(path=?path))]
    // TODO: deprecate in favour of get_response that works based on mime type in the response
    async fn get_json<P, T, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
    ) -> Result<T, HttpClientError>
    where
        P: RequestPath + Send + Sync,
        for<'a> T: Deserialize<'a>,
        K: AsRef<str> + Sync,
        V: AsRef<str> + Sync,
    {
        self.get_response(path, params).await
    }

    /// Attempt to parse a response object from an HTTP response
    async fn parse_response<T>(
        &self,
        res: Response,
        allow_empty: bool,
    ) -> Result<T, HttpClientError>
    where
        T: DeserializeOwned,
    {
        let url = Url::from(res.url());
        parse_response(res, allow_empty).await.inspect_err(|e| {
            if matches!(
                // if we encounter a read error while we attempt to parse it could be caused by censorship and we should
                // rotate hosts / enable fronting.
                e,
                HttpClientError::ResponseReadFailure {
                    url: _,
                    headers: _,
                    status: _,
                    source: _,
                }
            ) {
                self.maybe_rotate_hosts(Some(url.clone()));
                #[cfg(feature = "tunneling")]
                self.maybe_enable_fronting(url.host_str(), ("parse/read", url.as_str(), e));
            }
        })
    }

    /// 'get' data from the segment-defined path, e.g. `["api", "v1", "mixnodes"]`, with tuple
    /// defined key-value parameters, e.g. `[("since", "12345")]`. Attempt to parse the response
    /// into the provided type `T` based on the content type header
    #[instrument(level = "debug", skip_all, fields(path=?path))]
    async fn get_response<P, T, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
    ) -> Result<T, HttpClientError>
    where
        P: RequestPath + Send + Sync,
        for<'a> T: Deserialize<'a>,
        K: AsRef<str> + Sync,
        V: AsRef<str> + Sync,
    {
        let res = self
            .send_request(reqwest::Method::GET, path, params, None::<&()>)
            .await?;

        self.parse_response(res, false).await
    }

    /// 'post' json data to the segment-defined path, e.g. `["api", "v1", "mixnodes"]`, with tuple
    /// defined key-value parameters, e.g. `[("since", "12345")]`. Attempt to parse the response
    /// into the provided type `T`.
    async fn post_json<P, B, T, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
        json_body: &B,
    ) -> Result<T, HttpClientError>
    where
        P: RequestPath + Send + Sync,
        B: Serialize + ?Sized + Sync,
        for<'a> T: Deserialize<'a>,
        K: AsRef<str> + Sync,
        V: AsRef<str> + Sync,
    {
        let res = self
            .send_request(reqwest::Method::POST, path, params, Some(json_body))
            .await?;
        self.parse_response(res, false).await
    }

    /// 'delete' json data from the segment-defined path, e.g. `["api", "v1", "mixnodes"]`, with
    /// tuple defined key-value parameters, e.g. `[("since", "12345")]`. Attempt to parse the
    /// response into the provided type `T`.
    async fn delete_json<P, T, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
    ) -> Result<T, HttpClientError>
    where
        P: RequestPath + Send + Sync,
        for<'a> T: Deserialize<'a>,
        K: AsRef<str> + Sync,
        V: AsRef<str> + Sync,
    {
        let res = self
            .send_request(reqwest::Method::DELETE, path, params, None::<&()>)
            .await?;
        self.parse_response(res, false).await
    }

    /// 'patch' json data at the segment-defined path, e.g. `["api", "v1", "mixnodes"]`, with tuple
    /// defined key-value parameters, e.g. `[("since", "12345")]`. Attempt to parse the response
    /// into the provided type `T`.
    async fn patch_json<P, B, T, K, V>(
        &self,
        path: P,
        params: Params<'_, K, V>,
        json_body: &B,
    ) -> Result<T, HttpClientError>
    where
        P: RequestPath + Send + Sync,
        B: Serialize + ?Sized + Sync,
        for<'a> T: Deserialize<'a>,
        K: AsRef<str> + Sync,
        V: AsRef<str> + Sync,
    {
        let res = self
            .send_request(reqwest::Method::PATCH, path, params, Some(json_body))
            .await?;
        self.parse_response(res, false).await
    }

    /// `get` json data from the provided absolute endpoint, e.g. `"/api/v1/mixnodes?since=12345"`.
    /// Attempt to parse the response into the provided type `T`.
    async fn get_json_from<T, S>(&self, endpoint: S) -> Result<T, HttpClientError>
    where
        for<'a> T: Deserialize<'a>,
        S: AsRef<str> + Sync + Send,
    {
        let req = self.create_request_endpoint(reqwest::Method::GET, endpoint, None::<&()>)?;
        let res = self.send(req).await?;
        self.parse_response(res, false).await
    }

    /// `post` json data to the provided absolute endpoint, e.g. `"/api/v1/mixnodes?since=12345"`.
    /// Attempt to parse the response into the provided type `T`.
    async fn post_json_data_to<B, T, S>(
        &self,
        endpoint: S,
        json_body: &B,
    ) -> Result<T, HttpClientError>
    where
        B: Serialize + ?Sized + Sync,
        for<'a> T: Deserialize<'a>,
        S: AsRef<str> + Sync + Send,
    {
        let req = self.create_request_endpoint(reqwest::Method::POST, endpoint, Some(json_body))?;
        let res = self.send(req).await?;
        self.parse_response(res, false).await
    }

    /// `delete` json data from the provided absolute endpoint, e.g.
    /// `"/api/v1/mixnodes?since=12345"`. Attempt to parse the response into the provided type `T`.
    async fn delete_json_from<T, S>(&self, endpoint: S) -> Result<T, HttpClientError>
    where
        for<'a> T: Deserialize<'a>,
        S: AsRef<str> + Sync + Send,
    {
        let req = self.create_request_endpoint(reqwest::Method::DELETE, endpoint, None::<&()>)?;
        let res = self.send(req).await?;
        self.parse_response(res, false).await
    }

    /// `patch` json data at the provided absolute endpoint, e.g. `"/api/v1/mixnodes?since=12345"`.
    /// Attempt to parse the response into the provided type `T`.
    async fn patch_json_data_at<B, T, S>(
        &self,
        endpoint: S,
        json_body: &B,
    ) -> Result<T, HttpClientError>
    where
        B: Serialize + ?Sized + Sync,
        for<'a> T: Deserialize<'a>,
        S: AsRef<str> + Sync + Send,
    {
        let req =
            self.create_request_endpoint(reqwest::Method::PATCH, endpoint, Some(json_body))?;
        let res = self.send(req).await?;
        self.parse_response(res, false).await
    }
}

#[cfg_attr(target_arch = "wasm32", async_trait(?Send))]
#[cfg_attr(not(target_arch = "wasm32"), async_trait)]
impl<C> ApiClient for C where C: ApiClientCore + Sync {}

/// utility function that should solve the double slash problem in API urls forever.
fn sanitize_url<K: AsRef<str>, V: AsRef<str>>(
    base: &Url,
    request_path: impl RequestPath,
    params: Params<'_, K, V>,
) -> Url {
    let mut url = base.clone();
    let mut path_segments = url
        .path_segments_mut()
        .expect("provided validator url does not have a base!");

    path_segments.pop_if_empty();

    for segment in request_path.to_sanitized_segments() {
        path_segments.push(segment);
    }

    // I don't understand why compiler couldn't figure out that it's no longer used
    // and can be dropped
    drop(path_segments);

    if !params.is_empty() {
        url.query_pairs_mut().extend_pairs(params);
    }

    url
}

fn decode_as_text(bytes: &bytes::Bytes, headers: &HeaderMap) -> String {
    use encoding_rs::{Encoding, UTF_8};

    let content_type = try_get_mime_type(headers);

    let encoding_name = content_type
        .as_ref()
        .and_then(|mime| mime.get_param("charset").map(|charset| charset.as_str()))
        .unwrap_or("utf-8");

    let encoding = Encoding::for_label(encoding_name.as_bytes()).unwrap_or(UTF_8);

    let (text, _, _) = encoding.decode(bytes);
    text.into_owned()
}

/// Attempt to parse a response object from an HTTP response
#[instrument(level = "debug", skip_all)]
pub async fn parse_response<T>(res: Response, allow_empty: bool) -> Result<T, HttpClientError>
where
    T: DeserializeOwned,
{
    let status = res.status();
    let headers = res.headers().clone();
    let url = res.url().clone();

    tracing::trace!("status: {status} (success: {})", status.is_success());
    tracing::trace!("headers: {headers:?}");

    if !allow_empty && let Some(0) = res.content_length() {
        return Err(HttpClientError::EmptyResponse {
            url: Box::new(url),
            status,
            headers: Box::new(headers),
        });
    }

    if res.status().is_success() {
        // internally reqwest is first retrieving bytes and then performing parsing via serde_json
        // (and similarly does the same thing for text())
        let full = res
            .bytes()
            .await
            .map_err(|source| HttpClientError::ResponseReadFailure {
                url: Box::new(url),
                headers: Box::new(headers.clone()),
                status,
                source: ReqwestErrorWrapper(source),
            })?;
        decode_raw_response(&headers, full)
    } else if res.status() == StatusCode::NOT_FOUND {
        Err(HttpClientError::NotFound { url: Box::new(url) })
    } else if is_http_rate_limit_err(&res) {
        Err(HttpClientError::EndpointFailure {
            url: Box::new(url),
            status,
            headers: Box::new(headers),
            error: String::from("received rate limit response"),
        })
    } else {
        let Ok(plaintext) = res.text().await else {
            return Err(HttpClientError::RequestFailure {
                url: Box::new(url),
                status,
                headers: Box::new(headers),
            });
        };

        Err(HttpClientError::EndpointFailure {
            url: Box::new(url),
            status,
            headers: Box::new(headers),
            error: plaintext,
        })
    }
}

fn decode_as_json<T>(headers: &HeaderMap, content: Bytes) -> Result<T, HttpClientError>
where
    T: DeserializeOwned,
{
    match serde_json::from_slice(&content) {
        Ok(data) => Ok(data),
        Err(err) => {
            let content = decode_as_text(&content, headers);
            Err(HttpClientError::ResponseDecodeFailure {
                message: err.to_string(),
                content,
            })
        }
    }
}

fn decode_as_bincode<T>(headers: &HeaderMap, content: Bytes) -> Result<T, HttpClientError>
where
    T: DeserializeOwned,
{
    use bincode::Options;

    let opts = nym_http_api_common::make_bincode_serializer();
    match opts.deserialize(&content) {
        Ok(data) => Ok(data),
        Err(err) => {
            let content = decode_as_text(&content, headers);
            Err(HttpClientError::ResponseDecodeFailure {
                message: err.to_string(),
                content,
            })
        }
    }
}

fn decode_raw_response<T>(headers: &HeaderMap, content: Bytes) -> Result<T, HttpClientError>
where
    T: DeserializeOwned,
{
    // if content type header is missing, fallback to our old default, json
    let mime = try_get_mime_type(headers).unwrap_or(mime::APPLICATION_JSON);

    debug!("attempting to parse response as {mime}");

    // unfortunately we can't use stronger typing for subtype as "bincode" is not a defined mime type
    match (mime.type_(), mime.subtype().as_str()) {
        (mime::APPLICATION, "json") => decode_as_json(headers, content),
        (mime::APPLICATION, "bincode") => decode_as_bincode(headers, content),
        (_, _) => {
            debug!("unrecognised mime type {mime}. falling back to json decoding...");
            decode_as_json(headers, content)
        }
    }
}

fn try_get_mime_type(headers: &HeaderMap) -> Option<Mime> {
    headers
        .get(CONTENT_TYPE)
        .and_then(|value| value.to_str().ok())
        .and_then(|value| value.parse::<Mime>().ok())
}

#[cfg(test)]
mod tests;