cloud-sdk-testkit 0.25.0

//! Deterministic no-allocation mock transport.

use core::fmt;
use core::sync::atomic::{AtomicUsize, Ordering};

use cloud_sdk::Method;
use cloud_sdk::authentication::{
    AsyncAuthenticatedTransport, AuthenticatedRequest, BlockingAuthenticatedTransport,
};
use cloud_sdk::transport::{
    AsyncTransport, BlockingTransport, BoundTransport, EndpointIdentity, EndpointIdentityError,
    HeaderSensitivity, RequestHeaders, RequestTarget, ResponseContentType, ResponseHeaders,
    ResponseMetadata, ResponseWriter, TransportRequest,
};

use crate::{FixtureBodyError, ResponseFixture};

/// Expected request fields for one mock exchange.
#[derive(Clone, Copy)]
pub struct ExpectedRequest<'a> {
    method: Method,
    target: RequestTarget<'a>,
    body: &'a [u8],
    headers: RequestHeaders<'a>,
}

impl<'a> ExpectedRequest<'a> {
    /// Creates a bodyless expected request.
    #[must_use]
    pub const fn new(method: Method, target: RequestTarget<'a>) -> Self {
        Self {
            method,
            target,
            body: &[],
            headers: RequestHeaders::EMPTY,
        }
    }

    /// Adds the exact expected request body.
    #[must_use]
    pub const fn with_body(mut self, body: &'a [u8]) -> Self {
        self.body = body;
        self
    }

    /// Adds the exact expected ordered request headers.
    #[must_use]
    pub const fn with_headers(mut self, headers: RequestHeaders<'a>) -> Self {
        self.headers = headers;
        self
    }

    const fn method(self) -> Method {
        self.method
    }

    const fn target(self) -> RequestTarget<'a> {
        self.target
    }

    const fn body(self) -> &'a [u8] {
        self.body
    }

    const fn headers(self) -> RequestHeaders<'a> {
        self.headers
    }
}

impl fmt::Debug for ExpectedRequest<'_> {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter
            .debug_struct("ExpectedRequest")
            .field("method", &self.method)
            .field("target", &"[redacted]")
            .field("body", &"[redacted]")
            .field("headers", &self.headers)
            .finish()
    }
}

/// One expected request and deterministic response.
#[derive(Debug)]
pub struct MockExchange<'a> {
    request: ExpectedRequest<'a>,
    response: ResponseFixture<'a>,
}

impl<'a> MockExchange<'a> {
    /// Creates one mock exchange.
    #[must_use]
    pub const fn new(request: ExpectedRequest<'a>, response: ResponseFixture<'a>) -> Self {
        Self { request, response }
    }
}

/// Deterministic mock transport failure.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum MockError {
    /// No expected exchange remains.
    Exhausted,
    /// HTTP method differs from the next expectation.
    MethodMismatch,
    /// Request target differs from the next expectation.
    TargetMismatch,
    /// Request body differs from the next expectation.
    BodyMismatch,
    /// Request headers differ from the next expectation.
    HeadersMismatch,
    /// Caller response buffer cannot hold the complete fixture body.
    ResponseBufferTooSmall,
    /// Internal cursor arithmetic failed closed.
    CursorOverflow,
    /// Another request changed the ordered cursor during this exchange.
    ConcurrentRequest,
    /// Fixture metadata could not be represented by the core transport.
    InvalidFixtureMetadata,
    /// The core response writer rejected fixture output.
    ResponseWriterRejected,
}

impl_static_error!(MockError,
    Self::Exhausted => "mock transport has no expected exchange remaining",
    Self::MethodMismatch => "mock request method differs from expectation",
    Self::TargetMismatch => "mock request target differs from expectation",
    Self::BodyMismatch => "mock request body differs from expectation",
    Self::HeadersMismatch => "mock request headers differ from expectation",
    Self::ResponseBufferTooSmall => "mock response buffer is too small",
    Self::CursorOverflow => "mock transport cursor overflowed",
    Self::ConcurrentRequest => "mock transport cursor changed concurrently",
    Self::InvalidFixtureMetadata => "mock fixture metadata is invalid",
    Self::ResponseWriterRejected => "mock response writer rejected output",
);

/// Ordered no-allocation mock implementation of [`BlockingTransport`].
pub struct MockTransport<'a> {
    exchanges: &'a [MockExchange<'a>],
    cursor: AtomicUsize,
    endpoint: Option<EndpointIdentity<'a>>,
}

impl<'a> MockTransport<'a> {
    /// Creates a mock over an ordered exchange slice.
    #[must_use]
    pub const fn new(exchanges: &'a [MockExchange<'a>]) -> Self {
        Self {
            exchanges,
            cursor: AtomicUsize::new(0),
            endpoint: None,
        }
    }

    /// Binds the mock permanently to one normalized endpoint identity.
    #[must_use]
    pub const fn with_endpoint(mut self, endpoint: EndpointIdentity<'a>) -> Self {
        self.endpoint = Some(endpoint);
        self
    }

    /// Returns the number of exchanges not yet consumed.
    #[must_use]
    pub fn remaining(&self) -> usize {
        self.exchanges
            .len()
            .saturating_sub(self.cursor.load(Ordering::Acquire))
    }

    /// Reports whether every expected exchange was consumed.
    #[must_use]
    pub fn is_complete(&self) -> bool {
        self.remaining() == 0
    }

    fn send_inner(
        &self,
        request: TransportRequest<'_>,
        response: &mut ResponseWriter<'_>,
    ) -> Result<(), MockError> {
        if response.is_committed() {
            return Err(MockError::ResponseWriterRejected);
        }
        let mut response = response
            .begin_attempt()
            .map_err(|_| MockError::ResponseWriterRejected)?;
        let cursor = self.cursor.load(Ordering::Acquire);
        let exchange = self.exchanges.get(cursor).ok_or(MockError::Exhausted)?;
        if request.method() != exchange.request.method() {
            return Err(MockError::MethodMismatch);
        }
        if request.target() != exchange.request.target() {
            return Err(MockError::TargetMismatch);
        }
        if request.body() != exchange.request.body() {
            return Err(MockError::BodyMismatch);
        }
        if !request_headers_match(request.headers(), exchange.request.headers()) {
            return Err(MockError::HeadersMismatch);
        }
        let next_cursor = cursor.checked_add(1).ok_or(MockError::CursorOverflow)?;
        let _content_type = exchange
            .response
            .content_type()
            .map(ResponseContentType::new)
            .transpose()
            .map_err(|_| MockError::InvalidFixtureMetadata)?;
        let rate_limit = exchange
            .response
            .rate_limit()
            .map(|value| value.into_rate_limit())
            .transpose()
            .map_err(|_| MockError::InvalidFixtureMetadata)?;
        {
            let response_headers = response
                .headers_mut()
                .map_err(|_| MockError::ResponseWriterRejected)?;
            if let Some(source) = exchange.response.headers() {
                for header in source.iter() {
                    response_headers
                        .try_push(header.name(), header.value(), header.sensitivity())
                        .map_err(|_| MockError::InvalidFixtureMetadata)?;
                }
            }
            if let Some(value) = exchange.response.content_type() {
                response_headers
                    .try_push("content-type", value.as_bytes(), HeaderSensitivity::Public)
                    .map_err(|_| MockError::InvalidFixtureMetadata)?;
            }
            if let Some(value) = rate_limit {
                push_rate_limit_headers(response_headers, value)
                    .map_err(|_| MockError::InvalidFixtureMetadata)?;
            }
        }
        let body_len = exchange
            .response
            .body()
            .write_to(
                response
                    .body_mut()
                    .map_err(|_| MockError::ResponseWriterRejected)?,
            )
            .map_err(|error| match error {
                FixtureBodyError::OutputTooSmall | FixtureBodyError::TooLarge => {
                    MockError::ResponseBufferTooSmall
                }
            })?;
        let mut metadata = ResponseMetadata::EMPTY;
        if let Some(value) = rate_limit {
            metadata = metadata.with_rate_limit(value);
        }
        self.cursor
            .compare_exchange(cursor, next_cursor, Ordering::AcqRel, Ordering::Acquire)
            .map_err(|_| MockError::ConcurrentRequest)?;
        response
            .commit(exchange.response.status(), body_len, metadata)
            .map_err(|_| MockError::ResponseWriterRejected)
    }
}

fn request_headers_match(actual: RequestHeaders<'_>, expected: RequestHeaders<'_>) -> bool {
    let actual = actual.as_slice();
    let expected = expected.as_slice();
    actual.len() == expected.len()
        && actual.iter().zip(expected).all(|(actual, expected)| {
            actual.name() == expected.name()
                && actual.value().as_str().as_bytes() == expected.value().as_str().as_bytes()
                && actual.sensitivity() == expected.sensitivity()
        })
}

fn push_rate_limit_headers(
    headers: &mut ResponseHeaders,
    rate_limit: cloud_sdk::rate_limit::RateLimit,
) -> Result<(), ()> {
    let mut storage = [0_u8; 20];
    for (name, value) in [
        ("ratelimit-limit", rate_limit.limit()),
        ("ratelimit-remaining", rate_limit.remaining()),
        ("ratelimit-reset", rate_limit.reset_epoch_seconds()),
    ] {
        let text = write_decimal(value, &mut storage).ok_or(())?;
        headers
            .try_push(name, text.as_bytes(), HeaderSensitivity::Public)
            .map_err(|_| ())?;
    }
    Ok(())
}

fn write_decimal(value: u64, output: &mut [u8; 20]) -> Option<&str> {
    let mut value = value;
    let mut cursor = output.len();
    loop {
        cursor = cursor.checked_sub(1)?;
        let digit = u8::try_from(value % 10).ok()?;
        *output.get_mut(cursor)? = b'0'.checked_add(digit)?;
        value /= 10;
        if value == 0 {
            break;
        }
    }
    core::str::from_utf8(output.get(cursor..)?).ok()
}

impl BlockingTransport for MockTransport<'_> {
    type Error = MockError;

    fn send(
        &self,
        request: TransportRequest<'_>,
        response: &mut ResponseWriter<'_>,
    ) -> Result<(), Self::Error> {
        self.send_inner(request, response)
    }
}

impl BlockingAuthenticatedTransport for MockTransport<'_> {
    type Error = MockError;

    fn send_authenticated(
        &self,
        request: AuthenticatedRequest<'_, '_>,
        response: &mut ResponseWriter<'_>,
    ) -> Result<(), Self::Error> {
        self.send_inner(request.transport_request(), response)
    }
}

impl AsyncTransport for MockTransport<'_> {
    type Error = MockError;

    async fn send<'transport, 'request, 'writer>(
        &'transport self,
        request: TransportRequest<'request>,
        response: &'writer mut ResponseWriter<'_>,
    ) -> Result<(), Self::Error>
    where
        'transport: 'writer,
        'request: 'writer,
    {
        self.send_inner(request, response)
    }
}

impl AsyncAuthenticatedTransport for MockTransport<'_> {
    type Error = MockError;

    async fn send_authenticated<'transport, 'request, 'policy, 'writer>(
        &'transport self,
        request: AuthenticatedRequest<'request, 'policy>,
        response: &'writer mut ResponseWriter<'_>,
    ) -> Result<(), Self::Error>
    where
        'transport: 'writer,
        'request: 'writer,
        'policy: 'writer,
    {
        self.send_inner(request.transport_request(), response)
    }
}

impl BoundTransport for MockTransport<'_> {
    fn endpoint_identity(&self) -> Result<EndpointIdentity<'_>, EndpointIdentityError> {
        self.endpoint.ok_or(EndpointIdentityError::UnboundTransport)
    }
}

impl fmt::Debug for MockTransport<'_> {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter
            .debug_struct("MockTransport")
            .field("remaining", &self.remaining())
            .finish_non_exhaustive()
    }
}