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//! Tracing context.
use crate::client::Client;
use crate::error::Result;
use crate::header::Header;
use crate::lambda;
use crate::namespace::Namespace;
use crate::session::SubsegmentSession;
/// Context.
pub trait Context {
/// Client type.
type Client: Client;
/// Enters in a new subsegment.
///
/// [`SubsegmentSession`] records the end of the subsegment when it is
/// dropped.
fn enter_subsegment<N>(&self, namespace: N) -> SubsegmentSession<Self::Client, N>
where
N: Namespace + Send + Sync;
}
/// Context as a subsegment of an existing segment.
#[derive(Clone, Debug)]
pub struct SubsegmentContext<C> {
client: C,
header: Header,
name_prefix: String,
}
impl<C> SubsegmentContext<C> {
/// Creates a new context from the Lambda environment variable.
///
/// The following environment variable must be set:
/// - `_X_AMZN_TRACE_ID`: AWS X-Ray trace ID
///
/// Please refer to the [AWS documentation](https://docs.aws.amazon.com/lambda/latest/dg/configuration-envvars.html#configuration-envvars-runtime)
/// for more details.
pub fn from_lambda_env(client: C) -> Result<Self> {
let header = lambda::header()?;
Ok(Self {
client,
header,
name_prefix: "".to_string(),
})
}
/// Updates the context with a given name prefix.
///
/// The name prefix is prepended to the name of every custom subsegment.
/// Only subsegments associated with
/// [`CustomNamespace`][crate::namespace::CustomNamespace] are affected.
pub fn with_name_prefix(self, prefix: impl Into<String>) -> Self {
Self {
client: self.client,
header: self.header,
name_prefix: prefix.into(),
}
}
}
impl<C> Context for SubsegmentContext<C>
where
C: Client,
{
type Client = C;
fn enter_subsegment<N>(&self, namespace: N) -> SubsegmentSession<Self::Client, N>
where
N: Namespace + Send + Sync,
{
SubsegmentSession::new(
self.client.clone(),
&self.header,
namespace,
&self.name_prefix,
)
}
}
/// Infallible context.
///
/// This context is useful if you want to fall back to "no-op" when creation of
/// the underlying context fails.
pub enum InfallibleContext<T> {
/// Operational context.
Op(T),
/// Non-operational context.
Noop,
}
impl<T> InfallibleContext<T>
where
T: Context,
{
/// Constructs from a result of the underlying context creation.
pub fn new<E>(result: std::result::Result<T, E>) -> Self {
match result {
Ok(context) => Self::Op(context),
Err(_) => Self::Noop,
}
}
}
impl<T> Context for InfallibleContext<T>
where
T: Context,
{
type Client = T::Client;
fn enter_subsegment<N>(&self, namespace: N) -> SubsegmentSession<Self::Client, N>
where
N: Namespace + Send + Sync,
{
match self {
Self::Op(context) => context.enter_subsegment(namespace),
Self::Noop => SubsegmentSession::failed(),
}
}
}
impl<T> Clone for InfallibleContext<T>
where
T: Clone,
{
fn clone(&self) -> Self {
match self {
Self::Op(context) => Self::Op(context.clone()),
Self::Noop => Self::Noop,
}
}
}
impl<T> std::fmt::Debug for InfallibleContext<T>
where
T: std::fmt::Debug,
{
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Self::Op(context) => write!(f, "InfallibleContext::Op({:?})", context),
Self::Noop => write!(f, "InfallibleContext::Noop"),
}
}
}
/// Conversion into an infallible context.
///
/// You can convert `Result<Context, _>` into an infallible context by using
/// this trait.`
///
/// ```
/// use xray_lite::{
/// Context as _,
/// DaemonClient,
/// IntoInfallibleContext as _,
/// CustomNamespace,
/// SubsegmentContext,
/// };
///
/// fn main() {
/// # std::env::set_var("AWS_XRAY_DAEMON_ADDRESS", "127.0.0.1:2000");
/// let client = DaemonClient::from_lambda_env().unwrap();
/// let context = SubsegmentContext::from_lambda_env(client).into_infallible();
/// let _session = context.enter_subsegment(CustomNamespace::new("readme.example"));
/// }
/// ```
pub trait IntoInfallibleContext {
/// Underlying context type.
type Context: Context;
/// Converts into an infallible context.
fn into_infallible(self) -> InfallibleContext<Self::Context>;
}
impl<T, E> IntoInfallibleContext for std::result::Result<T, E>
where
T: Context,
{
type Context = T;
fn into_infallible(self) -> InfallibleContext<Self::Context> {
InfallibleContext::new(self)
}
}