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#38 in HTTP client

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Used in 2 crates (via witchcraft-server)




Conjure Rust Runtime



conjure-runtime is a client-side HTTP framework for the Rust programming language. It can operate both with generated Conjure interfaces and as a standalone client. See the crate's documentation for more details.


This repository is made available under the Apache 2.0 License.


An HTTP client for use with Conjure servers.

This crate provides both asynchronous and blocking clients. The clients can either be used in Conjure-generated wrapper types or standalone for use with non-Conjure servers.


While a conjure_runtime client can be built up programmatically, the more common approach is for the configuration to be deserialized from a service's runtime-reloadable configuration file. The ServicesConfig supports configuration for multiple downstream services, as well as allowing for both global and per-service configuration overrides:

      - https://auth.my-network.com/auth-service
      - https://cache-1.my-network.com/cache-service
      - https://cache-2.my-network.com/cache-service
    request-timeout: 10s
# options set at this level will apply as defaults to all configured services
  ca-file: var/security/ca.pem

Using the refreshable crate, a live-updating config file can be used with the ClientFactory type to create live-updating clients for the configured services.


First construct a raw Client:

use conjure_runtime::{UserAgent, Agent, Client};
use conjure_runtime::config::SecurityConfig;
use std::path::PathBuf;

let client = Client::builder()
    .user_agent(UserAgent::new(Agent::new("my-user-agent", "1.0.0")))

The client can then be used with Conjure-generated service interfaces:

use conjure_codegen::example_types::another::TestServiceAsyncClient;
use conjure_http::client::AsyncService;
use conjure_object::BearerToken;

let client = TestServiceAsyncClient::new(client);

let auth = BearerToken::new("my_auth_token").unwrap();
let file_systems = client.get_file_systems(&auth).await?;

The blocking::Client's API is identical, with the exception that you don't .await on methods:

use conjure_codegen::example_types::another::TestServiceClient;
use conjure_http::client::Service;
use conjure_object::BearerToken;

let client = TestServiceClient::new(client);

let auth = BearerToken::new("my_auth_token").unwrap();
let file_systems = client.get_file_systems(&auth)?;

The client can be used to communicate with non-Conjure APIs by directly using the low level Client and AsyncClient traits.


conjure_runtime wraps the hyper HTTP library with opinionated behavior designed to more effectively communicate between services in a distributed system. It is broadly designed to align with the dialogue Java library, though it does differ in various ways.

Error Propagation

Servers should use the standard Conjure error format to propagate application-specific errors to callers. Non-QoS (see below) errors received from the server are treated as fatal. By default, conjure_runtime will return a conjure_error::Error that will generate a generic 500 Internal Server Error response. Its cause will be a RemoteError object that contains the serialized Conjure error information sent by the server. The [Builder::service_error()] and [ClientFactory::service_error()] methods can be used to change that behavior to instead transparently propagate the error received from the server. Rather than producing a generic 500 response, the returned conjure_error::Error will produce the same response the client received from the server.

Call Tracing

The client propagates trace information via the zipkin crate using the traditional X-B3-* HTTP headers. It also creates local spans covering various stages of request processing:

  • conjure-runtime: request
    • conjure-runtime: attempt
      • conjure-runtime: acquire-permit - If client QoS is enabled and the node selection strategy is not Balanced, this span covers the time spent acquiring a concurrency limiter permit.
      • conjure-runtime: balanced-node-selection - If the node selection strategy is Balanced, this span covers the time spent selecting a node and (if client QoS is enabled) acquiring a concurrency limiter permit.
      • conjure-runtime: wait-for-headers - This span is sent to the server, and lasts until the server sends the headers of the response.
      • conjure-runtime: wait-for-body - This span is tracked along with the response body, and lasts until the ResponseBody object is dropped. It is "detached" from the zipkin tracer so new spans created outside of conjure-runtime will not be parented to it, and can outlive the parent conjure-runtime spans. It will not be created if an IO error occurs before headers are received.
    • conjure-runtime: backoff-with-jitter - If the request is retried, this span tracks the time spent waiting between attempts.
    • conjure-runtime: attempt
      • ...

Quality of Service: Retry, Failover, Throttling, and Backpressure

The client treats certain HTTP errors specially. Servers can advertise an overloaded state via the 429 Too Many Requests or 503 Service Unavailable status codes. Unlike other 4xx and 5xx status codes, these responses do not cause the request to fail. Instead, conjure_runtime will throttle itself and retry the request. Requests are retried a fixed number of times, with an exponentially growing backoff in between attempts. If a 429 response contains a Retry-After header, its backoff will be used rather than the default. IO errors also trigger a retry.

A 503 response or IO error will also cause that host to be temporarily put on "cooldown" so it will not be used by other requests unless there is no other option.

Only some requests can be retried. By default, conjure_runtime will only retry requests with HTTP methods identified as idempotent - GET, PUT, DELETE, HEAD, TRACE, and OPTIONS. Non-idempotent requests cannot be safely retried to avoid the risk of unexpected behavior if the request ends up being applied twice. The [Builder::idempotency()] and [ClientFactory::idempotency()] methods can be used to override this behavior and have the client assume all or no requests are idempotent. In addition, requests with streaming request bodies can only be retried if the body had either not started to be written when the error occurred or if it was successfully reset for another attempt.


Clients record metrics to both a standard MetricRegistry and a conjure_runtime-specific HostMetricsRegistry.

Standard Metrics

  • client.response (channel-name: <channel_name>, service-name: <service_name>, endpoint: <endpoint>, status: <status>) - A Timer recording request durations per endpoint. Note that the requests timed by this metric are the user-percieved request, including any backoffs/retries/etc. It only records the time until response headers are received, not until the entire response body is read. The status tag will be success if the response status was 2xx and will be failure otherwise (QoS failure, internal server error, IO error, etc).
  • tls.handshake (context: <service_name>, protocol: <protocol_version>, cipher: <cipher_name>) - A Meter tracking the rate of TLS handshakes, tagged by the service, TLS protocol version (e.g. TLSv1.3), and cipher name (e.g. TLS_CHACHA20_POLY1305_SHA256).
  • conjure-runtime.concurrencylimiter.max (service: <service_name>, hostIndex: <host_index>) - A Gauge reporting the maximum number of concurrent requests which are currently permitted to be made to a specific host.
  • conjure-runtime.concurrencylimiter.in-flight (service: <service_name>, hostIndex: <host_index>) - A Gauge reporting the current number of requests being made to a specific host.

Host Metrics

The HostMetricsRegistry contains metrics for every host of every service being actively used by a conjure_runtime client.


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