feat: introduce fetch crate

[martintmk]

Summary

Introduces fetch, a fast and safe HTTP client for the Oxidizer project that is runtime-agnostic and transport-agnostic. It bundles the capabilities real-world services need — TLS, resilience, observability, and testability — into a single client that works out of the box, while letting libraries defer the choice of runtime and HTTP transport to the consuming application.

The request pipeline is built around a swappable transport handler at its leaf, with resilience, observability, routing, logging, and retries layered on top. Tokio + hyper work out of the box, but you can plug in any async runtime/IO, or even reuse another HTTP client (e.g. reqwest) as the transport.

Highlights

• Secure by default: Strong TLS validation via rustls (with aws-lc-rs) and platform trust store verification, or native-tls as an alternative backend.
• Resilient by default: Built-in retries, timeouts, circuit breaking, and hedging powered by seatbelt, pre-configured in the standard pipeline.
• Observable by default: OpenTelemetry-compatible metrics and logging handlers.
• Composable pipeline: Modular RequestHandler-based pipeline (standard, custom, and minimal variants) for adding or customizing behaviors.
• Built-in testability: The test-util feature mocks responses and client behavior for fast, deterministic tests with no network access.
• Memory efficient: Smart pooling and zero-copy BytesView buffers for large responses.
• Ergonomic, familiar API: get(), post(), put(), delete(), fetch_text(), fetch_bytes(), fetch_json() / fetch_json_owned(), plus templated-URI support.

Examples

Simple case — create a client and fetch text:

use fetch::{HttpClient, HttpError, Response, StatusExt};

#[tokio::main]
async fn main() -> Result<(), HttpError> {
    let client: HttpClient = HttpClient::new_tokio();

    let response: Response<String> = client
        .get("https://example.com")
        .fetch_text()
        .await?
        .ensure_success()?;

    println!("response: {}", response.body());
    Ok(())
}

Customized request — headers, HTTP version, and a body:

let response = client
    .post("https://api.example.com/upload")
    .header(header::AUTHORIZATION, "Bearer token123")
    .header(header::CONTENT_TYPE, "application/json")
    .version(Version::HTTP_2)
    .text("{\"name\": \"document.pdf\"}")
    .fetch()
    .await?;

Builder case — configure telemetry and TLS on the client itself:

use fetch::HttpClient;
use fetch::tls::TlsOptions;

let client = HttpClient::builder_tokio(ctx)
    .meter_provider(&meter_provider)
    .tls_options(
        TlsOptions::builder_rustls()
            .server_certificate_verifier(custom_verifier)
            .build(),
    )
    // Share a base URI across requests (trailing slash is mandatory)
    .base_uri(BaseUri::from_static("https://example.com/api/v1/"))
    .build();

// Resolves to https://example.com/api/v1/foo/bar
let response = client.get("/foo/bar").fetch().await?;

Feature flags

• tokio — Tokio runtime integration (HttpClient::new_tokio / builder_tokio).
• json — JSON request/response support.
• tls / rustls — rustls backend with aws-lc-rs (recommended).
• native-tls — platform native TLS backend.
• test-util — response/client mocking for tests.

Comparison vs. reqwest

Both build on hyper by default, but fetch adds first-class custom runtime/transport support, built-in resilience, OTel metrics/logging, a composable request pipeline, zero-copy buffers, and testing tools out of the box. Some advanced features (cookies, redirects, forms) are not yet supported and may come later.

[github-actions]

⚠️ Breaking Changes Detected

--- failure struct_marked_non_exhaustive: struct marked #[non_exhaustive] ---

Description:
A public struct has been marked #[non_exhaustive], which will prevent it from being constructed using a struct literal outside of its crate. It previously had no private fields, so a struct literal could be used to construct it outside its crate.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#attr-adding-non-exhaustive
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.48.0/src/lints/struct_marked_non_exhaustive.ron

Failed in:
  struct ConnectionPoolOptions in /home/runner/work/oxidizer/oxidizer/crates/fetch_options/src/pooling.rs:87

error: failed to retrieve local crate data from git revision

Caused by:
    0: failed to retrieve manifest file from git revision source
    1: possibly due to errors: [
         failed to parse /home/runner/work/oxidizer/oxidizer/target/semver-checks/git-origin_main/81f5ccae65721f2f441fd09696a8a8b249d73da9/Cargo.toml: no `package` table,
         failed when reading /home/runner/work/oxidizer/oxidizer/target/semver-checks/git-origin_main/81f5ccae65721f2f441fd09696a8a8b249d73da9/scripts/crate-template/Cargo.toml: TOML parse error at line 9, column 26
         |
       9 | keywords = ["oxidizer", {{CRATE_KEYWORDS}}]
         |                          ^
       missing key for inline table element, expected key
       : TOML parse error at line 9, column 26
         |
       9 | keywords = ["oxidizer", {{CRATE_KEYWORDS}}]
         |                          ^
       missing key for inline table element, expected key
       ,
       ]
    2: package `fetch` not found in /home/runner/work/oxidizer/oxidizer/target/semver-checks/git-origin_main/81f5ccae65721f2f441fd09696a8a8b249d73da9

Stack backtrace:
   0: anyhow::error::<impl anyhow::Error>::msg
   1: cargo_semver_checks::rustdoc_gen::RustdocFromProjectRoot::get_crate_source
   2: cargo_semver_checks::rustdoc_gen::StatefulRustdocGenerator<cargo_semver_checks::rustdoc_gen::CoupledState>::prepare_generator
   3: cargo_semver_checks::Check::check_release::{{closure}}
   4: cargo_semver_checks::Check::check_release
   5: cargo_semver_checks::exit_on_error
   6: cargo_semver_checks::main
   7: std::sys::backtrace::__rust_begin_short_backtrace
   8: main
   9: <unknown>
  10: __libc_start_main
  11: _start

If the breaking changes are intentional then everything is fine - this message is merely informative.

Remember to apply a version number bump with the correct severity when publishing a version with breaking changes (1.x.x -> 2.x.x or 0.1.x -> 0.2.x).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.0%. Comparing base (4b0c91b) to head (f79b128).

Additional details and impacted files

@@           Coverage Diff            @@
##             main     #475    +/-   ##
========================================
  Coverage   100.0%   100.0%            
========================================
  Files         319      335    +16     
  Lines       24676    25586   +910     
========================================
+ Hits        24676    25586   +910     

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Pull request overview

Copilot reviewed 84 out of 85 changed files in this pull request and generated 3 comments.