Co-authored-by: trumpetinc 6618744+trumpetinc@users.noreply.github.com

Summary

This PR is the first step toward resolving #2734 — enabling request body streaming in Feign. It builds on the foundational work from @trumpetinc in #2754, which had become too outdated to merge directly.

The core idea is to change feign.Request.Body from a byte[]-backed structure to a streaming-ready abstraction. This means request bodies are no longer cached in memory unless explicitly needed — enabling Feign to send large files and streams without buffering.

What changed

Core changes

• feign.Request.Body is now an interface with:
  • writeTo(OutputStream) — the primary write mechanism
  • contentLength() — returns -1 for unknown/streaming bodies
  • isRepeatable() — false for non-repeatable bodies
  • writeToByteArray() and writeToString(Charset) — helper methods for repeatable bodies (use with caution)
  • Body.of(...) — factory methods for String, byte[] inputs
• feign.Request.BodyImpl is the default implementation for repeatable, non-streaming bodies. It overrides toString() for human-readable logging.
• feign.RequestTemplate now exposes a single body(Request.Body) setter. The old body(byte[], Charset) overload is @Deprecated for backward compatibility with spring-cloud-openfeign-core.
• feign.Request.body() now returns Optional<Request.Body> instead of byte[].
• feign.Request#length() removed — use Request.Body#contentLength() instead.
• feign.RequestTemplate#requestBody() returns Optional<Request.Body>.
• Removed feign.RequestTemplate#charset instance variable — charset should be read from Content-Type headers.
• Added feign.utils.ThrowingConsumer<T, E> functional interface.

HTTP client updates

All feign.Client implementations updated to stream bodies via Request.Body#writeTo:

Encoder updates

All encoder implementations updated to call template.body(Request.Body.of(...)):

• GsonEncoder, Jackson3Encoder, JAXBEncoder, JacksonJaxbJsonEncoder, Fastjson2Encoder, MoshiEncoder, SOAPEncoder, DefaultEncoder, JsonEncoder, Fastjson2Encoder

Vert.x streaming bridge

A new feign.vertx.OutputToReadStream class bridges Java blocking OutputStream to Vert.x ReadStream<Buffer>. It is adapted from io.cloudonix:vertx-java.io (MIT License) with a local compatibility fix to support both Vert.x 4 and Vert.x 5 (using onComplete instead of andThen to avoid a runtime linkage to io.vertx.core.Completable absent in Vert.x 4).

An issue has been filed upstream: cloudonix/vertx-java.io#8. Once fixed upstream, OutputToReadStream can be removed from this repo.

VertxFeign.Builder now requires .vertx(Vertx) in addition to .webClient(WebClient). A NullPointerException with a descriptive message is thrown if either is missing.

FeignException changes

• FeignException.errorReading(...) now passes null as the body (instead of request.body()), since the request body may be a non-repeatable stream and should not be cached.
• Related test assertions updated to expect isEmpty().

Logging

• Logger updated to use Request.Body#toString() (provided by BodyImpl) for repeatable bodies.

Metrics

• dropwizard-metrics4/5 MeteredEncoder: uses body.contentLength().
• micrometer MeteredEncoder: reads Content-Length header for recording.

mock module

• RequestKey no longer stores or compares Charset.
• RequestKey.Builder#charset(Charset) removed.

Known limitations / future work

1. spring-cloud-openfeign-core compatibility: RequestTemplate#body(byte[], Charset) kept as @Deprecated. Once the Spring team migrates to body(Request.Body), this can be removed.
2. Charset extraction: There is no trivial vanilla Java way to parse charset from Content-Type headers. UTF-8 is used as a fallback in writeToString. A separate issue/PR may be needed.
3. FeignException design: Response bodies are still cached as byte[] in FeignException. Reconsidering this is deferred to a future PR.
4. All tests pass, but the build should be triggered with -Djapicmp.skip=true property provided.

Credits

Special thanks to @trumpetinc whose original #2754 laid the groundwork for this change.

Related

• Partially implements Add support for streaming on requests (and add better handling for streaming in responses) #2734
• Based on Streaming bodies 3 #2754 by @trumpetinc
• Follow-up PRs planned:
  • Step 2: Make feign.form.MultipartFormContentProcessor streamable (introduce class MultipartBody implements feign.RequestBody)
  • Step 3: Make Response Body streamable