feat(provider-anthropic): AnthropicBridge with /v1/messages + typed SSE

[moonming]

Summary

Second concrete `Bridge` against the gateway trait — Anthropic's
Claude Messages API.

• wire.rs — Anthropic-specific request/response types.
  `split_system()` pulls leading system messages into Anthropic's
  top-level `system` field, `max_tokens` default fallback covers
  clients that omit the (required) field, and a typed `AnthropicStreamEvent`
  enum covers `message_start` / `content_block_delta` /
  `message_delta` / `message_stop` with a catch-all `Other`.
  `StreamState` carries message id/model across chunks so ChatChunk
  tagging stays consistent.
• bridge.rs — transport mirrors `OpenAiBridge` but sends
  `x-api-key` + `anthropic-version` headers and posts to
  `{base}/v1/messages`. Stream body pipes through `StreamState` so only
  content-bearing or finish-reason-bearing events become ChatChunks.
• `stop_reason` mapping: `end_turn → Stop`, `max_tokens → Length`,
  `tool_use → ToolCalls`, unknowns → `Other`. Tool role → `Config` error.
• `ANTHROPIC_VERSION` pinned to `2023-06-01` with builder escape hatch.

Test plan

• 19 new unit tests (10 wiremock-backed, 9 wire/translation)
  • happy path + 400 + malformed body + deadline + missing api_key
  • tool role → Config error
  • streaming happy path with typed SSE events
  • streaming 500 before stream starts
  • `split_system` merges/interleaves/rejects-tool
  • max_tokens default application
  • stop_reason mapping for all documented variants
• `cargo test --workspace` — 137 tests pass
• `cargo clippy --all-targets -- -D warnings` clean
• `cargo fmt --check` clean
• CI green across all 6 jobs

[Copilot]

Pull request overview

Adds a new provider implementation (aisix-provider-anthropic) that implements the gateway Bridge trait against Anthropic’s Claude Messages API (POST /v1/messages), including translation between the gateway’s OpenAI-shaped ChatFormat and Anthropic’s request/response shapes plus typed SSE streaming support.

Changes:

• Introduces Anthropic wire types and translation utilities (system-message collapsing, stop-reason mapping, typed stream events + stream state).
• Adds AnthropicBridge with reqwest transport, Anthropic-specific headers, /v1/messages endpoint handling, and SSE-to-ChatChunk streaming.
• Updates crate exports and dependencies to support streaming implementation and tests.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
crates/aisix-provider-anthropic/src/wire.rs	Adds Anthropic request/response models, system splitting, stop-reason mapping, typed SSE event parsing, and stream state/chunk translation.
crates/aisix-provider-anthropic/src/bridge.rs	Implements Bridge for Anthropic including non-streaming + streaming transport, SSE decoding, and wiremock-backed tests.
crates/aisix-provider-anthropic/src/lib.rs	Updates crate docs and exports AnthropicBridge + constants; declares modules.
crates/aisix-provider-anthropic/Cargo.toml	Adds runtime deps needed for streaming (tokio, futures, async-stream, bytes) plus test deps.
Cargo.lock	Locks new dependency graph entries for the Anthropic provider crate.

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[Copilot]

truncate() slices strings by byte index (&s[..n]), which can panic if the upstream body contains multi-byte UTF-8 and n lands mid-codepoint. Prefer truncating on a char boundary (e.g., using char_indices() to find the last valid boundary <= n) to avoid a potential crash while handling error responses.

Suggested change

	format!("{}…", &s[..n])
	let end = s
	.char_indices()
	.map(|(idx, _)| idx)
	.take_while(|&idx| idx <= n)
	.last()
	.unwrap_or(0);
	format!("{}…", &s[..end])

[Copilot]

build_chunk_stream() never calls decoder.finish() when the upstream closes the connection. If the final SSE event is not terminated by \n\n, it will remain buffered and be dropped, potentially losing the last delta/finish chunk. Consider flushing decoder.finish() after the while loop (similar to OpenAiBridge) and emitting any remaining event.

Suggested change

	}
	}
	for event in decoder.finish() {
	let SseEvent::Data(payload) = event else { continue };
	let parsed: AnthropicStreamEvent = serde_json::from_str(&payload)
	.map_err(|e| BridgeError::UpstreamDecode(e.to_string()))?;
	state.update(&parsed);
	if let Some(c) = state.to_chunk(&parsed) {
	yield c;
	}
	if StreamState::is_terminal(&parsed) {
	return;
	}
	}

[Copilot]

Module docs say the max_tokens default fallback is logged, but this file currently just applies unwrap_or(DEFAULT_MAX_TOKENS) with no tracing call. Either add the log at the point the default is chosen (so operators can see it), or update the docs to match actual behavior.

Suggested change

	//! when the client didn't set one, but log the fallback so operators
	//! can tune the default if desired.
	//! when the client didn't set one so requests remain valid.

[Copilot]

BridgeContext::deadline is documented as a deadline for the entire upstream call, but chat_stream() only applies it to the initial .send(); consuming the SSE body can run indefinitely after the deadline has elapsed. Consider enforcing the remaining deadline while reading the byte stream (e.g., track started + deadline in build_chunk_stream and return BridgeError::Timeout once exceeded, or wrap stream.next() with tokio::time::timeout).