feat(gateway): Hub/Bridge abstractions + SSE decoder

[moonming]

Summary

Provider-agnostic core that every `aisix-provider-*` crate implements
against and that the proxy layer dispatches through.

• chat.rs — `ChatFormat` (normalised OpenAI-compatible request) +
  `ChatMessage`, `Role`, `ChatResponse`, streaming `ChatChunk`/`ChatDelta`,
  `UsageStats`, `FinishReason`. Unknown request fields land in
  `extra` via `serde(flatten)` so Bridges can forward/ignore.
• bridge.rs — `Bridge` trait (`chat` + `chat_stream`),
  `BridgeContext` (request id, `Arc`, optional deadline), typed
  `BridgeError` with stable `http_status()` + `error_type()` mapping. 4xx
  upstream passes through; 5xx collapses to 502 to hide infrastructure
  bleed-through.
• hub.rs — `Provider → Arc` registry backed by
  `DashMap` so runtime swaps don't lock readers.
• sse.rs — byte-stream-in / `SseEvent`-out SSE decoder with state
  that survives partial feeds. Not built on `eventsource-stream` so the
  Bridge trait stays HTTP-client-agnostic.

Also derives `Hash` on `aisix_core::Provider` so it can be a `DashMap` key.

Test plan

• `cargo test --workspace` — 103 tests pass (28 new, 75 existing)
• `cargo clippy --all-targets -- -D warnings` clean
• `cargo fmt --check` clean
• CI green across all 6 jobs

[Copilot]

Pull request overview

Introduces a new provider-agnostic “gateway core” (aisix-gateway) that standardizes chat request/response types, defines a Bridge trait for provider implementations, provides a Hub for dispatching by provider, and includes an SSE byte-stream decoder for streaming responses.

Changes:

• Add Bridge/BridgeContext/BridgeError abstractions and normalized chat types (ChatFormat, streaming chunks, usage/finish reasons).
• Add Hub registry backed by DashMap and an SSE decoder (SseDecoder) with tests.
• Derive Hash for aisix_core::models::Provider to support usage as a DashMap key.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
crates/aisix-gateway/src/lib.rs	Documents and re-exports the new gateway core modules.
crates/aisix-gateway/src/bridge.rs	Defines the provider-facing Bridge trait and typed error/status mapping.
crates/aisix-gateway/src/chat.rs	Adds normalized chat request/response and streaming delta types.
crates/aisix-gateway/src/hub.rs	Implements provider→bridge registry via DashMap with tests.
crates/aisix-gateway/src/sse.rs	Adds a feed-driven SSE event decoder with unit tests.
crates/aisix-gateway/Cargo.toml	Adds dashmap and dev-dependency tokio for tests.
crates/aisix-core/src/models/model.rs	Adds Hash derive to Provider.
Cargo.lock	Records dashmap dependency addition.

Comments suppressed due to low confidence (1)

crates/aisix-gateway/Cargo.toml:31

• aisix-gateway’s code in this PR doesn’t reference several dependencies currently listed in [dependencies] (e.g. reqwest, eventsource-stream, bytes, tokio-stream, futures-util, anyhow, tracing, http). Keeping unused deps increases compile time and muddies the crate’s “transport-agnostic core” intent; consider removing any that are no longer needed and re-adding when a module actually uses them.

anyhow.workspace = true
tracing.workspace = true
http.workspace = true
dashmap.workspace = true

[dev-dependencies]
tokio = { workspace = true, features = ["macros", "rt"] }

---

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[Copilot]

Hub::get() uses self.bridges.get(&provider).map(|r| r.clone()). This relies on method resolution through Deref to clone the inner Arc, which is a bit subtle to readers. Consider making the intent explicit (e.g., cloning the value via r.value() / Arc::clone(...)) to avoid confusion about whether the DashMap ref/guard is being cloned.

Suggested change

	self.bridges.get(&provider).map(|r| r.clone())
	self.bridges.get(&provider).map(|r| Arc::clone(r.value()))

[Copilot]

feed() decodes each incoming chunk with String::from_utf8_lossy(&bytes) and appends it to a String buffer. If a valid multi-byte UTF-8 codepoint is split across HTTP chunks, decoding per-chunk will emit U+FFFD replacement chars even though the overall stream is valid UTF-8, corrupting JSON payloads. Consider buffering raw bytes (e.g., Vec<u8>/BytesMut) and only UTF-8 decoding once you’ve identified complete \n\n-terminated event frames, so split codepoints are handled correctly.

[Copilot]

ChatMessage is marked with #[serde(deny_unknown_fields)], which will reject OpenAI-compatible message objects that include additional fields (e.g. tool_calls, legacy function_call, or future extensions). This conflicts with the surrounding goal of being permissive/forward-compatible (like ChatFormat.extra). Consider either removing deny_unknown_fields here or adding an extra field with #[serde(flatten)] on ChatMessage as well.