docs: fix HTTP gateway streaming callback return type#296
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The streaming callback must return a non-opt StreamingCallbackHttpResponse, matching the real HTTP gateway (ic_boundary) implementation. The spec incorrectly wrapped the return type in opt. Confirmed by the StreamingCallbackFunction definition in dfinity/internet-identity and every shipping .did interface. Detected while adding e2e tests for streaming certified-assets (dfinity/certified-assets#96).
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Jun 17, 2026
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Summary
The streaming callback in the HTTP gateway protocol spec must return a non-opt
StreamingCallbackHttpResponse. The spec incorrectly wrapped the return type inopt, which no real gateway accepts — candid cannot coerce wire-typeopt Tinto the expectedT, so serving any multi-chunk (streamed) asset fails to decode.Fixed all three occurrences:
public/references/http-gateway.did(downloadable interface)docs/references/http-gateway-protocol-spec.md— full Canister HTTP Interface blockdocs/references/http-gateway-protocol-spec.md— Response Body Streaming Interface blockNote: only the callback's return type changes. The
token : opt Tokenfield insideStreamingCallbackHttpResponsestays optional — a null token (not a null response) terminates the stream.Verification
The real gateway decodes the callback reply into a non-opt
StreamingCallbackHttpResponse:ic-gateway→ic-http-gateway-protocol(tagv0.5.1) →ic-agent/ic-utilsic-http-gateway-protocol@ v0.5.1 —response_handler.rs#L116-L120: callshttp_request_stream_callbackand matchesOk((StreamingCallbackHttpResponse { body, token },))— the bare struct, noOption.ic-agent—ic-utils/src/interfaces/http_request.rs:http_request_stream_callback -> SyncCall<Value = (StreamingCallbackHttpResponse,)>, and the callback CandidTypefunc((ArgToken) -> (StreamingCallbackHttpResponse) query).Detected while adding e2e streaming tests for certified-assets (dfinity/certified-assets#96).
npm run buildpasses.