Alanxtl opened a new issue, #3444:
URL: https://github.com/apache/dubbo-go/issues/3444
### Problem
`triple_protocol.SetHeader` and `SetTrailer` document a unary handler usage
pattern, for example:
```go
func (srv *Server) Greet(ctx context.Context, req *greet.GreetRequest)
(*greet.GreetResponse, error) {
if err := triple.SetHeader(ctx, http.Header{"hi": []string{"triple"}});
err != nil {
return nil, err
}
if err := triple.SetTrailer(ctx, http.Header{"end": []string{"end"}});
err != nil {
return nil, err
}
return &greet.GreetResponse{}, nil
}
```
However, the generated Triple unary server path currently passes a `ctx`
that does not contain the internal `handlerOutgoingKey{}` connection value
required by `SetHeader` / `SetTrailer`.
As a result, calling either API from a generated unary service
implementation returns an error similar to:
```text
triple: failed to fetch the connection from the context ...
```
### Why this happens
The low-level unary handler in `protocol/triple/triple_protocol/handler.go`
embeds incoming metadata into the context with `newIncomingContext(ctx,
conn.RequestHeader())`, but it does not expose the handler connection through
`handlerOutgoingKey{}` before invoking the user handler.
Then `SetHeader` / `SetTrailer` in
`protocol/triple/triple_protocol/header.go` try to fetch:
```go
ctx.Value(handlerOutgoingKey{}).(StreamingHandlerConn)
```
and fail.
For generated unary handlers, the generated method wrapper also only calls
the business handler and wraps the returned business response with
`triple_protocol.NewResponse(res)`, so the application has no other
generated-level response metadata hook.
### Expected behavior
Generated Triple unary service implementations should be able to use
`triple.SetHeader(ctx, ...)` and `triple.SetTrailer(ctx, ...)` as documented,
and clients should be able to capture those values with
`client.WithResponseHeader` / `client.WithResponseTrailer`.
### Related context
Recent client-side work exposes unary response metadata capture through call
options. That solves the client read side, but this server-side generated unary
write path is still not usable with the documented API.
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