Add NewWireError

Currently, only the Connect runtime can create errors that return true
when tested by `IsWireError`. However, streaming RPCs commonly indicate
partial failure by including an error code and message in their response
message. To propagate these partial failures properly, clients need a
way to construct wire errors. This commit adds `NewWireError` to satisfy
this use case.

error.go

@@ -118,6 +118,25 @@ func NewError(c Code, underlying error) *Error {
 	return &Error{code: c, err: underlying}
 }
 
+// NewWireError is similar to [NewError], but the resulting *Error returns true
+// when tested with [IsWireError].
+//
+// This is useful for clients trying to propagate partial failures from
+// streaming RPCs. Often, these RPCs include error information in their
+// response messages (for example, [gRPC server reflection] and
+// OpenTelemtetry's [OTLP]). Clients propagating these errors up the stack
+// should use NewWireError to clarify that the error was explicitly sent by the
+// server (rather than inferred from a lower-level networking error or
+// timeout).
+//
+// [gRPC server reflection]: https://github.com/grpc/grpc/blob/v1.49.2/src/proto/grpc/reflection/v1alpha/reflection.proto#L132-L136
+// [OTLP]: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/otlp.md#partial-success
+func NewWireError(c Code, underlying error) *Error {
+	err := NewError(c, underlying)
+	err.wireErr = true
+	return err
+}
+
 // IsWireError checks whether the error was returned by the server, as opposed
 // to being synthesized by the client.
 //

protocol_connect.go

@@ -943,8 +943,7 @@ func (e *connectWireError) asError() *Error {
 	if e.Code < minCode || e.Code > maxCode {
 		e.Code = CodeUnknown
 	}
-	err := NewError(e.Code, errors.New(e.Message))
-	err.wireErr = true
+	err := NewWireError(e.Code, errors.New(e.Message))
 	if len(e.Details) > 0 {
 		err.details = make([]*ErrorDetail, len(e.Details))
 		for i, detail := range e.Details {

protocol_grpc.go

@@ -701,8 +701,7 @@ func grpcErrorFromTrailer(bufferPool *bufferPool, protobuf Codec, trailer http.H
 		return errorf(CodeInternal, "gRPC protocol error: invalid error code %q", codeHeader)
 	}
 	message := grpcPercentDecode(bufferPool, trailer.Get(grpcHeaderMessage))
-	retErr := NewError(Code(code), errors.New(message))
-	retErr.wireErr = true
+	retErr := NewWireError(Code(code), errors.New(message))
 
 	detailsBinaryEncoded := trailer.Get(grpcHeaderDetails)
 	if len(detailsBinaryEncoded) > 0 {