serveError does not call WriteHeader() before calling Write()

[melugoyal]

Description

Gin should call c.Writer.WriteHeader(code) before calling c.Writer.Write(defaultMessage) when handling errors here: https://github.com/gin-gonic/gin/blob/b04917c53e310e3746ec90cd93106cda8c956211/gin.go#L658

from the documentation of the Write() function in net/http's ResponseWriter interface:

If WriteHeader has not yet been called, Write calls WriteHeader(http.StatusOK) before writing the data

This is an issue when injecting a custom response writer into Gin that needs to know the status that was written before Write is called. Otherwise the custom response writer defaults to 200 OK per the documentation above, then Gin later tries writing a different header with WriteHeaderNow().

Environment

• go version: 1.18
• gin version (or commit ref): 1.7.7 (issue is present on current master as well: b04917c53)

[mstmdev]

To my understanding, the implementation of c.Writer is responseWriter, the responseWriter.Write will call the WriteHeader first.

[melugoyal]

Right, but i am using a custom ResponseWriter with Gin (injected into the context), and when doing so, expect Gin to call WriteHeader before calling Write, as is documented in the interface godoc:

If WriteHeader is not called explicitly, the first call to Write will trigger an implicit WriteHeader(http.StatusOK). Thus explicit calls to WriteHeader are mainly used to send error codes

[mstmdev]

I get it. It looks like it will break some existing conventions.