response.go

package middleware

import (
	"bufio"
	"fmt"
	"io"
	"net"
	"net/http"
)

// response is an interface used by an HTTP handler to construct an HTTP
// response. ResponseWriter may not be used after the Handler.ServeHTTP method
// has returned. Here it’s being used to include additional data for the logger
// such as the time spent responding to the HTTP request and the total size in
// bytes of the response.
type response struct {
	http.ResponseWriter
	Status int
	Length int
}

// WriteHeader sends an HTTP response header with status code.
//
// 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.
func (w *response) WriteHeader(status int) {
	w.Status = status
	w.ResponseWriter.WriteHeader(status)
}

// Write writes the data to the connection as part of an HTTP reply.
//
// If WriteHeader has not been called, Write calls WriteHeader(http.StatusOK)
// before writing the data. If the Header does not contain a Content-Type line,
// Write adds a Content-Type set to the result of passing the initial 512 bytes
// of written data to DetectContentType.
//
// Depending on the HTTP protocol version and the client, calling Write or
// WriteHeader may prevent future reads on the Request.Body. For HTTP/1.x
// requests, handlers should read any needed request body data before writing
// the response. Once the headers have been flushed (due to either an explicit
// Flusher.Flush call or writing enough data to trigger a flush), the request
// body may be unavailable. For HTTP/2 requests, the Go HTTP server permits
// handlers to continue to read the request body while concurrently writing the
// response. However, such behavior may not be supported by all HTTP/2 clients.
// Handlers should read before writing if possible to maximize compatibility.
func (w *response) Write(b []byte) (int, error) {
	if w.Status == 0 {
		w.Status = http.StatusOK
	}

	w.Length += len(b)

	return w.ResponseWriter.Write(b)
}

// ReadFrom implements io.ReaderFrom by delegating to the underlying
// ResponseWriter when it supports it. The net/http server exposes io.ReaderFrom
// so that io.Copy (used by http.FileServer) can take the zero-copy sendfile(2)
// fast path when serving static files. Wrapping the ResponseWriter hides that
// method, so we forward it here to keep the optimization. When the underlying
// writer does not implement io.ReaderFrom, a regular copy is used instead. In
// both cases the recorded status and byte count stay in sync for the logger.
func (w *response) ReadFrom(src io.Reader) (int64, error) {
	if w.Status == 0 {
		w.Status = http.StatusOK
	}

	if rf, ok := w.ResponseWriter.(io.ReaderFrom); ok {
		n, err := rf.ReadFrom(src)
		w.Length += int(n)
		return n, err
	}

	// The underlying writer cannot read directly from the source, so copy the
	// data over. io.Copy writes straight to the wrapped writer to avoid double
	// counting through the Write method above.
	n, err := io.Copy(w.ResponseWriter, src)
	w.Length += int(n)
	return n, err
}

// Flush implements http.Flusher by delegating to the underlying ResponseWriter.
func (w *response) Flush() {
	if f, ok := w.ResponseWriter.(http.Flusher); ok {
		f.Flush()
	}
}

// Hijack implements http.Hijacker by delegating to the underlying ResponseWriter.
func (w *response) Hijack() (net.Conn, *bufio.ReadWriter, error) {
	if h, ok := w.ResponseWriter.(http.Hijacker); ok {
		return h.Hijack()
	}
	return nil, nil, fmt.Errorf("underlying ResponseWriter does not implement http.Hijacker")
}

// Push implements http.Pusher by delegating to the underlying ResponseWriter.
func (w *response) Push(target string, opts *http.PushOptions) error {
	if p, ok := w.ResponseWriter.(http.Pusher); ok {
		return p.Push(target, opts)
	}
	return fmt.Errorf("underlying ResponseWriter does not implement http.Pusher")
}