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@ribice
Created May 7, 2021 10:45
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// NewWrapResponseWriter wraps an http.ResponseWriter, returning a proxy that allows you to
// hook into various parts of the response process.
func NewWrapResponseWriter(w http.ResponseWriter, protoMajor int) WrapResponseWriter {
_, fl := w.(http.Flusher)
bw := basicWriter{ResponseWriter: w}
if protoMajor == 2 {
_, ps := w.(http.Pusher)
if fl && ps {
return &http2FancyWriter{bw}
}
} else {
_, hj := w.(http.Hijacker)
_, rf := w.(io.ReaderFrom)
if fl && hj && rf {
return &httpFancyWriter{bw}
}
}
if fl {
return &flushWriter{bw}
}
return &bw
}
// WrapResponseWriter is a proxy around an http.ResponseWriter that allows you to hook
// into various parts of the response process.
type WrapResponseWriter interface {
http.ResponseWriter
// Status returns the HTTP status of the request, or 0 if one has not
// yet been sent.
Status() int
// BytesWritten returns the total number of bytes sent to the client.
BytesWritten() int
// Tee causes the response body to be written to the given io.Writer in
// addition to proxying the writes through. Only one io.Writer can be
// tee'd to at once: setting a second one will overwrite the first.
// Writes will be sent to the proxy before being written to this
// io.Writer. It is illegal for the tee'd writer to be modified
// concurrently with writes.
Tee(io.Writer)
// Unwrap returns the original proxied target.
Unwrap() http.ResponseWriter
}
// basicWriter wraps a http.ResponseWriter that implements the minimal
// http.ResponseWriter interface.
type basicWriter struct {
http.ResponseWriter
wroteHeader bool
code int
bytes int
tee io.Writer
}
func (b *basicWriter) WriteHeader(code int) {
if !b.wroteHeader {
b.code = code
b.wroteHeader = true
}
b.ResponseWriter.WriteHeader(code)
}
func (b *basicWriter) Write(buf []byte) (int, error) {
b.maybeWriteHeader()
n, err := b.ResponseWriter.Write(buf)
if b.tee != nil {
_, err2 := b.tee.Write(buf[:n])
// Prefer errors generated by the proxied writer.
if err == nil {
err = err2
}
}
b.bytes += n
return n, err
}
func (b *basicWriter) maybeWriteHeader() {
if !b.wroteHeader {
b.WriteHeader(http.StatusOK)
}
}
func (b *basicWriter) Status() int {
return b.code
}
func (b *basicWriter) BytesWritten() int {
return b.bytes
}
func (b *basicWriter) Tee(w io.Writer) {
b.tee = w
}
func (b *basicWriter) Unwrap() http.ResponseWriter {
return b.ResponseWriter
}
type flushWriter struct {
basicWriter
}
func (f *flushWriter) Flush() {
f.wroteHeader = true
fl := f.basicWriter.ResponseWriter.(http.Flusher)
fl.Flush()
}
var _ http.Flusher = &flushWriter{}
// httpFancyWriter is a HTTP writer that additionally satisfies
// http.Flusher, http.Hijacker, and io.ReaderFrom. It exists for the common case
// of wrapping the http.ResponseWriter that package http gives you, in order to
// make the proxied object support the full method set of the proxied object.
type httpFancyWriter struct {
basicWriter
}
func (f *httpFancyWriter) Flush() {
f.wroteHeader = true
fl := f.basicWriter.ResponseWriter.(http.Flusher)
fl.Flush()
}
func (f *httpFancyWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
hj := f.basicWriter.ResponseWriter.(http.Hijacker)
return hj.Hijack()
}
func (f *http2FancyWriter) Push(target string, opts *http.PushOptions) error {
return f.basicWriter.ResponseWriter.(http.Pusher).Push(target, opts)
}
func (f *httpFancyWriter) ReadFrom(r io.Reader) (int64, error) {
if f.basicWriter.tee != nil {
n, err := io.Copy(&f.basicWriter, r)
f.basicWriter.bytes += int(n)
return n, err
}
rf := f.basicWriter.ResponseWriter.(io.ReaderFrom)
f.basicWriter.maybeWriteHeader()
n, err := rf.ReadFrom(r)
f.basicWriter.bytes += int(n)
return n, err
}
var _ http.Flusher = &httpFancyWriter{}
var _ http.Hijacker = &httpFancyWriter{}
var _ http.Pusher = &http2FancyWriter{}
var _ io.ReaderFrom = &httpFancyWriter{}
// http2FancyWriter is a HTTP2 writer that additionally satisfies
// http.Flusher, and io.ReaderFrom. It exists for the common case
// of wrapping the http.ResponseWriter that package http gives you, in order to
// make the proxied object support the full method set of the proxied object.
type http2FancyWriter struct {
basicWriter
}
func (f *http2FancyWriter) Flush() {
f.wroteHeader = true
fl := f.basicWriter.ResponseWriter.(http.Flusher)
fl.Flush()
}
var _ http.Flusher = &http2FancyWriter{}
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