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// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0
package request // import "go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp/internal/request"
import (
"net/http"
"sync"
)
var _ http.ResponseWriter = &RespWriterWrapper{}
// RespWriterWrapper wraps a http.ResponseWriter in order to track the number of
// bytes written, the last error, and to catch the first written statusCode.
// TODO: The wrapped http.ResponseWriter doesn't implement any of the optional
// types (http.Hijacker, http.Pusher, http.CloseNotifier, etc)
// that may be useful when using it in real life situations.
type RespWriterWrapper struct {
http.ResponseWriter
OnWrite func(n int64) // must not be nil
mu sync.RWMutex
written int64
statusCode int
err error
wroteHeader bool
}
// NewRespWriterWrapper creates a new RespWriterWrapper.
//
// The onWrite attribute is a callback that will be called every time the data
// is written, with the number of bytes that were written.
func NewRespWriterWrapper(w http.ResponseWriter, onWrite func(int64)) *RespWriterWrapper {
return &RespWriterWrapper{
ResponseWriter: w,
OnWrite: onWrite,
statusCode: http.StatusOK, // default status code in case the Handler doesn't write anything
}
}
// Write writes the bytes array into the [ResponseWriter], and tracks the
// number of bytes written and last error.
func (w *RespWriterWrapper) Write(p []byte) (int, error) {
w.mu.Lock()
defer w.mu.Unlock()
if !w.wroteHeader {
w.writeHeader(http.StatusOK)
}
n, err := w.ResponseWriter.Write(p)
n1 := int64(n)
w.OnWrite(n1)
w.written += n1
w.err = err
return n, err
}
// WriteHeader persists initial statusCode for span attribution.
// All calls to WriteHeader will be propagated to the underlying ResponseWriter
// and will persist the statusCode from the first call.
// Blocking consecutive calls to WriteHeader alters expected behavior and will
// remove warning logs from net/http where developers will notice incorrect handler implementations.
func (w *RespWriterWrapper) WriteHeader(statusCode int) {
w.mu.Lock()
defer w.mu.Unlock()
w.writeHeader(statusCode)
}
// writeHeader persists the status code for span attribution, and propagates
// the call to the underlying ResponseWriter.
// It does not acquire a lock, and therefore assumes that is being handled by a
// parent method.
func (w *RespWriterWrapper) writeHeader(statusCode int) {
if !w.wroteHeader {
w.wroteHeader = true
w.statusCode = statusCode
}
w.ResponseWriter.WriteHeader(statusCode)
}
// Flush implements [http.Flusher].
func (w *RespWriterWrapper) Flush() {
w.mu.Lock()
defer w.mu.Unlock()
if !w.wroteHeader {
w.writeHeader(http.StatusOK)
}
if f, ok := w.ResponseWriter.(http.Flusher); ok {
f.Flush()
}
}
// BytesWritten returns the number of bytes written.
func (w *RespWriterWrapper) BytesWritten() int64 {
w.mu.RLock()
defer w.mu.RUnlock()
return w.written
}
// BytesWritten returns the HTTP status code that was sent.
func (w *RespWriterWrapper) StatusCode() int {
w.mu.RLock()
defer w.mu.RUnlock()
return w.statusCode
}
// Error returns the last error.
func (w *RespWriterWrapper) Error() error {
w.mu.RLock()
defer w.mu.RUnlock()
return w.err
}
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