blob: ea7b38c8fc6e0be959e65aa7e2f1648774cb16da [file] [log] [blame]
// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package httptrace provides mechanisms to trace the events within
// HTTP client requests.
package httptrace
import (
// unique type to prevent assignment.
type clientEventContextKey struct{}
// ContextClientTrace returns the ClientTrace associated with the
// provided context. If none, it returns nil.
func ContextClientTrace(ctx context.Context) *ClientTrace {
trace, _ := ctx.Value(clientEventContextKey{}).(*ClientTrace)
return trace
// WithClientTrace returns a new context based on the provided parent
// ctx. HTTP client requests made with the returned context will use
// the provided trace hooks, in addition to any previous hooks
// registered with ctx. Any hooks defined in the provided trace will
// be called first.
func WithClientTrace(ctx context.Context, trace *ClientTrace) context.Context {
if trace == nil {
panic("nil trace")
old := ContextClientTrace(ctx)
ctx = context.WithValue(ctx, clientEventContextKey{}, trace)
if trace.hasNetHooks() {
nt := &nettrace.Trace{
ConnectStart: trace.ConnectStart,
ConnectDone: trace.ConnectDone,
if trace.DNSStart != nil {
nt.DNSStart = func(name string) {
trace.DNSStart(DNSStartInfo{Host: name})
if trace.DNSDone != nil {
nt.DNSDone = func(netIPs []interface{}, coalesced bool, err error) {
addrs := make([]net.IPAddr, len(netIPs))
for i, ip := range netIPs {
addrs[i] = ip.(net.IPAddr)
Addrs: addrs,
Coalesced: coalesced,
Err: err,
ctx = context.WithValue(ctx, nettrace.TraceKey{}, nt)
return ctx
// ClientTrace is a set of hooks to run at various stages of an outgoing
// HTTP request. Any particular hook may be nil. Functions may be
// called concurrently from different goroutines and some may be called
// after the request has completed or failed.
// ClientTrace currently traces a single HTTP request & response
// during a single round trip and has no hooks that span a series
// of redirected requests.
// See for more.
type ClientTrace struct {
// GetConn is called before a connection is created or
// retrieved from an idle pool. The hostPort is the
// "host:port" of the target or proxy. GetConn is called even
// if there's already an idle cached connection available.
GetConn func(hostPort string)
// GotConn is called after a successful connection is
// obtained. There is no hook for failure to obtain a
// connection; instead, use the error from
// Transport.RoundTrip.
GotConn func(GotConnInfo)
// PutIdleConn is called when the connection is returned to
// the idle pool. If err is nil, the connection was
// successfully returned to the idle pool. If err is non-nil,
// it describes why not. PutIdleConn is not called if
// connection reuse is disabled via Transport.DisableKeepAlives.
// PutIdleConn is called before the caller's Response.Body.Close
// call returns.
// For HTTP/2, this hook is not currently used.
PutIdleConn func(err error)
// GotFirstResponseByte is called when the first byte of the response
// headers is available.
GotFirstResponseByte func()
// Got100Continue is called if the server replies with a "100
// Continue" response.
Got100Continue func()
// DNSStart is called when a DNS lookup begins.
DNSStart func(DNSStartInfo)
// DNSDone is called when a DNS lookup ends.
DNSDone func(DNSDoneInfo)
// ConnectStart is called when a new connection's Dial begins.
// If net.Dialer.DualStack (IPv6 "Happy Eyeballs") support is
// enabled, this may be called multiple times.
ConnectStart func(network, addr string)
// ConnectDone is called when a new connection's Dial
// completes. The provided err indicates whether the
// connection completedly successfully.
// If net.Dialer.DualStack ("Happy Eyeballs") support is
// enabled, this may be called multiple times.
ConnectDone func(network, addr string, err error)
// TLSHandshakeStart is called when the TLS handshake is started. When
// connecting to a HTTPS site via a HTTP proxy, the handshake happens after
// the CONNECT request is processed by the proxy.
TLSHandshakeStart func()
// TLSHandshakeDone is called after the TLS handshake with either the
// successful handshake's connection state, or a non-nil error on handshake
// failure.
TLSHandshakeDone func(tls.ConnectionState, error)
// WroteHeaders is called after the Transport has written
// the request headers.
WroteHeaders func()
// Wait100Continue is called if the Request specified
// "Expected: 100-continue" and the Transport has written the
// request headers but is waiting for "100 Continue" from the
// server before writing the request body.
Wait100Continue func()
// WroteRequest is called with the result of writing the
// request and any body. It may be called multiple times
// in the case of retried requests.
WroteRequest func(WroteRequestInfo)
// WroteRequestInfo contains information provided to the WroteRequest
// hook.
type WroteRequestInfo struct {
// Err is any error encountered while writing the Request.
Err error
// compose modifies t such that it respects the previously-registered hooks in old,
// subject to the composition policy requested in t.Compose.
func (t *ClientTrace) compose(old *ClientTrace) {
if old == nil {
tv := reflect.ValueOf(t).Elem()
ov := reflect.ValueOf(old).Elem()
structType := tv.Type()
for i := 0; i < structType.NumField(); i++ {
tf := tv.Field(i)
hookType := tf.Type()
if hookType.Kind() != reflect.Func {
of := ov.Field(i)
if of.IsNil() {
if tf.IsNil() {
// Make a copy of tf for tf to call. (Otherwise it
// creates a recursive call cycle and stack overflows)
tfCopy := reflect.ValueOf(tf.Interface())
// We need to call both tf and of in some order.
newFunc := reflect.MakeFunc(hookType, func(args []reflect.Value) []reflect.Value {
return of.Call(args)
// DNSStartInfo contains information about a DNS request.
type DNSStartInfo struct {
Host string
// DNSDoneInfo contains information about the results of a DNS lookup.
type DNSDoneInfo struct {
// Addrs are the IPv4 and/or IPv6 addresses found in the DNS
// lookup. The contents of the slice should not be mutated.
Addrs []net.IPAddr
// Err is any error that occurred during the DNS lookup.
Err error
// Coalesced is whether the Addrs were shared with another
// caller who was doing the same DNS lookup concurrently.
Coalesced bool
func (t *ClientTrace) hasNetHooks() bool {
if t == nil {
return false
return t.DNSStart != nil || t.DNSDone != nil || t.ConnectStart != nil || t.ConnectDone != nil
// GotConnInfo is the argument to the ClientTrace.GotConn function and
// contains information about the obtained connection.
type GotConnInfo struct {
// Conn is the connection that was obtained. It is owned by
// the http.Transport and should not be read, written or
// closed by users of ClientTrace.
Conn net.Conn
// Reused is whether this connection has been previously
// used for another HTTP request.
Reused bool
// WasIdle is whether this connection was obtained from an
// idle pool.
WasIdle bool
// IdleTime reports how long the connection was previously
// idle, if WasIdle is true.
IdleTime time.Duration