// 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 ( context.Context) *ClientTrace { , := .Value(clientEventContextKey{}).(*ClientTrace) return } // 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 ( context.Context, *ClientTrace) context.Context { if == nil { panic("nil trace") } := ContextClientTrace() .compose() = context.WithValue(, clientEventContextKey{}, ) if .hasNetHooks() { := &nettrace.Trace{ ConnectStart: .ConnectStart, ConnectDone: .ConnectDone, } if .DNSStart != nil { .DNSStart = func( string) { .DNSStart(DNSStartInfo{Host: }) } } if .DNSDone != nil { .DNSDone = func( []any, bool, error) { := make([]net.IPAddr, len()) for , := range { [] = .(net.IPAddr) } .DNSDone(DNSDoneInfo{ Addrs: , Coalesced: , Err: , }) } } = context.WithValue(, nettrace.TraceKey{}, ) } return } // 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 https://blog.golang.org/http-tracing 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() // Got1xxResponse is called for each 1xx informational response header // returned before the final non-1xx response. Got1xxResponse is called // for "100 Continue" responses, even if Got100Continue is also defined. // If it returns an error, the client request is aborted with that error value. Got1xxResponse func(code int, header textproto.MIMEHeader) error // 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 completed 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 an HTTPS site via an 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) // WroteHeaderField is called after the Transport has written // each request header. At the time of this call the values // might be buffered and not yet written to the network. WroteHeaderField func(key string, value []string) // WroteHeaders is called after the Transport has written // all request headers. WroteHeaders func() // Wait100Continue is called if the Request specified // "Expect: 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 ( *ClientTrace) ( *ClientTrace) { if == nil { return } := reflect.ValueOf().Elem() := reflect.ValueOf().Elem() := .Type() for := 0; < .NumField(); ++ { := .Field() := .Type() if .Kind() != reflect.Func { continue } := .Field() if .IsNil() { continue } if .IsNil() { .Set() continue } // Make a copy of tf for tf to call. (Otherwise it // creates a recursive call cycle and stack overflows) := reflect.ValueOf(.Interface()) // We need to call both tf and of in some order. := reflect.MakeFunc(, func( []reflect.Value) []reflect.Value { .Call() return .Call() }) .Field().Set() } } // 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 ( *ClientTrace) () bool { if == nil { return false } return .DNSStart != nil || .DNSDone != nil || .ConnectStart != nil || .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 }