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// Copyright 2018, OpenCensus Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package ochttp
import (
"bufio"
"context"
"errors"
"net"
"net/http"
"strconv"
"sync"
"time"
"go.opencensus.io/stats"
"go.opencensus.io/tag"
"go.opencensus.io/trace"
"go.opencensus.io/trace/propagation"
)
// Handler is a http.Handler that is aware of the incoming request's span.
//
// The extracted span can be accessed from the incoming request's
// context.
//
// span := trace.FromContext(r.Context())
//
// The server span will be automatically ended at the end of ServeHTTP.
//
// Incoming propagation mechanism is determined by the given HTTP propagators.
type Handler struct {
// Propagation defines how traces are propagated. If unspecified,
// B3 propagation will be used.
Propagation propagation.HTTPFormat
// Handler is the handler used to handle the incoming request.
Handler http.Handler
// StartOptions are applied to the span started by this Handler around each
// request.
//
// StartOptions.SpanKind will always be set to trace.SpanKindServer
// for spans started by this transport.
StartOptions trace.StartOptions
// IsPublicEndpoint should be set to true for publicly accessible HTTP(S)
// servers. If true, any trace metadata set on the incoming request will
// be added as a linked trace instead of being added as a parent of the
// current trace.
IsPublicEndpoint bool
}
func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
var traceEnd, statsEnd func()
r, traceEnd = h.startTrace(w, r)
defer traceEnd()
w, statsEnd = h.startStats(w, r)
defer statsEnd()
handler := h.Handler
if handler == nil {
handler = http.DefaultServeMux
}
handler.ServeHTTP(w, r)
}
func (h *Handler) startTrace(w http.ResponseWriter, r *http.Request) (*http.Request, func()) {
name := spanNameFromURL(r.URL)
ctx := r.Context()
var span *trace.Span
sc, ok := h.extractSpanContext(r)
if ok && !h.IsPublicEndpoint {
ctx, span = trace.StartSpanWithRemoteParent(ctx, name, sc,
trace.WithSampler(h.StartOptions.Sampler),
trace.WithSpanKind(trace.SpanKindServer))
} else {
ctx, span = trace.StartSpan(ctx, name,
trace.WithSampler(h.StartOptions.Sampler),
trace.WithSpanKind(trace.SpanKindServer),
)
if ok {
span.AddLink(trace.Link{
TraceID: sc.TraceID,
SpanID: sc.SpanID,
Type: trace.LinkTypeChild,
Attributes: nil,
})
}
}
span.AddAttributes(requestAttrs(r)...)
return r.WithContext(ctx), span.End
}
func (h *Handler) extractSpanContext(r *http.Request) (trace.SpanContext, bool) {
if h.Propagation == nil {
return defaultFormat.SpanContextFromRequest(r)
}
return h.Propagation.SpanContextFromRequest(r)
}
func (h *Handler) startStats(w http.ResponseWriter, r *http.Request) (http.ResponseWriter, func()) {
ctx, _ := tag.New(r.Context(),
tag.Upsert(Host, r.URL.Host),
tag.Upsert(Path, r.URL.Path),
tag.Upsert(Method, r.Method))
track := &trackingResponseWriter{
start: time.Now(),
ctx: ctx,
writer: w,
}
if r.Body == nil {
// TODO: Handle cases where ContentLength is not set.
track.reqSize = -1
} else if r.ContentLength > 0 {
track.reqSize = r.ContentLength
}
stats.Record(ctx, ServerRequestCount.M(1))
return track, track.end
}
type trackingResponseWriter struct {
ctx context.Context
reqSize int64
respSize int64
start time.Time
statusCode int
statusLine string
endOnce sync.Once
writer http.ResponseWriter
}
// Compile time assertions for widely used net/http interfaces
var _ http.CloseNotifier = (*trackingResponseWriter)(nil)
var _ http.Flusher = (*trackingResponseWriter)(nil)
var _ http.Hijacker = (*trackingResponseWriter)(nil)
var _ http.Pusher = (*trackingResponseWriter)(nil)
var _ http.ResponseWriter = (*trackingResponseWriter)(nil)
var errHijackerUnimplemented = errors.New("ResponseWriter does not implement http.Hijacker")
func (t *trackingResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
hj, ok := t.writer.(http.Hijacker)
if !ok {
return nil, nil, errHijackerUnimplemented
}
return hj.Hijack()
}
func (t *trackingResponseWriter) CloseNotify() <-chan bool {
cn, ok := t.writer.(http.CloseNotifier)
if !ok {
return nil
}
return cn.CloseNotify()
}
func (t *trackingResponseWriter) Push(target string, opts *http.PushOptions) error {
pusher, ok := t.writer.(http.Pusher)
if !ok {
return http.ErrNotSupported
}
return pusher.Push(target, opts)
}
func (t *trackingResponseWriter) end() {
t.endOnce.Do(func() {
if t.statusCode == 0 {
t.statusCode = 200
}
span := trace.FromContext(t.ctx)
span.SetStatus(TraceStatus(t.statusCode, t.statusLine))
m := []stats.Measurement{
ServerLatency.M(float64(time.Since(t.start)) / float64(time.Millisecond)),
ServerResponseBytes.M(t.respSize),
}
if t.reqSize >= 0 {
m = append(m, ServerRequestBytes.M(t.reqSize))
}
ctx, _ := tag.New(t.ctx, tag.Upsert(StatusCode, strconv.Itoa(t.statusCode)))
stats.Record(ctx, m...)
})
}
func (t *trackingResponseWriter) Header() http.Header {
return t.writer.Header()
}
func (t *trackingResponseWriter) Write(data []byte) (int, error) {
n, err := t.writer.Write(data)
t.respSize += int64(n)
return n, err
}
func (t *trackingResponseWriter) WriteHeader(statusCode int) {
t.writer.WriteHeader(statusCode)
t.statusCode = statusCode
t.statusLine = http.StatusText(t.statusCode)
}
func (t *trackingResponseWriter) Flush() {
if flusher, ok := t.writer.(http.Flusher); ok {
flusher.Flush()
}
}
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