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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 (
"context"
"io"
"net/http"
"strconv"
"sync"
"time"
"go.opencensus.io/stats"
"go.opencensus.io/tag"
"go.opencensus.io/trace"
"go.opencensus.io/trace/propagation"
)
// Handler is an http.Handler wrapper to instrument your HTTP server with
// OpenCensus. It supports both stats and tracing.
//
// Tracing
//
// This handler is aware of the incoming request's span, reading it from request
// headers as configured using the Propagation field.
// 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.
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
// FormatSpanName holds the function to use for generating the span name
// from the information found in the incoming HTTP Request. By default the
// name equals the URL Path.
FormatSpanName func(*http.Request) string
}
func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
var tags addedTags
r, traceEnd := h.startTrace(w, r)
defer traceEnd()
w, statsEnd := h.startStats(w, r)
defer statsEnd(&tags)
handler := h.Handler
if handler == nil {
handler = http.DefaultServeMux
}
r = r.WithContext(context.WithValue(r.Context(), addedTagsKey{}, &tags))
handler.ServeHTTP(w, r)
}
func (h *Handler) startTrace(w http.ResponseWriter, r *http.Request) (*http.Request, func()) {
if isHealthEndpoint(r.URL.Path) {
return r, func() {}
}
var name string
if h.FormatSpanName == nil {
name = spanNameFromURL(r)
} else {
name = h.FormatSpanName(r)
}
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(tags *addedTags)) {
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.wrappedResponseWriter(), 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 assertion for ResponseWriter interface
var _ http.ResponseWriter = (*trackingResponseWriter)(nil)
var logTagsErrorOnce sync.Once
func (t *trackingResponseWriter) end(tags *addedTags) {
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))
}
allTags := make([]tag.Mutator, len(tags.t)+1)
allTags[0] = tag.Upsert(StatusCode, strconv.Itoa(t.statusCode))
copy(allTags[1:], tags.t)
ctx, _ := tag.New(t.ctx, allTags...)
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)
}
// wrappedResponseWriter returns a wrapped version of the original
// ResponseWriter and only implements the same combination of additional
// interfaces as the original.
// This implementation is based on https://github.com/felixge/httpsnoop.
func (t *trackingResponseWriter) wrappedResponseWriter() http.ResponseWriter {
var (
hj, i0 = t.writer.(http.Hijacker)
cn, i1 = t.writer.(http.CloseNotifier)
pu, i2 = t.writer.(http.Pusher)
fl, i3 = t.writer.(http.Flusher)
rf, i4 = t.writer.(io.ReaderFrom)
)
switch {
case !i0 && !i1 && !i2 && !i3 && !i4:
return struct {
http.ResponseWriter
}{t}
case !i0 && !i1 && !i2 && !i3 && i4:
return struct {
http.ResponseWriter
io.ReaderFrom
}{t, rf}
case !i0 && !i1 && !i2 && i3 && !i4:
return struct {
http.ResponseWriter
http.Flusher
}{t, fl}
case !i0 && !i1 && !i2 && i3 && i4:
return struct {
http.ResponseWriter
http.Flusher
io.ReaderFrom
}{t, fl, rf}
case !i0 && !i1 && i2 && !i3 && !i4:
return struct {
http.ResponseWriter
http.Pusher
}{t, pu}
case !i0 && !i1 && i2 && !i3 && i4:
return struct {
http.ResponseWriter
http.Pusher
io.ReaderFrom
}{t, pu, rf}
case !i0 && !i1 && i2 && i3 && !i4:
return struct {
http.ResponseWriter
http.Pusher
http.Flusher
}{t, pu, fl}
case !i0 && !i1 && i2 && i3 && i4:
return struct {
http.ResponseWriter
http.Pusher
http.Flusher
io.ReaderFrom
}{t, pu, fl, rf}
case !i0 && i1 && !i2 && !i3 && !i4:
return struct {
http.ResponseWriter
http.CloseNotifier
}{t, cn}
case !i0 && i1 && !i2 && !i3 && i4:
return struct {
http.ResponseWriter
http.CloseNotifier
io.ReaderFrom
}{t, cn, rf}
case !i0 && i1 && !i2 && i3 && !i4:
return struct {
http.ResponseWriter
http.CloseNotifier
http.Flusher
}{t, cn, fl}
case !i0 && i1 && !i2 && i3 && i4:
return struct {
http.ResponseWriter
http.CloseNotifier
http.Flusher
io.ReaderFrom
}{t, cn, fl, rf}
case !i0 && i1 && i2 && !i3 && !i4:
return struct {
http.ResponseWriter
http.CloseNotifier
http.Pusher
}{t, cn, pu}
case !i0 && i1 && i2 && !i3 && i4:
return struct {
http.ResponseWriter
http.CloseNotifier
http.Pusher
io.ReaderFrom
}{t, cn, pu, rf}
case !i0 && i1 && i2 && i3 && !i4:
return struct {
http.ResponseWriter
http.CloseNotifier
http.Pusher
http.Flusher
}{t, cn, pu, fl}
case !i0 && i1 && i2 && i3 && i4:
return struct {
http.ResponseWriter
http.CloseNotifier
http.Pusher
http.Flusher
io.ReaderFrom
}{t, cn, pu, fl, rf}
case i0 && !i1 && !i2 && !i3 && !i4:
return struct {
http.ResponseWriter
http.Hijacker
}{t, hj}
case i0 && !i1 && !i2 && !i3 && i4:
return struct {
http.ResponseWriter
http.Hijacker
io.ReaderFrom
}{t, hj, rf}
case i0 && !i1 && !i2 && i3 && !i4:
return struct {
http.ResponseWriter
http.Hijacker
http.Flusher
}{t, hj, fl}
case i0 && !i1 && !i2 && i3 && i4:
return struct {
http.ResponseWriter
http.Hijacker
http.Flusher
io.ReaderFrom
}{t, hj, fl, rf}
case i0 && !i1 && i2 && !i3 && !i4:
return struct {
http.ResponseWriter
http.Hijacker
http.Pusher
}{t, hj, pu}
case i0 && !i1 && i2 && !i3 && i4:
return struct {
http.ResponseWriter
http.Hijacker
http.Pusher
io.ReaderFrom
}{t, hj, pu, rf}
case i0 && !i1 && i2 && i3 && !i4:
return struct {
http.ResponseWriter
http.Hijacker
http.Pusher
http.Flusher
}{t, hj, pu, fl}
case i0 && !i1 && i2 && i3 && i4:
return struct {
http.ResponseWriter
http.Hijacker
http.Pusher
http.Flusher
io.ReaderFrom
}{t, hj, pu, fl, rf}
case i0 && i1 && !i2 && !i3 && !i4:
return struct {
http.ResponseWriter
http.Hijacker
http.CloseNotifier
}{t, hj, cn}
case i0 && i1 && !i2 && !i3 && i4:
return struct {
http.ResponseWriter
http.Hijacker
http.CloseNotifier
io.ReaderFrom
}{t, hj, cn, rf}
case i0 && i1 && !i2 && i3 && !i4:
return struct {
http.ResponseWriter
http.Hijacker
http.CloseNotifier
http.Flusher
}{t, hj, cn, fl}
case i0 && i1 && !i2 && i3 && i4:
return struct {
http.ResponseWriter
http.Hijacker
http.CloseNotifier
http.Flusher
io.ReaderFrom
}{t, hj, cn, fl, rf}
case i0 && i1 && i2 && !i3 && !i4:
return struct {
http.ResponseWriter
http.Hijacker
http.CloseNotifier
http.Pusher
}{t, hj, cn, pu}
case i0 && i1 && i2 && !i3 && i4:
return struct {
http.ResponseWriter
http.Hijacker
http.CloseNotifier
http.Pusher
io.ReaderFrom
}{t, hj, cn, pu, rf}
case i0 && i1 && i2 && i3 && !i4:
return struct {
http.ResponseWriter
http.Hijacker
http.CloseNotifier
http.Pusher
http.Flusher
}{t, hj, cn, pu, fl}
case i0 && i1 && i2 && i3 && i4:
return struct {
http.ResponseWriter
http.Hijacker
http.CloseNotifier
http.Pusher
http.Flusher
io.ReaderFrom
}{t, hj, cn, pu, fl, rf}
default:
return struct {
http.ResponseWriter
}{t}
}
}