transport: add oc exporter to this repo, change import path

This copies contrib.go.opencensus.io/exporters/stackdriver/propogation
to our local package. The aforementioned path is deprecated
with intent to live in this repo, since this repo has
google-specific code (and opencensus does not want company-
-specific code).

Note: the github location for contrib.go.etc.etc lives here:
https://github.com/census-ecosystem/opencensus-go-exporter-stackdriver/tree/2f26a5d1900c27d75297423079bda98fedb6712b/propagation

Change-Id: I2137002a15562232cd743ceeac2d075a238750e3
Reviewed-on: https://code-review.googlesource.com/32351
Reviewed-by: Brad Fitzpatrick <[email protected]>
Reviewed-by: Ramon Nogueira <[email protected]>

transport/http/go18.go

@@ -19,8 +19,8 @@ package http
 import (
 	"net/http"
 
-	"contrib.go.opencensus.io/exporter/stackdriver/propagation"
 	"go.opencensus.io/plugin/ochttp"
+	"google.golang.org/api/transport/http/internal/propagation"
 )
 
 func addOCTransport(trans http.RoundTripper) http.RoundTripper {

transport/http/internal/propagation/http.go

@@ -0,0 +1,94 @@
+// Copyright 2018 Google LLC
+//
+// 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 propagation implements X-Cloud-Trace-Context header propagation used
+// by Google Cloud products.
+package propagation
+
+import (
+	"encoding/binary"
+	"encoding/hex"
+	"fmt"
+	"net/http"
+	"strconv"
+	"strings"
+
+	"go.opencensus.io/trace"
+	"go.opencensus.io/trace/propagation"
+)
+
+const (
+	httpHeaderMaxSize = 200
+	httpHeader        = `X-Cloud-Trace-Context`
+)
+
+var _ propagation.HTTPFormat = (*HTTPFormat)(nil)
+
+// HTTPFormat implements propagation.HTTPFormat to propagate
+// traces in HTTP headers for Google Cloud Platform and Stackdriver Trace.
+type HTTPFormat struct{}
+
+// SpanContextFromRequest extracts a Stackdriver Trace span context from incoming requests.
+func (f *HTTPFormat) SpanContextFromRequest(req *http.Request) (sc trace.SpanContext, ok bool) {
+	h := req.Header.Get(httpHeader)
+	// See https://cloud.google.com/trace/docs/faq for the header HTTPFormat.
+	// Return if the header is empty or missing, or if the header is unreasonably
+	// large, to avoid making unnecessary copies of a large string.
+	if h == "" || len(h) > httpHeaderMaxSize {
+		return trace.SpanContext{}, false
+	}
+
+	// Parse the trace id field.
+	slash := strings.Index(h, `/`)
+	if slash == -1 {
+		return trace.SpanContext{}, false
+	}
+	tid, h := h[:slash], h[slash+1:]
+
+	buf, err := hex.DecodeString(tid)
+	if err != nil {
+		return trace.SpanContext{}, false
+	}
+	copy(sc.TraceID[:], buf)
+
+	// Parse the span id field.
+	spanstr := h
+	semicolon := strings.Index(h, `;`)
+	if semicolon != -1 {
+		spanstr, h = h[:semicolon], h[semicolon+1:]
+	}
+	sid, err := strconv.ParseUint(spanstr, 10, 64)
+	if err != nil {
+		return trace.SpanContext{}, false
+	}
+	binary.BigEndian.PutUint64(sc.SpanID[:], sid)
+
+	// Parse the options field, options field is optional.
+	if !strings.HasPrefix(h, "o=") {
+		return sc, true
+	}
+	o, err := strconv.ParseUint(h[2:], 10, 64)
+	if err != nil {
+		return trace.SpanContext{}, false
+	}
+	sc.TraceOptions = trace.TraceOptions(o)
+	return sc, true
+}
+
+// SpanContextToRequest modifies the given request to include a Stackdriver Trace header.
+func (f *HTTPFormat) SpanContextToRequest(sc trace.SpanContext, req *http.Request) {
+	sid := binary.BigEndian.Uint64(sc.SpanID[:])
+	header := fmt.Sprintf("%s/%d;o=%d", hex.EncodeToString(sc.TraceID[:]), sid, int64(sc.TraceOptions))
+	req.Header.Set(httpHeader, header)
+}

transport/http/internal/propagation/http_test.go

@@ -0,0 +1,70 @@
+// Copyright 2018 Google LLC
+//
+// 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 propagation
+
+import (
+	"net/http"
+	"reflect"
+	"testing"
+
+	"go.opencensus.io/trace"
+)
+
+func TestHTTPFormat(t *testing.T) {
+	format := &HTTPFormat{}
+	traceID := [16]byte{16, 84, 69, 170, 120, 67, 188, 139, 242, 6, 177, 32, 0, 16, 0, 0}
+	spanID1 := [8]byte{255, 0, 0, 0, 0, 0, 0, 123}
+	spanID2 := [8]byte{0, 0, 0, 0, 0, 0, 0, 123}
+	tests := []struct {
+		incoming        string
+		wantSpanContext trace.SpanContext
+	}{
+		{
+			incoming: "105445aa7843bc8bf206b12000100000/18374686479671623803;o=1",
+			wantSpanContext: trace.SpanContext{
+				TraceID:      traceID,
+				SpanID:       spanID1,
+				TraceOptions: 1,
+			},
+		},
+		{
+			incoming: "105445aa7843bc8bf206b12000100000/123;o=0",
+			wantSpanContext: trace.SpanContext{
+				TraceID:      traceID,
+				SpanID:       spanID2,
+				TraceOptions: 0,
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.incoming, func(t *testing.T) {
+			req, _ := http.NewRequest("GET", "http://example.com", nil)
+			req.Header.Add(httpHeader, tt.incoming)
+			sc, ok := format.SpanContextFromRequest(req)
+			if !ok {
+				t.Errorf("exporter.SpanContextFromRequest() = false; want true")
+			}
+			if got, want := sc, tt.wantSpanContext; !reflect.DeepEqual(got, want) {
+				t.Errorf("exporter.SpanContextFromRequest() returned span context %v; want %v", got, want)
+			}
+
+			req, _ = http.NewRequest("GET", "http://example.com", nil)
+			format.SpanContextToRequest(sc, req)
+			if got, want := req.Header.Get(httpHeader), tt.incoming; got != want {
+				t.Errorf("exporter.SpanContextToRequest() returned header %q; want %q", got, want)
+			}
+		})
+	}
+}