Update GCS storage library to support GetObject API on gzipped objects (#6506)

Fixes #6280

vendor/contrib.go.opencensus.io/exporter/stackdriver/propagation/http.go

@@ -0,0 +1,94 @@
+// 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 propagation implement X-Cloud-Trace-Context header propagation used
+// by Google Cloud products.
+package propagation // import "contrib.go.opencensus.io/exporter/stackdriver/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)
+}