Vendor dependencies for GCS

vendor/cloud.google.com/go/internal/tracecontext/tracecontext.go

@@ -0,0 +1,83 @@
+// Copyright 2017 Google Inc. All Rights Reserved.
+//
+// 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 tracecontext provides encoders and decoders for Stackdriver Trace contexts.
+package tracecontext
+
+import "encoding/binary"
+
+const (
+	versionID    = 0
+	traceIDField = 0
+	spanIDField  = 1
+	optsField    = 2
+
+	traceIDLen = 16
+	spanIDLen  = 8
+	optsLen    = 1
+
+	// Len represents the length of trace context.
+	Len = 1 + 1 + traceIDLen + 1 + spanIDLen + 1 + optsLen
+)
+
+// Encode encodes trace ID, span ID and options into dst. The number of bytes
+// written will be returned. If len(dst) isn't big enough to fit the trace context,
+// a negative number is returned.
+func Encode(dst []byte, traceID []byte, spanID uint64, opts byte) (n int) {
+	if len(dst) < Len {
+		return -1
+	}
+	var offset = 0
+	putByte := func(b byte) { dst[offset] = b; offset++ }
+	putUint64 := func(u uint64) { binary.LittleEndian.PutUint64(dst[offset:], u); offset += 8 }
+
+	putByte(versionID)
+	putByte(traceIDField)
+	for _, b := range traceID {
+		putByte(b)
+	}
+	putByte(spanIDField)
+	putUint64(spanID)
+	putByte(optsField)
+	putByte(opts)
+
+	return offset
+}
+
+// Decode decodes the src into a trace ID, span ID and options. If src doesn't
+// contain a valid trace context, ok = false is returned.
+func Decode(src []byte) (traceID []byte, spanID uint64, opts byte, ok bool) {
+	if len(src) < Len {
+		return traceID, spanID, 0, false
+	}
+	var offset = 0
+	readByte := func() byte { b := src[offset]; offset++; return b }
+	readUint64 := func() uint64 { v := binary.LittleEndian.Uint64(src[offset:]); offset += 8; return v }
+
+	if readByte() != versionID {
+		return traceID, spanID, 0, false
+	}
+	for offset < len(src) {
+		switch readByte() {
+		case traceIDField:
+			traceID = src[offset : offset+traceIDLen]
+			offset += traceIDLen
+		case spanIDField:
+			spanID = readUint64()
+		case optsField:
+			opts = readByte()
+		}
+	}
+	return traceID, spanID, opts, true
+}