└── propagation
    └── http.go


/propagation/http.go:
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 1 | // Copyright 2018, OpenCensus Authors
 2 | //
 3 | // Licensed under the Apache License, Version 2.0 (the "License");
 4 | // you may not use this file except in compliance with the License.
 5 | // You may obtain a copy of the License at
 6 | //
 7 | //     http://www.apache.org/licenses/LICENSE-2.0
 8 | //
 9 | // Unless required by applicable law or agreed to in writing, software
10 | // distributed under the License is distributed on an "AS IS" BASIS,
11 | // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 | // See the License for the specific language governing permissions and
13 | // limitations under the License.
14 | 
15 | // Package propagation implement X-Cloud-Function-Trace-Context header propagation used
16 | // by Google Cloud products.
17 | package propagation // import "github.com/kelseyhightower/functions/propagation"
18 | 
19 | import (
20 | 	"encoding/binary"
21 | 	"encoding/hex"
22 | 	"fmt"
23 | 	"net/http"
24 | 	"strconv"
25 | 	"strings"
26 | 
27 | 	"go.opencensus.io/trace"
28 | )
29 | 
30 | const (
31 | 	httpHeaderMaxSize = 200
32 | 	httpHeader        = `X-Cloud-Function-Trace-Context`
33 | )
34 | 
35 | 
36 | // SpanContextFromRequest extracts a Stackdriver Trace span context from incoming requests.
37 | func SpanContextFromRequest(req *http.Request) (sc trace.SpanContext, ok bool) {
38 | 	h := req.Header.Get(httpHeader)
39 | 	// See https://cloud.google.com/trace/docs/faq for the header HTTPFormat.
40 | 	// Return if the header is empty or missing, or if the header is unreasonably
41 | 	// large, to avoid making unnecessary copies of a large string.
42 | 	if h == "" || len(h) > httpHeaderMaxSize {
43 | 		return trace.SpanContext{}, false
44 | 	}
45 | 
46 | 	// Parse the trace id field.
47 | 	slash := strings.Index(h, `/`)
48 | 	if slash == -1 {
49 | 		return trace.SpanContext{}, false
50 | 	}
51 | 	tid, h := h[:slash], h[slash+1:]
52 | 
53 | 	buf, err := hex.DecodeString(tid)
54 | 	if err != nil {
55 | 		return trace.SpanContext{}, false
56 | 	}
57 | 	copy(sc.TraceID[:], buf)
58 | 
59 | 	// Parse the span id field.
60 | 	spanstr := h
61 | 	semicolon := strings.Index(h, `;`)
62 | 	if semicolon != -1 {
63 | 		spanstr, h = h[:semicolon], h[semicolon+1:]
64 | 	}
65 | 	sid, err := strconv.ParseUint(spanstr, 10, 64)
66 | 	if err != nil {
67 | 		return trace.SpanContext{}, false
68 | 	}
69 | 	binary.BigEndian.PutUint64(sc.SpanID[:], sid)
70 | 
71 | 	// Parse the options field, options field is optional.
72 | 	if !strings.HasPrefix(h, "o=") {
73 | 		return sc, true
74 | 	}
75 | 	o, err := strconv.ParseUint(h[2:], 10, 64)
76 | 	if err != nil {
77 | 		return trace.SpanContext{}, false
78 | 	}
79 | 	sc.TraceOptions = trace.TraceOptions(o)
80 | 	return sc, true
81 | }
82 | 
83 | // SpanContextToRequest modifies the given request to include a Stackdriver Trace header.
84 | func SpanContextToRequest(sc trace.SpanContext, req *http.Request) {
85 | 	sid := binary.BigEndian.Uint64(sc.SpanID[:])
86 | 	header := fmt.Sprintf("%s/%d;o=%d", hex.EncodeToString(sc.TraceID[:]), sid, int64(sc.TraceOptions))
87 | 	req.Header.Set(httpHeader, header)
88 | }
89 | 


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