-
-
Notifications
You must be signed in to change notification settings - Fork 972
/
request_id.go
96 lines (84 loc) · 2.9 KB
/
request_id.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
package middleware
// Ported from Goji's middleware, source:
// https://github.com/zenazn/goji/tree/master/web/middleware
import (
"context"
"crypto/rand"
"encoding/base64"
"fmt"
"net/http"
"os"
"strings"
"sync/atomic"
)
// Key to use when setting the request ID.
type ctxKeyRequestID int
// RequestIDKey is the key that holds the unique request ID in a request context.
const RequestIDKey ctxKeyRequestID = 0
// RequestIDHeader is the name of the HTTP Header which contains the request id.
// Exported so that it can be changed by developers
var RequestIDHeader = "X-Request-Id"
var prefix string
var reqid uint64
// A quick note on the statistics here: we're trying to calculate the chance that
// two randomly generated base62 prefixes will collide. We use the formula from
// http://en.wikipedia.org/wiki/Birthday_problem
//
// P[m, n] \approx 1 - e^{-m^2/2n}
//
// We ballpark an upper bound for $m$ by imagining (for whatever reason) a server
// that restarts every second over 10 years, for $m = 86400 * 365 * 10 = 315360000$
//
// For a $k$ character base-62 identifier, we have $n(k) = 62^k$
//
// Plugging this in, we find $P[m, n(10)] \approx 5.75%$, which is good enough for
// our purposes, and is surely more than anyone would ever need in practice -- a
// process that is rebooted a handful of times a day for a hundred years has less
// than a millionth of a percent chance of generating two colliding IDs.
func init() {
hostname, err := os.Hostname()
if hostname == "" || err != nil {
hostname = "localhost"
}
var buf [12]byte
var b64 string
for len(b64) < 10 {
rand.Read(buf[:])
b64 = base64.StdEncoding.EncodeToString(buf[:])
b64 = strings.NewReplacer("+", "", "/", "").Replace(b64)
}
prefix = fmt.Sprintf("%s/%s", hostname, b64[0:10])
}
// RequestID is a middleware that injects a request ID into the context of each
// request. A request ID is a string of the form "host.example.com/random-0001",
// where "random" is a base62 random string that uniquely identifies this go
// process, and where the last number is an atomically incremented request
// counter.
func RequestID(next http.Handler) http.Handler {
fn := func(w http.ResponseWriter, r *http.Request) {
ctx := r.Context()
requestID := r.Header.Get(RequestIDHeader)
if requestID == "" {
myid := atomic.AddUint64(&reqid, 1)
requestID = fmt.Sprintf("%s-%06d", prefix, myid)
}
ctx = context.WithValue(ctx, RequestIDKey, requestID)
next.ServeHTTP(w, r.WithContext(ctx))
}
return http.HandlerFunc(fn)
}
// GetReqID returns a request ID from the given context if one is present.
// Returns the empty string if a request ID cannot be found.
func GetReqID(ctx context.Context) string {
if ctx == nil {
return ""
}
if reqID, ok := ctx.Value(RequestIDKey).(string); ok {
return reqID
}
return ""
}
// NextRequestID generates the next request ID in the sequence.
func NextRequestID() uint64 {
return atomic.AddUint64(&reqid, 1)
}