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requestid.go
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requestid.go
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package gojiid
import (
"crypto/rand"
"encoding/base64"
"fmt"
"goji.io"
"golang.org/x/net/context"
"net/http"
"os"
"strings"
"sync/atomic"
)
// not exported to avoid collision with other context keys
type key int
// requestIdKey is the context key for the request id.
const requestIdKey key = 0
// Type for configuring the middleware to get the request id using custom HTTP headers and/or a custom generator
// Headers is a slice of HTTP Header keys used to look for the request id in the HTTP request
// Generator is a custom function that will return a new request id if one is not already found in the HTTP headers
type RequestIdConfig struct {
Headers []string
Generator func(req *http.Request) string
}
var prefix string
var idcounter uint64
// initializes default values for use with the default generator
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])
}
// creates the default middleware that just generates an id using the default generator
func NewRequestId() func(goji.Handler) goji.Handler {
config := &RequestIdConfig{make([]string, 0), defaultGenerator}
return NewCustomRequestId(config)
}
// creates the middleware configured with custom Headers and Generator function
func NewCustomRequestId(config *RequestIdConfig) func(goji.Handler) goji.Handler {
return func(h goji.Handler) goji.Handler {
fn := func(ctx context.Context, w http.ResponseWriter, r *http.Request) {
reqId, ok := fromHeaders(config.Headers, r)
if !ok {
reqId = config.Generator(r)
}
if len(reqId) > 0 {
ctx = context.WithValue(ctx, requestIdKey, reqId)
}
h.ServeHTTPC(ctx, w, r)
}
return goji.HandlerFunc(fn)
}
}
// Returns the request id that may have been previously set in the Context.
// If no request id was set, returns blank
func FromContext(ctx context.Context) string {
requestId, ok := ctx.Value(requestIdKey).(string)
if ok {
return requestId
} else {
return ""
}
}
func defaultGenerator(req *http.Request) string {
myid := atomic.AddUint64(&idcounter, 1)
return fmt.Sprintf("%s-%06d", prefix, myid)
}
func fromHeaders(headerKeys []string, req *http.Request) (string, bool) {
var reqId string
ok := false
for _, key := range headerKeys {
reqId = req.Header.Get(key)
if len(reqId) > 0 {
ok = true
break
}
}
return reqId, ok
}