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request_id.go
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request_id.go
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package middleware
import (
"crypto/rand"
"encoding/base64"
"fmt"
"os"
"strings"
"sync/atomic"
"github.com/emicklei/go-restful"
)
// Key to use when setting the request ID.
const RequestIDKey = "reqID"
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(req *restful.Request, resp *restful.Response, chain *restful.FilterChain) {
myid := atomic.AddUint64(&reqid, 1)
val := fmt.Sprintf("%s-%06d", prefix, myid)
req.SetAttribute(RequestIDKey, val)
chain.ProcessFilter(req, resp)
}
// 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(req *restful.Request) string {
v := req.Attribute(RequestIDKey)
if v == nil {
return ""
}
if reqID, ok := v.(string); ok {
return reqID
}
return ""
}