1 files changed, 88 insertions, 0 deletions
diff --git a/vendor/github.com/zenazn/goji/web/middleware/request_id.go b/vendor/github.com/zenazn/goji/web/middleware/request_id.go
new file mode 100644
index 0000000..834d8e3
--- /dev/null
+++ b/vendor/github.com/zenazn/goji/web/middleware/request_id.go
@@ -0,0 +1,88 @@
+package middleware
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"net/http"
+	"os"
+	"strings"
+	"sync/atomic"
+
+	"github.com/zenazn/goji/web"
+)
+
+// 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(c *web.C, h http.Handler) http.Handler {
+	fn := func(w http.ResponseWriter, r *http.Request) {
+		if c.Env == nil {
+			c.Env = make(map[interface{}]interface{})
+		}
+		myid := atomic.AddUint64(&reqid, 1)
+		c.Env[RequestIDKey] = fmt.Sprintf("%s-%06d", prefix, myid)
+
+		h.ServeHTTP(w, r)
+	}
+
+	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(c web.C) string {
+	if c.Env == nil {
+		return ""
+	}
+	v, ok := c.Env[RequestIDKey]
+	if !ok {
+		return ""
+	}
+	if reqID, ok := v.(string); ok {
+		return reqID
+	}
+	return ""
+}