Log once a day how many connections had client_ip.

This is a sanity check against any catastrophic failure of our parsing
code.

server/server.go

@@ -269,6 +269,8 @@ func main() {
 		log.Fatalf("error in setup: %s", err)
 	}
 
+	go statsThread()
+
 	var certManager *autocert.Manager
 	if !disableTLS {
 		log.Printf("ACME hostnames: %q", acmeHostnames)

server/stats.go

@@ -0,0 +1,42 @@
+package main
+
+// This code handled periodic statistics logging.
+//
+// The only thing it keeps track of is how many connections had the client_ip
+// parameter. Write true to statsChannel to record a connection with client_ip;
+// write false for without.
+
+import (
+	"log"
+	"time"
+)
+
+const (
+	statsInterval = 24 * time.Hour
+)
+
+var (
+	statsChannel = make(chan bool)
+)
+
+func statsThread() {
+	var numClientIP, numConnections uint64
+	prevTime := time.Now()
+	for {
+		select {
+		case v := <-statsChannel:
+			if v {
+				numClientIP += 1
+			}
+			numConnections += 1
+		case <-time.After(statsInterval):
+			now := time.Now()
+			log.Printf("in the past %.g s, %d/%d connections had client_ip",
+				(now.Sub(prevTime)).Seconds(),
+				numClientIP, numConnections)
+			numClientIP = 0
+			numConnections = 0
+			prevTime = now
+		}
+	}
+}