net/sockstats: expose debug info

Exposes some internal state of the sockstats package via the C2N and
PeerAPI endpoints, so that it can be used for debugging. For now this
includes the estimated radio on percentage and a second-by-second view
of the times the radio was active.

Also fixes another off-by-one error in the radio on percentage that
was leading to >100% values (if n seconds have passed since we started
to monitor, there may be n + 1 possible seconds where the radio could
have been on).

Updates tailscale/corp#9230

Signed-off-by: Mihai Parparita <mihai@tailscale.com>

ipn/ipnlocal/c2n.go

@@ -17,6 +17,7 @@ import (
 	"time"
 
 	"tailscale.com/envknob"
+	"tailscale.com/net/sockstats"
 	"tailscale.com/tailcfg"
 	"tailscale.com/util/clientmetric"
 	"tailscale.com/util/goroutines"
@@ -94,7 +95,8 @@ func (b *LocalBackend) handleC2N(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 		b.sockstatLogger.Flush()
-		fmt.Fprintln(w, b.sockstatLogger.LogID())
+		fmt.Fprintf(w, "logid: %s\n", b.sockstatLogger.LogID())
+		fmt.Fprintf(w, "debug info: %v\n", sockstats.DebugInfo())
 	default:
 		http.Error(w, "unknown c2n path", http.StatusBadRequest)
 	}

ipn/ipnlocal/peerapi.go

@@ -947,6 +947,12 @@ func (h *peerAPIHandler) handleServeSockStats(w http.ResponseWriter, r *http.Req
 	fmt.Fprintln(w, "</tfoot>")
 
 	fmt.Fprintln(w, "</table>")
+
+	fmt.Fprintln(w, "<h2>Debug Info</h2>")
+
+	fmt.Fprintln(w, "<pre>")
+	fmt.Fprintln(w, html.EscapeString(sockstats.DebugInfo()))
+	fmt.Fprintln(w, "</pre>")
 }
 
 type incomingFile struct {