client/local: use an iterator to stream bus events (#16269)

This means the caller does not have to remember to close the reader, and avoids
having to duplicate the logic to decode JSON into events.

Updates #15160

Change-Id: I20186fabb02f72522f61d5908c4cc80b86b8936b
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>

client/local/local.go

@@ -1,12 +1,11 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
-//go:build go1.22
-
 // Package local contains a Go client for the Tailscale LocalAPI.
 package local
 
 import (
+	"bufio"
 	"bytes"
 	"cmp"
 	"context"
@@ -16,6 +15,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"iter"
 	"net"
 	"net/http"
 	"net/http/httptrace"
@@ -42,6 +42,7 @@ import (
 	"tailscale.com/types/dnstype"
 	"tailscale.com/types/key"
 	"tailscale.com/types/tkatype"
+	"tailscale.com/util/eventbus"
 	"tailscale.com/util/syspolicy/setting"
 )
 
@@ -414,24 +415,42 @@ func (lc *Client) TailDaemonLogs(ctx context.Context) (io.Reader, error) {
 	return res.Body, nil
 }
 
-// StreamBusEvents returns a stream of the Tailscale bus events as they arrive.
+// StreamBusEvents returns an iterator of Tailscale bus events as they arrive.
-// Close the context to stop the stream.
+// Each pair is a valid event and a nil error, or a zero event a non-nil error.
-// Expected response from the server is newline-delimited JSON.
+// In case of error, the iterator ends after the pair reporting the error.
-// The caller must close the reader when it is finished reading.
+// Iteration stops if ctx ends.
-func (lc *Client) StreamBusEvents(ctx context.Context) (io.ReadCloser, error) {
+func (lc *Client) StreamBusEvents(ctx context.Context) iter.Seq2[eventbus.DebugEvent, error] {
-	req, err := http.NewRequestWithContext(ctx, "GET",
+	return func(yield func(eventbus.DebugEvent, error) bool) {
-		"http://"+apitype.LocalAPIHost+"/localapi/v0/debug-bus-events", nil)
+		req, err := http.NewRequestWithContext(ctx, "GET",
-	if err != nil {
+			"http://"+apitype.LocalAPIHost+"/localapi/v0/debug-bus-events", nil)
-		return nil, err
+		if err != nil {
+			yield(eventbus.DebugEvent{}, err)
+			return
+		}
+		res, err := lc.doLocalRequestNiceError(req)
+		if err != nil {
+			yield(eventbus.DebugEvent{}, err)
+			return
+		}
+		if res.StatusCode != http.StatusOK {
+			yield(eventbus.DebugEvent{}, errors.New(res.Status))
+			return
+		}
+		defer res.Body.Close()
+		dec := json.NewDecoder(bufio.NewReader(res.Body))
+		for {
+			var evt eventbus.DebugEvent
+			if err := dec.Decode(&evt); err == io.EOF {
+				return
+			} else if err != nil {
+				yield(eventbus.DebugEvent{}, err)
+				return
+			}
+			if !yield(evt, nil) {
+				return
+			}
+		}
 	}
-	res, err := lc.doLocalRequestNiceError(req)
-	if err != nil {
-		return nil, err
-	}
-	if res.StatusCode != http.StatusOK {
-		return nil, errors.New(res.Status)
-	}
-	return res.Body, nil
 }
 
 // Pprof returns a pprof profile of the Tailscale daemon.

cmd/derper/depaware.txt

@@ -157,7 +157,7 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa
      💣 tailscale.com/util/deephash                                  from tailscale.com/util/syspolicy/setting
    L 💣 tailscale.com/util/dirwalk                                   from tailscale.com/metrics
         tailscale.com/util/dnsname                                   from tailscale.com/hostinfo+
-        tailscale.com/util/eventbus                                  from tailscale.com/net/netmon
+        tailscale.com/util/eventbus                                  from tailscale.com/net/netmon+
      💣 tailscale.com/util/hashx                                     from tailscale.com/util/deephash
         tailscale.com/util/httpm                                     from tailscale.com/client/tailscale
         tailscale.com/util/lineiter                                  from tailscale.com/hostinfo+

cmd/tailscale/cli/debug.go

@@ -791,21 +791,14 @@ func runDaemonLogs(ctx context.Context, args []string) error {
 }
 
 func runDaemonBusEvents(ctx context.Context, args []string) error {
-	logs, err := localClient.StreamBusEvents(ctx)
+	for line, err := range localClient.StreamBusEvents(ctx) {
-	if err != nil {
-		return err
-	}
-	defer logs.Close()
-	d := json.NewDecoder(bufio.NewReader(logs))
-	for {
-		var line eventbus.DebugEvent
-		err := d.Decode(&line)
 		if err != nil {
 			return err
 		}
 		fmt.Printf("[%d][%q][from: %q][to: %q] %s\n", line.Count, line.Type,
 			line.From, line.To, line.Event)
 	}
+	return nil
 }
 
 var metricsArgs struct {