cmd/dlv: add --continue to continue process on launch/attach (go-delv…

…e#1585)

* Add --continue to continue process on launch/attach

* Add small test of --continue

* regenerate usage docs

* minor cleanup

* Use similar approach to `trace` and connect and detach using a client instance

* back out previous attempt

* regen usage doc

* fix up continue test

* fix TestContinue to properly test --continue

* back out unnecessary changes

* update faq

Documentation/faq.md

@@ -28,14 +28,10 @@ And then connect to it from outside the container:
 dlv connect :4040
 ```
 
-The program will not start executing until you connect to Delve and send the `continue` command. If you want the program to start immediately you can do that by:
-
-1. Passing the `--accept-multiclient` option to the headless instance of delve: `dlv exec --headless --listen :4040 --accept-multiclient /path/to/executable`
-2. Using the following script:
+The program will not start executing until you connect to Delve and send the `continue` command.  If you want the program to start immediately you can do that by passing the `--continue` and `--accept-multiclient` options to Delve:
 
 ```
-#!/bin/bash
-while true; do sleep 1; dlv connect :4040 --init <(echo quit -c) && exit; done
+dlv exec --headless --continue --listen :4040 --accept-multiclient /path/to/executable
 ```
 
 Note that the connection to Delve is unauthenticated and will allow arbitrary remote code execution: *do not do this in production*.

Documentation/usage/dlv_debug.md

@@ -19,6 +19,7 @@ dlv debug [package]
 ### Options
 
 ```
+      --continue        Continue the debugged process on start.
       --output string   Output path for the binary. (default "./__debug_bin")
 ```
 

Documentation/usage/dlv_exec.md

@@ -17,6 +17,12 @@ or later, -gcflags="-N -l" on earlier versions of Go.
 dlv exec <path/to/binary>
 ```
 
+### Options
+
+```
+      --continue   Continue the debugged process on start.
+```
+
 ### Options inherited from parent commands
 
 ```

cmd/dlv/cmds/commands.go

@@ -33,6 +33,8 @@ var (
 	LogDest string
 	// Headless is whether to run without terminal.
 	Headless bool
+	// ContinueOnStart is whether to continue the process on startup
+	ContinueOnStart bool
 	// APIVersion is the requested API version while running headless
 	APIVersion int
 	// AcceptMulti allows multiple clients to connect to the same server
@@ -172,6 +174,7 @@ session.`,
 		Run: debugCmd,
 	}
 	debugCommand.Flags().String("output", "./__debug_bin", "Output path for the binary.")
+	debugCommand.Flags().BoolVar(&ContinueOnStart, "continue", false, "Continue the debugged process on start.")
 	RootCommand.AddCommand(debugCommand)
 
 	// 'exec' subcommand.
@@ -195,6 +198,7 @@ or later, -gcflags="-N -l" on earlier versions of Go.`,
 			os.Exit(execute(0, args, conf, "", executingExistingFile))
 		},
 	}
+	execCommand.Flags().BoolVar(&ContinueOnStart, "continue", false, "Continue the debugged process on start.")
 	RootCommand.AddCommand(execCommand)
 
 	// Deprecated 'run' subcommand.
@@ -561,7 +565,17 @@ func execute(attachPid int, processArgs []string, conf *config.Config, coreFile
 	defer logflags.Close()
 
 	if Headless && (InitFile != "") {
-		fmt.Fprint(os.Stderr, "Warning: init file ignored\n")
+		fmt.Fprint(os.Stderr, "Warning: init file ignored with --headless\n")
+	}
+	if ContinueOnStart {
+		if !Headless {
+			fmt.Fprint(os.Stderr, "Error: --continue only works with --headless; use an init file\n")
+			return 1
+		}
+		if !AcceptMulti {
+			fmt.Fprint(os.Stderr, "Error: --continue requires --accept-multiclient\n")
+			return 1
+		}
 	}
 
 	if !Headless && AcceptMulti {
@@ -633,6 +647,11 @@ func execute(attachPid int, processArgs []string, conf *config.Config, coreFile
 
 	var status int
 	if Headless {
+		if ContinueOnStart {
+			var client *rpc2.RPCClient
+			client = rpc2.NewClient(listener.Addr().String())
+			client.Disconnect(true) // true = continue after disconnect
+		}
 		ch := make(chan os.Signal, 1)
 		signal.Notify(ch, syscall.SIGINT)
 		select {

cmd/dlv/dlv_test.go

@@ -218,6 +218,39 @@ func TestOutput(t *testing.T) {
 	}
 }
 
+// TestContinue verifies that the debugged executable starts immediately with --continue
+func TestContinue(t *testing.T) {
+	const listenAddr = "localhost:40573"
+
+	dlvbin, tmpdir := getDlvBin(t)
+	defer os.RemoveAll(tmpdir)
+
+	buildtestdir := filepath.Join(protest.FindFixturesDir(), "buildtest")
+	cmd := exec.Command(dlvbin, "debug", "--headless", "--continue", "--accept-multiclient", "--listen", listenAddr)
+	cmd.Dir = buildtestdir
+	stdout, err := cmd.StdoutPipe()
+	assertNoError(err, t, "stderr pipe")
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("could not start headless instance: %v", err)
+	}
+
+	scan := bufio.NewScanner(stdout)
+	// wait for the debugger to start
+	for scan.Scan() {
+		t.Log(scan.Text())
+		if scan.Text() == "hello world!" {
+			break
+		} 
+	}
+
+	// and detach from and kill the headless instance
+	client := rpc2.NewClient(listenAddr)
+	if err := client.Detach(true); err != nil {
+		t.Fatalf("error detaching from headless instance: %v", err)
+	}
+	cmd.Wait()
+}
+
 func checkAutogenDoc(t *testing.T, filename, gencommand string, generated []byte) {
 	saved := slurpFile(t, filepath.Join(projectRoot(), filename))