inspector: document bad usage for --inspect-port

Document --inspect-port, and fix the reporting for when it is misused.

The option requires an argument, but when the argument was omitted, the
error message incorrectly reported --inspect-port as being bad, as if
was not supported at all:

    % node --inspect-port
    node: bad option: --inspect-port
    % node --none-such
    node: bad option: --none-such

It is now correctly reported as requiring an argument:

    % ./node --inspect-port
    ./node: --inspect-port requires an argument

PR-URL: #12581
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/cli.md

@@ -112,6 +112,18 @@ added: v7.6.0
 -->
 
 Activate inspector on host:port and break at start of user script.
+Default host:port is 127.0.0.1:9229.
+
+
+### `--inspect-port=[host:]port`
+<!-- YAML
+added: v7.6.0
+-->
+
+Set the host:port to be used when the inspector is activated.
+Useful when activating the inspector by sending the `SIGUSR1` signal.
+
+Default host is 127.0.0.1.
 
 
 ### `--no-deprecation`

doc/node.1

@@ -106,6 +106,10 @@ instances for debugging and profiling. It uses the Chrome Debugging Protocol.
 .BR \-\-inspect-brk \fI[=[host:]port]\fR
 Activate inspector on host:port and break at start of user script.
 
+.TP
+.BR \-\-inspect-port \fI=[host:]port\fR
+Set the host:port to be used when the inspector is activated.
+
 .TP
 .BR \-\-no\-deprecation
 Silence deprecation warnings.

src/node.cc

@@ -3612,6 +3612,8 @@ static void PrintHelp() {
          "  --inspect-brk[=[host:]port]\n"
          "                             activate inspector on host:port\n"
          "                             and break at start of user script\n"
+         "  --inspect-port=[host:]port\n"
+         "                             set host:port for inspector\n"
 #endif
          "  --no-deprecation           silence deprecation warnings\n"
          "  --trace-deprecation        show stack traces on deprecations\n"
@@ -3798,7 +3800,7 @@ static void ParseArgs(int* argc,
 
     CheckIfAllowedInEnv(argv[0], is_env, arg);
 
-    if (debug_options.ParseOption(arg)) {
+    if (debug_options.ParseOption(argv[0], arg)) {
       // Done, consumed by DebugOptions::ParseOption().
     } else if (strcmp(arg, "--version") == 0 || strcmp(arg, "-v") == 0) {
       printf("%s\n", NODE_VERSION);

src/node_debug_options.cc

@@ -62,7 +62,7 @@ DebugOptions::DebugOptions() :
                                wait_connect_(false), http_enabled_(false),
                                host_name_("127.0.0.1"), port_(-1) { }
 
-bool DebugOptions::ParseOption(const std::string& option) {
+bool DebugOptions::ParseOption(const char* argv0, const std::string& option) {
   bool enable_inspector = false;
   bool has_argument = false;
   std::string option_name;
@@ -72,21 +72,28 @@ bool DebugOptions::ParseOption(const std::string& option) {
   if (pos == std::string::npos) {
     option_name = option;
   } else {
-    has_argument = true;
     option_name = option.substr(0, pos);
     argument = option.substr(pos + 1);
+
+    if (argument.length() > 0)
+      has_argument = true;
+    else
+      argument.clear();
   }
 
   if (option_name == "--inspect") {
     enable_inspector = true;
   } else if (option_name == "--inspect-brk") {
     enable_inspector = true;
     wait_connect_ = true;
-  } else if ((option_name != "--debug-port" &&
-              option_name != "--inspect-port") ||
-              !has_argument) {
-    // only other valid possibility is --inspect-port,
-    // which requires an argument
+  } else if (option_name == "--debug-port" ||
+             option_name == "--inspect-port") {
+    if (!has_argument) {
+      fprintf(stderr, "%s: %s requires an argument\n",
+              argv0, option.c_str());
+      exit(9);
+    }
+  } else {
     return false;
   }
 

src/node_debug_options.h

@@ -9,7 +9,7 @@ namespace node {
 class DebugOptions {
  public:
   DebugOptions();
-  bool ParseOption(const std::string& option);
+  bool ParseOption(const char* argv0, const std::string& option);
   bool inspector_enabled() const {
 #if HAVE_INSPECTOR
     return inspector_enabled_;

test/parallel/test-cli-bad-options.js

@@ -0,0 +1,23 @@
+'use strict';
+require('../common');
+
+// Tests that node exits consistently on bad option syntax.
+
+const assert = require('assert');
+const spawn = require('child_process').spawnSync;
+
+requiresArgument('--inspect-port');
+requiresArgument('--inspect-port=');
+requiresArgument('--debug-port');
+requiresArgument('--debug-port=');
+requiresArgument('--eval');
+
+function requiresArgument(option) {
+  const r = spawn(process.execPath, [option], {encoding: 'utf8'});
+
+  assert.strictEqual(r.status, 9);
+
+  const msg = r.stderr.split(/\r?\n/)[0];
+  assert.strictEqual(msg, process.execPath + ': ' + option +
+                     ' requires an argument');
+}