src: add -r/--require flags for preloading modules

-r/--require can be used to preload modules on node startup. The option
takes a single module name. The option can be repeated as necessary to
preload multiple modules.

This patch allows 'vendors' (such a cloud host) to inject functionality
that gets executed at application startup without requiring an explicit
require from the user's application. This can be useful to load vendor
specific application monitoring APIs transparently.

PR-URL: https://github.com/iojs/io.js/pull/881
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>

doc/iojs.1

@@ -52,6 +52,8 @@ and servers.
   -i, --interactive      always enter the REPL even if stdin
                          does not appear to be a terminal
 
+  -r, --require          module to preload at startup
+
   --no-deprecation       silence deprecation warnings
 
   --trace-deprecation    show stack traces on deprecations

src/node.cc

@@ -114,6 +114,8 @@ static bool trace_deprecation = false;
 static bool throw_deprecation = false;
 static bool abort_on_uncaught_exception = false;
 static const char* eval_string = nullptr;
+static unsigned int preload_module_count = 0;
+static const char** preload_modules = nullptr;
 static bool use_debug_agent = false;
 static bool debug_wait_connect = false;
 static int debug_port = 5858;
@@ -2765,6 +2767,19 @@ void SetupProcessObject(Environment* env,
     READONLY_PROPERTY(process, "_forceRepl", True(env->isolate()));
   }
 
+  if (preload_module_count) {
+    CHECK(preload_modules);
+    Local<Array> array = Array::New(env->isolate());
+    for (unsigned int i = 0; i < preload_module_count; ++i) {
+      Local<String> module = String::NewFromUtf8(env->isolate(),
+                                                 preload_modules[i]);
+      array->Set(i, module);
+    }
+    READONLY_PROPERTY(process,
+                      "_preload_modules",
+                      array);
+  }
+
   // --no-deprecation
   if (no_deprecation) {
     READONLY_PROPERTY(process, "noDeprecation", True(env->isolate()));
@@ -2989,6 +3004,7 @@ static void PrintHelp() {
          "  -p, --print          evaluate script and print result\n"
          "  -i, --interactive    always enter the REPL even if stdin\n"
          "                       does not appear to be a terminal\n"
+         "  -r, --require        module to preload (option can be repeated)\n"
          "  --no-deprecation     silence deprecation warnings\n"
          "  --throw-deprecation  throw an exception anytime a deprecated "
          "function is used\n"
@@ -3046,11 +3062,13 @@ static void ParseArgs(int* argc,
   const char** new_exec_argv = new const char*[nargs];
   const char** new_v8_argv = new const char*[nargs];
   const char** new_argv = new const char*[nargs];
+  const char** local_preload_modules = new const char*[nargs];
 
   for (unsigned int i = 0; i < nargs; ++i) {
     new_exec_argv[i] = nullptr;
     new_v8_argv[i] = nullptr;
     new_argv[i] = nullptr;
+    local_preload_modules[i] = nullptr;
   }
 
   // exec_argv starts with the first option, the other two start with argv[0].
@@ -3099,6 +3117,15 @@ static void ParseArgs(int* argc,
           eval_string += 1;
         }
       }
+    } else if (strcmp(arg, "--require") == 0 ||
+               strcmp(arg, "-r") == 0) {
+      const char* module = argv[index + 1];
+      if (module == nullptr) {
+        fprintf(stderr, "%s: %s requires an argument\n", argv[0], arg);
+        exit(9);
+      }
+      args_consumed += 1;
+      local_preload_modules[preload_module_count++] = module;
     } else if (strcmp(arg, "--interactive") == 0 || strcmp(arg, "-i") == 0) {
       force_repl = true;
     } else if (strcmp(arg, "--no-deprecation") == 0) {
@@ -3145,6 +3172,16 @@ static void ParseArgs(int* argc,
   memcpy(argv, new_argv, new_argc * sizeof(*argv));
   delete[] new_argv;
   *argc = static_cast<int>(new_argc);
+
+  // Copy the preload_modules from the local array to an appropriately sized
+  // global array.
+  if (preload_module_count > 0) {
+    CHECK(!preload_modules);
+    preload_modules = new const char*[preload_module_count];
+    memcpy(preload_modules, local_preload_modules,
+           preload_module_count * sizeof(*preload_modules));
+  }
+  delete[] local_preload_modules;
 }
 
 

src/node.js

@@ -68,7 +68,18 @@
       var d = NativeModule.require('_debug_agent');
       d.start();
 
-    } else if (process._eval != null) {
+    } else {
+      // There is user code to be run
+
+      // Load any preload modules
+      if (process._preload_modules) {
+        var Module = NativeModule.require('module');
+        process._preload_modules.forEach(function(module) {
+          Module._load(module);
+        });
+      }
+
+      if (process._eval != null) {
         // User passed '-e' or '--eval' arguments to Node.
         evalScript('[eval]');
       } else if (process.argv[1]) {
@@ -149,6 +160,7 @@
         }
       }
     }
+  }
 
   startup.globalVariables = function() {
     global.process = process;

test/fixtures/printA.js

@@ -0,0 +1 @@
+console.log('A')

test/fixtures/printB.js

@@ -0,0 +1 @@
+console.log('B')

test/fixtures/printC.js

@@ -0,0 +1 @@
+console.log('C')

test/parallel/test-preload.js

@@ -0,0 +1,75 @@
+var common = require('../common'),
+    assert = require('assert'),
+    path = require('path'),
+    child_process = require('child_process');
+
+var nodeBinary = process.argv[0];
+
+var preloadOption = function(preloads) {
+  var option = '';
+  preloads.forEach(function(preload, index) {
+    // TODO: randomly pick -r or --require
+    option += '-r ' + preload + ' ';
+  });
+  return option;
+}
+
+var fixture = function(name) {
+  return path.join(__dirname, '../fixtures/' + name);
+}
+
+var fixtureA = fixture('printA.js');
+var fixtureB = fixture('printB.js');
+var fixtureC = fixture('printC.js')
+var fixtureThrows = fixture('throws_error4.js');
+
+// test preloading a single module works
+child_process.exec(nodeBinary + ' '
+  + preloadOption([fixtureA]) + ' '
+  + fixtureB,
+  function(err, stdout, stderr) {
+    if (err) throw err;
+    assert.equal(stdout, 'A\nB\n');
+  });
+
+// test preloading multiple modules works
+child_process.exec(nodeBinary + ' '
+  + preloadOption([fixtureA, fixtureB]) + ' '
+  + fixtureC,
+  function(err, stdout, stderr) {
+    if (err) throw err;
+    assert.equal(stdout, 'A\nB\nC\n');
+  });
+
+// test that preloading a throwing module aborts
+child_process.exec(nodeBinary + ' '
+  + preloadOption([fixtureA, fixtureThrows]) + ' '
+  + fixtureB,
+  function(err, stdout, stderr) {
+    if (err) {
+      assert.equal(stdout, 'A\n');
+    } else {
+      throw new Error('Preload should have failed');
+    }
+  });
+
+// test that preload can be used with --eval
+child_process.exec(nodeBinary + ' '
+  + preloadOption([fixtureA])
+  + '-e \'console.log("hello");\'',
+  function(err, stdout, stderr) {
+    if (err) throw err;
+    assert.equal(stdout, 'A\nhello\n');
+  });
+
+// test that preload placement at other points in the cmdline
+// also test that duplicated preload only gets loaded once
+child_process.exec(nodeBinary + ' '
+  + preloadOption([fixtureA])
+  + '-e \'console.log("hello");\' ' 
+  + preloadOption([fixtureA, fixtureB]),
+  function(err, stdout, stderr) {
+    if (err) throw err;
+    assert.equal(stdout, 'A\nB\nhello\n');
+  });
+