fs: add access() and accessSync()

fs.exists() and fs.existsSync() do not follow the typical
error first callback convention. access() and accessSync()
are added as alternatives in this commit.

Fixes: https://github.com/joyent/node/pull/8714
PR-URL: https://github.com/iojs/io.js/pull/114
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Domenic Denicola <domenic@domenicdenicola.com>

doc/api/fs.markdown

@@ -656,10 +656,43 @@ that leaves you vulnerable to race conditions: another process may remove the
 file between the calls to `fs.exists()` and `fs.open()`.  Just open the file
 and handle the error when it's not there.
 
+`fs.exists()` will be deprecated.
+
 ## fs.existsSync(path)
 
 Synchronous version of `fs.exists`.
 
+`fs.existsSync()` will be deprecated.
+
+## fs.access(path[, mode], callback)
+
+Tests a user's permissions for the file specified by `path`. `mode` is an
+optional integer that specifies the accessibility checks to be performed. The
+following constants define the possible values of `mode`. It is possible to
+create a mask consisting of the bitwise OR of two or more values.
+
+- `fs.F_OK` - File is visible to the calling process. This is useful for
+determining if a file exists, but says nothing about `rwx` permissions.
+Default if no `mode` is specified.
+- `fs.R_OK` - File can be read by the calling process.
+- `fs.W_OK` - File can be written by the calling process.
+- `fs.X_OK` - File can be executed by the calling process. This has no effect
+on Windows (will behave like `fs.F_OK`).
+
+The final argument, `callback`, is a callback function that is invoked with
+a possible error argument. If any of the accessibility checks fail, the error
+argument will be populated. The following example checks if the file
+`/etc/passwd` can be read and written by the current process.
+
+    fs.access('/etc/passwd', fs.R_OK | fs.W_OK, function(err) {
+      util.debug(err ? 'no access!' : 'can read/write');
+    });
+
+## fs.accessSync(path[, mode])
+
+Synchronous version of `fs.access`. This throws if any accessibility checks
+fail, and does nothing otherwise.
+
 ## Class: fs.Stats
 
 Objects returned from `fs.stat()`, `fs.lstat()` and `fs.fstat()` and their

lib/fs.js

@@ -51,6 +51,10 @@ var O_RDWR = constants.O_RDWR || 0;
 var O_SYNC = constants.O_SYNC || 0;
 var O_TRUNC = constants.O_TRUNC || 0;
 var O_WRONLY = constants.O_WRONLY || 0;
+var F_OK = constants.F_OK || 0;
+var R_OK = constants.R_OK || 0;
+var W_OK = constants.W_OK || 0;
+var X_OK = constants.X_OK || 0;
 
 var isWindows = process.platform === 'win32';
 
@@ -183,6 +187,39 @@ fs.Stats.prototype.isSocket = function() {
   return this._checkModeProperty(constants.S_IFSOCK);
 };
 
+fs.F_OK = F_OK;
+fs.R_OK = R_OK;
+fs.W_OK = W_OK;
+fs.X_OK = X_OK;
+
+fs.access = function(path, mode, callback) {
+  if (!nullCheck(path, callback))
+    return;
+
+  if (typeof mode === 'function') {
+    callback = mode;
+    mode = F_OK;
+  } else if (typeof callback !== 'function') {
+    throw new TypeError('callback must be a function');
+  }
+
+  mode = mode | 0;
+  var req = new FSReqWrap();
+  req.oncomplete = makeCallback(callback);
+  binding.access(pathModule._makeLong(path), mode, req);
+};
+
+fs.accessSync = function(path, mode) {
+  nullCheck(path);
+
+  if (mode === undefined)
+    mode = F_OK;
+  else
+    mode = mode | 0;
+
+  binding.access(pathModule._makeLong(path), mode);
+};
+
 fs.exists = function(path, callback) {
   if (!nullCheck(path, cb)) return;
   var req = new FSReqWrap();

src/node_constants.cc

@@ -1107,6 +1107,22 @@ void DefineSystemConstants(Handle<Object> target) {
 #ifdef S_IXOTH
   NODE_DEFINE_CONSTANT(target, S_IXOTH);
 #endif
+
+#ifdef F_OK
+  NODE_DEFINE_CONSTANT(target, F_OK);
+#endif
+
+#ifdef R_OK
+  NODE_DEFINE_CONSTANT(target, R_OK);
+#endif
+
+#ifdef W_OK
+  NODE_DEFINE_CONSTANT(target, W_OK);
+#endif
+
+#ifdef X_OK
+  NODE_DEFINE_CONSTANT(target, X_OK);
+#endif
 }
 
 void DefineUVConstants(Handle<Object> target) {

src/node_file.cc

@@ -165,6 +165,7 @@ static void After(uv_fs_t *req) {
 
     switch (req->fs_type) {
       // These all have no data to pass.
+      case UV_FS_ACCESS:
       case UV_FS_CLOSE:
       case UV_FS_RENAME:
       case UV_FS_UNLINK:
@@ -317,6 +318,28 @@ struct fs_req_wrap {
 #define SYNC_RESULT err
 
 
+static void Access(const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args.GetIsolate());
+  HandleScope scope(env->isolate());
+
+  if (args.Length() < 2)
+    return THROW_BAD_ARGS;
+  if (!args[0]->IsString())
+    return TYPE_ERROR("path must be a string");
+  if (!args[1]->IsInt32())
+    return TYPE_ERROR("mode must be an integer");
+
+  node::Utf8Value path(args[0]);
+  int mode = static_cast<int>(args[1]->Int32Value());
+
+  if (args[2]->IsObject()) {
+    ASYNC_CALL(access, args[2], *path, mode);
+  } else {
+    SYNC_CALL(access, *path, *path, mode);
+  }
+}
+
+
 static void Close(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
 
@@ -1112,6 +1135,7 @@ void InitFs(Handle<Object> target,
   target->Set(FIXED_ONE_BYTE_STRING(env->isolate(), "FSInitialize"),
               env->NewFunctionTemplate(FSInitialize)->GetFunction());
 
+  env->SetMethod(target, "access", Access);
   env->SetMethod(target, "close", Close);
   env->SetMethod(target, "open", Open);
   env->SetMethod(target, "read", Read);

test/simple/test-fs-access.js

@@ -0,0 +1,99 @@
+// Copyright io.js contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+var fs = require('fs');
+var path = require('path');
+var doesNotExist = __filename + '__this_should_not_exist';
+var readOnlyFile = path.join(common.tmpDir, 'read_only_file');
+
+var removeFile = function(file) {
+  try {
+    fs.unlinkSync(file);
+  } catch (err) {
+    // Ignore error
+  }
+};
+
+var createReadOnlyFile = function(file) {
+  removeFile(file);
+  fs.writeFileSync(file, '');
+  fs.chmodSync(file, 0444);
+};
+
+createReadOnlyFile(readOnlyFile);
+
+assert(typeof fs.F_OK === 'number');
+assert(typeof fs.R_OK === 'number');
+assert(typeof fs.W_OK === 'number');
+assert(typeof fs.X_OK === 'number');
+
+fs.access(__filename, function(err) {
+  assert.strictEqual(err, null, 'error should not exist');
+});
+
+fs.access(__filename, fs.R_OK, function(err) {
+  assert.strictEqual(err, null, 'error should not exist');
+});
+
+fs.access(doesNotExist, function(err) {
+  assert.notEqual(err, null, 'error should exist');
+  assert.strictEqual(err.code, 'ENOENT');
+  assert.strictEqual(err.path, doesNotExist);
+});
+
+fs.access(readOnlyFile, fs.F_OK | fs.R_OK, function(err) {
+  assert.strictEqual(err, null, 'error should not exist');
+});
+
+fs.access(readOnlyFile, fs.W_OK, function(err) {
+  assert.notEqual(err, null, 'error should exist');
+  assert.strictEqual(err.path, readOnlyFile);
+});
+
+assert.throws(function() {
+  fs.access(100, fs.F_OK, function(err) {});
+}, /path must be a string/);
+
+assert.throws(function() {
+  fs.access(__filename, fs.F_OK);
+}, /callback must be a function/);
+
+assert.doesNotThrow(function() {
+  fs.accessSync(__filename);
+});
+
+assert.doesNotThrow(function() {
+  var mode = fs.F_OK | fs.R_OK | fs.W_OK;
+
+  fs.accessSync(__filename, mode);
+});
+
+assert.throws(function() {
+  fs.accessSync(doesNotExist);
+}, function (err) {
+  return err.code === 'ENOENT' && err.path === doesNotExist;
+});
+
+process.on('exit', function() {
+  removeFile(readOnlyFile);
+});