Add a system() call to the d8 shell (Unix only).

src/d8-posix.cc

Index: src/d8-posix.cc
===================================================================
--- src/d8-posix.cc	(revision 0)
+++ src/d8-posix.cc	(revision 0)
@@ -0,0 +1,504 @@
+// Copyright 2009 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
+#include <stdlib.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/time.h>
+#include <time.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/wait.h>
+#include <signal.h>
+
+
+#include "d8.h"
+#include "d8-debug.h"
+#include "debug.h"
+
+
+namespace v8 {
+
+
+// If the buffer ends in the middle of a UTF-8 sequence then we return
+// the length of the string up to but not including the incomplete UTF-8
+// sequence.  If the buffer ends with a valid UTF-8 sequence then we
+// return the whole buffer.
+static int LengthWithoutIncompleteUtf8(char* buffer, int len) {
+  int answer = len;
+  // 1-byte encoding.
+  static const int kUtf8SingleByteMask = 0x80;
+  static const int kUtf8SingleByteValue = 0x00;
+  // 2-byte encoding.
+  static const int kUtf8TwoByteMask = 0xe0;
+  static const int kUtf8TwoByteValue = 0xc0;
+  // 3-byte encoding.
+  static const int kUtf8ThreeByteMask = 0xf0;
+  static const int kUtf8ThreeByteValue = 0xe0;
+  // 4-byte encoding.
+  static const int kUtf8FourByteMask = 0xf8;
+  static const int kUtf8FourByteValue = 0xf0;
+  // Subsequent bytes of a multi-byte encoding.
+  static const int kMultiByteMask = 0xc0;
+  static const int kMultiByteValue = 0x80;
+  int multi_byte_bytes_seen = 0;
+  while (answer > 0) {
+    int c = buffer[answer - 1];
+    // Ends in valid single-byte sequence?
+    if ((c & kUtf8SingleByteMask) == kUtf8SingleByteValue) return answer;
+    // Ends in one or more subsequent bytes of a multi-byte value?
+    if ((c & kMultiByteMask) == kMultiByteValue) {
+      multi_byte_bytes_seen++;
+      answer--;
+    } else {
+      if ((c & kUtf8TwoByteMask) == kUtf8TwoByteValue) {
+        if (multi_byte_bytes_seen >= 1) {
+          return answer + 2;
+        }
+        return answer - 1;
+      } else if ((c & kUtf8ThreeByteMask) == kUtf8ThreeByteValue) {
+        if (multi_byte_bytes_seen >= 2) {
+          return answer + 3;
+        }
+        return answer - 1;
+      } else if ((c & kUtf8FourByteMask) == kUtf8FourByteValue) {
+        if (multi_byte_bytes_seen >= 3) {
+          return answer + 4;
+        }
+        return answer - 1;
+      } else {
+        return answer;  // Malformed UTF-8.
+      }
+    }
+  }
+  return 0;
+}
+
+
+// Suspends the thread until there is data available from the child process.
+// Returns false on timeout, true on data ready.
+static bool WaitOnFD(int fd,
+                     int read_timeout,
+                     int* total_timeout,
+                     struct timeval& start_time) {
+  fd_set readfds, writefds, exceptfds;
+  struct timeval timeout;
+  if (*total_timeout != -1) {
+    struct timeval time_now;
+    gettimeofday(&time_now, NULL);
+    int seconds = time_now.tv_sec - start_time.tv_sec;
+    int gone = seconds * 1000 + (time_now.tv_usec - start_time.tv_usec) / 1000;
+    if (gone >= *total_timeout) return false;
+    *total_timeout -= gone;
+  }
+  FD_ZERO(&readfds);
+  FD_ZERO(&writefds);
+  FD_ZERO(&exceptfds);
+  FD_SET(fd, &readfds);
+  FD_SET(fd, &exceptfds);
+  if (read_timeout == -1 ||
+      (*total_timeout != -1 && *total_timeout < read_timeout)) {
+    read_timeout = *total_timeout;
+  }
+  timeout.tv_usec = (read_timeout % 1000) * 1000;
+  timeout.tv_sec = read_timeout / 1000;
+  int number_of_fds_ready = select(fd + 1,
+                                   &readfds,
+                                   &writefds,
+                                   &exceptfds,
+                                   read_timeout != -1 ? &timeout : NULL);
+  return number_of_fds_ready == 1;
+}
+
+
+// Checks whether we ran out of time on the timeout.  Returns true if we ran out
+// of time, false if we still have time.
+static bool TimeIsOut(const struct timeval& start_time, const int& total_time) {
+  if (total_time == -1) return false;
+  struct timeval time_now;
+  gettimeofday(&time_now, NULL);
+  // Careful about overflow.
+  int seconds = time_now.tv_sec - start_time.tv_sec;
+  if (seconds > 100) {
+    if (seconds * 1000 > total_time) return true;
+    return false;
+  }
+  int useconds = time_now.tv_usec - start_time.tv_usec;
+  if (seconds * 1000000 + useconds > total_time * 1000) {
+    return true;
+  }
+  return false;
+}
+
+
+// A utility class that does a non-hanging waitpid on the child process if we
+// bail out of the System() function early.  If you don't ever do a waitpid on
+// a subprocess then it turns into one of those annoying 'zombie processes'.
+class ZombieProtector {
+ public:
+  explicit ZombieProtector(int pid): pid_(pid) { }
+  ~ZombieProtector() { if (pid_ != 0) waitpid(pid_, NULL, WNOHANG); }
+  void ChildIsDeadNow() { pid_ = 0; }
+ private:
+  int pid_;
+};
+
+
+// A utility class that closes a file descriptor when it goes out of scope.
+class OpenFDCloser {
+ public:
+  explicit OpenFDCloser(int fd): fd_(fd) { }
+  ~OpenFDCloser() { close(fd_); }
+ private:
+  int fd_;
+};
+
+
+// A utility class that takes the array of command arguments and puts then in an
+// array of new[]ed UTF-8 C strings.  Deallocates them again when it goes out of
+// scope.
+class ExecArgs {
+ public:
+  ExecArgs(Handle<Value> arg0, Handle<Array> command_args) {
+    String::Utf8Value prog(arg0);
+    int len = prog.length() + 1;
+    char* c_arg = new char[len];
+    snprintf(c_arg, len, "%s", *prog);
+    exec_args_[0] = c_arg;
+    int i = 1;
+    for (unsigned j = 0; j < command_args->Length(); i++, j++) {
+      Handle<Value> arg(command_args->Get(Integer::New(j)));
+      String::Utf8Value utf8_arg(arg);
+      int len = utf8_arg.length() + 1;
+      char* c_arg = new char[len];
+      snprintf(c_arg, len, "%s", *utf8_arg);
+      exec_args_[i] = c_arg;
+    }
+    exec_args_[i] = NULL;
+  }
+  ~ExecArgs() {
+    for (unsigned i = 0; i < kMaxArgs; i++) {
+      if (exec_args_[i] == NULL) {
+        return;
+      }
+      delete [] exec_args_[i];
+      exec_args_[i] = 0;
+    }
+  }
+  static const unsigned kMaxArgs = 1000;
+  char** arg_array() { return exec_args_; }
+  char* arg0() { return exec_args_[0]; }
+ private:
+  char* exec_args_[kMaxArgs + 1];
+};
+
+
+// Gets the optional timeouts from the arguments to the system() call.
+static bool GetTimeouts(const Arguments& args,
+                        int* read_timeout,
+                        int* total_timeout) {
+  if (args.Length() > 3) {
+    if (args[3]->IsNumber()) {
+      *total_timeout = args[3]->Int32Value();
+    } else {
+      ThrowException(String::New("system: Argument 4 must be a number"));
+      return false;
+    }
+  }
+  if (args.Length() > 2) {
+    if (args[2]->IsNumber()) {
+      *read_timeout = args[2]->Int32Value();
+    } else {
+      ThrowException(String::New("system: Argument 3 must be a number"));
+      return false;
+    }
+  }
+  return true;
+}
+
+
+static const int kReadFD = 0;
+static const int kWriteFD = 1;
+
+
+// This is run in the child process after fork() but before exec().  It normally
+// ends with the child process being replaced with the desired child program.
+// It only returns if an error occurred.
+static void ExecSubprocess(int* exec_error_fds,
+                           int* stdout_fds,
+                           ExecArgs& exec_args) {
+  close(exec_error_fds[kReadFD]);  // Don't need this in the child.
+  close(stdout_fds[kReadFD]);      // Don't need this in the child.
+  close(1);                        // Close stdout.
+  dup2(stdout_fds[kWriteFD], 1);   // Dup pipe fd to stdout.
+  close(stdout_fds[kWriteFD]);     // Don't need the original fd now.
+  fcntl(exec_error_fds[kWriteFD], F_SETFD, FD_CLOEXEC);
+  execvp(exec_args.arg0(), exec_args.arg_array());
+  // Only get here if the exec failed.  Write errno to the parent to tell
+  // them it went wrong.  If it went well the pipe is closed.
+  int err = errno;
+  write(exec_error_fds[kWriteFD], &err, sizeof(err));
+  // Return (and exit child process).
+}
+
+
+// Runs in the parent process.  Checks that the child was able to exec (closing
+// the file desriptor), or reports an error if it failed.
+static bool ChildLaunchedOK(int* exec_error_fds) {
+  int bytes_read;
+  int err;
+  do {
+    bytes_read = read(exec_error_fds[kReadFD], &err, sizeof(err));
+  } while (bytes_read == -1 && errno == EINTR);
+  if (bytes_read != 0) {
+    ThrowException(String::New(strerror(err)));
+    return false;
+  }
+  return true;
+}
+
+
+// Accumulates the output from the child in a string handle.  Returns true if it
+// succeeded or false if an exception was thrown.
+static Handle<Value> GetStdout(int child_fd,
+                               struct timeval& start_time,
+                               int read_timeout,
+                               int* total_timeout) {
+  Handle<String> accumulator = String::Empty();
+  const char* source = "function(a, b) { return a + b; }";
+  Handle<Value> cons_as_obj(Script::Compile(String::New(source))->Run());
+  Handle<Function> cons_function(Function::Cast(*cons_as_obj));
+  Handle<Value> cons_args[2];
+
+  int fullness = 0;
+  static const int kStdoutReadBufferSize = 4096;
+  char buffer[kStdoutReadBufferSize];
+
+  if (fcntl(child_fd, F_SETFL, O_NONBLOCK) != 0) {
+    return ThrowException(String::New(strerror(errno)));
+  }
+
+  int bytes_read;
+  do {
+    bytes_read = read(child_fd,
+                      buffer + fullness,
+                      kStdoutReadBufferSize - fullness);
+    if (bytes_read == -1) {
+      if (errno == EAGAIN) {
+        if (!WaitOnFD(child_fd,
+                      read_timeout,
+                      total_timeout,
+                      start_time) ||
+            (TimeIsOut(start_time, *total_timeout))) {
+          return ThrowException(String::New("Timed out waiting for output"));
+        }
+        continue;
+      } else if (errno == EINTR) {
+        continue;
+      } else {
+        break;
+      }
+    }
+    if (bytes_read + fullness > 0) {
+      int length = bytes_read == 0 ?
+                   bytes_read + fullness :
+                   LengthWithoutIncompleteUtf8(buffer, bytes_read + fullness);
+      Handle<String> addition = String::New(buffer, length);
+      cons_args[0] = accumulator;
+      cons_args[1] = addition;
+      accumulator = Handle<String>::Cast(cons_function->Call(
+          Shell::utility_context()->Global(),
+          2,
+          cons_args));
+      fullness = bytes_read + fullness - length;
+      memcpy(buffer, buffer + length, fullness);
+    }
+  } while (bytes_read != 0);
+  return accumulator;
+}
+
+
+// Modern Linux has the waitid call, which is like waitpid, but more useful
+// if you want a timeout.  If we don't have waitid we can't limit the time
+// waiting for the process to exit without losing the information about
+// whether it exited normally.  In the common case this doesn't matter because
+// we don't get here before the child has closed stdout and most programs don't
+// do that before they exit.
+#if defined(WNOWAIT) && !defined(ANDROID)
+#define HAS_WAITID 1
+#endif
+
+
+// Get exit status of child.
+static bool WaitForChild(int pid,
+                         ZombieProtector& child_waiter,
+                         struct timeval& start_time,
+                         int read_timeout,
+                         int total_timeout) {
+#ifdef HAS_WAITID
+
+  siginfo_t child_info;
+  child_info.si_pid = 0;
+  int useconds = 1;
+  // Wait for child to exit.
+  while (child_info.si_pid == 0) {
+    waitid(P_PID, pid, &child_info, WEXITED | WNOHANG | WNOWAIT);
+    usleep(useconds);
+    if (useconds < 1000000) useconds <<= 1;
+    if ((read_timeout != -1 && useconds / 1000 > read_timeout) ||
+        (TimeIsOut(start_time, total_timeout))) {
+      ThrowException(String::New("Timed out waiting for process to terminate"));
+      kill(pid, SIGINT);
+      return false;
+    }
+  }
+  child_waiter.ChildIsDeadNow();
+  if (child_info.si_code == CLD_KILLED) {
+    char message[999];
+    snprintf(message,
+             sizeof(message),
+             "Child killed by signal %d",
+             child_info.si_status);
+    ThrowException(String::New(message));
+    return false;
+  }
+  if (child_info.si_code == CLD_EXITED && child_info.si_status != 0) {
+    char message[999];
+    snprintf(message,
+             sizeof(message),
+             "Child exited with status %d",
+             child_info.si_status);
+    ThrowException(String::New(message));
+    return false;
+  }
+
+#else  // No waitid call.
+
+  int child_status;
+  printf("waitpid");
+  waitpid(pid, &child_status, 0);  // We hang here if the child doesn't exit.
+  child_waiter.ChildIsDeadNow();
+  if (WIFSIGNALED(child_status)) {
+    char message[999];
+    snprintf(message,
+             sizeof(message),
+             "Child killed by signal %d",
+             WTERMSIG(child_status));
+    ThrowException(String::New(message));
+    return false;
+  }
+  if (WEXITSTATUS(child_status) != 0) {
+    char message[999];
+    int exit_status = WEXITSTATUS(child_status);
+    snprintf(message,
+             sizeof(message),
+             "Child exited with status %d",
+             exit_status);
+    ThrowException(String::New(message));
+    return false;
+  }
+
+#endif  // No waitid call.
+
+  return true;
+}
+
+
+// Implementation of the system() function (see d8.h for details).
+Handle<Value> Shell::System(const Arguments& args) {
+  HandleScope scope;
+  int read_timeout = -1;
+  int total_timeout = -1;
+  if (!GetTimeouts(args, &read_timeout, &total_timeout)) return v8::Undefined();
+  Handle<Array> command_args;
+  if (args.Length() > 1) {
+    if (!args[1]->IsArray()) {
+      return ThrowException(String::New("system: Argument 2 must be an array"));
+    }
+    command_args = Handle<Array>::Cast(args[1]);
+  } else {
+    command_args = Array::New(0);
+  }
+  if (command_args->Length() > ExecArgs::kMaxArgs) {
+    return ThrowException(String::New("Too many arguments to system()"));
+  }
+  if (args.Length() < 1) {
+    return ThrowException(String::New("Too few arguments to system()"));
+  }
+
+  struct timeval start_time;
+  gettimeofday(&start_time, NULL);
+
+  ExecArgs exec_args(args[0], command_args);
+  int exec_error_fds[2];
+  int stdout_fds[2];
+
+  if (pipe(exec_error_fds) != 0) {
+    return ThrowException(String::New("pipe syscall failed."));
+  }
+  if (pipe(stdout_fds) != 0) {
+    return ThrowException(String::New("pipe syscall failed."));
+  }
+
+  pid_t pid = fork();
+  if (pid == 0) {  // Child process.
+    ExecSubprocess(exec_error_fds, stdout_fds, exec_args);
+    exit(1);
+  }
+
+  // Parent process.  Ensure that we clean up if we exit this function early.
+  ZombieProtector child_waiter(pid);
+  close(exec_error_fds[kWriteFD]);
+  close(stdout_fds[kWriteFD]);
+  OpenFDCloser error_read_closer(exec_error_fds[kReadFD]);
+  OpenFDCloser stdout_read_closer(stdout_fds[kReadFD]);
+
+  if (!ChildLaunchedOK(exec_error_fds)) return v8::Undefined();
+
+  Handle<Value> accumulator = GetStdout(stdout_fds[kReadFD],
+                                        start_time,
+                                        read_timeout,
+                                        &total_timeout);
+  if (accumulator->IsUndefined()) {
+    kill(pid, SIGINT);  // On timeout, kill the subprocess.
+    return accumulator;
+  }
+
+  if (!WaitForChild(pid,
+                    child_waiter,
+                    start_time,
+                    read_timeout,
+                    total_timeout)) {
+    return v8::Undefined();
+  }
+
+  return scope.Close(accumulator);
+}
+
+
+}  // namespace v8