chromeos/process_proxy/process_output_watcher.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "chromeos/process_proxy/process_output_watcher.h"
   6
   7 #include <sys/ioctl.h>
   8 #include <sys/select.h>
   9 #include <unistd.h>
  10
  11 #include <algorithm>
  12 #include <cstdio>
  13 #include <cstring>
  14
  15 #include "base/logging.h"
  16 #include "base/posix/eintr_wrapper.h"
  17 #include "base/third_party/icu/icu_utf.h"
  18
  19 namespace {
  20
  21 void InitReadFdSet(int out_fd, int stop_fd, fd_set* set) {
  22   FD_ZERO(set);
  23   if (out_fd != -1)
  24     FD_SET(out_fd, set);
  25   FD_SET(stop_fd, set);
  26 }
  27
  28 void CloseFd(int* fd) {
  29   if (*fd >= 0) {
  30     if (IGNORE_EINTR(close(*fd)) != 0)
  31       DPLOG(WARNING) << "close fd " << *fd << " failed.";
  32   }
  33   *fd = -1;
  34 }
  35
  36 // Gets byte size for a UTF8 character given it's leading byte. The character
  37 // size is encoded as number of leading '1' bits in the character's leading
  38 // byte. If the most significant bit is '0', the character is a valid ASCII
  39 // and it's byte size is 1.
  40 // The method returns 1 if the provided byte is invalid leading byte.
  41 size_t UTF8SizeFromLeadingByte(uint8 leading_byte) {
  42   size_t byte_count = 0;
  43   uint8 mask = 1 << 7;
  44   uint8 error_mask = 1 << (7 - CBU8_MAX_LENGTH);
  45   while (leading_byte & mask) {
  46     if (mask & error_mask)
  47       return 1;
  48     mask >>= 1;
  49     ++byte_count;
  50   }
  51   return byte_count ? byte_count : 1;
  52 }
  53
  54 }  // namespace
  55
  56 namespace chromeos {
  57
  58 // static
  59 bool ProcessOutputWatcher::VerifyFileDescriptor(int fd) {
  60   return (fd >= 0) && (fd < FD_SETSIZE);
  61 }
  62
  63 ProcessOutputWatcher::ProcessOutputWatcher(
  64     int out_fd,
  65     int stop_fd,
  66     const ProcessOutputCallback& callback)
  67     : read_buffer_size_(0),
  68       out_fd_(out_fd),
  69       stop_fd_(stop_fd),
  70       on_read_callback_(callback) {
  71   CHECK(VerifyFileDescriptor(out_fd_));
  72   CHECK(VerifyFileDescriptor(stop_fd_));
  73   max_fd_ = std::max(out_fd_, stop_fd_);
  74   // We want to be sure we will be able to add 0 at the end of the input, so -1.
  75   read_buffer_capacity_ = arraysize(read_buffer_) - 1;
  76 }
  77
  78 void ProcessOutputWatcher::Start() {
  79   WatchProcessOutput();
  80   OnStop();
  81 }
  82
  83 ProcessOutputWatcher::~ProcessOutputWatcher() {
  84   CloseFd(&out_fd_);
  85   CloseFd(&stop_fd_);
  86 }
  87
  88 void ProcessOutputWatcher::WatchProcessOutput() {
  89   while (true) {
  90     // This has to be reset with every watch cycle.
  91     fd_set rfds;
  92     DCHECK_GE(stop_fd_, 0);
  93     InitReadFdSet(out_fd_, stop_fd_, &rfds);
  94
  95     int select_result =
  96         HANDLE_EINTR(select(max_fd_ + 1, &rfds, NULL, NULL, NULL));
  97
  98     if (select_result < 0) {
  99       DPLOG(WARNING) << "select failed";
 100       return;
 101     }
 102
 103     // Check if we were stopped.
 104     if (FD_ISSET(stop_fd_, &rfds)) {
 105       return;
 106     }
 107
 108     if (out_fd_ != -1 && FD_ISSET(out_fd_, &rfds)) {
 109       ReadFromFd(PROCESS_OUTPUT_TYPE_OUT, &out_fd_);
 110     }
 111   }
 112 }
 113
 114 void ProcessOutputWatcher::ReadFromFd(ProcessOutputType type, int* fd) {
 115   // We don't want to necessary read pipe until it is empty so we don't starve
 116   // other streams in case data is written faster than we read it. If there is
 117   // more than read_buffer_size_ bytes in pipe, it will be read in the next
 118   // iteration.
 119   DCHECK_GT(read_buffer_capacity_, read_buffer_size_);
 120   ssize_t bytes_read =
 121       HANDLE_EINTR(read(*fd,
 122                         &read_buffer_[read_buffer_size_],
 123                         read_buffer_capacity_ - read_buffer_size_));
 124   if (bytes_read < 0)
 125     DPLOG(WARNING) << "read from buffer failed";
 126
 127   if (bytes_read > 0)
 128     ReportOutput(type, bytes_read);
 129
 130   // If there is nothing on the output the watched process has exited (slave end
 131   // of pty is closed).
 132   if (bytes_read <= 0) {
 133     // Slave pseudo terminal has been closed, we won't need master fd anymore.
 134     CloseFd(fd);
 135
 136     // We have lost contact with the process, so report it.
 137     on_read_callback_.Run(PROCESS_OUTPUT_TYPE_EXIT, "");
 138   }
 139 }
 140
 141 size_t ProcessOutputWatcher::OutputSizeWithoutIncompleteUTF8() {
 142   // Find the last non-trailing character byte. This byte should be used to
 143   // infer the last UTF8 character length.
 144   int last_lead_byte = read_buffer_size_ - 1;
 145   while (true) {
 146     // If the series of trailing bytes is too long, something's not right.
 147     // Report the whole output, without waiting for further character bytes.
 148     if (read_buffer_size_ - last_lead_byte > CBU8_MAX_LENGTH)
 149       return read_buffer_size_;
 150
 151     // If there are trailing characters, there must be a leading one in the
 152     // buffer for a valid UTF8 character. Getting past the buffer begining
 153     // signals something's wrong, or the buffer is empty. In both cases return
 154     // the whole current buffer.
 155     if (last_lead_byte < 0)
 156       return read_buffer_size_;
 157
 158     // Found the starting character byte; stop searching.
 159     if (!CBU8_IS_TRAIL(read_buffer_[last_lead_byte]))
 160       break;
 161
 162     --last_lead_byte;
 163   }
 164
 165   size_t last_length = UTF8SizeFromLeadingByte(read_buffer_[last_lead_byte]);
 166
 167   // Note that if |last_length| == 0 or
 168   // |last_length| + |last_read_byte| < |read_buffer_size_|, the string is
 169   // invalid UTF8. In that case, send the whole read buffer to the observer
 170   // immediately, just as if there is no trailing incomplete UTF8 bytes.
 171   if (!last_length || last_length + last_lead_byte <= read_buffer_size_)
 172     return read_buffer_size_;
 173
 174   return last_lead_byte;
 175 }
 176
 177 void ProcessOutputWatcher::ReportOutput(ProcessOutputType type,
 178                                         size_t new_bytes_count) {
 179   read_buffer_size_ += new_bytes_count;
 180   size_t output_to_report = OutputSizeWithoutIncompleteUTF8();
 181
 182   on_read_callback_.Run(type, std::string(read_buffer_, output_to_report));
 183
 184   // Move the bytes that were left behind to the beginning of the buffer and
 185   // update the buffer size accordingly.
 186   if (output_to_report < read_buffer_size_) {
 187     for (size_t i = output_to_report; i < read_buffer_size_; ++i) {
 188       read_buffer_[i - output_to_report] = read_buffer_[i];
 189     }
 190   }
 191   read_buffer_size_ -= output_to_report;
 192 }
 193
 194 void ProcessOutputWatcher::OnStop() {
 195   delete this;
 196 }
 197
 198 }  // namespace chromeos