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      1 // Copyright 2014 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 "mojo/embedder/platform_channel_pair.h"
      6 
      7 #include <fcntl.h>
      8 #include <sys/socket.h>
      9 #include <sys/types.h>
     10 #include <unistd.h>
     11 
     12 #include "base/command_line.h"
     13 #include "base/logging.h"
     14 #include "base/posix/global_descriptors.h"
     15 #include "base/strings/string_number_conversions.h"
     16 #include "build/build_config.h"
     17 #include "mojo/embedder/platform_handle.h"
     18 
     19 namespace mojo {
     20 namespace embedder {
     21 
     22 namespace {
     23 
     24 bool IsTargetDescriptorUsed(
     25     const base::FileHandleMappingVector& file_handle_mapping,
     26     int target_fd) {
     27   for (size_t i = 0; i < file_handle_mapping.size(); i++) {
     28     if (file_handle_mapping[i].second == target_fd)
     29       return true;
     30   }
     31   return false;
     32 }
     33 
     34 }  // namespace
     35 
     36 PlatformChannelPair::PlatformChannelPair() {
     37   // Create the Unix domain socket and set the ends to nonblocking.
     38   int fds[2];
     39   // TODO(vtl): Maybe fail gracefully if |socketpair()| fails.
     40   PCHECK(socketpair(AF_UNIX, SOCK_STREAM, 0, fds) == 0);
     41   PCHECK(fcntl(fds[0], F_SETFL, O_NONBLOCK) == 0);
     42   PCHECK(fcntl(fds[1], F_SETFL, O_NONBLOCK) == 0);
     43 
     44 #if defined(OS_MACOSX)
     45   // This turns off |SIGPIPE| when writing to a closed socket (causing it to
     46   // fail with |EPIPE| instead). On Linux, we have to use |send...()| with
     47   // |MSG_NOSIGNAL| -- which is not supported on Mac -- instead.
     48   int no_sigpipe = 1;
     49   PCHECK(setsockopt(fds[0], SOL_SOCKET, SO_NOSIGPIPE, &no_sigpipe,
     50                     sizeof(no_sigpipe)) == 0);
     51   PCHECK(setsockopt(fds[1], SOL_SOCKET, SO_NOSIGPIPE, &no_sigpipe,
     52                     sizeof(no_sigpipe)) == 0);
     53 #endif  // defined(OS_MACOSX)
     54 
     55   server_handle_.reset(PlatformHandle(fds[0]));
     56   DCHECK(server_handle_.is_valid());
     57   client_handle_.reset(PlatformHandle(fds[1]));
     58   DCHECK(client_handle_.is_valid());
     59 }
     60 
     61 // static
     62 ScopedPlatformHandle PlatformChannelPair::PassClientHandleFromParentProcess(
     63     const base::CommandLine& command_line) {
     64   std::string client_fd_string =
     65       command_line.GetSwitchValueASCII(kMojoPlatformChannelHandleSwitch);
     66   int client_fd = -1;
     67   if (client_fd_string.empty() ||
     68       !base::StringToInt(client_fd_string, &client_fd) ||
     69       client_fd < base::GlobalDescriptors::kBaseDescriptor) {
     70     LOG(ERROR) << "Missing or invalid --" << kMojoPlatformChannelHandleSwitch;
     71     return ScopedPlatformHandle();
     72   }
     73 
     74   return ScopedPlatformHandle(PlatformHandle(client_fd));
     75 }
     76 
     77 void PlatformChannelPair::PrepareToPassClientHandleToChildProcess(
     78     base::CommandLine* command_line,
     79     base::FileHandleMappingVector* handle_passing_info) const {
     80   DCHECK(command_line);
     81   DCHECK(handle_passing_info);
     82   // This is an arbitrary sanity check. (Note that this guarantees that the loop
     83   // below will terminate sanely.)
     84   CHECK_LT(handle_passing_info->size(), 1000u);
     85 
     86   DCHECK(client_handle_.is_valid());
     87 
     88   // Find a suitable FD to map our client handle to in the child process.
     89   // This has quadratic time complexity in the size of |*handle_passing_info|,
     90   // but |*handle_passing_info| should be very small (usually/often empty).
     91   int target_fd = base::GlobalDescriptors::kBaseDescriptor;
     92   while (IsTargetDescriptorUsed(*handle_passing_info, target_fd))
     93     target_fd++;
     94 
     95   handle_passing_info->push_back(std::pair<int, int>(client_handle_.get().fd,
     96                                                      target_fd));
     97   // Log a warning if the command line already has the switch, but "clobber" it
     98   // anyway, since it's reasonably likely that all the switches were just copied
     99   // from the parent.
    100   LOG_IF(WARNING, command_line->HasSwitch(kMojoPlatformChannelHandleSwitch))
    101       << "Child command line already has switch --"
    102       << kMojoPlatformChannelHandleSwitch << "="
    103       << command_line->GetSwitchValueASCII(kMojoPlatformChannelHandleSwitch);
    104   // (Any existing switch won't actually be removed from the command line, but
    105   // the last one appended takes precedence.)
    106   command_line->AppendSwitchASCII(kMojoPlatformChannelHandleSwitch,
    107                                   base::IntToString(target_fd));
    108 }
    109 
    110 }  // namespace embedder
    111 }  // namespace mojo
    112