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// Copyright 2021 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "src/utils/io/command.h"
#include <sys/poll.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>
#include <sstream>
#include <vector>
namespace tint {
namespace utils {
namespace {
/// File is a simple wrapper around a POSIX file descriptor
class File {
constexpr static const int kClosed = -1;
public:
/// Constructor
File() : handle_(kClosed) {}
/// Constructor
explicit File(int handle) : handle_(handle) {}
/// Destructor
~File() { Close(); }
/// Move assignment operator
File& operator=(File&& rhs) {
Close();
handle_ = rhs.handle_;
rhs.handle_ = kClosed;
return *this;
}
/// Closes the file (if it wasn't already closed)
void Close() {
if (handle_ != kClosed) {
close(handle_);
}
handle_ = kClosed;
}
/// @returns the file handle
operator int() { return handle_; }
/// @returns true if the file is not closed
operator bool() { return handle_ != kClosed; }
private:
File(const File&) = delete;
File& operator=(const File&) = delete;
int handle_ = kClosed;
};
/// Pipe is a simple wrapper around a POSIX pipe() function
class Pipe {
public:
/// Constructs the pipe
Pipe() {
int pipes[2] = {};
if (pipe(pipes) == 0) {
read = File(pipes[0]);
write = File(pipes[1]);
}
}
/// Closes both the read and write files (if they're not already closed)
void Close() {
read.Close();
write.Close();
}
/// @returns true if the pipe has an open read or write file
operator bool() { return read || write; }
/// The reader end of the pipe
File read;
/// The writer end of the pipe
File write;
};
bool ExecutableExists(const std::string& path) {
struct stat s {};
if (stat(path.c_str(), &s) != 0) {
return false;
}
return s.st_mode & S_IXUSR;
}
std::string FindExecutable(const std::string& name) {
if (ExecutableExists(name)) {
return name;
}
if (name.find("/") == std::string::npos) {
auto* path_env = getenv("PATH");
if (!path_env) {
return "";
}
std::istringstream path{path_env};
std::string dir;
while (getline(path, dir, ':')) {
auto test = dir + "/" + name;
if (ExecutableExists(test)) {
return test;
}
}
}
return "";
}
} // namespace
Command::Command(const std::string& path) : path_(path) {}
Command Command::LookPath(const std::string& executable) {
return Command(FindExecutable(executable));
}
bool Command::Found() const {
return ExecutableExists(path_);
}
Command::Output Command::Exec(
std::initializer_list<std::string> arguments) const {
if (!Found()) {
Output out;
out.err = "Executable not found";
return out;
}
// Pipes used for piping std[in,out,err] to / from the target process.
Pipe stdin_pipe;
Pipe stdout_pipe;
Pipe stderr_pipe;
if (!stdin_pipe || !stdout_pipe || !stderr_pipe) {
Output output;
output.err = "Command::Exec(): Failed to create pipes";
return output;
}
// execv() and friends replace the current process image with the target
// process image. To keep process that called this function going, we need to
// fork() this process into a child and parent process.
//
// The child process is responsible for hooking up the pipes to
// std[in,out,err]_pipes to STD[IN,OUT,ERR]_FILENO and then calling execv() to
// run the target command.
//
// The parent process is responsible for feeding any input to the stdin_pipe
// and collectting output from the std[out,err]_pipes.
int child_id = fork();
if (child_id < 0) {
Output output;
output.err = "Command::Exec(): fork() failed";
return output;
}
if (child_id > 0) {
// fork() - parent
// Close the stdout and stderr writer pipes.
// This is required for getting poll() POLLHUP events.
stdout_pipe.write.Close();
stderr_pipe.write.Close();
// Write the input to the child process
if (!input_.empty()) {
ssize_t n = write(stdin_pipe.write, input_.data(), input_.size());
if (n != static_cast<ssize_t>(input_.size())) {
Output output;
output.err = "Command::Exec(): write() for stdin failed";
return output;
}
}
stdin_pipe.write.Close();
// Accumulate the stdout and stderr output from the child process
pollfd poll_fds[2];
poll_fds[0].fd = stdout_pipe.read;
poll_fds[0].events = POLLIN;
poll_fds[1].fd = stderr_pipe.read;
poll_fds[1].events = POLLIN;
Output output;
bool stdout_open = true;
bool stderr_open = true;
while (stdout_open || stderr_open) {
if (poll(poll_fds, 2, -1) < 0) {
break;
}
char buf[256];
if (poll_fds[0].revents & POLLIN) {
auto n = read(stdout_pipe.read, buf, sizeof(buf));
if (n > 0) {
output.out += std::string(buf, buf + n);
}
}
if (poll_fds[0].revents & POLLHUP) {
stdout_open = false;
}
if (poll_fds[1].revents & POLLIN) {
auto n = read(stderr_pipe.read, buf, sizeof(buf));
if (n > 0) {
output.err += std::string(buf, buf + n);
}
}
if (poll_fds[1].revents & POLLHUP) {
stderr_open = false;
}
}
// Get the resulting error code
waitpid(child_id, &output.error_code, 0);
return output;
} else {
// fork() - child
// Redirect the stdin, stdout, stderr pipes for the execv process
if ((dup2(stdin_pipe.read, STDIN_FILENO) == -1) ||
(dup2(stdout_pipe.write, STDOUT_FILENO) == -1) ||
(dup2(stderr_pipe.write, STDERR_FILENO) == -1)) {
fprintf(stderr, "Command::Exec(): Failed to redirect pipes");
exit(errno);
}
// Close the pipes, once redirected above, we're now done with them.
stdin_pipe.Close();
stdout_pipe.Close();
stderr_pipe.Close();
// Run target executable
std::vector<const char*> args;
args.emplace_back(path_.c_str());
for (auto& arg : arguments) {
args.emplace_back(arg.c_str());
}
args.emplace_back(nullptr);
auto res = execv(path_.c_str(), const_cast<char* const*>(args.data()));
exit(res);
}
}
} // namespace utils
} // namespace tint