src/common/linux/scoped_pipe.h

// Copyright 2022 Google LLC
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#ifndef COMMON_LINUX_SCOPED_PIPE_H_
#define COMMON_LINUX_SCOPED_PIPE_H_

#include <stdint.h>
#include <string>

namespace google_breakpad {

// Small RAII wrapper for a pipe pair.
//
// Example (both ends of pipe in same process):
//   ScopedPipe tmp;
//   std::string line;
//   if (tmp.Init() && tmp.Write(bytes, bytes_len)) {
//     tmp.CloseWriteFd();
//     while (tmp.ReadLine(&line)) {
//       std::cerr << line << std::endl;
//     }
//   }
//
// Example (reading output from a child process):
//   ScopedPipe tmp;
//   if (fork()) {
//     // Parent process, read from the read end of the pipe.
//     std::string line;
//     while (tmp.ReadLine(line)) {
//       // Process output...
//     }
//     // Close read pipe once done processing the output that we wanted, this
//     // should ensure that the child process exits even if we didn't read all
//     // of the output.
//     tmp.CloseReadFd();
//     // Parent process should handle waiting for child to exit here...
//   } else {
//     // Child process, close the read fd and dup the write fd before exec'ing.
//     tmp.CloseReadFd();
//     tmp.Dup2WriteFd(STDOUT_FILENO);
//     tmp.Dup2WriteFd(STDERR_FILENO);
//     execl("some-command", "some-arguments");
//   }
class ScopedPipe {
 public:
  ScopedPipe();
  ~ScopedPipe();

  // Creates the pipe pair - returns false on error.
  bool Init();

  // Close the read pipe. This only needs to be used when the read pipe needs to
  // be closed earlier.
  void CloseReadFd();

  // Close the write pipe. This only needs to be used when the write pipe needs
  // to be closed earlier.
  void CloseWriteFd();

  // Reads characters until newline or end of pipe. On read failure this will
  // close the read pipe, but continue to return true and read buffered lines
  // until the internal buffering is exhausted. This will block if there is no
  // data available on the read pipe.
  bool ReadLine(std::string& line);

  // Writes bytes to the write end of the pipe, returns false and closes write
  // pipe on failure.
  bool WriteForTesting(const void* bytes, size_t bytes_len);

  // Calls the dup2 system call to replace any existing open file descriptor
  // with number new_fd with a copy of the current write end file descriptor
  // for the pipe.
  int Dup2WriteFd(int new_fd) const;

 private:
  int GetReadFd() const {
    return fds_[0];
  }

  int GetWriteFd() const {
    return fds_[1];
  }

  int fds_[2];
  std::string read_buffer_;
};

}  // namespace google_breakpad

#endif // COMMON_LINUX_SCOPED_PIPE_H_