Add Coprocess class

It provides a convenient way to spawn a process and read from/write to
its stdin/stdout.

coprocess-unix.cpp

@@ -0,0 +1,186 @@
+/*
+ * Copyright 2015 Andrew Ayer
+ *
+ * This file is part of git-crypt.
+ *
+ * git-crypt is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * git-crypt is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with git-crypt.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Additional permission under GNU GPL version 3 section 7:
+ *
+ * If you modify the Program, or any covered work, by linking or
+ * combining it with the OpenSSL project's OpenSSL library (or a
+ * modified version of that library), containing parts covered by the
+ * terms of the OpenSSL or SSLeay licenses, the licensors of the Program
+ * grant you additional permission to convey the resulting work.
+ * Corresponding Source for a non-source form of such a combination
+ * shall include the source code for the parts of OpenSSL used as well
+ * as that of the covered work.
+ */
+
+#include "coprocess.hpp"
+#include "util.hpp"
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <errno.h>
+
+static int execvp (const std::string& file, const std::vector<std::string>& args)
+{
+	std::vector<const char*>	args_c_str;
+	args_c_str.reserve(args.size());
+	for (std::vector<std::string>::const_iterator arg(args.begin()); arg != args.end(); ++arg) {
+		args_c_str.push_back(arg->c_str());
+	}
+	args_c_str.push_back(NULL);
+	return execvp(file.c_str(), const_cast<char**>(&args_c_str[0]));
+}
+
+Coprocess::Coprocess ()
+{
+	pid = -1;
+	stdin_pipe_reader = -1;
+	stdin_pipe_writer = -1;
+	stdin_pipe_ostream = NULL;
+	stdout_pipe_reader = -1;
+	stdout_pipe_writer = -1;
+	stdout_pipe_istream = NULL;
+}
+
+Coprocess::~Coprocess ()
+{
+	close_stdin();
+	close_stdout();
+}
+
+std::ostream*	Coprocess::stdin_pipe ()
+{
+	if (!stdin_pipe_ostream) {
+		int	fds[2];
+		if (pipe(fds) == -1) {
+			throw System_error("pipe", "", errno);
+		}
+		stdin_pipe_reader = fds[0];
+		stdin_pipe_writer = fds[1];
+		stdin_pipe_ostream = new ofhstream(this, write_stdin);
+	}
+	return stdin_pipe_ostream;
+}
+
+void		Coprocess::close_stdin ()
+{
+	delete stdin_pipe_ostream;
+	stdin_pipe_ostream = NULL;
+	if (stdin_pipe_writer != -1) {
+		close(stdin_pipe_writer);
+		stdin_pipe_writer = -1;
+	}
+	if (stdin_pipe_reader != -1) {
+		close(stdin_pipe_reader);
+		stdin_pipe_reader = -1;
+	}
+}
+
+std::istream*	Coprocess::stdout_pipe ()
+{
+	if (!stdout_pipe_istream) {
+		int	fds[2];
+		if (pipe(fds) == -1) {
+			throw System_error("pipe", "", errno);
+		}
+		stdout_pipe_reader = fds[0];
+		stdout_pipe_writer = fds[1];
+		stdout_pipe_istream = new ifhstream(this, read_stdout);
+	}
+	return stdout_pipe_istream;
+}
+
+void		Coprocess::close_stdout ()
+{
+	delete stdout_pipe_istream;
+	stdout_pipe_istream = NULL;
+	if (stdout_pipe_writer != -1) {
+		close(stdout_pipe_writer);
+		stdout_pipe_writer = -1;
+	}
+	if (stdout_pipe_reader != -1) {
+		close(stdout_pipe_reader);
+		stdout_pipe_reader = -1;
+	}
+}
+
+void		Coprocess::spawn (const std::vector<std::string>& args)
+{
+	pid = fork();
+	if (pid == -1) {
+		throw System_error("fork", "", errno);
+	}
+	if (pid == 0) {
+		if (stdin_pipe_writer != -1) {
+			close(stdin_pipe_writer);
+		}
+		if (stdout_pipe_reader != -1) {
+			close(stdout_pipe_reader);
+		}
+		if (stdin_pipe_reader != -1) {
+			dup2(stdin_pipe_reader, 0);
+			close(stdin_pipe_reader);
+		}
+		if (stdout_pipe_writer != -1) {
+			dup2(stdout_pipe_writer, 1);
+			close(stdout_pipe_writer);
+		}
+
+		execvp(args[0], args);
+		perror(args[0].c_str());
+		_exit(-1);
+	}
+	if (stdin_pipe_reader != -1) {
+		close(stdin_pipe_reader);
+		stdin_pipe_reader = -1;
+	}
+	if (stdout_pipe_writer != -1) {
+		close(stdout_pipe_writer);
+		stdout_pipe_writer = -1;
+	}
+}
+
+int		Coprocess::wait ()
+{
+	int		status = 0;
+	if (waitpid(pid, &status, 0) == -1) {
+		throw System_error("waitpid", "", errno);
+	}
+	return status;
+}
+
+size_t		Coprocess::write_stdin (void* handle, const void* buf, size_t count)
+{
+	const int	fd = static_cast<Coprocess*>(handle)->stdin_pipe_writer;
+	ssize_t		ret;
+	while ((ret = write(fd, buf, count)) == -1 && errno == EINTR); // restart if interrupted
+	if (ret < 0) {
+		throw System_error("write", "", errno);
+	}
+	return ret;
+}
+
+size_t		Coprocess::read_stdout (void* handle, void* buf, size_t count)
+{
+	const int	fd = static_cast<Coprocess*>(handle)->stdout_pipe_reader;
+	ssize_t		ret;
+	while ((ret = read(fd, buf, count)) == -1 && errno == EINTR); // restart if interrupted
+	if (ret < 0) {
+		throw System_error("read", "", errno);
+	}
+	return ret;
+}