1 /**

     2  * Relational pipes

     3  * Copyright © 2019 František Kučera (Frantovo.cz, GlobalCode.info)

     4  *

     5  * This program is free software: you can redistribute it and/or modify

     6  * it under the terms of the GNU General Public License as published by

     7  * the Free Software Foundation, version 3 of the License.

     8  *

     9  * This program is distributed in the hope that it will be useful,

    10  * but WITHOUT ANY WARRANTY; without even the implied warranty of

    11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

    12  * GNU General Public License for more details.

    13  *

    14  * You should have received a copy of the GNU General Public License

    15  * along with this program. If not, see <http://www.gnu.org/licenses/>.

    16  */

    17 #pragma once

    18 

    19 #include <vector>

    20 #include <sstream>

    21 #include <fcntl.h>

    22 #include <unistd.h>

    23 #include <sys/wait.h>

    24 #include <ext/stdio_filebuf.h>

    25 

    26 #include <relpipe/writer/typedefs.h>

    27 #include <relpipe/cli/RelpipeCLIException.h>

    28 

    29 namespace relpipe {

    30 namespace in {

    31 namespace filesystem {

    32 

    33 /**

    34  * Simple wrapper for a system process (fork+exec) that captures and returns just the STDOUT.

    35  */

    36 class SystemProcess {

    37 private:

    38 	/**

    39 	 * the command + its arguments

    40 	 */

    41 	std::vector<std::string> commandLine;

    42 	int nullFile = -1;

    43 

    44 	/**

    45 	 * TODO: move to a common library (copied from the AWK module) 

    46 	 * @param args

    47 	 */

    48 	void execp(const std::vector<std::string>& args) {

    49 		const char** a = new const char*[args.size() + 1];

    50 		for (size_t i = 0; i < args.size(); i++) a[i] = args[i].c_str();

    51 		a[args.size()] = nullptr;

    52 

    53 		execvp(a[0], (char*const*) a);

    54 

    55 		delete[] a;

    56 		throw relpipe::cli::RelpipeCLIException(L"Unable to do execvp().", relpipe::cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exception?

    57 	}

    58 

    59 	/**

    60 	 * TODO: move to a common library (copied from the AWK module) 

    61 	 * @param readerFD

    62 	 * @param writerFD

    63 	 */

    64 	void createPipe(int& readerFD, int& writerFD) {

    65 		int fds[2];

    66 		int result = pipe(fds);

    67 		readerFD = fds[0];

    68 		writerFD = fds[1];

    69 		if (result < 0) throw relpipe::cli::RelpipeCLIException(L"Unable to create a pipe.", relpipe::cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exception?

    70 	}

    71 

    72 	/**

    73 	 * TODO: move to a common library (copied from the AWK module) 

    74 	 */

    75 	void redirectFD(int oldfd, int newfd) {

    76 		int result = dup2(oldfd, newfd);

    77 		if (result < 0) throw relpipe::cli::RelpipeCLIException(L"Unable redirect FD.", relpipe::cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exception?

    78 	}

    79 

    80 	/**

    81 	 * TODO: move to a common library (copied from the AWK module) 

    82 	 */

    83 	void closeOrThrow(int fd) {

    84 		int error = close(fd);

    85 		if (error) throw relpipe::cli::RelpipeCLIException(L"Unable to close FD: " + to_wstring(fd) + L" from PID: " + to_wstring(getpid()), relpipe::cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exception?

    86 	}

    87 

    88 public:

    89 

    90 	SystemProcess(std::vector<std::string> commandLine) : commandLine(commandLine) {

    91 		nullFile = open("/dev/null", O_RDWR);

    92 	}

    93 

    94 	virtual ~SystemProcess() {

    95 		close(nullFile);

    96 	}

    97 

    98 	std::string execute() {

    99 

   100 		std::stringstream result;

   101 

   102 		int hashReaderFD;

   103 		int hashWriterFD;

   104 		createPipe(hashReaderFD, hashWriterFD);

   105 		

   106 		__pid_t hashPid = fork();

   107 

   108 		if (hashPid < 0) {

   109 			throw relpipe::cli::RelpipeCLIException(L"Unable to fork the hash process.", relpipe::cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exception?

   110 		} else if (hashPid == 0) {

   111 			// Child process

   112 			closeOrThrow(hashReaderFD);

   113 			redirectFD(nullFile, STDIN_FILENO);

   114 			redirectFD(nullFile, STDERR_FILENO);

   115 			redirectFD(hashWriterFD, STDOUT_FILENO);

   116 			execp(commandLine);

   117 		} else {

   118 			// Parent process

   119 			closeOrThrow(hashWriterFD);

   120 

   121 			__gnu_cxx::stdio_filebuf<char> hashReaderBuffer(hashReaderFD, std::ios::in);

   122 			std::istream hashReader(&hashReaderBuffer);

   123 			

   124 			for (char ch; hashReader.read(&ch, 1).good();) result.put(ch);

   125 			

   126 			int waitError;

   127 			__pid_t waitPID = wait(&waitError);

   128 			if (waitError) throw relpipe::cli::RelpipeCLIException(L"The child process returned an error exit code.", relpipe::cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exception?

   129 		}

   130 

   131 		return result.str();

   132 	}

   133 };

   134 

   135 }

   136 }

   137 }