path: root/zen/process_exec.cpp

// *****************************************************************************
// * This file is part of the FreeFileSync project. It is distributed under    *
// * GNU General Public License: https://www.gnu.org/licenses/gpl-3.0          *
// * Copyright (C) Zenju (zenju AT freefilesync DOT org) - All Rights Reserved *
// *****************************************************************************

#include "process_exec.h"
#include <chrono>
#include "guid.h"
#include "file_access.h"
#include "file_io.h"

    #include <unistd.h> //fork, pipe
    #include <sys/wait.h> //waitpid
    #include <fcntl.h>

using namespace zen;


Zstring zen::escapeCommandArg(const Zstring& arg)
{
//*INDENT-OFF*
    Zstring output;
    for (const Zchar c : arg)
        switch (c)
        {
            case  '"': output += "\\\""; break; //Windows: not needed; " cannot be used as file name
            case '\\': output += "\\\\"; break; //Windows: path separator! => don't escape
            case '`':  output += "\\`";  break; //yes, used in some paths => Windows: no escaping required
            default: output += c; break;
        }
//*INDENT-ON*
    if (contains(output, Zstr(' ')))
        output = Zstr('"') + output + Zstr('"'); //Windows: escaping a single blank instead would not work

    return output;
}




namespace
{
std::pair<int /*exit code*/, std::string> processExecuteImpl(const Zstring& filePath, const std::vector<Zstring>& arguments,
                                                             std::optional<int> timeoutMs) //throw SysError, SysErrorTimeOut
{
    const Zstring tempFilePath = appendSeparator(getTempFolderPath()) + //throw FileError
                                 Zstr("FFS-") + utfTo<Zstring>(formatAsHexString(generateGUID()));
    /*  can't use popen(): does NOT return the exit code on Linux (despite the documentation!), although it works correctly on macOS
          => use pipes instead: https://linux.die.net/man/2/waitpid
             bonus: no need for "2>&1" to redirect STDERR to STDOUT

             What about premature exit via SysErrorTimeOut?
                Linux: child process' end of the pipe *still works* even after the parent process is gone:
                        There does not seem to be any output buffer size limit + no observable strain on system memory or disk space! :)
                macOS: child process exits if parent end of pipe is closed: fuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu..........

       => solution: buffer output in temporary file

       Unresolved problem: premature exit via SysErrorTimeOut (=> no waitpid()) creates zombie proceses:
                "As long as a zombie is not removed from the system via a wait,
                 it will consume a slot in the kernel process table, and if this table fills,
                 it will not be possible to create further processes."                 */

    const int EC_CHILD_LAUNCH_FAILED = 120; //avoid 127: used by the system, e.g. failure to execute due to missing .so file

    //use O_TMPFILE? sounds nice, but support is probably crap: https://github.com/libvips/libvips/issues/1151
    const int fdTempFile = ::open(tempFilePath.c_str(), O_CREAT | O_EXCL | O_RDWR | O_CLOEXEC,
                                  S_IRUSR | S_IWUSR); //0600
    if (fdTempFile == -1)
        THROW_LAST_SYS_ERROR("open");
    auto guardTmpFile = makeGuard<ScopeGuardRunMode::onExit>([&] { ::close(fdTempFile); });

    //"deleting while handle is open" == FILE_FLAG_DELETE_ON_CLOSE
    if (::unlink(tempFilePath.c_str()) != 0)
        THROW_LAST_SYS_ERROR("unlink");

    //--------------------------------------------------------------
    //waitpid() is a useless pile of garbage without time out => check EOF from dummy pipe instead
    int pipe[2] = {};
    if (::pipe2(pipe, O_CLOEXEC) != 0)
        THROW_LAST_SYS_ERROR("pipe2");

    const int fdLifeSignR = pipe[0]; //for parent process
    const int fdLifeSignW = pipe[1]; //for child process
    ZEN_ON_SCOPE_EXIT(::close(fdLifeSignR));
    auto guardFdLifeSignW = makeGuard<ScopeGuardRunMode::onExit>([&] { ::close(fdLifeSignW ); });

    //--------------------------------------------------------------

    //follow implemenation of ::system(): https://github.com/lattera/glibc/blob/master/sysdeps/posix/system.c
    const pid_t pid = ::fork();
    if (pid < 0) //pids are never negative, empiric proof: https://linux.die.net/man/2/wait
        THROW_LAST_SYS_ERROR("fork");

    if (pid == 0) //child process
        try
        {
            //first task: set STDOUT redirection in case an error needs to be reported
            if (::dup2(fdTempFile, STDOUT_FILENO) != STDOUT_FILENO) //O_CLOEXEC does NOT propagate with dup2()
                THROW_LAST_SYS_ERROR("dup2(STDOUT)");

            if (::dup2(fdTempFile, STDERR_FILENO) != STDERR_FILENO) //O_CLOEXEC does NOT propagate with dup2()
                THROW_LAST_SYS_ERROR("dup2(STDERR)");

            //avoid blocking scripts waiting for user input
            // => appending " < /dev/null" is not good enough! e.g. hangs for: read -p "still hanging here"; echo fuuuuu...
            const int fdDevNull = ::open("/dev/null", O_RDONLY | O_CLOEXEC);
            if (fdDevNull == -1) //don't check "< 0" -> docu seems to allow "-2" to be a valid file handle
                THROW_LAST_SYS_ERROR("open(/dev/null)");
            ZEN_ON_SCOPE_EXIT(::close(fdDevNull));

            if (::dup2(fdDevNull, STDIN_FILENO) != STDIN_FILENO) //O_CLOEXEC does NOT propagate with dup2()
                THROW_LAST_SYS_ERROR("dup2(STDIN)");

            //*leak* the fd and have it closed automatically on child process exit after execv()
            if (::dup(fdLifeSignW) == -1) //O_CLOEXEC does NOT propagate with dup()
                THROW_LAST_SYS_ERROR("dup(fdLifeSignW)");

            std::vector<const char*> argv{filePath.c_str()};
            for (const Zstring& arg : arguments)
                argv.push_back(arg.c_str());
            argv.push_back(nullptr);

            /*int rv =*/::execv(argv[0], const_cast<char**>(&argv[0])); //only returns if an error occurred
            //safe to cast away const: https://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html
            //  "The statement about argv[] and envp[] being constants is included to make explicit to future
            //   writers of language bindings that these objects are completely constant. Due to a limitation of
            //   the ISO C standard, it is not possible to state that idea in standard C."
            THROW_LAST_SYS_ERROR("execv");
        }
        catch (const SysError& e)
        {
            ::puts(utfTo<std::string>(e.toString()).c_str());
            ::fflush(stdout); //note: stderr is unbuffered by default
            ::_exit(EC_CHILD_LAUNCH_FAILED); //[!] avoid flushing I/O buffers or doing other clean up from child process like with "exit()"!
        }
    //else: parent process


    if (timeoutMs)
    {
        guardFdLifeSignW.dismiss();
        ::close(fdLifeSignW); //[!] make sure we get EOF when fd is closed by child!

        const int flags = ::fcntl(fdLifeSignR, F_GETFL);
        if (flags == -1)
            THROW_LAST_SYS_ERROR("fcntl(F_GETFL)");

        //fcntl() success: Linux: 0
        //                 macOS: "Value other than -1."
        if (::fcntl(fdLifeSignR, F_SETFL, flags | O_NONBLOCK) == -1)
            THROW_LAST_SYS_ERROR("fcntl(F_SETFL, O_NONBLOCK)");


        const auto endTime = std::chrono::steady_clock::now() + std::chrono::milliseconds(*timeoutMs);
        for (;;) //EINTR handling? => allow interruption!?
        {
            //read until EAGAIN
            char buf[16];
            const ssize_t bytesRead = ::read(fdLifeSignR, buf, sizeof(buf));
            if (bytesRead < 0)
            {
                if (errno != EAGAIN)
                    THROW_LAST_SYS_ERROR("read");
            }
            else if (bytesRead > 0)
                throw SysError(formatSystemError("read", L"", L"Unexpected data."));
            else //bytesRead == 0: EOF
                break;

            //wait for stream input
            const auto now = std::chrono::steady_clock::now();
            if (now > endTime)
                throw SysErrorTimeOut(_P("Operation timed out after 1 second.", "Operation timed out after %x seconds.", *timeoutMs / 1000));

            const auto waitTimeMs = std::chrono::duration_cast<std::chrono::milliseconds>(endTime - now).count();

            timeval tv = {};
            tv.tv_sec  = static_cast<long>(waitTimeMs / 1000);
            tv.tv_usec = static_cast<long>(waitTimeMs - tv.tv_sec * 1000) * 1000;

            fd_set rfd = {}; //includes FD_ZERO
            FD_SET(fdLifeSignR, &rfd);

            if (const int rv = ::select(fdLifeSignR + 1, //int nfds
                                        &rfd,            //fd_set* readfds
                                        nullptr,         //fd_set* writefds
                                        nullptr,         //fd_set* exceptfds
                                        &tv);            //struct timeval* timeout
                rv < 0)
                THROW_LAST_SYS_ERROR("select");
            else if (rv == 0)
                throw SysErrorTimeOut(_P("Operation timed out after 1 second.", "Operation timed out after %x seconds.", *timeoutMs / 1000));
        }
    }

    //https://linux.die.net/man/2/waitpid
    int statusCode = 0;
    if (::waitpid(pid,         //pid_t pid
                  &statusCode, //int* status
                  0) != pid)   //int options
        THROW_LAST_SYS_ERROR("waitpid");


    if (::lseek(fdTempFile, 0, SEEK_SET) != 0)
        THROW_LAST_SYS_ERROR("lseek");

    guardTmpFile.dismiss();
    FileInput streamIn(fdTempFile, tempFilePath, nullptr /*notifyUnbufferedIO*/); //takes ownership!
    std::string output = bufferedLoad<std::string>(streamIn); //throw FileError

    if (!WIFEXITED(statusCode)) //signalled, crashed?
        throw SysError(formatSystemError("waitpid", WIFSIGNALED(statusCode) ?
                                         L"Killed by signal " + numberTo<std::wstring>(WTERMSIG(statusCode)) :
                                         L"Exit status "      + numberTo<std::wstring>(statusCode),
                                         utfTo<std::wstring>(trimCpy(output))));

    const int exitCode = WEXITSTATUS(statusCode); //precondition: "WIFEXITED() == true"
    if (exitCode == EC_CHILD_LAUNCH_FAILED || //child process should already have provided details to STDOUT
        exitCode == 127) //details should have been streamed to STDERR: used by /bin/sh, e.g. failure to execute due to missing .so file
        throw SysError(utfTo<std::wstring>(trimCpy(output)));

    return {exitCode, output};
}
}


std::pair<int /*exit code*/, Zstring> zen::consoleExecute(const Zstring& cmdLine, std::optional<int> timeoutMs) //throw SysError, SysErrorTimeOut
{
    const auto& [exitCode, output] = processExecuteImpl("/bin/sh", {"-c", cmdLine.c_str()}, timeoutMs); //throw SysError, SysErrorTimeOut
    return {exitCode, copyStringTo<Zstring>(output)};
}


void zen::openWithDefaultApp(const Zstring& itemPath) //throw FileError
{
    try
    {
        std::optional<int> timeoutMs;
        const Zstring cmdTemplate = R"(xdg-open "%x")"; //*might* block!
        timeoutMs = 0; //e.g. on Lubuntu if Firefox is started and not already running => no need for time out! https://freefilesync.org/forum/viewtopic.php?t=8260
        const Zstring cmdLine = replaceCpy(cmdTemplate, Zstr("%x"), itemPath);

        if (const auto& [exitCode, output] = consoleExecute(cmdLine, timeoutMs); //throw SysError, SysErrorTimeOut
            exitCode != 0)
            throw SysError(formatSystemError(utfTo<std::string>(cmdTemplate),
                                             replaceCpy(_("Exit code %x"), L"%x", numberTo<std::wstring>(exitCode)), utfTo<std::wstring>(output)));
    }
    catch (SysErrorTimeOut&) {} //child process not failed yet => probably fine :>
    catch (const SysError& e) { throw FileError(replaceCpy(_("Cannot open file %x."), L"%x", fmtPath(itemPath)), e.toString()); }
}