distinguish child errors from failing to exec

[libi2ncommon] / src / pipestream.cpp

 /*
The software in this package is distributed under the GNU General
Public License version 2 (with a special exception described below).

A copy of GNU General Public License (GPL) is included in this distribution,
in the file COPYING.GPL.

As a special exception, if other files instantiate templates or use macros
or inline functions from this file, or you compile this file and link it
with other works to produce a work based on this file, this file
does not by itself cause the resulting work to be covered
by the GNU General Public License.

However the source code for this file must still be made available
in accordance with section (3) of the GNU General Public License.

This exception does not invalidate any other reasons why a work based
on this file might be covered by the GNU General Public License.
*/
/***************************************************************************
              inpipestream.cpp  -  C++ streambuffer wrapper 
                             -------------------
    begin                : Thu Dec 27 2001
    copyright            : (C) 2001 by Intra2net AG
 ***************************************************************************/

#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <unistd.h>

#include <streambuf>
#include <istream>
#include <ostream>
#include <cstdio>
#include <boost/foreach.hpp>
#include <boost/shared_array.hpp>

#include "exception.hxx"
#include "stringfunc.hxx"
#include "pipestream.hxx"

/** @brief runs command and returns it's output as string
 *  @param command the full command with all parameters
 *  @param rescode struct containing the return code, if the program exited normally and so on
 *  @param out Whether to collect \c stdout.
 *  @param err Whether to collect \c stderr; combines with \c out.
 *  @param path Wether to look up the executable in \c $PATH.
 *  @returns the output (stdout) of the called program
 */
template <typename CmdT>
std::string capture_exec(CmdT command, ExecResult &rescode,
                         const bool out, const bool err,
                         const bool path)
{
    std::string output;

    bool exit_set = false;
    int exit_status_waitpid;

    // set the results to false until we are sure we have proper values
    rescode.normal_exit = false;
    rescode.terminated_by_signal = false;

    try
    {
        {
            inpipestream ips(command, out, err, path);

            ips.store_exit_status(&exit_set, &exit_status_waitpid);

            char buffer[2048];
            while (ips.good())
            {
                ips.read(buffer, sizeof(buffer));
                output.append(buffer, ips.gcount());
            }
        }

        // exit_status_waitpid only valid after destruction of the inpipestream

        if (exit_set)
        {
            rescode.normal_exit = WIFEXITED(exit_status_waitpid);
            if (rescode.normal_exit)
                rescode.return_code = WEXITSTATUS(exit_status_waitpid);

            rescode.terminated_by_signal = WIFSIGNALED(exit_status_waitpid);
            if (rescode.terminated_by_signal)
                rescode.signal = WTERMSIG(exit_status_waitpid);
        }
    }
    catch (pipestream_error &e)
    {
        rescode.error_message = e.what();
    }

    return output;
}

/** @brief      Instantiation of \c capture_exec for STL string arguments.
 *              Caveat emptor: this will cause the backing stream to use \c
 *              popen(3). To avoid shelling out, please refer to one of the
 *              variants that allow passing an argument list.
 *
 *  @param command    String specifying the shell expression to be executed.
 *  @param res        (Out parameter) Store information about the termination
 *                    state in this struct.
 *
 *  @returns          Result of \c stdout. Note that due to the use of \c
 *                    popen, the correct way to collect stderr output as
 *                    well is to use shell redirection inside the expression
 *                    passed.
 */
std::string capture_exec (const std::string &command, ExecResult &res)
{ return capture_exec<const std::string &>(command, res, true, false, false); }

/** @brief      Instantiation of \c capture_exec for argument lists. The
 *              pipestream used to run the command will not shell out.
 *              One of \c out or \c err must be set.
 *
 *  @param command    List of \c char* specifying the \c argv array of the
 *                    command to run. Note that the binary to executed is
 *                    assumed to be present at index 0 and that the input
 *                    is properly \c NULL terminated.
 *  @param res        (Out parameter) Store information about the termination
 *                    state in this struct.
 *  @param out        Whether to collect \c stdout.
 *  @param err        Whether to collect \c stderr; combines with \c out.
 *  @param path       Wether to look up the executable in \c $PATH.
 *
 *  @returns          Captured output, combined into one string.
 */
std::string capture_exec (const char *const *command, ExecResult &res,
                          const bool out, const bool err, const bool path)
{ return capture_exec<const char *const *>(command, res, out, err, path); }

/** @brief      Instantiation of \c capture_exec for argument lists. The
 *              pipestream used to run the command will not shell out.
 *              One of \c out or \c err must be set.
 *
 *  @param command    String vector specifying the \c argv array of the
 *                    command to run. Note that the binary to executed is
 *                    assumed to be present at index 0.
 *  @param res        (Out parameter) Store information about the termination
 *                    state in this struct.
 *  @param out        Whether to collect \c stdout.
 *  @param err        Whether to collect \c stderr; combines with \c out.
 *  @param path       Wether to look up the executable in \c $PATH.
 *
 *  @returns          Captured output, combined into one string.
 */
std::string capture_exec (const std::vector<std::string> &command, ExecResult &res,
                          const bool out, const bool err, const bool path)
{
    return capture_exec<const std::vector<std::string> &>
        (command, res, out, err, path);
}

#define PIPE_CTOR_FAIL(where) \
    do { \
        throw EXCEPTION (pipestream_error, \
                         std::string (where) + ": error " \
                         + I2n::to_string (errno) \
                         + " (" + std::string (strerror (errno)) + ")"); \
    } while (0)

/** @brief      Convert a string vector to a refcounted \c char**
 *              that is \c NULL terminated for use with e. g. \c execve(2).
 *
 *  @param command    List of arguments including the binary at index 0.
 *
 *  @returns          A \c boost::shared_array of pointers to the
 *                    arguments plus a trailing \c NULL. Note that
 *                    while the array itself is refcounted, the
 *                    pointees are assumed owned by the caller and
 *                    *not copyied*. I. e. they lose validity if the
 *                    original strings are freed.
 */
static boost::shared_array <char *>
mk_argv (const std::vector<std::string> &command)
{
    char **ret = NULL;

    try {
        ret = new char *[command.size () * sizeof (ret[0]) + 1];
    } catch (std::bad_alloc &) {
        return boost::shared_array<char *> ();
    }

    size_t cur = 0;
    BOOST_FOREACH(const std::string &arg, command) {
        /*
         * Casting away constness is safe since the data is always
         * kept alive until after exec().
         */
        ret [cur++] = const_cast<char *> (arg.c_str ());
    }

    ret [cur] = NULL;

    return boost::shared_array<char *> (ret);
}

/** @brief      Helper for redirecting a file descriptor to \c /dev/null.
 *              This will only acquire an fd the first time it is called
 *              or if it is called after unsuccessfully attempting to
 *              acquire one.
 *
 *  @param fd         The open file descriptor to operate on.
 *  @param save_errno Out parameter: stores errno here after a syscall failure.
 *
 *  @returns          \c true on success, \c false otherwise (the call to
 *                    either \c open(2) or \c dup2(2) failed), with errno
 *                    communicated through saved_errno.
 */
static bool
redirect_devnull (const int fd, int &save_errno)
{
    static int nullfd = -1;
    
    errno = 0;
    if (nullfd == -1 && (nullfd = open ("/dev/null", O_RDWR)) == -1) {
        save_errno = errno;
        return false;
    }

    errno = 0;
    if (dup2 (nullfd, fd) == -1) {
        save_errno = errno;
        return false;
    }

    return true;
}

/** @brief      Helper aggregating common code for the shell-free ctors.
 *
 *  @param argv       Argument list prepared for \c execve(2).
 *  @param out        Whether to capture \c stdout.
 *  @param err        Whether to capture \c stderr.
 *
 *  @returns          A \c FILE* handle for streaming if successful, \c NULL
 *                    otherwise.
 */
std::pair <pid_t, FILE *>
inpipebuf::init_without_shell (const char *const *argv,
                               const bool out,
                               const bool err,
                               const bool path) const
{
    FILE *pipeobj = NULL;
    int pipefd [2]; /* for reading output from the child */
    int errfd  [2]; /* for determining a successful exec() */
    sigset_t oldmask, newmask;

    if (!out && !err) {
        errno = EINVAL;
        PIPE_CTOR_FAIL("ctor");
    }

    errno = 0;
    if (   ::pipe2 (pipefd, O_CLOEXEC) == -1
        || ::pipe2 (errfd , O_CLOEXEC) == -1) {
        PIPE_CTOR_FAIL("pipe2");
    }

    sigfillset (&newmask);
    sigprocmask (SIG_SETMASK, &newmask, &oldmask);

    errno = 0;
    pid_t childpid = fork ();
    switch (childpid) {
        case -1: {
            sigprocmask (SIG_SETMASK, &oldmask, NULL);
            PIPE_CTOR_FAIL("fork");
            break;
        }
        case 0: {
            close (pipefd [0]);
            close (errfd  [0]);

            fcntl (pipefd [1], F_SETFD, 0);

            int save_errno = 0;
            if (!out) {
                if (!redirect_devnull (STDOUT_FILENO, save_errno)) {
                    (void)write (errfd [1], (char *)&save_errno, sizeof(save_errno));
                    exit (EXIT_FAILURE);
                }
            } else if (dup2 (pipefd[1], STDOUT_FILENO) == -1) {
                (void)write (errfd [1], (char *)&save_errno, sizeof(save_errno));
                exit (EXIT_FAILURE);
            }

            if (!err) {
                if (!redirect_devnull (STDERR_FILENO, save_errno)) {
                    (void)write (errfd [1], (char *)&save_errno, sizeof(save_errno));
                    exit (EXIT_FAILURE);
                }
            } else if (dup2 (pipefd[1], STDERR_FILENO) == -1) {
                (void)write (errfd [1], (char *)&save_errno, sizeof(save_errno));
                exit (EXIT_FAILURE);
            }

            close (pipefd [1]);

            sigprocmask (SIG_SETMASK, &oldmask, NULL);

            errno = 0;
            if (path) {
                execvpe (argv [0], const_cast <char *const *>(argv), environ);
            } else {
                execve (argv [0], const_cast <char *const *>(argv), NULL);
            }

            (void)write (errfd [1], (char *)&errno, sizeof(errno));
            exit (EXIT_FAILURE);
            break;
        }
        default: {
            break;
        }
    }

    close (pipefd [1]);
    close (errfd  [1]);

    /*
     * Check whether the child exec()’ed by reading from the error pipe.
     * The call to read(2) will block, uninterruptible due to signals being
     * blocked. If all went well, the read(2) will return zero bytes and we can
     * ditch the error channel.
     *
     * Otherwise either the read(2) failed or we actually received something
     * through the error pipe. Both cases are treated as errors and cause an
     * exit from the ctor.
     */
    char buf [sizeof (errno)];
    int ret;
    memset (buf, 0, sizeof (buf));
    errno = 0;
    if ((ret = read (errfd [0], buf, sizeof (buf))) != 0) {
        close (pipefd [0]);
        close (errfd  [0]);
        sigprocmask (SIG_SETMASK, &oldmask, NULL);
        if (ret == - 1) {
            /* read(2) failed */
            PIPE_CTOR_FAIL("read");
        } else {
            /*
             * We received data on the error channel indicating the child
             * process never successfully exec()’ed. We grab the error code
             * from the buffer and bail.
             */
            errno = *((int *)&buf[0]);
            PIPE_CTOR_FAIL("child failed to exec()");
        }
    }

    /*
     * read(2) yielded zero bytes; it’s safe to use the pipe so close our end
     * and continue.
     */
    close (errfd [0]);

    sigprocmask (SIG_SETMASK, &oldmask, NULL);

    errno = 0;
    if ((pipeobj = fdopen (pipefd [0], "r")) == NULL) {
        close (pipefd [0]);
        PIPE_CTOR_FAIL("fdopen");
    }

    return std::make_pair (childpid, pipeobj);
}

inpipebuf::inpipebuf(const char *const *command,
                     const bool out,
                     const bool err,
                     const bool path)
    : pipe (NULL) /* brr: shadowing global ident */
    , pid (-1)
    , status_set (NULL)
    , exit_status (NULL)
{
    if (command == NULL || command [0] == NULL) {
        PIPE_CTOR_FAIL("command");
    }

    std::pair <pid_t, FILE *> tmp =
        this->init_without_shell (command, out, err, path);
    this->pid  = tmp.first; /* no std::tie :/ */
    this->pipe = tmp.second;

    setg (&buffer, &buffer, &buffer);
}

inpipebuf::inpipebuf(const std::vector<std::string> &command,
                     const bool out,
                     const bool err,
                     const bool path)
    : pipe (NULL) /* brr: shadowing global ident */
    , pid (-1)
    , status_set (NULL)
    , exit_status (NULL)
{
    if (command.empty ()) {
        PIPE_CTOR_FAIL("command");
    }

    const boost::shared_array <char *> argv = mk_argv (command);
    if (!argv) {
        PIPE_CTOR_FAIL("malloc");
    }

    std::pair <pid_t, FILE *> tmp =
        this->init_without_shell (argv.get (), out, err, path);
    this->pid  = tmp.first;
    this->pipe = tmp.second;

    setg (&buffer, &buffer, &buffer);
}

inpipebuf::inpipebuf(const std::string& command,
                     const bool _ignored_out,
                     const bool _ignored_err,
                     const bool _ignored_path)
    : pid (-1)
    , status_set (NULL)
    , exit_status (NULL)
{
    pipe = popen (command.c_str(), "r");
    if (pipe == NULL)
        throw EXCEPTION (pipestream_error, "can't open program or permission denied");

    // force underflow
    setg (&buffer, &buffer, &buffer);
}

inpipebuf::~inpipebuf()
{
    if (pipe != NULL) {
        int status;

        if (this->pid == -1)
        {
            errno = 0;
            status = pclose (pipe);
            if (status != -1) {
                if (exit_status != NULL) {
                    *exit_status = status;
                    if (status_set != NULL) {
                        *status_set = true;
                    }
                }
            }
        }
        else
        {
            errno = 0;
            status = fclose (pipe);
            if (status != EOF) {
                if (exit_status != NULL) {
                    *exit_status = status; /* might be overwritten below */
                    if (status_set != NULL) {
                        *status_set = true;
                    }
                }
            }

            errno = 0;
            while (waitpid (this->pid, &status, 0) == -1) {
                if (errno != EINTR) {
                    status = -1;
                    break;
                }
            }
            if (status != 0 && exit_status != NULL) {
                *exit_status = status; /* might overwrite pipe status above */
                if (status_set != NULL) {
                    *status_set = true;
                }
            }
        }

        pipe = NULL;
    }
}

/** note: exit status only available after destruction */
void inpipebuf::store_exit_status(bool *_status_set, int *_exit_status)
{ 
    status_set = _status_set; 
    exit_status = _exit_status; 
}

inpipebuf::int_type inpipebuf::underflow()
{
    if (gptr() < egptr())
        return traits_type::to_int_type(*gptr());

    buffer = fgetc (pipe);
    if (feof (pipe))
    {
        // ERROR or EOF
        return EOF;
    }

    setg (&buffer, &buffer, &buffer+sizeof(char));

    return traits_type::to_int_type(*gptr());
}

outpipebuf::outpipebuf(const std::string& command)
{
    status_set = NULL;
    exit_status = NULL;

    pipe = popen (command.c_str(), "w");
    if (pipe == NULL)
        throw EXCEPTION (pipestream_error, "can't open program or permission denied");
}

outpipebuf::~outpipebuf()
{
    if (pipe != NULL) {
        int pclose_exit = pclose (pipe);

        if (exit_status && pclose_exit != -1)
        {
            if (status_set)
                *status_set = true;
            *exit_status = pclose_exit;
        }

        pipe = NULL;
    }
}

/** note: exit status only available after destruction */
void outpipebuf::store_exit_status(bool *_status_set, int *_exit_status)
{ 
    status_set = _status_set; 
    exit_status = _exit_status; 
}

outpipebuf::int_type outpipebuf::overflow(int_type c)
{
    if (c != EOF)
    {
        if (fputc(c,pipe)==EOF)
            return EOF;
    }
    return c;
}

std::streamsize outpipebuf::xsputn(const char* s, std::streamsize num)
{
    return fwrite(s,num,1,pipe);
}