popen.c

C标准库源代码

/***
*popen.c - initiate a pipe and a child command
*
*       Copyright (c) 1989-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       Defines _popen() and _pclose().
*
*******************************************************************************/


#include <cruntime.h>
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <process.h>
#include <io.h>
#include <fcntl.h>
#include <internal.h>
#include <errno.h>
#include <msdos.h>
#include <mtdll.h>
#include <oscalls.h>
#include <tchar.h>
#include <dbgint.h>

/* size for pipe buffer
 */
#define PSIZE     1024

#define STDIN     0
#define STDOUT    1


/* definitions for table of stream pointer - process handle pairs. the table
 * is created, maintained and accessed by the idtab function. _popen and
 * _pclose gain access to table entries only by calling idtab. Note that the
 * table is expanded as necessary (by idtab) and free table entries are reused
 * (an entry is free if its stream field is NULL), but the table is never
 * contracted.
 */

typedef struct {
        FILE *stream;
        int prochnd;
} IDpair;

/* number of entries in idpairs table
 */
#ifndef _UNICODE
unsigned __idtabsiz = 0;
#else  /* _UNICODE */
extern unsigned __idtabsiz;
#endif  /* _UNICODE */

/* pointer to first table entry
 */
#ifndef _UNICODE
IDpair *__idpairs = NULL;
#else  /* _UNICODE */
extern IDpair *__idpairs;
#endif  /* _UNICODE */

/* function to find specified table entries. also, creates and maintains
 * the table.
 */
static IDpair * __cdecl idtab(FILE *);


/***
*FILE *_popen(cmdstring,type) - initiate a pipe and a child command
*
*Purpose:
*       Creates a pipe and asynchronously executes a child copy of the command
*       processor with cmdstring (see system()). If the type string contains
*       an 'r', the calling process can read child command's standard output
*       via the returned stream. If the type string contains a 'w', the calling
*       process can write to the child command's standard input via the
*       returned stream.
*
*Entry:
*       _TSCHAR *cmdstring - command to be executed
*       _TSCHAR *type   - string of the form "r|w[b|t]", determines the mode
*                         of the returned stream (i.e., read-only vs write-only,
*                         binary vs text mode)
*
*Exit:
*       If successful, returns a stream associated with one end of the created
*       pipe (the other end of the pipe is associated with either the child
*       command's standard input or standard output).
*
*       If an error occurs, NULL is returned.
*
*Exceptions:
*
*******************************************************************************/

FILE * __cdecl _tpopen (
        const _TSCHAR *cmdstring,
        const _TSCHAR *type
        )
{

        int phdls[2];             /* I/O handles for pipe */
        int ph_open[2];           /* flags, set if correspond phdls is open */
        int i1;                   /* index into phdls[] */
        int i2;                   /* index into phdls[] */

        int tm = 0;               /* flag indicating text or binary mode */

        int stdhdl;               /* either STDIN or STDOUT */
        HANDLE osfhndsv1;         /* used to save _osfhnd(stdhdl) */
        long osfhndsv2;           /* used to save _osfhnd(phdls[i2]) */
        char osfilesv1;           /* used to save _osfile(stdhdl) */
        char osfilesv2;           /* used to save _osfile(phdls[i2]) */

        HANDLE oldhnd;            /* used to hold OS file handle values... */
        HANDLE newhnd;            /* ...in calls to DuplicateHandle API */

        FILE *pstream;            /* stream to be associated with pipe */

        HANDLE prochnd;           /* handle for current process */

        _TSCHAR *cmdexe;                  /* pathname for the command processor */
        int childhnd;             /* handle for child process (cmd.exe) */

        IDpair *locidpair;        /* pointer to IDpair table entry */


        /* first check for errors in the arguments
         */
        if ( (cmdstring == NULL) || (type == NULL) || ((*type != 'w') &&
             (*type != _T('r'))) )
                goto error1;

        /* do the _pipe(). note that neither of the resulting handles will
         * be inheritable.
         */

        if ( *(type + 1) == _T('t') )
                tm = _O_TEXT;
        else if ( *(type + 1) == _T('b') )
                tm = _O_BINARY;

        tm |= _O_NOINHERIT;

        if ( _pipe( phdls, PSIZE, tm ) == -1 )
                goto error1;

        /* test *type and set stdhdl, i1 and i2 accordingly.
         */
        if ( *type == _T('w') ) {
                stdhdl = STDIN;
                i1 = 0;
                i2 = 1;
        }
        else {
                stdhdl = STDOUT;
                i1 = 1;
                i2 = 0;
        }

        /* the pipe now exists. the following steps must be carried out before
         * the child process (cmd.exe) may be spawned:
         *
         *      1. save a non-inheritable dup of stdhdl
         *
         *      2. force stdhdl to be a dup of ph[i1]. close both ph[i1] and
         *         the original OS handle underlying stdhdl
         *
         *      3. associate a stdio-level stream with ph[i2].
         */

        /* set flags to indicate pipe handles are open. note, these are only
         * used for error recovery.
         */
        ph_open[ 0 ] = ph_open[ 1 ] = 1;


        /* get the process handle, it will be needed in some API calls
         */
        prochnd = GetCurrentProcess();

        /* MULTI-THREAD: ASSERT LOCK ON STDHDL HERE!!!!
         */
        _lock_fh( stdhdl );

        /* save a non-inheritable copy of stdhdl for later restoration.
         */

        oldhnd = (HANDLE)_osfhnd( stdhdl );

        if ( (oldhnd == INVALID_HANDLE_VALUE) ||
             !DuplicateHandle( prochnd,
                               oldhnd,
                               prochnd,
                               &osfhndsv1,
                               0L,
                               FALSE,                   /* non-inheritable */
                               DUPLICATE_SAME_ACCESS )
        ) {
                goto error2;
        }

        osfilesv1 = _osfile( stdhdl );

        /* force stdhdl to an inheritable dup of phdls[i1] (i.e., force
         * STDIN to the pipe read handle or STDOUT to the pipe write handle)
         * and close phdls[i1] (so there won't be a stray open handle on the
         * pipe after a _pclose). also, clear ph_open[i1] flag so that error
         * recovery won't try to close it again.
         */

        if ( !DuplicateHandle( prochnd,
                               (HANDLE)_osfhnd( phdls[i1] ),
                               prochnd,
                               &newhnd,
                               0L,
                               TRUE,                    /* inheritable */
                               DUPLICATE_SAME_ACCESS )
        ) {
                goto error3;
        }

        (void)CloseHandle( (HANDLE)_osfhnd(stdhdl) );
        _free_osfhnd( stdhdl );

        _set_osfhnd( stdhdl, (long)newhnd );
        _osfile( stdhdl ) = _osfile( phdls[i1] );

        (void)_close( phdls[i1] );
        ph_open[ i1 ] = 0;


        /* associate a stream with phdls[i2]. note that if there are no
         * errors, pstream is the return value to the caller.
         */
        if ( (pstream = _tfdopen( phdls[i2], type )) == NULL )
                goto error4;

        /* MULTI-THREAD: ASSERT LOCK ON IDPAIRS HERE!!!!
         */
        _mlock( _POPEN_LOCK );

        /* next, set locidpair to a free entry in the idpairs table.
         */
        if ( (locidpair = idtab( NULL )) == NULL )
                goto error5;


        /* temporarily change the osfhnd and osfile entries so that
         * the child doesn't get any entries for phdls[i2].
         */
        osfhndsv2 = _osfhnd( phdls[i2] );
        _osfhnd( phdls[i2] ) = (long)INVALID_HANDLE_VALUE;
        osfilesv2 = _osfile( phdls[i2] );
        _osfile( phdls[i2] ) = 0;

        /* spawn the child copy of cmd.exe. the algorithm is adapted from
         * SYSTEM.C, and behaves the same way.
         */
        if ( ((cmdexe = _tgetenv(_T("COMSPEC"))) == NULL) ||
             (((childhnd = _tspawnl( _P_NOWAIT,
                                    cmdexe,
                                    cmdexe,