seek.c

一套很值得分析的短信SMS开发源代码。是我今年早些时候从taobao上买来的。但我现在也没看完（先说清楚

/* Copyright 2000-2005 The Apache Software Foundation or its licensors, as
 * applicable.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "win32/apr_arch_file_io.h"
#include "apr_file_io.h"
#include <errno.h>
#include <string.h>

static apr_status_t setptr(apr_file_t *thefile, apr_off_t pos )
{
    apr_off_t newbufpos;
    DWORD rc;

    if (thefile->direction == 1) {
        apr_file_flush(thefile);
        thefile->bufpos = thefile->direction = thefile->dataRead = 0;
    }

    newbufpos = pos - (thefile->filePtr - thefile->dataRead);

    if (newbufpos >= 0 && newbufpos <= thefile->dataRead) {
        thefile->bufpos = (apr_size_t)newbufpos;
        rc = 0;
    } else {
        DWORD offlo = (DWORD)pos;
        DWORD offhi = (DWORD)(pos >> 32);
        rc = SetFilePointer(thefile->filehand, offlo, &offhi, FILE_BEGIN);

        if (rc == 0xFFFFFFFF)
            rc = apr_get_os_error();
        else
            rc = APR_SUCCESS;
        if (rc == APR_SUCCESS) {
            thefile->eof_hit = thefile->bufpos = thefile->dataRead = 0;
            thefile->filePtr = pos;
        }
    }

    return rc;
}


APR_DECLARE(apr_status_t) apr_file_seek(apr_file_t *thefile, apr_seek_where_t where, apr_off_t *offset)
{
    apr_finfo_t finfo;
    apr_status_t rc = APR_SUCCESS;

    thefile->eof_hit = 0;

    if (thefile->buffered) {
        switch (where) {
            case APR_SET:
                rc = setptr(thefile, *offset);
                break;

            case APR_CUR:
                rc = setptr(thefile, thefile->filePtr - thefile->dataRead 
                                      + thefile->bufpos + *offset);
                break;

            case APR_END:
                rc = apr_file_info_get(&finfo, APR_FINFO_SIZE, thefile);
                if (rc == APR_SUCCESS)
                    rc = setptr(thefile, finfo.size + *offset);
                break;

            default:
                return APR_EINVAL;
        }

        *offset = thefile->filePtr - thefile->dataRead + thefile->bufpos;
        return rc;
    } 
    /* A file opened with APR_XTHREAD has been opened for overlapped i/o. 
     * APR must explicitly track the file pointer in this case.
     */
    else if (thefile->pOverlapped || thefile->flags & APR_XTHREAD) {
        switch(where) {
            case APR_SET:
                thefile->filePtr = *offset;
                break;
        
            case APR_CUR:
                thefile->filePtr += *offset;
                break;
        
            case APR_END:
                rc = apr_file_info_get(&finfo, APR_FINFO_SIZE, thefile);
                if (rc == APR_SUCCESS && finfo.size - *offset < 0)
                    thefile->filePtr = finfo.size - *offset;
                break;

            default:
                return APR_EINVAL;
        }
        *offset = thefile->filePtr;
        return rc;
    }
    else {
        DWORD howmove;
        DWORD offlo = (DWORD)*offset;
        DWORD offhi = (DWORD)(*offset >> 32);

        switch(where) {
            case APR_SET:
                howmove = FILE_BEGIN;   break;
            case APR_CUR:
                howmove = FILE_CURRENT; break;
            case APR_END:
                howmove = FILE_END;     break;
            default:
                return APR_EINVAL;
        }
        offlo = SetFilePointer(thefile->filehand, (LONG)offlo, 
                               (LONG*)&offhi, howmove);
        if (offlo == 0xFFFFFFFF)
            rc = apr_get_os_error();
        else
            rc = APR_SUCCESS;
        /* Since we can land at 0xffffffff we will measure our APR_SUCCESS */
        if (rc == APR_SUCCESS)
            *offset = ((apr_off_t)offhi << 32) | offlo;
        return rc;
    }
}


APR_DECLARE(apr_status_t) apr_file_trunc(apr_file_t *thefile, apr_off_t offset)
{
    apr_status_t rv;
    DWORD offlo = (DWORD)offset;
    DWORD offhi = (DWORD)(offset >> 32);
    DWORD rc;

    rc = SetFilePointer(thefile->filehand, offlo, &offhi, FILE_BEGIN);
    if (rc == 0xFFFFFFFF)
        if ((rv = apr_get_os_error()) != APR_SUCCESS)
            return rv;

    if (!SetEndOfFile(thefile->filehand))
        return apr_get_os_error();

    if (thefile->buffered) {
        return setptr(thefile, offset);
    }

    return APR_SUCCESS;
}