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 "apr_arch_file_io.h"

static apr_status_t setptr(apr_file_t *thefile, unsigned long pos )
{
    long newbufpos;
    int 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 = newbufpos;
        rc = 0;
    } 
    else {
        rc = lseek(thefile->filedes, pos, SEEK_SET);

        if (rc != -1 ) {
            thefile->bufpos = thefile->dataRead = 0;
            thefile->filePtr = pos;
            rc = 0;
        }
        else {
            rc = errno;
        }
    }

    return rc;
}


APR_DECLARE(apr_status_t) apr_file_seek(apr_file_t *thefile, apr_seek_where_t where, apr_off_t *offset)
{
    apr_off_t rv;

    thefile->eof_hit = 0;

    if (thefile->buffered) {
        int rc = EINVAL;
        apr_finfo_t finfo;

        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;
        }

        *offset = thefile->filePtr - thefile->dataRead + thefile->bufpos;
        return rc;
    } else {

        rv = lseek(thefile->filedes, *offset, where);
        if (rv == -1) {
            *offset = -1;
            return errno;
        }
        else {
            *offset = rv;
            return APR_SUCCESS;
        }
    }
}

apr_status_t apr_file_trunc(apr_file_t *fp, apr_off_t offset)
{
    if (ftruncate(fp->filedes, offset) == -1) {
        return errno;
    }
    return setptr(fp, offset);
}