C语言构建WEB管理系统（五）：CGI实现上传文件

来源：互联网发布：mysql 先排序后去重编辑：程序博客网时间：2024/05/16 08:10

在很多网站中经常会遇到有向服务器上传文件的情况，比如在博客或空间中上传自己的头像。这一节我们来看一下在后台如何使用C语言实现文件上传这一功能。

首先创建一个html文档来上传文件，然后使用wireshark抓取数据包来分析一下上传文件的文件内容如何解析。html文档如下：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"><html>    <head>        <meta http-equiv="content-type" content="text/html; charset=utf-8" />        <title>CGI 实现文件上传</title>    </head>    <body>        <form action="/cgi-bin/upload.cgi" method="post" enctype="multipart/form-data">            <input type="file" name="upfilename" value="fname" /> <br>            <input type="file" name="upfilename_sec" value="fname_sec" />            <p><input type="submit" value="提交" /></p>        </form>    </body></html>

下面为wireshark抓包获取的数据：

所以要解析出文件内容需要首先从content_type中获取boundry，以下为在解析出boundry基础上将文件内容写入到一个临时文件中的处理函数：

int sln_cgi_input_multi_content_parse(const char *content_input,                                            int content_length, const char *boundary){    char        attr[SLN_ATTR_MAX], value[SLN_MAX_VALUE_LEN],                filename[SLN_MAX_FILENAME_LEN], tfilename[SLN_MAX_FILENAME_LEN],                tmpname[SLN_MAX_FILENAME_LEN];    char        *start, *end, *pname, *quote;    int         boundary_len, attr_len, value_len, filename_len, file_size = 0;    FILE        *fp = NULL;    boundary_len = strlen(boundary);    start = (char *)content_input;    if ((end = strstr(start, boundary))) {        start = end + boundary_len;    }    while (start) { // search boundary        attr[0] = '\0', filename[0] = '\0', filename[0] = '\0', tfilename[0] = '\0';        if (0 == memcmp(start, "--\r\n", 4)) { //reach the end            break;        } else {            start += 2; //strlen("\r\n") = 2;        }        /*         * betwen the start and end is a form data,         * "name" and "filename"(probably) is in it         */        end = strstr(start, "\r\n\r\n");        if (NULL == end) {            break;        }        *end = '\0';        /* get attr name */        pname = strstr(start, "name=\"");        if (NULL == pname) {            start = end + 1;            continue;        }        quote = strchr(pname + 6, '\"');    //strlen("name=\"") = 6;        if (NULL == quote) {            start = end + 1;            continue;        }        attr_len = quote - (pname + 6);        strncpy(attr, pname + 6, attr_len);        attr[attr_len] = '\0';        printf("<p>attr(len=%d): %s</p>\n", attr_len, attr);        /* try to get filename */        pname = strstr(start, "filename=\"");        if (NULL != pname) {            quote = strchr(pname + 10, '\"'); //strlen("filename=\"") = 10;            if (NULL == quote) {                start = end + 1;                continue;            }            filename_len = quote - (pname + 10);            strncpy(filename, pname + 10, filename_len);            filename[filename_len] = '\0';            printf("<p>filename(len=%d): %s</p>\n", filename_len, filename);        }        start = end + 4;                //strlen("\r\n\r\n") = 4;        if ('\0' == filename[0]) {          // not file, to get value            end = strstr(start, boundary);            if (NULL != end) {                value_len = (end-4) - start; //"\r\n--"                if (value_len > sizeof(value)) {                    value_len = sizeof(value) - 1;                }                strncpy(value, start, value_len);                value[value_len - 1] = '\0';                printf("<p>value(len=%d): %s</p>\n", value_len, value);                start = end + strlen(boundary);            }        } else {                            //is file, to get file content            end = sln_memsearch(start, content_length - (start-content_input), boundary, boundary_len);            if (NULL != end) {                file_size = (end-4) - start; //"\r\n--"                //sln_dump_mem((unsigned char *)end, 8);                // generate tmp file                if (NULL == tmpnam(tmpname)) {                    snprintf(tfilename, SLN_MAX_FILENAME_LEN, "%s", filename);                } else {                    snprintf(tfilename, SLN_MAX_FILENAME_LEN, "%s", tmpname);                }                // write file content to tmp file                file_size =                    file_size > SLN_MAX_CONTENT_LEN ? SLN_MAX_CONTENT_LEN : file_size;                fp = fopen(tfilename, "w+");                if (NULL != fp) {                    fwrite(start, 1, file_size, fp);                    fclose(fp);                } else {                    //SLN_CGI_ERR("fopen <%s> failed!\n", tfilename);                }                printf("<p>tfilename: %s, file_size: %d</p>\n", tfilename, file_size);                //sln_dump_mem((unsigned char *)start, file_size);                start = end + strlen(boundary);            }        }    }    return 0;}

最后将代码编译成可执行文件upload.cgi，在页面上传两个文件，如下：

提交后页面跳转到如下页面：

我们将所示文件cat出来看一下文件内容，如下：

[root@shallnet 4_upload]# cat /tmp/fileke5tvT The strings in the environment list are of the form name=value.[root@shallnet 4_upload]# [root@shallnet 4_upload]# cat /tmp/file7dP091 This page is part of release 3.22 of the Linux man-pages project.[root@shallnet 4_upload]#

可以看到文件上传成功！

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