apache2 开发C++模块 —— 基于cximage实现图片、缩略图下载功能

素颜马尾好姑娘i 2022-08-09 11:59 43阅读 0赞

[ 之前的博客][Link 1]中有提到基于apache2的模块开发，提供了下载文件的demo。但后来发现不仅仅是文件(准确说是图片)下载，还需要根据相关参数，提供图片缩略图下载、裁剪图下载或原图下载等功能。

**一、编译问题：**

种种原因，选用cximage库来提供图片处理功能。但坑爹的是这个库是C++的，而apache是c的，apxs怎么才能编译C++代码呢？ 当然可以把cximage封装一下，提供一个C接口的库。但本人比较懒，还是希望直接将cximage编译到apache2模块中。主要解决步骤如下：

1、 模块代码中包含cximage的头文件、直接定义cximage类对象，以C++方式调用相关接口。

2、 代码编写完成后通过apxs编译。

#apxs编译代码的命令中需要指定c++头文件，并通过-S参数将gcc替换成g++
    /usr/local/apache2/bin/apxs -L /usr/include/c++/ -L /usr/include/c++/3.4.6/x86_64-redhat-linux/  -i -c -a -S CC=g++  mod_api.c

3、 执行上述编译命令仍然报错：

libCxImage.a(ximatran.o): relocation R_X86_64_32S against `.rodata' can not be used when making a shared object; recompile with -fPIC
    /home/apache-module/api/libCxImage.a: could not read symbols: Bad value

这应该不是一个普遍问题，主要是编译cximage时没有指定-fPIC，添加-fPIC选项重新编译cximage库，就可以了。

4、编译成功后，修改httpd.conf，加载mod\_api.so，并设置handler.

实际上通过apxs编译的时候，应该会自动添加LoadModule的配置，但是 SetHandler还是需要自己手动加的。

<Location /api>  
          SetHandler api  
    </Location>

5、重启apache2服务，发现加载mod\_api.so报错：

httpd: Syntax error on line 56 of /usr/local/apache2/conf/httpd.conf: Cannot load /usr/local/apache2/modules/mod_api.so into server: /usr/local/apache2/modules/mod_api.so: undefined symbol: jpeg_resync_to_restart

解决方法：应该是编译mod\_api.so是缺少cximage相关的.a文件。用find cximage -name \*.a 找出所有的.a文件，然后逐个添加到编译选项中测试，最终确定需要以下几个.a(顺序上被依赖的库放在后面，需要依赖别人的库放在前面)：

\-lCxImage -ljasper -lpng -ltiff -lzlib -ljpeg

所以最终的编译命令如下：

/usr/local/apache2/bin/apxs -L /usr/include/c++/ -L /usr/include/c++/3.4.6/x86_64-redhat-linux/  -i -c -a -S CC=g++  mod_api.c -L./lib -lCxImage -ljasper -lpng -ltiff -lzlib -ljpeg

PS：

另外网上还有说需要在httpd.conf的LoadModule之前加上一句LoadFile，已加载C++模块：

LoadFile /usr/lib64/libstdc++.so.6
    LoadModule api_module   modules/mod_api.so

**但实际测试了一下，不加这句似乎也没有什么问题。**

**二、模块代码编写**

概括的说，主要有三类需求：首先从调用我们内部的SDK从其他内部平台下载图片原始文件，然后根据参数

1) 返回原图；2)返回缩略图；3)裁剪指定范围的图片

这里忽略了调用sdk的步骤，假设图片就在服务器本地，且直接在url路径中表示本地路径，设计的url规则如下：

url参数定义： 
    以下参数中 file、mode 是必须参数，其他参数是否需要视mode取值而定。 
    格式为： file=xxx&mode=xxx&ratio=xxx 参数组合的顺序可以任意。
    
    file 文件路径和名称
    mode 图片下载模式，有以下三种取值：
    normal 原图下载，忽略除file、mode之外的其他参数；
    thumbnail 缩略图，还需要提供压缩比例: ratio，此时忽略图片裁剪相关的参数；
    crop 图片裁剪，还需提供参裁剪范围参数: left，top，right，bottom， 此时忽略缩略图相关参数
    ratio 图片压缩比例
    left 图片裁剪区域左上角x坐标
    top 图片裁剪区域左上角y坐标
    right 图片裁剪区域右下角x坐标
    bottom 图片裁剪区域右下角y坐标

原图

http://192.168.1.100:8080/api?file=/home/tmp/test-img.jpeg&mode=normal
    缩略图
    http://192.168.1.100:8080/api?file=/home/tmp/test-img.jpeg&mode=thumbnail&ratio=2
    图片裁剪
    http://192.168.1.100:8080/api?file=/home/tmp/test-img.jpeg&mode=crop&left=50&top=80&right=300&bottom=600

**2.1 参数解析**

参考apache[2.4官方文档][2.4] ，可以使用 ap\_args\_to\_table 和 apr\_table\_get 解析参数，前者将query中的参数都解析到一个列表中，后者从该列表中查找指定的参数。

示例代码：

/* parse args from uri */
        apr_table_t *GET;
        apr_array_header_t *POST;
        ap_args_to_table(r, &GET);
        ap_parse_form_data(r, NULL, &POST, -1, MAX_ARGS_BUF);
        /*http://192.168.1.100:8080/api?file=/home/tmp/test-img.jpeg&mode=crop&left=50&top=80&right=300&bottom=600*/
        const char* file_path = apr_table_get(GET, "file");
        const char* mode = apr_table_get(GET, "mode");

**另外，如果url中还有子目录，**例如 192.168.1.100:8080/api/downloads?XXXXXX ，那么downloads 字段会体现在request\_rec结构的uri和path\_info中：（以下是gdb调试时打印出来的request\_rec结构体部分字段）

unparsed_uri = 0x8ed008 "/api/downloads?file=abc.txt&type=2", 
      uri = 0x8ed028 "/api/downloads", 
      filename = 0x8e38a8 "/usr/local/apache2/htdocs/api", 
      canonical_filename = 0x8e38a8 "/usr/local/apache2/htdocs/api", 
      path_info = 0x8e37ec "downloads", 
      args = 0x8ed038 "file=/home/abc.txt&type=2",

PS： **如果用的是apache 2.2 的版本，那么是没有这两个函数的。可以参照2.4的代码，将这两个函数以及其依赖的代码移植到2.2中。**

**2.2 图片处理：缩略图提取或裁剪**

由于这部分是比较定制化的需求，与apache2没有必然关系，这里仅为了逻辑的完整性贴出调用cximage处理图片的示例代码，不做过多解释。

CxImage src_img;
    	CxImage dest_img;
    	long img_size = 0;
    	BYTE* img_buf = NULL;
        if ( 0 == strcmp("normal", mode)) {              // 原图下载
    		img_buf = (BYTE *)read_buf;
    		img_size = len;
        }else if ( 0 == strcmp("thumbnail", mode) ) {    // 缩略图下载
        	/* parse resample rate from uri */
        	const char* ratio_str = apr_table_get(GET, "ratio");
    		if ( NULL == ratio_str ) {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to parse resample ratio from uri query : %s", query);
        		return HTTP_BAD_REQUEST;
    		}
        	int  ratio = atoi(ratio_str);
    		if ( 0 == ratio ) {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "invalid resample rate : %s", ratio_str);
        		return HTTP_BAD_REQUEST;
    		}
    		if ( !src_img.Decode((BYTE *)read_buf, sizeof(read_buf), CXIMAGE_FORMAT_JPG) ) {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to decode picture");
    			return HTTP_INTERNAL_SERVER_ERROR;
    		}
    		if (src_img.Resample(src_img.GetWidth()/ratio,src_img.GetHeight()/ratio, 1, &dest_img)) {
    			dest_img.Encode( img_buf, img_size, CXIMAGE_FORMAT_JPG );
    		} else {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to resample picture : %s, ratio : %d", file_path, ratio);
    			return HTTP_INTERNAL_SERVER_ERROR;
    		}
        }else if ( 0 == strcmp("crop", mode) ) {         // 图片裁剪
    		src_img.Decode((BYTE *)read_buf, sizeof(read_buf) ,CXIMAGE_FORMAT_JPG);
        	const char* left_str = apr_table_get(GET, "left");
        	const char* top_str = apr_table_get(GET, "top");
        	const char* right_str = apr_table_get(GET, "right");
        	const char* bottom_str = apr_table_get(GET, "bottom");
        	if (NULL == left_str || NULL == top_str || NULL == right_str || NULL == bottom_str ) {
        		ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to parse crop region from uri query : %s", query);
        		return HTTP_BAD_REQUEST;
        	}
    		int left   = atoi(left_str);
    		int top    = atoi(top_str);
    		int right  = atoi(right_str);
    		int bottom = atoi(bottom_str);
    		if (left < 0 || top < 0 || right < 0 || bottom < 0) {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "invalid crop region: (%d, %d), (%d, %d)", left, top, right, bottom);
        		return HTTP_BAD_REQUEST;
    		}
    		if ( !src_img.Decode((BYTE *)read_buf, sizeof(read_buf), CXIMAGE_FORMAT_JPG) ) {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to decode picture");
    			return HTTP_INTERNAL_SERVER_ERROR;
    		}
    		if (src_img.Crop( left, top, right, bottom, &dest_img )) {
    			dest_img.Encode( img_buf, img_size, CXIMAGE_FORMAT_JPG );
    		}else {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to crop picture : %s, (%s, %s), (%s, %s)", file_path, left_str, top_str, right_str, bottom_str);
    			return HTTP_INTERNAL_SERVER_ERROR;
    		}
        }

**2.3 下载：将图片数据发送给客户端**

这一部分与上一篇《[c apache2模块开发--根据自定义业务逻辑实现文件下载][Link 1]》中相同：

调用 ap\_rwrite 接口循环发送数据。 稍微有点区别，我们改成在发送数据之前才设置Content-Length，因为结合前面的逻辑，数据的长度只有待缩略图/剪切图生成后才能最终确定。其他的就没什么变化了。

/* we can get file length only after converted picture format */
        /* Content-Length:xxxx */
        char file_len_str[MAX_FILE_LEN_DIGITS];
        memset(file_len_str, 0, sizeof(file_len_str));
        snprintf(file_len_str, sizeof(file_len_str)-1, "%d", img_size);
        apr_table_add(r->headers_out,"Content-Length", file_len_str);
    	
    	int send_bytes = 0;
    	while( send_bytes < img_size ){
    		/*ap_flush_conn(r->connection);*/
    		int send_ret = ap_rwrite( img_buf, img_size - send_bytes, r );
    		if( send_ret >= 0 ) {
    			send_bytes += send_ret;
    		} else {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to send buffer to client");
    			return HTTP_INTERNAL_SERVER_ERROR;
    		}
    	}

**完整示例代码如下：**

/* 
    **  mod_api.c -- Apache sample api module
    **  [Autogenerated via ``apxs -n api -g'']
    **
    **  To play with this sample module first compile it into a
    **  DSO file and install it into Apache's modules directory 
    **  by running:
    **
    **    $ apxs -c -i mod_api.c
    **
    **  Then activate it in Apache's httpd.conf file for instance
    **  for the URL /api in as follows:
    **
    **    #   httpd.conf
    **    LoadModule api_module modules/mod_api.so
    **    <Location /api>
    **    SetHandler api
    **    </Location>
    **
    **  Then after restarting Apache via
    **
    **    $ apachectl restart
    **
    **  you immediately can request the URL /api and watch for the
    **  output of this module. This can be achieved for instance via:
    **
    **    $ lynx -mime_header http://localhost/api 
    **
    **  The output should be similar to the following one:
    **
    **    HTTP/1.1 200 OK
    **    Date: Tue, 31 Mar 1998 14:42:22 GMT
    **    Server: Apache/1.3.4 (Unix)
    **    Connection: close
    **    Content-Type: text/html
    **  
    **    The sample page from mod_api.c
    */ 
    
    #include "httpd.h"
    #include "http_config.h"
    #include "http_protocol.h"
    #include "ap_config.h"
    /*#include "http_connection.h"*/
    #include "ap_regex.h"
    #include "http_log.h"
    #include "util_script.h"
    #include "ximage.h"
    #include <stdio.h>
    
    #define  MAX_PATH_LEN          256
    #define  MAX_FILE_LEN_DIGITS   64
    #define  FILE_BUF_SIZE         1024
    #define  MAX_ARGS_BUF          8192
    
    
    /* get file name from the abolute path
     * eg:  input   /home/downloads/test.so
     *      output  test.so
     */
    const char* get_file_name(const char* path)
    {
        if (NULL == path) {
            return NULL;
        }
        int  path_len = strlen(path);
        const char *pos = path + path_len;
        while (*pos != '/' && pos != path) {
            pos--;
        }
        if (pos == path) {
            return path+1;
        }else {
            int len = len - (pos - path);
            return (pos + 1);
        }
    }
    
    int get_file_length(const char* file_path, request_rec *r)
    {
        int len = 0;
        apr_finfo_t  info;
        apr_stat(&info, file_path, APR_FINFO_SIZE, r->pool);
        len = (apr_size_t)info.size;
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0,r->server, "file :%s, len:%d", file_path, len);
        return len;
    }
    
    /* The sample content handler */
    static int api_handler(request_rec *r)
    {
        if (strcmp(r->handler, "api")) {
            return DECLINED;
        }
    
        /* only support GET or POST request */
        if ((r->method_number != M_GET) && (r->method_number != M_POST)) {
            return HTTP_METHOD_NOT_ALLOWED;
        }
    
        /* full url : http://192.168.1.100:8080/helloworld?file=/home/test.txt&type=2*/
        /* r->parsed_uri.query : file=/home/test.txt&type=2 */
        if ( NULL == r->parsed_uri.query ){
            ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server,"uri param is empty");
            return HTTP_BAD_REQUEST;
        }
    	const char* query = r->parsed_uri.query;
    	
        /* parse args from uri */
        apr_table_t *GET;
        apr_array_header_t *POST;
        ap_args_to_table(r, &GET);
        ap_parse_form_data(r, NULL, &POST, -1, MAX_ARGS_BUF);
        /* http://192.168.1.100:8080/api?file=/home/tmp/test-img.jpeg&type=1&left=0&top=0&right=100&bottom=100&resizerate=3 */
        //const char* bucket = apr_table_get(GET, "bucket");
        const char* file_path = apr_table_get(GET, "file");
        const char* mode = apr_table_get(GET, "mode");
    
        /* file,mode should not be empty */
        if ( NULL == file_path || NULL == mode ) {
        	ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to parse file/mode from uri query: %s", query);
        	return HTTP_BAD_REQUEST;
        }
    
        /* set response headers */
        /* Content-Type:application/octet-stream */
        r->content_type = "application/octet-stream";                   /* "text/html" */
        /* Content-Disposition:attachment;filename=test.txt */
        char file_name[24 + (MAX_PATH_LEN)] = {0};   /* length of "attachment;filename=" is 20 */
        sprintf(file_name, "attachment;filename=%s", get_file_name(file_path));
        apr_table_add(r->headers_out,"Content-Disposition", file_name);
    	/* we can get file length only after converted picture format */
        /* Content-Length:xxxx */
    
    	
    	/* TODO: call our SDK to get picture */
        /* load picture from file to memory */
    	/* suppose that we have already downloaded files from other platform, and all the files are in the memory.
         * so just return the memory data to client */
        FILE*  fp = fopen(file_path, "rb");
        if ( NULL == fp ) {
            ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server,"failed to open file %s", file_path);
            return HTTP_NON_AUTHORITATIVE;
        }
        int read_ret = 0;
    	int len = get_file_length(file_path, r);
        char read_buf[len];
    	//while( !feof( fp ) ){
    		memset( read_buf, 0, sizeof( read_buf ) );
    		read_ret = fread( read_buf, 1, len, fp );
    		if( ferror( fp ) ){
    			/* todo log error */
    			fclose(fp);
    			return HTTP_INTERNAL_SERVER_ERROR;
    		}
    	//}
    	fclose(fp);
    	
       
    	// for test
    	CxImage src_img;
    	CxImage dest_img;
    	long img_size = 0;
    	BYTE* img_buf = NULL;
        if ( 0 == strcmp("normal", mode)) {              // 原图下载
    		img_buf = (BYTE *)read_buf;
    		img_size = len;
        }else if ( 0 == strcmp("thumbnail", mode) ) {    // 缩略图下载
        	/* parse resample rate from uri */
        	const char* ratio_str = apr_table_get(GET, "ratio");
    		if ( NULL == ratio_str ) {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to parse resample ratio from uri query : %s", query);
        		return HTTP_BAD_REQUEST;
    		}
        	int  ratio = atoi(ratio_str);
    		if ( 0 == ratio ) {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "invalid resample rate : %s", ratio_str);
        		return HTTP_BAD_REQUEST;
    		}
    		if ( !src_img.Decode((BYTE *)read_buf, sizeof(read_buf), CXIMAGE_FORMAT_JPG) ) {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to decode picture");
    			return HTTP_INTERNAL_SERVER_ERROR;
    		}
    		if (src_img.Resample(src_img.GetWidth()/ratio,src_img.GetHeight()/ratio, 1, &dest_img)) {
    			dest_img.Encode( img_buf, img_size, CXIMAGE_FORMAT_JPG );
    		} else {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to resample picture : %s, ratio : %d", file_path, ratio);
    			// todo :失败的情况下是否需要调用 dest_img.FreeMemory(img_buf);
    			return HTTP_INTERNAL_SERVER_ERROR;
    		}
        }else if ( 0 == strcmp("crop", mode) ) {         // 图片裁剪
    		src_img.Decode((BYTE *)read_buf, sizeof(read_buf) ,CXIMAGE_FORMAT_JPG);
        	const char* left_str = apr_table_get(GET, "left");
        	const char* top_str = apr_table_get(GET, "top");
        	const char* right_str = apr_table_get(GET, "right");
        	const char* bottom_str = apr_table_get(GET, "bottom");
        	if (NULL == left_str || NULL == top_str || NULL == right_str || NULL == bottom_str ) {
        		ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to parse crop region from uri query : %s", query);
        		return HTTP_BAD_REQUEST;
        	}
    		int left   = atoi(left_str);
    		int top    = atoi(top_str);
    		int right  = atoi(right_str);
    		int bottom = atoi(bottom_str);
    		if (left < 0 || top < 0 || right < 0 || bottom < 0) {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "invalid crop region: (%d, %d), (%d, %d)", left, top, right, bottom);
        		return HTTP_BAD_REQUEST;
    		}
    		if ( !src_img.Decode((BYTE *)read_buf, sizeof(read_buf), CXIMAGE_FORMAT_JPG) ) {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to decode picture");
    			return HTTP_INTERNAL_SERVER_ERROR;
    		}
    		if (src_img.Crop( left, top, right, bottom, &dest_img )) {
    			dest_img.Encode( img_buf, img_size, CXIMAGE_FORMAT_JPG );
    		}else {
    			// todo :失败的情况下是否需要调用 dest_img.FreeMemory(img_buf);
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to crop picture : %s, (%s, %s), (%s, %s)", file_path, left_str, top_str, right_str, bottom_str);
    			return HTTP_INTERNAL_SERVER_ERROR;
    		}
        }
        
    	/* we can get file length only after converted picture format */
        /* Content-Length:xxxx */
        char file_len_str[MAX_FILE_LEN_DIGITS];
        memset(file_len_str, 0, sizeof(file_len_str));
        snprintf(file_len_str, sizeof(file_len_str)-1, "%d", img_size);
        apr_table_add(r->headers_out,"Content-Length", file_len_str);
    	
    	int send_bytes = 0;
    	while( send_bytes < img_size ){
    		/*ap_flush_conn(r->connection);*/
    		int send_ret = ap_rwrite( img_buf, img_size - send_bytes, r );
    		if( send_ret >= 0 ) {
    			send_bytes += send_ret;
    		} else {
    			ap_log_error(APLOG_MARK, APLOG_ERR, 0,r->server, "failed to send buffer to client");
    			return HTTP_INTERNAL_SERVER_ERROR;
    		}
    	}
    	if (img_buf != (BYTE*)read_buf) {            /* (img_buf == read_buf)  means download the original picture, and haven't call dest_img.Encode() */
    		dest_img.FreeMemory(img_buf);
    		img_buf = NULL;
    	}	
        return OK;
    }
    
    static void api_register_hooks(apr_pool_t *p)
    {
        ap_hook_handler(api_handler, NULL, NULL, APR_HOOK_MIDDLE);
    }
    
    /* Dispatch list for API hooks */
    module AP_MODULE_DECLARE_DATA api_module = {
        STANDARD20_MODULE_STUFF, 
        NULL,                  /* create per-dir    config structures */
        NULL,                  /* merge  per-dir    config structures */
        NULL,                  /* create per-server config structures */
        NULL,                  /* merge  per-server config structures */
        NULL,                  /* table of config file commands       */
        api_register_hooks  /* register hooks                      */
    };

[Link 1]: http://blog.csdn.net/icycode/article/details/48935533
[2.4]: http://httpd.apache.org/docs/2.4/developer/modguide.html