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

      之前的博客中有提到基于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.6LoadModule 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apache2.4官方文档 ，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》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 testCxImage 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                      */};