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.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 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                      */
};

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

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