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
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>
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 */
};