OSS在完成文件（Object）上传时可以提供回调（Callback）给应用服务器。您只需要在发送给OSS的请求中携带相应的Callback参数，即可实现上传回调。
注意事项
本文以华东1（杭州）外网Endpoint为例。如果您希望通过与OSS同地域的其他阿里云产品访问OSS，请使用内网Endpoint。关于OSS支持的Region与Endpoint的对应关系，请参见OSS地域和访问域名。
本文以OSS域名新建OSSClient为例。如果您希望通过自定义域名、STS等方式新建OSSClient，请参见初始化。
示例代码
以下代码用于上传回调：
#include "oss_api.h"
#include "aos_http_io.h"
/* yourEndpoint填写Bucket所在地域对应的Endpoint。以华东1（杭州）为例，Endpoint填写为https://oss-cn-hangzhou.aliyuncs.com。*/
const char *endpoint = "yourEndpoint";
/* 填写Bucket名称，例如examplebucket。*/
const char *bucket_name = "examplebucket";
/* 填写Object完整路径，完整路径中不能包含Bucket名称，例如exampledir/exampleobject.txt。*/
const char *object_name = "exampledir/exampleobject.txt";
const char *object_content = "More than just cloud.";
/* yourRegion填写Bucket所在地域对应的Region。以华东1（杭州）为例，Region填写为cn-hangzhou。*/
const char *region = "yourRegion";
void init_options(oss_request_options_t *options)
{
options->config = oss_config_create(options->pool);
/* 用char*类型的字符串初始化aos_string_t类型。*/
aos_str_set(&options->config->endpoint, endpoint);
/* 从环境变量中获取访问凭证。运行本代码示例之前，请确保已设置环境变量OSS_ACCESS_KEY_ID和OSS_ACCESS_KEY_SECRET。*/
aos_str_set(&options->config->access_key_id, getenv("OSS_ACCESS_KEY_ID"));
aos_str_set(&options->config->access_key_secret, getenv("OSS_ACCESS_KEY_SECRET"));
//需要额外配置以下两个参数
aos_str_set(&options->config->region, region);
options->config->signature_version = 4;
/* 是否使用了CNAME。0表示不使用。*/
options->config->is_cname = 0;
/* 设置网络相关参数，比如超时时间等。*/
options->ctl = aos_http_controller_create(options->pool, 0);
}
int main(int argc, char *argv[])
{
aos_pool_t *p = NULL;
aos_status_t *s = NULL;
aos_string_t bucket;
aos_string_t object;
aos_table_t *headers = NULL;
oss_request_options_t *options = NULL;
aos_table_t *resp_headers = NULL;
aos_list_t resp_body;
aos_list_t buffer;
aos_buf_t *content;
char *buf = NULL;
int64_t len = 0;
int64_t size = 0;
int64_t pos = 0;
char b64_buf[1024];
int b64_len;
/* 采用JSON格式。*/
/*（可选）设置回调请求消息头中Host的值，如您的服务器配置Host的值。*/
char *callback = "{"
"\"callbackUrl\":\"http://oss-demo.aliyuncs.com:23450\","
"\"callbackHost\":\"yourCallbackHost\","
"\"callbackBody\":\"bucket=${bucket}&object=${object}&size=${size}&mimeType=${mimeType}\","
"\"callbackBodyType\":\"application/x-www-form-urlencoded\""
"}";
/* 在程序入口调用aos_http_io_initialize方法来初始化网络、内存等全局资源。*/
if (aos_http_io_initialize(NULL, 0) != AOSE_OK) {
exit(1);
}
/* 初始化参数。*/
aos_pool_create(&p, NULL);
options = oss_request_options_create(p);
init_options(options);
aos_str_set(&bucket, bucket_name);
aos_str_set(&object, object_name);
aos_list_init(&resp_body);
aos_list_init(&buffer);
content = aos_buf_pack(options->pool, object_content, strlen(object_content));
aos_list_add_tail(&content->node, &buffer);
/* 将callback放入header。*/
b64_len = aos_base64_encode((unsigned char*)callback, strlen(callback), b64_buf);
b64_buf[b64_len] = '\0';
headers = aos_table_make(p, 1);
apr_table_set(headers, OSS_CALLBACK, b64_buf);
/* 上传回调。*/
s = oss_do_put_object_from_buffer(options, &bucket, &object, &buffer,
headers, NULL, NULL, &resp_headers, &resp_body);
if (aos_status_is_ok(s)) {
printf("put object from buffer succeeded\n");
} else {
printf("put object from buffer failed\n");
}
/* 获取buffer长度。*/
len = aos_buf_list_len(&resp_body);
buf = (char *)aos_pcalloc(p, (apr_size_t)(len + 1));
buf[len] = '\0';
/* 拷贝buffer内容到内存。*/
aos_list_for_each_entry(aos_buf_t, content, &resp_body, node) {
size = aos_buf_size(content);
memcpy(buf + pos, content->pos, (size_t)size);
pos += size;
}
/* 释放内存池，相当于释放了请求过程中各资源分配的内存。*/
aos_pool_destroy(p);
/* 释放之前分配的全局资源。*/
aos_http_io_deinitialize();
return 0;
}