OSS在完成檔案（Object）上傳時可以提供回調（Callback）給應用伺服器。您只需要在發送給OSS的請求中攜帶相應的Callback參數，即可實現上傳回調。
注意事項
本文以華東1（杭州）外網Endpoint為例。如果您希望通過與OSS同地區的其他阿里雲產品訪問OSS，請使用內網Endpoint。關於OSS支援的Region與Endpoint的對應關係，請參見訪問網域名稱和資料中心。
本文以OSS網域名稱建立OSSClient為例。如果您希望通過自訂網域名、STS等方式建立OSSClient，請參見初始化。
範例程式碼
以下代碼用於上傳回調：
#include "oss_api.h"
#include "aos_http_io.h"
/* yourEndpoint填寫Bucket所在地區對應的Endpoint。以華東1（杭州）為例，Endpoint填寫為https://oss-cn-hangzhou.aliyuncs.com。*/
const char *endpoint = "yourEndpoint";
/* 填寫Bucket名稱，例如examplebucket。*/
const char *bucket_name = "examplebucket";
/* 填寫Object完整路徑，完整路徑中不能包含Bucket名稱，例如exampledir/exampleobject.txt。*/
const char *object_name = "exampledir/exampleobject.txt";
const char *object_content = "More than just cloud.";
void init_options(oss_request_options_t *options)
{
options->config = oss_config_create(options->pool);
/* 用char*類型的字串初始化aos_string_t類型。*/
aos_str_set(&options->config->endpoint, endpoint);
/* 從環境變數中擷取訪問憑證。運行本程式碼範例之前，請確保已設定環境變數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"));
/* 是否使用了CNAME。0表示不使用。*/
options->config->is_cname = 0;
/* 設定網路相關參數，比如逾時時間等。*/
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;
/* 採用JSON格式。*/
/*（可選）設定回調請求訊息頭中Host的值，如您的伺服器配置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\""
"}";
/* 在程式入口調用aos_http_io_initialize方法來初始化網路、記憶體等全域資源。*/
if (aos_http_io_initialize(NULL, 0) != AOSE_OK) {
exit(1);
}
/* 初始化參數。*/
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);
/* 將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);
/* 上傳回調。*/
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");
}
/* 擷取buffer長度。*/
len = aos_buf_list_len(&resp_body);
buf = (char *)aos_pcalloc(p, (apr_size_t)(len + 1));
buf[len] = '\0';
/* 拷貝buffer內容到記憶體。*/
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;
}
/* 釋放記憶體池，相當於釋放了請求過程中各資源分派的記憶體。*/
aos_pool_destroy(p);
/* 釋放之前分配的全域資源。*/
aos_http_io_deinitialize();
return 0;
}