OSS提供的分片上传(Multipart Upload)功能,将要上传的较大文件(Object)分成多个数据块(Part)来分别上传,上传完成后再调用CompleteMultipartUpload接口将这些Part组合成一个Object来达到断点续传的效果。

分片上传流程

分片上传(Multipart Upload)分为以下三个步骤:

  1. 初始化一个分片上传事件。

    调用oss_init_multipart_upload方法返回OSS创建的全局唯一的uploadId。

  2. 上传分片。

    调用oss_upload_part_from_file方法上传分片数据。

    说明
    • 对于同一个UploadId,分片号(PartNumber)标识了该分片在整个文件内的相对位置。如果使用同一个分片号上传了新的数据,那么OSS上这个分片已有的数据将会被覆盖。
    • OSS将收到的分片数据的MD5值放在ETag头内返回给用户。
    • OSS计算上传数据的MD5值,并与SDK计算的MD5值比较,如果不一致则返回InvalidDigest错误码。
  3. 完成分片上传。

    所有分片上传完成后,调用oss_complete_multipart_upload方法将所有分片合并成完整的文件。

分片上传完整示例

以下通过一个完整的示例对分片上传的流程进行逐步解析:

#include "oss_api.h"
#include "aos_http_io.h"
#include <sys/stat.h>
const char *endpoint = "<yourEndpoint>";
const char *access_key_id = "<yourAccessKeyId>";
const char *access_key_secret = "<yourAccessKeySecret>";
const char *bucket_name = "<yourBucketName>";
const char *object_name = "<yourObjectName>";
const char *local_filename = "<yourLocalFilename>";
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);
    aos_str_set(&options->config->access_key_id, access_key_id);
    aos_str_set(&options->config->access_key_secret, access_key_secret);
    /* 是否使用CNAME访问OSS服务。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);
}
int64_t get_file_size(const char *file_path)
{
    int64_t filesize = -1;
    struct stat statbuff;
    if(stat(file_path, &statbuff) < 0){
        return filesize;
    } else {
        filesize = statbuff.st_size;
    }
    return filesize;
}
int main(int argc, char *argv[])
{
    /* 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);
    }
    /* 用于内存管理的内存池(pool),等价于apr_pool_t。其实现代码在apr库中。*/
    aos_pool_t *pool;
    /* 重新创建一个内存池,第二个参数是NULL,表示没有继承其它内存池。*/
    aos_pool_create(&pool, NULL);
    /* 创建并初始化options,该参数包括endpoint、access_key_id、acces_key_secret、is_cname、curl等全局配置信息。*/
    oss_request_options_t *oss_client_options;
    /* 在内存池中分配内存给options。*/
    oss_client_options = oss_request_options_create(pool);
    /* 初始化Client的选项oss_client_options。*/
    init_options(oss_client_options);
    /* 初始化参数。*/
    aos_string_t bucket;
    aos_string_t object;
    oss_upload_file_t *upload_file = NULL;
    aos_string_t upload_id;   
    aos_table_t *headers = NULL;
    aos_table_t *complete_headers = NULL;
    aos_table_t *resp_headers = NULL;
    aos_status_t *resp_status = NULL; 
    aos_str_set(&bucket, bucket_name);
    aos_str_set(&object, object_name);
    aos_str_null(&upload_id);
    headers = aos_table_make(pool, 1);
    complete_headers = aos_table_make(pool, 1);
    int part_num = 1;
    /* 初始化分片上传,获取一个上传ID(upload_id)。*/
    resp_status = oss_init_multipart_upload(oss_client_options, &bucket, &object, &upload_id, headers, &resp_headers);
    /* 判断分片上传初始化是否成功。*/
    if (aos_status_is_ok(resp_status)) {
        printf("Init multipart upload succeeded, upload_id:%.*s\n", 
               upload_id.len, upload_id.data);
    } else {
        printf("Init multipart upload failed, upload_id:%.*s\n", 
               upload_id.len, upload_id.data);
    }
    /* 上传分片。*/
    int64_t file_length = 0;
    int64_t pos = 0;
    aos_list_t complete_part_list;
       oss_complete_part_content_t* complete_content = NULL;
    char* part_num_str = NULL;
    char* etag = NULL;
    aos_list_init(&complete_part_list);
    file_length = get_file_size(local_filename);
    while(pos < file_length) {
        upload_file = oss_create_upload_file(pool);
        aos_str_set(&upload_file->filename, local_filename);
        upload_file->file_pos = pos;
        pos += 100 * 1024;
        upload_file->file_last = pos < file_length ? pos : file_length;
        resp_status = oss_upload_part_from_file(oss_client_options, &bucket, &object, &upload_id, part_num++, upload_file, &resp_headers);

        /* 保存分片号和Etag。*/
        complete_content = oss_create_complete_part_content(pool);
        part_num_str = apr_psprintf(pool, "%d", part_num-1);
        aos_str_set(&complete_content->part_number, part_num_str);
        etag = apr_pstrdup(pool,
        (char*)apr_table_get(resp_headers, "ETag"));
        aos_str_set(&complete_content->etag, etag);
        aos_list_add_tail(&complete_content->node, &complete_part_list);

        if (aos_status_is_ok(resp_status)) {
            printf("Multipart upload part from file succeeded\n");
        } else {
            printf("Multipart upload part from file failed\n");
        }
    }

    /* 完成分片上传。*/
    resp_status = oss_complete_multipart_upload(oss_client_options, &bucket, &object, &upload_id,
            &complete_part_list, complete_headers, &resp_headers);
    /* 判断分片上传是否完成。*/
    if (aos_status_is_ok(resp_status)) {
        printf("Complete multipart upload from file succeeded, upload_id:%.*s\n", 
               upload_id.len, upload_id.data);
    } else {
        printf("Complete multipart upload from file failed\n");
    }
    /* 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(pool);
    /* 释放之前分配的全局资源。*/
    aos_http_io_deinitialize();
    return 0;
}

获取已经上传的分片,调用oss_complete_multipart_upload接口时需要每个分片的ETag值。您可以通过以下两种方式获取ETag值:

  • 上传每个分片时,返回结果中会包含这个分片的ETag值,供您直接保存使用。
  • 通过调用oss_list_upload_part接口获取已经上传的分片的ETag值。上述示例采用的此种方式。

取消分片上传事件

以下代码用于取消分片上传事件:

#include "oss_api.h"
#include "aos_http_io.h"
const char *endpoint = "<yourEndpoint>";
const char *access_key_id = "<yourAccessKeyId>";
const char *access_key_secret = "<yourAccessKeySecret>";
const char *bucket_name = "<yourBucketName>";
const char *object_name = "<yourObjectName>";
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);
    aos_str_set(&options->config->access_key_id, access_key_id);
    aos_str_set(&options->config->access_key_secret, access_key_secret);
    /* 是否使用CNAME访问OSS服务。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[])
{
    /* 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);
    }
    /* 用于内存管理的内存池(pool),等价于apr_pool_t。其实现代码在apr库中。*/
    aos_pool_t *pool;
    /* 重新创建一个内存池,第二个参数是NULL,表示没有继承其它内存池。*/
    aos_pool_create(&pool, NULL);
    /* 创建并初始化options,该参数包括endpoint、access_key_id、acces_key_secret、is_cname、curl等全局配置信息。*/
    oss_request_options_t *oss_client_options;
    /* 在内存池中分配内存给options。*/
    oss_client_options = oss_request_options_create(pool);
    /* 初始化Client的选项oss_client_options。*/
    init_options(oss_client_options);
    /* 初始化参数。*/
    aos_string_t bucket;
    aos_string_t object;
    aos_string_t upload_id;   
    aos_table_t *headers = NULL;
    aos_table_t *resp_headers = NULL;
    aos_status_t *resp_status = NULL; 
    aos_str_set(&bucket, bucket_name);
    aos_str_set(&object, object_name);
    aos_str_null(&upload_id);
    /* 初始化分片上传,获取一个上传ID(upload_id)。*/
    resp_status = oss_init_multipart_upload(oss_client_options, &bucket, &object, &upload_id, headers, &resp_headers);
    /* 判断是否初始化分片上传成功。 */
    if (aos_status_is_ok(resp_status)) {
        printf("Init multipart upload succeeded, upload_id:%.*s\n", 
               upload_id.len, upload_id.data);
    } else {
        printf("Init multipart upload failed, upload_id:%.*s\n", 
               upload_id.len, upload_id.data);
    }
    /* 取消这次分片上传。*/
    resp_status = oss_abort_multipart_upload(oss_client_options, &bucket, &object, &upload_id, &resp_headers);
    /* 判断取消分片上传是否成功。*/
    if (aos_status_is_ok(resp_status)) {
        printf("Abort multipart upload succeeded, upload_id::%.*s\n", 
               upload_id.len, upload_id.data);
    } else {
        printf("Abort multipart upload failed\n"); 
    }
    /* 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(pool);
    /* 释放之前分配的全局资源。*/
    aos_http_io_deinitialize();
    return 0;
}
说明 当一个分片上传事件被取消后,就不能再使用upload_id做任何操作,已经上传的分片数据也会被删除。