Range download

If you only need part of the data in an object, you can use range downloads to download specified content.

Run the following code for range download:

#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);
    /* Use a char* string to initialize the aos_string_t type. */
    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);
    /* Determine whether the CNAME is used. 0 indicates that the CNAME is not used. */
    options->config->is_cname = 0;
    /* Used to configure network parameters, such as timeout. */
    options->ctl = aos_http_controller_create(options->pool, 0);
}
int main(int argc, char *argv[])
{
    /* Call the aos_http_io_initialize method in main() to initialize global resources, such as networks and memories. */
    if (aos_http_io_initialize(NULL, 0) != AOSE_OK) {
        exit(1);
    }
    /* Memory pool used to manage memories, which is equivalent to apr_pool_t. The implementation code is included in the apr library. */
    aos_pool_t *pool;
    /* Re-create a new memory pool. The second parameter is NULL, indicating that it does not inherit from any other memory pools. */
    aos_pool_create(&pool, NULL);
    /* Create and initialize options. This parameter mainly includes global configuration information, such as endpoint, access_key_id, acces_key_secret, is_cname, and curl. */
    oss_request_options_t *oss_client_options;
    /* Allocate memories in the memory pool to options. */
    oss_client_options = oss_request_options_create(pool);
    /* Use oss_client_options to initialize client options. */
    init_options(oss_client_options);
    /* Initialization parameters. */
    aos_string_t bucket;
    aos_string_t object;
    aos_list_t buffer;
    aos_buf_t *content = NULL;
    aos_table_t *params = NULL;
    aos_table_t *headers = NULL;
    aos_table_t *resp_headers = NULL; 
    aos_status_t *resp_status = NULL; 
    char *buf = NULL;
    int64_t len = 0;
    int64_t size = 0;
    int64_t pos = 0;
    aos_str_set(&bucket, bucket_name);
    aos_str_set(&object, object_name);
    aos_list_init(&buffer);
    headers = aos_table_make(pool, 1);
    /* Set the download range, which ranges from the 20th byte to the 100th byte. */
    apr_table_set(headers, "Range", "bytes=20-100");
    /* Download the object to memory. */
    resp_status = oss_get_object_to_buffer(oss_client_options, &bucket, &object, headers, params, &buffer, &resp_headers);
    if (aos_status_is_ok(resp_status)) {
        printf("get object to buffer succeeded\n");
        /* Obtain the buffer length. */
        aos_list_for_each_entry(aos_buf_t, content, &buffer, node) {
            len += aos_buf_size(content);
        }
        buf = aos_pcalloc(pool, (apr_size_t)(len + 1));
        buf[len] = '\0';
        /* Copy the content in the buffer to memory. */
        aos_list_for_each_entry(aos_buf_t, content, &buffer, node) {
            size = aos_buf_size(content);
            memcpy(buf + pos, content->pos, (size_t)size);
            pos += size;
        }
    }
    else {
        printf("get object to buffer failed\n");  
    }
    /* Release the memory pool, that is, memories allocated to resources during the request. */
    aos_pool_destroy(pool);
    /* Release allocated global resources. */
    aos_http_io_deinitialize();
    return 0;
}