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Querying Object Metadata

Last updated: 2022-01-23 14:17:47

    Overview

    This document provides an overview of APIs and SDK code samples related to querying object metadata.

    API Operation Description
    HEAD Object Querying object metadata Queries the metadata of an object

    Querying Object Metadata

    Description

    This API is used to query the metadata of an object.

    Method prototype

    cos_status_t *cos_head_object(const cos_request_options_t *options, 
                                const cos_string_t *bucket, 
                                const cos_string_t *object,
                                cos_table_t *headers, 
                                cos_table_t **resp_headers);
    

    Parameter description

    Parameter Description Type
    options COS request options Struct
    bucket Bucket name in the format: BucketName-APPID String
    object Object name String
    headers Additional headers of a COS request Struct
    resp_headers Returns the HTTP response headers Struct

    Response description

    Response Parameter Description Type
    code Error code Int
    error_code Error code content String
    error_msg Error code description String
    req_id Request message ID String

    Sample

    #include "cos_http_io.h"
    #include "cos_api.h"
    #include "cos_log.h"
    // `endpoint` is the COS access domain name. For more information, see https://www.tencentcloud.com/document/product/436/6224.
    static char TEST_COS_ENDPOINT[] = "cos.ap-guangzhou.myqcloud.com";
    // A developer-owned secret ID/key used for the project. It can be obtained at https://console.tencentcloud.com/cam/capi.
    static char *TEST_ACCESS_KEY_ID;                // Your SecretId
    static char *TEST_ACCESS_KEY_SECRET;            // Your SecretKey
    // A unique user-level resource identifier for COS access. It can be obtained at https://console.tencentcloud.com/cam/capi.
    static char TEST_APPID[] = "<APPID>";    // Your APPID
    // COS bucket name, in the format of [bucket]-[appid], for example `mybucket-1253666666`. It can be obtained at https://console.tencentcloud.com/cos5/bucket.
    static char TEST_BUCKET_NAME[] = "<bucketname-appid>";    
    // A unique identifier of an object stored in COS. For more information about objects and object keys, please see https://www.tencentcloud.com/document/product/436/13324.
    static char TEST_OBJECT_NAME1[] = "1.txt";
    static void print_headers(cos_table_t *headers)
    {
      const cos_array_header_t *tarr;
      const cos_table_entry_t *telts;
      int i = 0;
       if (apr_is_empty_table(headers)) {
          return;
      }
       tarr = cos_table_elts(headers);
      telts = (cos_table_entry_t*)tarr->elts;
       printf("headers:\n");
      for (; i < tarr->nelts; i++) {
          telts = (cos_table_entry_t*)(tarr->elts + i * tarr->elt_size);
          printf("%s: %s\n", telts->key, telts->val);
      }
    }
    void init_test_config(cos_config_t *config, int is_cname)
    {
      cos_str_set(&config->endpoint, TEST_COS_ENDPOINT);
      cos_str_set(&config->access_key_id, TEST_ACCESS_KEY_ID);
      cos_str_set(&config->access_key_secret, TEST_ACCESS_KEY_SECRET);
      cos_str_set(&config->appid, TEST_APPID);
      config->is_cname = is_cname;
    }
    void init_test_request_options(cos_request_options_t *options, int is_cname)
    {
      options->config = cos_config_create(options->pool);
      init_test_config(options->config, is_cname);
      options->ctl = cos_http_controller_create(options->pool, 0);
    }
    void test_head_object()
    {
      cos_pool_t *p = NULL;
      int is_cname = 0;
      cos_status_t *s = NULL;
      cos_request_options_t *options = NULL;
      cos_string_t bucket;
      cos_string_t object;
      cos_table_t *resp_headers = NULL;
       // Create a memory pool
      cos_pool_create(&p, NULL);
       // Initialize the request options
      options = cos_request_options_create(p);
      init_test_request_options(options, is_cname);
      cos_str_set(&bucket, TEST_BUCKET_NAME);
       // Get object metadata
      cos_str_set(&object, TEST_OBJECT_NAME1);
      s = cos_head_object(options, &bucket, &object, NULL, &resp_headers);
      print_headers(resp_headers);
      if (cos_status_is_ok(s)) {
          printf("head object succeeded\n");
      } else {
          printf("head object failed\n");
      }
       // Destroy the memory pool.
      cos_pool_destroy(p); 
    }
    int main(int argc, char *argv[])
    {
      // Get SecretId and SecretKey from environment variables
      TEST_ACCESS_KEY_ID     = getenv("COS_SECRETID");
      TEST_ACCESS_KEY_SECRET = getenv("COS_SECRETKEY");
        if (cos_http_io_initialize(NULL, 0) != COSE_OK) {
         exit(1);
      }
       // Set the log level. Default value: `COS_LOG_WARN`
      cos_log_set_level(COS_LOG_WARN);
       // Set log output. Default value: `stderr`
      cos_log_set_output(NULL);
       test_head_object();
       cos_http_io_deinitialize();
       return 0;
    }
    
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