support customizing part_size per meta-request

include/aws/s3/s3_client.h

@@ -389,21 +389,36 @@ struct aws_s3_client_config {
      */
     struct aws_signing_config_aws *signing_config;
 
-    /* Size of parts the files will be downloaded or uploaded in. */
+    /**
+     * Optional.
+     * Size of parts the object will be downloaded or uploaded in, in bytes.
+     * This only affects AWS_S3_META_REQUEST_TYPE_GET_OBJECT and AWS_S3_META_REQUEST_TYPE_PUT_OBJECT.
+     * If set, this should be at least 5MiB.
+     * If not set, this defaults to 8MiB.
+     *
+     * You can also set this per meta-request, via `aws_s3_meta_request_options.part_size`.
+     */
     uint64_t part_size;
 
     /* If the part size needs to be adjusted for service limits, this is the maximum size it will be adjusted to. On 32
      * bit machine, it will be forced to SIZE_MAX, which is around 4GiB. The server limit is 5GiB, but object size limit
      * is 5TiB for now. We should be good enough for all the cases. */
     uint64_t max_part_size;
 
-    /* The size threshold in bytes for when to use multipart uploads for a AWS_S3_META_REQUEST_TYPE_PUT_OBJECT meta
-     * request. Uploads over this size will automatically use a multipart upload strategy,while uploads smaller or
-     * equal to this threshold will use a single request to upload the whole object. If not set, `part_size` will be
-     * used as threshold. */
+    /**
+     * Optional.
+     * The size threshold in bytes for when to use multipart uploads.
+     * Uploads larger than this will use the multipart upload strategy.
+     * Uploads smaller or equal to this will use a single HTTP request.
+     * This only affects AWS_S3_META_REQUEST_TYPE_PUT_OBJECT.
+     * If set, this should be at least `part_size`.
+     * If not set, `part_size` will be used as the threshold.
+     *
+     * You can also set this per meta-request, via `aws_s3_meta_request_options.multipart_upload_threshold`.
+     */
     uint64_t multipart_upload_threshold;
 
-    /* Throughput target in Gbps that we are trying to reach. */
+    /* Throughput target in gigabits per second (Gbps) that we are trying to reach. */
     double throughput_target_gbps;
 
     /* How much memory can we use. */
@@ -612,6 +627,28 @@ struct aws_s3_meta_request_options {
      */
     const struct aws_s3_checksum_config *checksum_config;
 
+    /**
+     * Optional.
+     * Size of parts the object will be downloaded or uploaded in, in bytes.
+     * This only affects AWS_S3_META_REQUEST_TYPE_GET_OBJECT and AWS_S3_META_REQUEST_TYPE_PUT_OBJECT.
+     * If set, this should be at least 5MiB.
+     * If not set, the value from `aws_s3_client_config.part_size` is used, which defaults to 8MiB.
+     */
+    uint64_t part_size;
+
+    /**
+     * Optional.
+     * The size threshold in bytes for when to use multipart uploads.
+     * Uploads larger than this will use the multipart upload strategy.
+     * Uploads smaller or equal to this will use a single HTTP request.
+     * This only affects AWS_S3_META_REQUEST_TYPE_PUT_OBJECT.
+     * If set, this should be at least `part_size`.
+     * If not set, `part_size` will be used as the threshold.
+     * If both `part_size` and `multipart_upload_threshold` are not set,
+     * the values from `aws_s3_client_config` are used, which default to 8MiB.
+     */
+    uint64_t multipart_upload_threshold;
+
     /* User data for all callbacks. */
     void *user_data;