fix the logic for empty file

Author: TingDaoK

include/aws/s3/s3_client.h

@@ -315,7 +315,11 @@ enum aws_s3_recv_file_options {
     AWS_S3_RECV_FILE_WRITE_TO_POSITION,
 };
 
-/* Controls how client performance file I/O operations. Only applies to the file based workload. */
+/**
+ * WARNING: experimental/unstable:
+ * Controls how client performance file I/O operations. Only applies to the file based
+ * workload.
+ **/
 struct aws_s3_file_io_options {
     /**
      * Skip buffering the part in memory before sending the request.

source/s3_auto_ranged_get.c

@@ -112,6 +112,7 @@ struct aws_s3_meta_request *aws_s3_meta_request_auto_ranged_get_new(
         }
     }
     auto_ranged_get->initial_message_has_if_match_header = aws_http_headers_has(headers, g_if_match_header_name);
+
     auto_ranged_get->synced_data.first_part_size = auto_ranged_get->base.part_size;
     if (options->object_size_hint != NULL) {
         auto_ranged_get->object_size_hint_available = true;
@@ -764,22 +765,28 @@ static void s_s3_auto_ranged_get_request_finished(
             goto update_synced_data;
         }
         /* Always extract ETag header for part size estimation */
-        struct aws_byte_cursor etag_header_value;
-        if (aws_http_headers_get(request->send_data.response_headers, g_etag_header_name, &etag_header_value) ==
-            AWS_OP_SUCCESS) {
-            AWS_LOGF_TRACE(
-                AWS_LS_S3_META_REQUEST,
-                "id=%p ETag received for the meta request. value is: " PRInSTR "",
-                (void *)meta_request,
-                AWS_BYTE_CURSOR_PRI(etag_header_value));
+        if (!request_failed || first_part_size_mismatch) {
+            struct aws_byte_cursor etag_header_value;
+            AWS_ASSERT(auto_ranged_get->etag == NULL);
+            if (aws_http_headers_get(request->send_data.response_headers, g_etag_header_name, &etag_header_value) ==
+                AWS_OP_SUCCESS) {
+                AWS_LOGF_TRACE(
+                    AWS_LS_S3_META_REQUEST,
+                    "id=%p ETag received for the meta request. value is: " PRInSTR "",
+                    (void *)meta_request,
+                    AWS_BYTE_CURSOR_PRI(etag_header_value));
 
-            /* Store ETag if needed for If-Match header */
-            if ((!request_failed || first_part_size_mismatch) &&
-                !auto_ranged_get->initial_message_has_if_match_header) {
-                AWS_ASSERT(auto_ranged_get->etag == NULL);
-                auto_ranged_get->etag = aws_string_new_from_cursor(auto_ranged_get->base.allocator, &etag_header_value);
+                if (!auto_ranged_get->initial_message_has_if_match_header) {
+                    /* Store ETag if needed for If-Match header */
+                    auto_ranged_get->etag =
+                        aws_string_new_from_cursor(auto_ranged_get->base.allocator, &etag_header_value);
+                }
+            } else {
+                AWS_LOGF_ERROR(AWS_LS_S3_META_REQUEST, "id=%p ETag headers are missing", (void *)meta_request);
+                aws_raise_error(AWS_ERROR_S3_MISSING_ETAG);
+                error_code = AWS_ERROR_S3_MISSING_ETAG;
+                goto update_synced_data;
             }
-
             /* Extract number of parts from ETag and calculate estimated part size */
             uint32_t num_parts = 0;
             if (aws_s3_extract_parts_from_etag(etag_header_value, &num_parts) == AWS_OP_SUCCESS && num_parts > 0) {
@@ -794,16 +801,11 @@ static void s_s3_auto_ranged_get_request_finished(
                     num_parts,
                     auto_ranged_get->estimated_object_stored_part_size);
             } else {
-                /* failed to parse ETag header, error out */
+                /* Failed to parse ETags */
                 aws_raise_error(AWS_ERROR_S3_MISSING_ETAG);
                 error_code = AWS_ERROR_S3_MISSING_ETAG;
                 goto update_synced_data;
             }
-        } else {
-            /* No ETag header found, error out */
-            aws_raise_error(AWS_ERROR_S3_MISSING_ETAG);
-            error_code = AWS_ERROR_S3_MISSING_ETAG;
-            goto update_synced_data;
         }
 
         /* If we were able to discover the object-range/content length successfully, then any error code that was passed