Fix bug when Range: bytes=0-0 (#278)

This is a valid way to request the first byte.

There was a bug where, if some internal range_start and range_end variables were both 0, it was assumed that meant they were unset, because the object was 0 bytes.

Fix by adding separate bool to indicate whether the object is empty.

Author: graebm

include/aws/s3/private/s3_auto_ranged_get.h

@@ -20,10 +20,12 @@ struct aws_s3_auto_ranged_get {
     enum aws_s3_checksum_algorithm validation_algorithm;
     /* Members to only be used when the mutex in the base type is locked. */
     struct {
-        /* The starting byte of the data that we will be retrieved from the object.*/
+        /* The starting byte of the data that we will be retrieved from the object.
+         * (ignore this if object_range_empty) */
         uint64_t object_range_start;
 
-        /* The last byte of the data that will be retrieved from the object.*/
+        /* The last byte of the data that will be retrieved from the object.
+         * (ignore this if object_range_empty) */
         uint64_t object_range_end;
 
         /* The total number of parts that are being used in downloading the object range. Note that "part" here
@@ -37,6 +39,10 @@ struct aws_s3_auto_ranged_get {
         uint32_t num_parts_checksum_validated;
 
         uint32_t object_range_known : 1;
+
+        /* True if object_range_known, and it's found to be empty.
+         * If this is true, ignore object_range_start and object_range_end */
+        uint32_t object_range_empty : 1;
         uint32_t head_object_sent : 1;
         uint32_t head_object_completed : 1;
         uint32_t get_without_range_sent : 1;

source/s3_auto_ranged_get.c

@@ -196,8 +196,7 @@ static bool s_s3_auto_ranged_get_update(
             }
 
             /* If the object range is known and that range is empty, then we have an empty file to request. */
-            if (auto_ranged_get->synced_data.object_range_start == 0 &&
-                auto_ranged_get->synced_data.object_range_end == 0) {
+            if (auto_ranged_get->synced_data.object_range_empty != 0) {
                 if (auto_ranged_get->synced_data.get_without_range_sent) {
                     if (auto_ranged_get->synced_data.get_without_range_completed) {
                         goto no_work_remaining;
@@ -653,6 +652,7 @@ static void s_s3_auto_ranged_get_request_finished(
             AWS_ASSERT(!auto_ranged_get->synced_data.object_range_known);
 
             auto_ranged_get->synced_data.object_range_known = true;
+            auto_ranged_get->synced_data.object_range_empty = (total_content_length == 0);
             auto_ranged_get->synced_data.object_range_start = object_range_start;
             auto_ranged_get->synced_data.object_range_end = object_range_end;
             auto_ranged_get->synced_data.total_num_parts =

tests/s3_data_plane_tests.c

@@ -4295,6 +4295,9 @@ static int s_test_s3_range_requests(struct aws_allocator *allocator, void *ctx)
         // Single byte range.
         AWS_BYTE_CUR_INIT_FROM_STRING_LITERAL("bytes=8-8"),
 
+        // Single byte range (first byte).
+        AWS_BYTE_CUR_INIT_FROM_STRING_LITERAL("bytes=0-0"),
+
         // First 8K.  8K < client's 16K part size.
         AWS_BYTE_CUR_INIT_FROM_STRING_LITERAL("bytes=0-8191"),