Add helper to check for transient errors (#537)

Co-authored-by: Dengke Tang <dengket@amazon.com>
Co-authored-by: Krish <>

Author: azkrishpy

include/aws/http/http.h

@@ -123,6 +123,14 @@ void aws_http_library_init(struct aws_allocator *alloc);
 AWS_HTTP_API
 void aws_http_library_clean_up(void);
 
+/*
+ * This API provides a recommendation on whether an error code should be considered retryable for transient
+ * errors like host resolution, sockets, and TLS.
+ * Note: This is a recommendation only. Retry behavior should be determined based on your specific use case.
+ */
+AWS_HTTP_API
+bool aws_http_error_code_is_retryable(int error_code);
+
 /**
  * Returns the description of common status codes.
  * Ex: 404 -> "Not Found"

source/http.c

@@ -556,6 +556,19 @@ void aws_http_fatal_assert_library_initialized(void) {
     }
 }
 
+/*
+ * This might need to get updated with more http error codes based on consensus.
+ */
+bool aws_http_error_code_is_retryable(int error_code) {
+    switch (error_code) {
+        case AWS_ERROR_HTTP_CONNECTION_CLOSED:
+        case AWS_ERROR_HTTP_SERVER_CLOSED:
+        case AWS_ERROR_HTTP_PROXY_CONNECT_FAILED_RETRYABLE:
+            return true;
+    }
+    return aws_io_error_code_is_retryable(error_code);
+}
+
 const struct aws_byte_cursor aws_http_method_get = AWS_BYTE_CUR_INIT_FROM_STRING_LITERAL("GET");
 const struct aws_byte_cursor aws_http_method_head = AWS_BYTE_CUR_INIT_FROM_STRING_LITERAL("HEAD");
 const struct aws_byte_cursor aws_http_method_post = AWS_BYTE_CUR_INIT_FROM_STRING_LITERAL("POST");

tests/CMakeLists.txt

@@ -18,6 +18,8 @@ macro(add_h2_decoder_test_set NAME)
     add_test_case("${NAME}_one_byte_at_a_time")
 endmacro()
 
+add_test_case(test_http_error_code_is_retryable)
+
 add_test_case(headers_add)
 add_test_case(headers_add_array)
 add_test_case(headers_set)

tests/test_http.c

@@ -0,0 +1,31 @@
+/**
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0.
+ */
+
+#include <aws/http/http.h>
+#include <aws/testing/aws_test_harness.h>
+
+static int s_test_http_error_code_is_retryable(struct aws_allocator *allocator, void *ctx) {
+    (void)allocator;
+    (void)ctx;
+
+    int error_code = 0;
+    ASSERT_FALSE(aws_http_error_code_is_retryable(error_code));
+
+    {
+        error_code = AWS_ERROR_HTTP_CONNECTION_CLOSED;
+        ASSERT_TRUE(aws_http_error_code_is_retryable(error_code));
+    }
+    {
+        error_code = AWS_ERROR_HTTP_SERVER_CLOSED;
+        ASSERT_TRUE(aws_http_error_code_is_retryable(error_code));
+    }
+
+    error_code = AWS_ERROR_SUCCESS;
+    ASSERT_FALSE(aws_http_error_code_is_retryable(error_code));
+
+    return AWS_OP_SUCCESS;
+}
+
+AWS_TEST_CASE(test_http_error_code_is_retryable, s_test_http_error_code_is_retryable);