Add append and update function to common (#554)

include/aws/common/byte_buf.h

@@ -368,6 +368,15 @@ int aws_byte_buf_append_with_lookup(
 AWS_COMMON_API
 int aws_byte_buf_append_dynamic(struct aws_byte_buf *to, const struct aws_byte_cursor *from);
 
+/**
+ * Copy contents of cursor to buffer, then update cursor to reference the memory stored in the buffer.
+ * If buffer is too small, AWS_ERROR_DEST_COPY_TOO_SMALL will be returned.
+ *
+ * The cursor is permitted to reference memory from earlier in the buffer.
+ */
+AWS_COMMON_API
+int aws_byte_buf_append_and_update(struct aws_byte_buf *to, struct aws_byte_cursor *from_and_update);
+
 /**
  * Attempts to increase the capacity of a buffer to the requested capacity
  *

source/byte_buf.c

@@ -1349,3 +1349,15 @@ bool aws_byte_buf_write_float_be64(struct aws_byte_buf *buf, double x) {
     x = aws_htonf64(x);
     return aws_byte_buf_write(buf, (uint8_t *)&x, 8);
 }
+
+int aws_byte_buf_append_and_update(struct aws_byte_buf *to, struct aws_byte_cursor *from_and_update) {
+    AWS_PRECONDITION(aws_byte_buf_is_valid(to));
+    AWS_PRECONDITION(aws_byte_cursor_is_valid(from_and_update));
+
+    if (aws_byte_buf_append(to, from_and_update)) {
+        return AWS_OP_ERR;
+    }
+
+    from_and_update->ptr = to->buffer + (to->len - from_and_update->len);
+    return AWS_OP_SUCCESS;
+}

tests/CMakeLists.txt

@@ -239,6 +239,8 @@ add_test_case(test_byte_buf_reserve_relative)
 add_test_case(test_byte_buf_reset)
 add_test_case(test_byte_cursor_compare_lexical)
 add_test_case(test_byte_cursor_compare_lookup)
+add_test_case(test_byte_buf_append_and_update_fail)
+add_test_case(test_byte_buf_append_and_update_success)
 
 add_test_case(test_byte_cursor_find_str)
 add_test_case(test_byte_cursor_find_str_not_found)

tests/byte_buf_test.c

@@ -766,3 +766,51 @@ static int s_test_byte_cursor_compare_lookup(struct aws_allocator *allocator, vo
     return 0;
 }
 AWS_TEST_CASE(test_byte_cursor_compare_lookup, s_test_byte_cursor_compare_lookup)
+
+static int s_test_byte_buf_append_and_update_fail(struct aws_allocator *allocator, void *ctx) {
+    (void)ctx;
+    (void)allocator;
+
+    struct aws_byte_buf buffer;
+    aws_byte_buf_init(&buffer, allocator, 10);
+
+    struct aws_byte_cursor test_cursor = AWS_BYTE_CUR_INIT_FROM_STRING_LITERAL("TOOOOOOOO LONG");
+    struct aws_byte_cursor test_cursor_copy = test_cursor;
+
+    ASSERT_FAILS(aws_byte_buf_append_and_update(&buffer, &test_cursor));
+    ASSERT_TRUE((test_cursor.ptr == test_cursor_copy.ptr) && (test_cursor.len == test_cursor_copy.len));
+
+    aws_byte_buf_clean_up(&buffer);
+
+    return 0;
+}
+AWS_TEST_CASE(test_byte_buf_append_and_update_fail, s_test_byte_buf_append_and_update_fail)
+
+static int s_test_byte_buf_append_and_update_success(struct aws_allocator *allocator, void *ctx) {
+    (void)ctx;
+    (void)allocator;
+
+    struct aws_byte_buf buffer;
+    aws_byte_buf_init(&buffer, allocator, 12);
+
+    struct aws_byte_cursor test_cursor = AWS_BYTE_CUR_INIT_FROM_STRING_LITERAL("SHORT");
+    struct aws_byte_cursor test_cursor_copy = test_cursor;
+
+    ASSERT_SUCCESS(aws_byte_buf_append_and_update(&buffer, &test_cursor));
+    ASSERT_TRUE(test_cursor.ptr == buffer.buffer);
+    ASSERT_TRUE(aws_byte_cursor_eq(&test_cursor, &test_cursor_copy));
+
+    struct aws_byte_cursor test_cursor2 = AWS_BYTE_CUR_INIT_FROM_STRING_LITERAL("STOP");
+    struct aws_byte_cursor test_cursor_copy2 = test_cursor2;
+
+    ASSERT_SUCCESS(aws_byte_buf_append_and_update(&buffer, &test_cursor2));
+    ASSERT_TRUE(test_cursor2.ptr == buffer.buffer + test_cursor.len);
+    ASSERT_TRUE(aws_byte_cursor_eq(&test_cursor2, &test_cursor_copy2));
+
+    ASSERT_TRUE(buffer.len == test_cursor.len + test_cursor2.len);
+
+    aws_byte_buf_clean_up(&buffer);
+
+    return 0;
+}
+AWS_TEST_CASE(test_byte_buf_append_and_update_success, s_test_byte_buf_append_and_update_success)