Use custom YAML emitter for CloudFormation dumps

Author: hssyoo

.changes/next-release/bugfix-cloudformationpackage-51640.json

@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "cloudformation package",
+  "description": "Restore prior YAML dump behavior when breaking lines."
+}

awscli/customizations/cloudformation/yamlhelper.py

@@ -16,7 +16,7 @@
 from botocore.compat import OrderedDict, json
 from ruamel.yaml.resolver import ScalarNode, SequenceNode
 
-from awscli.utils import dump_yaml_to_str
+from awscli.utils import SafeLineBreakEmitter, dump_yaml_to_str
 
 
 def intrinsics_multi_constructor(loader, tag_prefix, node):
@@ -87,6 +87,7 @@ def yaml_dump(dict_to_dump):
 
     yaml = ruamel.yaml.YAML(typ="safe", pure=True)
     yaml.default_flow_style = False
+    yaml.Emitter = SafeLineBreakEmitter
     yaml.Representer = FlattenAliasRepresenter
     _add_yaml_1_1_boolean_resolvers(yaml.Resolver)
     yaml.Representer.add_representer(OrderedDict, _dict_representer)

awscli/utils.py

@@ -21,6 +21,7 @@
 import sys
 from subprocess import PIPE, Popen
 
+import ruamel.yaml
 from botocore.configprovider import BaseProvider
 from botocore.useragent import UserAgentComponent
 from botocore.utils import (
@@ -488,6 +489,95 @@ def dump_yaml_to_str(yaml, data):
     return stream.getvalue()
 
 
+class SafeLineBreakEmitter(ruamel.yaml.emitter.Emitter):
+    """Emitter that always uses backslash escapes at line breaks in
+    double-quoted scalars.
+
+    Derived from ruamel.yaml's Emitter.write_double_quoted (MIT license).
+
+    ruamel.yaml >= 0.17.23 added a heuristic that sometimes omits the
+    trailing backslash when wrapping long double-quoted strings, relying
+    on YAML line-folding rules to preserve the value. Consumers that don't
+    properly parse the value may experience failures.
+
+    This subclass restores the pre-0.17.23 behaviour of unconditionally
+    emitting a backslash at every line break in double-quoted scalars.
+    """
+
+    def write_double_quoted(self, text, split=True):
+        if self.root_context:
+            if self.requested_indent is not None:
+                self.write_line_break()
+                if self.requested_indent != 0:
+                    self.write_indent()
+        self.write_indicator('"', True)
+        start = end = 0
+        while end <= len(text):
+            ch = None
+            if end < len(text):
+                ch = text[end]
+            if (
+                ch is None
+                or ch in '"\\\x85\u2028\u2029\ufeff'
+                or not (
+                    '\x20' <= ch <= '\x7e'
+                    or (
+                        self.allow_unicode
+                        and (
+                            ('\xa0' <= ch <= '\ud7ff')
+                            or ('\ue000' <= ch <= '\ufffd')
+                            or ('\U00010000' <= ch <= '\U0010ffff')
+                        )
+                    )
+                )
+            ):
+                if start < end:
+                    data = text[start:end]
+                    self.column += len(data)
+                    if bool(self.encoding):
+                        data = data.encode(self.encoding)
+                    self.stream.write(data)
+                    start = end
+                if ch is not None:
+                    if ch in self.ESCAPE_REPLACEMENTS:
+                        data = '\\' + self.ESCAPE_REPLACEMENTS[ch]
+                    elif ch <= '\xff':
+                        data = '\\x%02X' % ord(ch)
+                    elif ch <= '\uffff':
+                        data = '\\u%04X' % ord(ch)
+                    else:
+                        data = '\\U%08X' % ord(ch)
+                    self.column += len(data)
+                    if bool(self.encoding):
+                        data = data.encode(self.encoding)
+                    self.stream.write(data)
+                    start = end + 1
+            if (
+                0 < end < len(text) - 1
+                and (ch == ' ' or start >= end)
+                and self.column + (end - start) > self.best_width
+                and split
+            ):
+                data = text[start:end] + '\\'
+                if start < end:
+                    start = end
+                self.column += len(data)
+                if bool(self.encoding):
+                    data = data.encode(self.encoding)
+                self.stream.write(data)
+                self.write_indent()
+                self.whitespace = False
+                self.indention = False
+                if text[start] == ' ':
+                    data = '\\'
+                    self.column += len(data)
+                    if bool(self.encoding):
+                        data = data.encode(self.encoding)
+                    self.stream.write(data)
+            end += 1
+        self.write_indicator('"', False)
+
+
 class ShapeWalker:
     def walk(self, shape, visitor):
         """Walk through and visit shapes for introspection

tests/unit/test_utils.py

@@ -32,6 +32,7 @@
     InstanceMetadataRegionFetcher,
     LazyPager,
     OutputStreamFactory,
+    SafeLineBreakEmitter,
     ShapeRecordingVisitor,
     ShapeWalker,
     add_command_lineage_to_user_agent_extra,
@@ -644,11 +645,12 @@ def test_can_set_imds_service_endpoint(self):
         provider.provide()
         args, _ = self._send.call_args
         self.assertIn('http://myendpoint/', args[0].url)
-    
+
     def test_can_set_imds_service_endpoint_custom(self):
         driver = create_clidriver()
         driver.session.set_config_variable(
-            'ec2_metadata_service_endpoint', 'http://myendpoint')
+            'ec2_metadata_service_endpoint', 'http://myendpoint'
+        )
         self.add_imds_token_response()
         self.add_get_region_imds_response()
         provider = IMDSRegionProvider(driver.session)
@@ -859,6 +861,28 @@ def test_dump_to_str(self):
         self.assertEqual(result, expected_result)
 
 
+@pytest.fixture
+def yaml_safe_emitter():
+    yaml = ruamel.yaml.YAML(typ="safe", pure=True)
+    yaml.default_flow_style = False
+    yaml.Emitter = SafeLineBreakEmitter
+    yaml.width = 25
+    return yaml
+
+
+class TestSafeLineBreakEmitter:
+    def test_backslash_at_every_line_break(self, yaml_safe_emitter):
+        data = {"key": "hello\nworld foo bar baz"}
+        output = dump_yaml_to_str(yaml_safe_emitter, data)
+        assert output == 'key: "hello\\nworld foo bar\\\n  \\ baz"\n'
+
+    def test_roundtrip_with_multiline_content(self, yaml_safe_emitter):
+        original = "line1\nline2 with spaces\nline3"
+        output = dump_yaml_to_str(yaml_safe_emitter, {"key": original})
+        result = ruamel.yaml.YAML(typ="safe", pure=True).load(output)
+        assert result["key"] == original
+
+
 class TestShapeWalker(BaseShapeTest):
     def setUp(self):
         super(TestShapeWalker, self).setUp()