Apply an excessively permissive large string length limit by default

changelog/@unreleased/pr-2601.v2.yml

@@ -0,0 +1,6 @@
+type: improvement
+improvement:
+  description: Apply a large StreamReadConstraints maxStringLength to reduce friction
+    in preparation for jackson 2.15 adoption
+  links:
+  - https://github.com/palantir/conjure-java-runtime/pull/2601

conjure-java-jackson-serialization/src/main/java/com/palantir/conjure/java/serialization/ObjectMappers.java

@@ -243,8 +243,8 @@ public static CBORFactory cborFactory() {
 
     /** Configures provided JsonFactory with Conjure default settings. */
     private static <F extends JsonFactory, B extends TSFBuilder<F, B>> B withDefaults(B builder) {
-        return builder
+        return ReflectiveStreamReadConstraints.withDefaultConstraints(builder
                 // Interning introduces excessive contention https://github.com/FasterXML/jackson-core/issues/946
-                .disable(JsonFactory.Feature.INTERN_FIELD_NAMES);
+                .disable(JsonFactory.Feature.INTERN_FIELD_NAMES));
     }
 }

conjure-java-jackson-serialization/src/main/java/com/palantir/conjure/java/serialization/ReflectiveStreamReadConstraints.java

@@ -0,0 +1,76 @@
+/*
+ * (c) Copyright 2023 Palantir Technologies Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.palantir.conjure.java.serialization;
+
+import com.fasterxml.jackson.core.JsonFactory;
+import com.fasterxml.jackson.core.TSFBuilder;
+import com.palantir.logsafe.logger.SafeLogger;
+import com.palantir.logsafe.logger.SafeLoggerFactory;
+import java.lang.reflect.Method;
+
+/**
+ * This class exists to ensure default values match our expectations in cases where jackson is
+ * upgraded transitively prior to a CJR release which expects 2.15.0+. After this library upgrades, the
+ * reflection may be replaced by the following:
+ *<pre>{@code
+ * return builder.streamReadConstraints(StreamReadConstraints.builder()
+ *         .maxStringLength(MAX_STRING_LENGTH)
+ *         .build());
+ * }</pre>
+ */
+final class ReflectiveStreamReadConstraints {
+    private static final SafeLogger log = SafeLoggerFactory.get(ReflectiveStreamReadConstraints.class);
+
+    // 50mb up from the default 5mb as a more permissive value to begin with, which we can ratchet down over time.
+    // This allows us to decouple the initial risk of adopting string length limits from the risk introduced by taking
+    // a dependency upgrade.
+    private static final int MAX_STRING_LENGTH = 50_000_000;
+
+    @SuppressWarnings("unchecked")
+    static <F extends JsonFactory, B extends TSFBuilder<F, B>> B withDefaultConstraints(B builder) {
+        try {
+            // Use the same classloader which loaded the TSFBuilder
+            ClassLoader classLoader = builder.getClass().getClassLoader();
+            Class<?> streamReadConstraintsClass =
+                    Class.forName("com.fasterxml.jackson.core.StreamReadConstraints", true, classLoader);
+            Object constraints = createConjureDefaultStreamReadConstraints(streamReadConstraintsClass);
+            return (B) builder.getClass()
+                    .getMethod("streamReadConstraints", streamReadConstraintsClass)
+                    .invoke(builder, constraints);
+        } catch (ClassNotFoundException cnfe) {
+            // Log at debug in the expected case using jackson 2.14 which does not support limits.
+            log.debug("StreamReadConstraints class does not exist, nothing to do", cnfe);
+        } catch (ReflectiveOperationException e) {
+            log.warn("Failed to update StreamReadConstraints, upstream default values will be used", e);
+        }
+        return builder;
+    }
+
+    private static Object createConjureDefaultStreamReadConstraints(Class<?> streamReadConstraintsClass)
+            throws ReflectiveOperationException {
+        Method builderMethod = streamReadConstraintsClass.getMethod("builder");
+        Object streamReadConstraintsBuilder = builderMethod.invoke(null);
+        Class<?> streamReadConstraintsBuilderClass = streamReadConstraintsBuilder.getClass();
+        // Default to a max size of 50mb (up from the 5mb default)
+        streamReadConstraintsBuilderClass
+                .getMethod("maxStringLength", int.class)
+                .invoke(streamReadConstraintsBuilder, MAX_STRING_LENGTH);
+        return streamReadConstraintsBuilderClass.getMethod("build").invoke(streamReadConstraintsBuilder);
+    }
+
+    private ReflectiveStreamReadConstraints() {}
+}

conjure-java-jackson-serialization/src/test/java/com/palantir/conjure/java/serialization/ObjectMappersTest.java

@@ -497,6 +497,15 @@ private void testMapKeysAreNotInterned(ObjectMapper mapper) throws IOException {
                 .isEmpty();
     }
 
+    @Test
+    public void testExtraordinarilyLargeStrings() throws IOException {
+        // Value must sit between StreamReadConstraints.DEFAULT_MAX_STRING_LEN and
+        // ReflectiveStreamReadConstraints.MAX_STRING_LENGTH.
+        int size = 10_000_000;
+        String parsed = ObjectMappers.newServerJsonMapper().readValue('"' + "a".repeat(size) + '"', String.class);
+        assertThat(parsed).hasSize(size);
+    }
+
     private static String ser(Object object) throws IOException {
         return MAPPER.writeValueAsString(object);
     }