Disallow trailing tokens in JSON files #1204
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Motivation:
We observed an unexpected deserialization outcome with malformed JSON.
Jackson does not fail on that data but silently drops part of the data.
For example, we expected Jackson to fail to parse the data.
```json5
{
"a" : {},
"b" : {},
"c" : {
},
"c1" : true
} // a malformed JSON
"d" : {},
"e": {}
}
```
But Jackson just drops `d` and `e` fields and parses the JSON into:
```
{
"a":{},
"b":{},
"c":{},
"c1":true
}
```
The maintainer of Jackson said it is an expected behavior but not a bug.
FasterXML/jackson-core#808 (comment)
> But this is intended behavior, not a bug: Jackson only reads as much
> content as it needs for a valid JSON Value. It does not try to consume
> everything there might be available, given that the white-space-separated
> content streams are commonly used.
He suggested enabling `DeserializationFeature.FAIL_ON_TRAILING_TOKENS`
to fail on the malformed data added after the end of the top-level JSON.
Modifications:
- Enable `DeserializationFeature.FAIL_ON_TRAILING_TOKENS` to the default
Jackson `ObjectMapper` in Central Dogma
- Breaking) Central Dogma no longer allow tailing commas in JSON
Result:
Central Dogma now correctly rejects malformed JSON when parsing JSON
data.
WalkthroughEnables strict JSON deserialization by turning on FAIL_ON_TRAILING_TOKENS in Jackson mappers, adds a unit test and a malformed JSON resource to verify parsing fails on trailing/extra tokens, and removes a Java-8 compile.release override from build.gradle. Changes
Sequence Diagram(s)sequenceDiagram
autonumber
participant Test as Unit Test
participant JacksonUtil as Jackson.readTree
participant Mapper as ObjectMapper (compact/pretty)
participant Err as MismatchedInputException
Test->>JacksonUtil: readTree(bytes from fixture)
JacksonUtil->>Mapper: parse JSON (FAIL_ON_TRAILING_TOKENS enabled)
alt trailing/extra tokens present
Mapper-->>Err: throw MismatchedInputException
Err-->>Test: observed as cause of IOError
else valid JSON
Mapper-->>Test: return JsonNode
end
Estimated code review effort🎯 3 (Moderate) | ⏱️ ~20 minutes
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Actionable comments posted: 2
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📒 Files selected for processing (3)
common/src/main/java/com/linecorp/centraldogma/internal/Jackson.java(2 hunks)server/src/test/java/com/linecorp/centraldogma/server/InvalidJsonParsingTest.java(1 hunks)server/src/test/resources/invalid-content-after-trailing-comma.json(1 hunks)
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server/src/test/java/com/linecorp/centraldogma/server/InvalidJsonParsingTest.java (1)
common/src/main/java/com/linecorp/centraldogma/internal/Jackson.java (1)
Jackson(69-393)
🪛 Biome (2.1.2)
server/src/test/resources/invalid-content-after-trailing-comma.json
[error] 10-10: End of file expected
Use an array for a sequence of values: [1, 2]
(parse)
[error] 10-10: End of file expected
Use an array for a sequence of values: [1, 2]
(parse)
[error] 10-11: End of file expected
Use an array for a sequence of values: [1, 2]
(parse)
[error] 11-11: End of file expected
Use an array for a sequence of values: [1, 2]
(parse)
[error] 12-12: End of file expected
Use an array for a sequence of values: [1, 2]
(parse)
[error] 12-12: End of file expected
Use an array for a sequence of values: [1, 2]
(parse)
[error] 12-13: End of file expected
Use an array for a sequence of values: [1, 2]
(parse)
[error] 13-14: End of file expected
Use an array for a sequence of values: [1, 2]
(parse)
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🔇 Additional comments (4)
common/src/main/java/com/linecorp/centraldogma/internal/Jackson.java (2)
42-42: LGTM!The import is correctly added to support the new deserialization feature.
81-82: LGTM!Enabling
FAIL_ON_TRAILING_TOKENSon both mappers ensures consistent validation of JSON content. This addresses the issue where Jackson could silently drop fields when malformed JSON contains trailing content.server/src/test/java/com/linecorp/centraldogma/server/InvalidJsonParsingTest.java (1)
38-40: LGTM!The assertion correctly verifies that malformed JSON with trailing content triggers an
IOErrorwithMismatchedInputExceptionas the cause, which aligns with the enabledFAIL_ON_TRAILING_TOKENSfeature.server/src/test/resources/invalid-content-after-trailing-comma.json (1)
1-14: LGTM!This test resource is intentionally invalid JSON to verify that the
FAIL_ON_TRAILING_TOKENSfeature correctly rejects malformed content. The missing comma after line 9's closing brace creates the exact scenario the feature is designed to catch.
server/src/test/java/com/linecorp/centraldogma/server/InvalidJsonParsingTest.java
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ikhoon
changed the title
| // Target Java 8 except for spring-boot3 | ||
| if (!project.name.startsWith("java-spring-boot3")) { | ||
| tasks.withType(JavaCompile) { | ||
| if (JavaVersion.current() >= JavaVersion.VERSION_1_9) { | ||
| options.release = 8 | ||
| } | ||
| } | ||
| } | ||
|
|
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Removed this hard-coded logic. I believe options.release is properly set through java.gradle according to javaTargetCompatibility and javaN flags.
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Actionable comments posted: 1
🧹 Nitpick comments (1)
server/src/test/java/com/linecorp/centraldogma/server/InvalidJsonParsingTest.java (1)
35-37: Consider adding null-check for better test diagnostics.If the resource is not found,
getResourceAsStreamreturnsnull, and callingreadAllBytes()onnullproduces an NPE. While acceptable for a unit test, an explicit null-check or assertion would provide a clearer error message during test failures.For example:
try (InputStream is = InvalidJsonParsingTest.class.getResourceAsStream( "/invalid-content-after-trailing-comma.json")) { + assertThat(is).isNotNull(); final byte[] bytes = is.readAllBytes();
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server/src/test/java/com/linecorp/centraldogma/server/InvalidJsonParsingTest.java(1 hunks)
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server/src/test/java/com/linecorp/centraldogma/server/InvalidJsonParsingTest.java (1)
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Jackson(69-393)
🔇 Additional comments (1)
server/src/test/java/com/linecorp/centraldogma/server/InvalidJsonParsingTest.java (1)
34-36: Past issues resolved correctly.The typo in the method name has been fixed ("Trailing" instead of "Tailing"), and the resource leak has been properly addressed using try-with-resources.
| void shouldFailOnInvalidJsonAfterTrailingComma() throws IOException { | ||
| try (InputStream is = InvalidJsonParsingTest.class.getResourceAsStream( | ||
| "/invalid-content-after-trailing-comma.json")) { | ||
| final byte[] bytes = is.readAllBytes(); | ||
| assertThatThrownBy(() -> Jackson.readTree(bytes)) | ||
| .isInstanceOf(IOError.class) | ||
| .hasCauseInstanceOf(MismatchedInputException.class); | ||
| } |
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🧩 Analysis chain
Verify test resource aligns with FAIL_ON_TRAILING_TOKENS feature.
The test name and resource name suggest testing "invalid JSON after trailing comma," but FAIL_ON_TRAILING_TOKENS specifically addresses cases where valid top-level JSON is followed by additional tokens that Jackson would otherwise silently ignore.
If the test resource contains already-malformed JSON (e.g., syntax errors like {"a":1,} with a trailing comma inside the object), it would fail parsing even without this feature enabled, which would not properly validate the PR's objective.
Please confirm the test resource contains a valid JSON value followed by additional content (e.g., {"a":1}{"b":2} or {"a":1}\n{"b":2}) to properly test the scenario described in the PR motivation.
🏁 Script executed:
#!/bin/bash
# Display the test resource content to verify it matches the intended scenario
cat server/src/test/resources/invalid-content-after-trailing-comma.jsonLength of output: 98
Correct test resource to properly validate FAIL_ON_TRAILING_TOKENS feature.
The test resource contains malformed JSON with structural syntax errors (mismatched braces, missing commas, orphaned keys), which fails parsing regardless of whether FAIL_ON_TRAILING_TOKENS is enabled. This does not validate the feature's actual purpose: rejecting valid JSON values followed by additional tokens that would otherwise be silently ignored.
Replace the resource file content with valid JSON followed by trailing content. Example: {"a":1}{"b":2} or {"a":1}\nextra, which demonstrates the exact scenario the feature addresses.
🤖 Prompt for AI Agents
In
server/src/test/java/com/linecorp/centraldogma/server/InvalidJsonParsingTest.java
around lines 34 to 41, the test currently uses a resource containing
structurally invalid JSON which causes parsing to fail irrespective of
FAIL_ON_TRAILING_TOKENS; replace the test resource file
(/invalid-content-after-trailing-comma.json) with content that is syntactically
valid JSON followed by extra tokens (for example: {"a":1}{"b":2} or
{"a":1}\nextra) so the test exercises rejection of trailing tokens specifically,
then keep the assertion expecting an IOError caused by MismatchedInputException.
3 participants
Motivation:
We observed an unexpected deserialization outcome with malformed JSON. Jackson does not fail on that data but silently drops part of the data.
For example, we expected Jackson to fail to parse the data.
But Jackson just drops
dandefields and parses the JSON into:{ "a":{}, "b":{}, "c":{}, "c1":true }The maintainer of Jackson said it is an expected behavior but not a bug. FasterXML/jackson-core#808 (comment)
He suggested enabling
DeserializationFeature.FAIL_ON_TRAILING_TOKENSto fail on the malformed data added after the end of the top-level JSON.Modifications:
DeserializationFeature.FAIL_ON_TRAILING_TOKENSto the default JacksonObjectMapperin Central DogmaResult:
Central Dogma now correctly rejects malformed JSON when parsing JSON data.
Summary by CodeRabbit
Bug Fixes
Tests
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