`ObjectMapper.valueToTree()` Fails When `DeserializationFeature.FAIL_ON_TRAILING_TOKENS` Is Enabled

[raphaelNguyen]

Describe the bug
ObjectMapper.valueToTree() throws the following error when being called on an ObjectMapper instance made with DeserializationFeature.FAIL_ON_TRAILING_TOKENS feature enabled.

Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Trailing token (of type START_OBJECT) found after value (bound as com.fasterxml.jackson.databind.JsonNode): not allowed as per DeserializationFeature.FAIL_ON_TRAILING_TOKENS
at [Source: UNKNOWN; byte offset: #UNKNOWN]
at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63)
at com.fasterxml.jackson.databind.DeserializationContext.reportTrailingTokens(DeserializationContext.java:1814)
at com.fasterxml.jackson.databind.ObjectMapper._verifyNoTrailingTokens(ObjectMapper.java:4783)
at com.fasterxml.jackson.databind.ObjectMapper._readValue(ObjectMapper.java:4656)
at com.fasterxml.jackson.databind.ObjectMapper.readTree(ObjectMapper.java:2941)
at com.fasterxml.jackson.databind.ObjectMapper.valueToTree(ObjectMapper.java:3392)

Version information
2.13.0

To Reproduce
Create an ObjectMapper with the fail on trailing tokens option enabled and call valueToTree() using that mapper.
ObjectMapper mapper = JsonMapper.builder().enable(DeserializationFeature.FAIL_ON_TRAILING_TOKENS).build;

Expected behavior
ObjectMapper should return a JsonNode representation of the object without any error.

Additional context
From what I can see debugging the method valueToTree(). It seems that the method works by serializing the java Object into a TokenBuffer before deserializing that buffer back into JsonNode.

However, as can be seen in the snippet referenced below, a recent change (2e986df) has added a line to serialize the java Object into the buffer (context.serializeValue(buf, fromValue)) without deleting the old code that does the same thing (writeValue(buf, fromValue)). This cause the buffer to contain 2 copies of the deserialized object instead of one.

The subsequent readTree() will serialize the 1st copy of the object out and judge the remaining 2nd copy of the serialized object to be trailing garbage token and failed according to the DeserializationFeature.FAIL_ON_TRAILING_TOKENS feature.

It seems to me that the fix is to simply remove the redundant call to writeValue in this method. Please advise if this is indeed a problem or I've made a mistake somewhere.

jackson-databind/src/main/java/com/fasterxml/jackson/databind/ObjectMapper.java

Lines 3388 to 3393 in 70c5dfb

	try {
	context.serializeValue(buf, fromValue);
	writeValue(buf, fromValue);
	try (JsonParser p = buf.asParser()) {
	return readTree(p);
	}

[raphaelNguyen]

@cowtowncoder Glad to be of help.

[cowtowncoder]

Fix will be included in 2.13.1 -- was regression it seems, should not occurs with 2.12 or earlier.

[mosesn]

@cowtowncoder would you mind cutting a release of this? we just upgraded to 2.13.0 but might have to roll back because we can't take the performance hit of serializing twice.

[cowtowncoder]

At some point, yes, it's always a balance between my spending 2-3 hours cutting the release -- no, it's not a trivial thing to do unfortunately, as every repo must be released for full patch set -- and timely delivery of fixes. At this point the job that pays for bills (no real revenue from my OSS work) is busy enough that I don't have much extra time so it'll have to be one of weekends.

I probably won't have time to do 2.13.1 release this week or next, but will try to get it out by November.

[mosesn]

That makes sense, thanks for being clear about it!