JSON "INF" handling question / bug (?)

[alzimmermsft]

If non-numeric numbers are allowed while reading JSON, when the JSON value is exactly INF it results in a parsing exception.

This appears to be due to how ReaderBasedJsonParser._handleOddValue(int) and UTF8StreamJsonParser._handleUnexpectedValue(int) handle I being the integer value passed. When I is the leading character both methods explicitly look for Infinity only, and do not support INF. But if +INF is the JSON value this is handled without exception as both methods call into their internal _handleInvalidNumberStart(int, boolean) method which checks for leading I and then checks for both INF and Infinity.

Here is a small sample application:

public static void main(String[] args) {
    JsonFactory factory = JsonFactory.builder()
        .enable(JsonReadFeature.ALLOW_NON_NUMERIC_NUMBERS)
        .build();

    try (JsonParser parser = factory.createParser(new StringReader("INF"))) {
        parser.nextToken();
        System.out.println(parser.getDoubleValue());
    } catch (Exception e) {
        e.printStackTrace();
    }

    try (JsonParser parser = factory.createParser("INF".getBytes(StandardCharsets.UTF_8))) {
        parser.nextToken();
        System.out.println(parser.getDoubleValue());
    } catch (Exception e) {
        e.printStackTrace();
    }
}

Both will result in the catch block being triggered and printing out the stack traces. Those will be something along the lines of:

com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'INF': was expecting (JSON String, Number (or 'NaN'/'+INF'/'-INF'), Array, Object or token 'null', 'true' or 'false')
 at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); line: 1, column: 4]
	at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:2584)
	at com.fasterxml.jackson.core.JsonParser._constructReadException(JsonParser.java:2610)
	at com.fasterxml.jackson.core.JsonParser._constructReadException(JsonParser.java:2618)
	at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:825)
	at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._reportInvalidToken(ReaderBasedJsonParser.java:3017)
	at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._reportInvalidToken(ReaderBasedJsonParser.java:2995)
	at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._matchToken2(ReaderBasedJsonParser.java:2776)
	at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._matchToken(ReaderBasedJsonParser.java:2754)
	at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._handleOddValue(ReaderBasedJsonParser.java:2035)
	at com.fasterxml.jackson.core.json.ReaderBasedJsonParser.nextToken(ReaderBasedJsonParser.java:780)
	at org.example.Main.main(Main.java:19)

and

com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'INF': was expecting (JSON String, Number (or 'NaN'/'+INF'/'-INF'), Array, Object or token 'null', 'true' or 'false')
 at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); line: 1, column: 4]
	at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:2584)
	at com.fasterxml.jackson.core.JsonParser._constructReadException(JsonParser.java:2610)
	at com.fasterxml.jackson.core.JsonParser._constructReadException(JsonParser.java:2618)
	at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:825)
	at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._reportInvalidToken(UTF8StreamJsonParser.java:3662)
	at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._reportInvalidToken(UTF8StreamJsonParser.java:3635)
	at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._matchToken2(UTF8StreamJsonParser.java:2976)
	at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._matchToken(UTF8StreamJsonParser.java:2954)
	at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._handleUnexpectedValue(UTF8StreamJsonParser.java:2733)
	at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._nextTokenNotInObject(UTF8StreamJsonParser.java:867)
	at com.fasterxml.jackson.core.json.UTF8StreamJsonParser.nextToken(UTF8StreamJsonParser.java:753)
	at org.example.Main.main(Main.java:26)

It seems a bit odd that Infinity, +Infinity, and -Infinity are supported but only +INF and -INF are supported but INF isn't.

A quick change to ReaderBasedJsonParser._handleOddValue(int) and UTF8StreamJsonParser._handleUnexpectedValue(int) to have I handling be:

case 'I':
    return _handleInvalidNumberStart(c, false);
//    _matchToken("Infinity", 1);
//    if ((_features & FEAT_MASK_NON_NUM_NUMBERS) != 0) {
//        return resetAsNaN("Infinity", Double.POSITIVE_INFINITY);
//    }
//    _reportError(
//        "Non-standard token 'Infinity': enable JsonParser.Feature.ALLOW_NON_NUMERIC_NUMBERS to allow");
//    break;

Allows for INF to be handled without exception. Though I don't know if that change is 100% safe.

[pjfanning]

code expects +INF or -INF, not INF.

jackson-core/src/main/java/com/fasterxml/jackson/core/base/ParserBase.java

Line 1459 in 0e6016d

return "(JSON String, Number (or 'NaN'/'+INF'/'-INF'), Array, Object or token 'null', 'true' or 'false')";

[alzimmermsft]

Yeah, I think this issue was more a question on why INF isn't supported where Infinity is, as both forms support their leading + and - cases. I stumbled upon this question when adding some tests and blindly added Infinity, +Infinity and -Infinity and the same for the shorthand INF, +INF, and -INF.'

I'm also fine with closing this as Works as expected if no changes should be made to support INF.