Implement document length tracking for DataInput-backed JSON parsers via subclass

[pjfanning]

One possible way to support max document len on DataInput use case.
The count and validation overhead only kicks in if you set a non-negative max document len - which is not the default case.

[cowtowncoder]

I would want to see performance testing (esp. for non-validating case) since this seems it could wreck performance (overrides and indirection) -- f.ex with https://github.com/FasterXML/jackson-benchmarks/ .

[pjfanning]

@cowtowncoder I'll put together a benchmark but would expect it to have quite an impact. The parser itself is already not very efficient becuase it reads byte by byte and I would recommend that users try to get an InputStream instead of a DataInput instance to parse if it at all possible.

• The normal case of no max doc len will not be affect noticeably by this change
• This change will allow users to at least parse DataInput inputs again if they do set a max doc len (because recent code changes cause this code path to throw an exception - deliberately)
• One option would be to add a JsonReadFeature that controls whether the max doc len is set case fails deliberately or uses this inefficient approach.

[cowtowncoder]

The normal case of no max doc len will not be affect noticeably by this change

I would not assume that without measurements, due to inlining effects.
Depends on how JVM handles optimizations I suppose & benchmarking can give answer.

As to failing, configurability -- while possible, I don't think it's necessary at this point.

[pjfanning]

@cowtowncoder I created a benchmark suite and compared the v2.21.1 parser with one that has the overridable shared readUnsignedByte method and a 3rd parser that applies the size limit.

The results for all 3 parsers are almost the same. So close that I nearly suspect that I have a mistake in the test suite.

I tested with different JSON sizes and Java versions and in no run was there any significant diff in perf between the 3 parsers.

I'll double check my test suite logic over the next few days.

https://github.com/pjfanning/jackson-bench/blob/main/src/jmh/java/org/example/jackson/DataInputBench.java

[pjfanning]

@cowtowncoder this change seems to work ok. I see a small overhead when the max doc len is enabled but it is only a few percent.

One example run (Limited is the benchmark with the check enabled)

Benchmark                              Mode  Cnt     Score     Error  Units
DataInputBench.benchDataInput         thrpt    5  5176.015 ± 574.007  ops/s
DataInputBench.benchDataInputLimited  thrpt    5  5027.761 ± 319.194  ops/s
DataInputBench.benchDataInputNew      thrpt    5  5299.451 ± 130.896  ops/s

[cowtowncoder]

@pjfanning Sounds good so far. Could you also run test against unchanged build from 3.x (or official 3.1.0 which should be about the same)?

[pjfanning]

@cowtowncoder You want to create a new benchmark that uses Jackson 3 instead of Jackson 2?

[cowtowncoder]

@cowtowncoder You want to create a new benchmark that uses Jackson 3 instead of Jackson 2?

I thought this PR is for 3.x? Wasn't thinking we implement this functionality for 2.x, only 3.x

But if we are talking about changes 2.x, comparison to unmodified version (2.21.1 would be fine) vs new versions.

[pjfanning]

The jackson3 based benchmarks behave similarly to the jackson2 ones.

Benchmark                                      Mode  Cnt     Score     Error  Units
DataInputJackson3Bench.benchDataInput         thrpt    5  1969.188 ± 297.992  ops/s
DataInputJackson3Bench.benchDataInputLimited  thrpt    5  1908.798 ± 106.280  ops/s
DataInputJackson3Bench.benchDataInputNew      thrpt    5  2037.195 ±  66.618  ops/s

[github-actions]

📈 Overall Code Coverage

Metric	Coverage	Change
Instructions	83.07%	📉 -0.010%
Branches	75.74%	📈 +0.010%

Overall project coverage from JaCoCo test results. Change values compare against the latest base branch build.

[cowtowncoder]

@pjfanning Does "benchDataInput" refer to pre-changes version from 3.x, and "benchDataInputLimited" / "benchDataInputNew" to modified version with and withou limitations?

If so, differences do indeed look insignificant.

[pjfanning]

@pjfanning Does "benchDataInput" refer to pre-changes version from 3.x, and "benchDataInputLimited" / "benchDataInputNew" to modified version with and withou limitations?

If so, differences do indeed look insignificant.

@cowtowncoder your interpretation of the names is correct