Fix issue #10508 where PARANOID mode slow down about 1000 times compared to ADVANCED.
Also fix a rare issue when internal buffer was growing over a limit, it was partially discarded
using `discardReadBytes()` which causes bad changes within previously discovered HttpData.
Reasons were:
Too many `readByte()` method calls while other ways exist (such as keep in memory the last scan position when trying to find a delimiter or using `bytesBefore(firstByte)` instead of looping externally).
Changes done:
- major change on way buffer are parsed: instead of read byte per byte until found delimiter, try to find the delimiter using `bytesBefore()` and keep the last unfound position to skeep already parsed parts (algorithms are the same but implementation of scan are different)
- Change the condition to discard read bytes when refCnt is at most 1.
Observations using Async-Profiler:
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1) Without optimizations, most of the time (more than 95%) is through `readByte()` method within `loadDataMultipartStandard` method.
2) With using `bytesBefore(byte)` instead of `readByte()` to find various delimiter, the `loadDataMultipartStandard` method is going down to 19 to 33% depending on the test used. the `readByte()` method or equivalent `getByte(pos)` method are going down to 15% (from 95%).
Times are confirming those profiling:
- With optimizations, in SIMPLE mode about 82% better, in ADVANCED mode about 79% better and in PARANOID mode about 99% better (most of the duplicate read accesses are removed or make internally through `bytesBefore(byte)` method)
A benchmark is added to show the behavior of the various cases (one big item, such as File upload, and many items) and various level of detection (Disabled, Simple, Advanced, Paranoid). This benchmark is intend to alert if new implementations make too many differences (such as the previous version where about PARANOID gives about 1000 times slower than other levels, while it is now about at most 10 times).
Extract of Benchmark run:
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Run complete. Total time: 00:13:27
Benchmark Mode Cnt Score Error Units
HttpPostMultipartRequestDecoderBenchmark.multipartRequestDecoderBigAdvancedLevel thrpt 6 2,248 ± 0,198 ops/ms
HttpPostMultipartRequestDecoderBenchmark.multipartRequestDecoderBigDisabledLevel thrpt 6 2,067 ± 1,219 ops/ms
HttpPostMultipartRequestDecoderBenchmark.multipartRequestDecoderBigParanoidLevel thrpt 6 1,109 ± 0,038 ops/ms
HttpPostMultipartRequestDecoderBenchmark.multipartRequestDecoderBigSimpleLevel thrpt 6 2,326 ± 0,314 ops/ms
HttpPostMultipartRequestDecoderBenchmark.multipartRequestDecoderHighAdvancedLevel thrpt 6 1,444 ± 0,226 ops/ms
HttpPostMultipartRequestDecoderBenchmark.multipartRequestDecoderHighDisabledLevel thrpt 6 1,462 ± 0,642 ops/ms
HttpPostMultipartRequestDecoderBenchmark.multipartRequestDecoderHighParanoidLevel thrpt 6 0,159 ± 0,003 ops/ms
HttpPostMultipartRequestDecoderBenchmark.multipartRequestDecoderHighSimpleLevel thrpt 6 1,522 ± 0,049 ops/ms
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