Bug 45915 - I18N: ByteEncoding.GetMaxByteCount ignores EncoderFallback.MaxCharCount
Summary: I18N: ByteEncoding.GetMaxByteCount ignores EncoderFallback.MaxCharCount
Alias: None
Product: Class Libraries
Classification: Mono
Component: mscorlib ()
Version: master
Hardware: PC All
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
Depends on:
Reported: 2016-10-26 12:39 UTC by Oleg
Modified: 2018-03-13 15:09 UTC (History)
4 users (show)

Is this bug a regression?: ---
Last known good build:

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Description Oleg 2016-10-26 12:39:19 UTC
ByteEncoding.GetMaxByteCount ignores EncoderFallback.MaxCharCount.

Code to reproduce:

    private static void Reproduce()
        var encoding = Encoding.GetEncoding(1251, new MyEncoderFallback(), DecoderFallback.ExceptionFallback);

    private class MyEncoderFallback : EncoderFallback
        public override EncoderFallbackBuffer CreateFallbackBuffer()
            return new MyEncoderFallbackBuffer();

        public override int MaxCharCount => 16;

    private class MyEncoderFallbackBuffer : EncoderFallbackBuffer
        public override int Remaining => 0;

        public override bool Fallback(char charUnknown, int index)
            return true;

        public override bool Fallback(char charUnknownHigh, char charUnknownLow, int index)
            return true;

        public override char GetNextChar()
            return '\0';

        public override bool MovePrevious()
            return false;

It will print 1024 on Mono, 16400 on Windows .NET.

This can cause "Reading would overrun buffer" exception while using StreamWriter with this kind of encodings.