Broken FlowControlHandler when auto-read is disabled (caused by #10326)

[ursaj]

Expected behavior (v.4.1.44)

In my handler:

ctx.read()
    readComplete(ctx) // when no messages in network
        ctx.read() // multiple messages arrived simultaneously
            channelRead(ctx, msg) // single message
            // no more calls for channelRead or readComplete

Expected behavior (v.4.1.51+)

In my handler:

ctx.read()
    readComplete(ctx) // when no messages in network + reset inner counter 
        ctx.read() // multiple messages arrived simultaneously
            channelRead(ctx, msg) // single message
            // no more calls for channelRead or readComplete

or

ctx.read()
    // no readComplete(ctx) when no messages in network
    channelRead(ctx, msg) // when message actually arrived
        ctx.read()
            channelRead(ctx, msg) // single message
            readComplete() // only when no messages in network and no more messages requested from flow control handler

Note, there are a lot of corner-cases to think of:

• inner counter
• buffer state
• readComplete called
• stack overflow, when ctx.read is called from channelRead or readComplete
• don't do any inner re-scheduling (if possible)
• etc...

Actual behavior

ctx.read() // inner counter = 1
    readComplete(ctx)
        ctx.read() // inner counter = 2
            channelRead(ctx, msg) // expected, ok
            channelRead(ctx, msg) // unexpected, overflow => big BOOM!

Root cause

#10326

Netty versions

4.1.44
4.1.51

JVM version (e.g. java -version)

% java -version
openjdk version "1.8.0_242"
OpenJDK Runtime Environment (AdoptOpenJDK)(build 1.8.0_242-b08)
OpenJDK 64-Bit Server VM (AdoptOpenJDK)(build 25.242-b08, mixed mode)

OS version (e.g. uname -a)

% uname -a
Darwin MBPWORK 19.5.0 Darwin Kernel Version 19.5.0: Tue May 26 20:41:44 PDT 2020; root:xnu-6153.121.2~2/RELEASE_X86_64 x86_64

[normanmaurer]

@ursaj so do you say that this is a regression?

[ursaj]

exactly

[normanmaurer]

@ursaj got it... sounds like we better revert this one. thanks for the report

[normanmaurer]

Done...