RFR: 8301255: Http2Connection may send too many GOAWAY frames

[Daniel Fuchs]

The following behavior was observed in a test log:

DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] Http2Connection(SSLTube(SocketTube(2))) Shutting down h2c (closed=true): java.io.EOFException: HTTP/2 client stopped
DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] Http2Connection(SSLTube(SocketTube(2))) Close all streams
DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] Http2Connection(SSLTube(SocketTube(2))) Close all streams
DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] Http2Connection(SSLTube(SocketTube(2))) sending frame: GOAWAY: length=25, streamid=0, flags=0 Error: Not an error Debugdata: Requested by user
DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] AsyncSSLConnection(SSLTube(SocketTube(2))) added 34 bytes to the write queue
DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] AsyncSSLConnection(SSLTube(SocketTube(2))) signalling the publisher of the write queue
DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] Http2Connection(SSLTube(SocketTube(2))) Shutting down h2c (closed=true): java.io.EOFException: HTTP/2 client stopped
DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] Http2Connection(SSLTube(SocketTube(2))) Close all streams
DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] Http2Connection(SSLTube(SocketTube(2))) Close all streams
DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] Http2Connection(SSLTube(SocketTube(2))) sending frame: GOAWAY: length=25, streamid=0, flags=0 Error: Not an error Debugdata: Requested by user
DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] AsyncSSLConnection(SSLTube(SocketTube(2))) added 34 bytes to the write queue
DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] AsyncSSLConnection(SSLTube(SocketTube(2))) signalling the publisher of the write queue
DEBUG: [HttpClient-2-SelectorManager] [2s 716ms] Http2Connection(SSLTube(SocketTube(2))) Shutting down h2c (closed=true): java.io.EOFException: HTTP/2 client stopped 
etc...

What happens here is that attempting to send a GOAWAY frame after some error was detected might cause an error which triggers an attempt to shutdown the connection again and cause a new GOAWAY frame to be sent. This seems to happen when trying to shutdown the client and close HTTP/2 TLS connections gracefully. 

The fix changes the simple 'closed' boolean into a bit mask that can combined the several closed states of the connection: `Http2Connection::shutdown` has  been called, SHUTDOWN is requested (previously was closed=true), a GOAWAY frame has been sent (the connection is half closed local), a GOAWAY connection has been received (the connection is half closed remote). 

If the connection is already half-closed locally - a GOAWAY frame has been sent already and there's no need to send a new one.

This will also better help diagnose the actual state of the connection at the time `Http2Connection::shutdown` is called.

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Commit messages:
 - 8301255

Changes: https://git.openjdk.org/jdk/pull/12263/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12263&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301255
  Stats: 106 lines in 3 files changed: 73 ins; 5 del; 28 mod
  Patch: https://git.openjdk.org/jdk/pull/12263.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12263/head:pull/12263

PR: https://git.openjdk.org/jdk/pull/12263