Suppress writes triggered by EOF reads

[Cory Benfield]

When a child channel is "closed while open", we deliver any pending reads into the Channel:

swift-nio-http2/Sources/NIOHTTP2/HTTP2StreamChannel.swift

Lines 818 to 821 in 39ed0e7

 if self.pendingReads.count > 0 && self._isActive { 
     self.unsatisfiedRead = false 
     self.deliverPendingReads() 
 } 

After that, we actually close the stream:

swift-nio-http2/Sources/NIOHTTP2/HTTP2StreamChannel.swift

Lines 823 to 829 in 39ed0e7

 if let reason = reason { 
     // To receive from the network, it must be safe to force-unwrap here. 
     let err = NIOHTTP2Errors.streamClosed(streamID: self.streamID!, errorCode: reason) 
     self.errorEncountered(error: err) 
 } else { 
     self.closedCleanly() 
 } 

The problem with this is that these reads may trigger some writes. Those writes are doomed to fail, but we let them run into the parent channel before they fail. We could fail them faster by making the stream channel state a little more complex. This will also prevent errors triggered by these writes from having to propagate through the parent channel, which can trigger weird follow-on issues.