Drop UDP packets on no buffer space available

Tolerate only on data channel. Control channel should never reach
high speeds.

Fixes #87

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - SoftEther sends an incomplete PUSH_REPLY. [#86](https://github.com/keeshux/tunnelkit/issues/86)
 - Authentication/Decrypt errors with TLS wrapping. [#88](https://github.com/keeshux/tunnelkit/issues/88), [#61](https://github.com/keeshux/tunnelkit/issues/61)
 - Broken DNS when no servers provided. [#84](https://github.com/keeshux/tunnelkit/issues/84)
+- UDP may disconnect on high-speed upload link. [#87](https://github.com/keeshux/tunnelkit/issues/87)
 
 ## 1.6.2 (2019-04-17)
 

TunnelKit/Sources/Core/SessionProxy.swift

@@ -1143,6 +1143,13 @@ public class SessionProxy {
             controlChannel.addSentDataCount(encryptedPackets.flatCount)
             link?.writePackets(encryptedPackets) { [weak self] (error) in
                 if let error = error {
+                    
+                    // try mitigating "No buffer space available"
+                    if let posixError = error as? POSIXError, posixError.code == POSIXErrorCode.ENOBUFS {
+                        log.warning("Data: Packets dropped, no buffer space available")
+                        return
+                    }
+                    
                     self?.queue.sync {
                         log.error("Data: Failed LINK write during send data: \(error)")
                         self?.deferStop(.shutdown, SessionError.failedLinkWrite)