TUN-4597: Add a QUIC server skeleton

- Added a QUIC server to accept streams
- Unit test for this server also tests ALPN
- Temporary echo capability for HTTP ConnectionType

vendor/github.com/lucas-clemente/quic-go/mockgen_private.sh

@@ -0,0 +1,51 @@
+#!/bin/bash
+
+DEST=$2
+PACKAGE=$3
+TMPFILE="mockgen_tmp.go"
+# uppercase the name of the interface
+ORIG_INTERFACE_NAME=$4
+INTERFACE_NAME="$(tr '[:lower:]' '[:upper:]' <<< ${ORIG_INTERFACE_NAME:0:1})${ORIG_INTERFACE_NAME:1}"
+
+# Gather all files that contain interface definitions.
+# These interfaces might be used as embedded interfaces,
+# so we need to pass them to mockgen as aux_files.
+AUX=()
+for f in *.go; do
+  if [[ -z ${f##*_test.go} ]]; then
+    # skip test files
+    continue;
+  fi
+  if $(egrep -qe "type (.*) interface" $f); then
+    AUX+=("github.com/lucas-clemente/quic-go=$f")
+  fi
+done
+
+# Find the file that defines the interface we're mocking.
+for f in *.go; do
+  if [[ -z ${f##*_test.go} ]]; then
+    # skip test files
+    continue;
+  fi
+  INTERFACE=$(sed -n "/^type $ORIG_INTERFACE_NAME interface/,/^}/p" $f)
+  if [[ -n "$INTERFACE" ]]; then
+    SRC=$f
+    break
+  fi
+done
+
+if [[ -z "$INTERFACE" ]]; then
+  echo "Interface $ORIG_INTERFACE_NAME not found."
+  exit 1
+fi
+
+AUX_FILES=$(IFS=, ; echo "${AUX[*]}")
+
+## create a public alias for the interface, so that mockgen can process it
+echo -e "package $1\n" > $TMPFILE
+echo "$INTERFACE" | sed "s/$ORIG_INTERFACE_NAME/$INTERFACE_NAME/" >> $TMPFILE
+goimports -w $TMPFILE
+mockgen -package $1 -self_package $3 -destination $DEST -source=$TMPFILE -aux_files $AUX_FILES
+goimports -w $DEST
+sed "s/$TMPFILE/$SRC/" "$DEST" > "$DEST.new" && mv "$DEST.new" "$DEST"
+rm "$TMPFILE"