Kill child process if we are killed

src/kcptun

@@ -2,6 +2,30 @@
 # use sh rather than bash in order to work correctly on router device which has no bash installed.
 set -e
 
+child_pid=
+
+func_trap() {
+    local signal="$1"
+    # we can't kill background child process with signal INT
+    if [[ "$signal" == INT ]]; then signal=TERM; fi
+    if [[ -n "$child_pid" ]]; then
+        kill -s "$signal" "$child_pid" || true
+    fi
+}
+
+trap_with_arg() {
+    local func sig
+    func="$1"
+    shift
+    for sig ; do
+        trap "$func $sig" "$sig"
+    done
+}
+
+has_builtin() {
+    [[ "$(command -v "$1")" == "$1" ]]
+}
+
 execute() {
     local type bin key0 value0 key1 value1
 
@@ -130,7 +154,29 @@ execute() {
         fi
 
         unset SS_LOCAL_HOST SS_LOCAL_PORT SS_REMOTE_HOST SS_REMOTE_PORT SS_PLUGIN_OPTIONS
-        "$bin" "$key0" "$value0" "$key1" "$value1" "$@"
+        if has_builtin wait && has_builtin trap && has_builtin kill; then
+            "$bin" "$key0" "$value0" "$key1" "$value1" "$@" &
+            child_pid=$!
+            if [[ -z "$child_pid" ]]; then
+                echo Unknown error occur, cannot get process id of child process. >&2
+                exit 1
+            fi
+            # Send all signal to kcptun
+            trap_with_arg func_trap HUP INT QUIT ILL TRAP ABRT BUS FPE USR1 SEGV USR2 PIPE ALRM TERM
+            local wait_result=0
+            while true; do
+                local value=0
+                wait "$child_pid" 2>/dev/null || value=$?
+                # 127 means this pid is not child process of our shell.
+                if [[ "$value" == 127 ]]; then break; fi
+                wait_result="$value"
+                if [[ "$value" == 0 ]]; then break; fi
+            done
+            child_pid=
+            return $wait_result
+        else
+            "$bin" "$key0" "$value0" "$key1" "$value1" "$@"
+        fi
     }
 
     findBinary