fix: declare peer_conn can only be used in the http subsystem

lualib/resty/kong/peer_conn.lua

@@ -6,35 +6,39 @@ local errmsg           = base.get_errmsg_ptr()
 local C                = ffi.C
 local ffi_str          = ffi.string
 local get_phase        = ngx.get_phase
+local subsystem        = ngx.config.subsystem
 local NGX_ERROR        = ngx.ERROR
 
 local error            = error
 
 
-ffi.cdef[[
-int
-ngx_http_lua_kong_ffi_get_last_peer_connection_cached(ngx_http_request_t *r,
-    char **err);
-]]
-
-
-local function get_last_peer_connection_cached()
-    if get_phase() ~= "balancer" then
-        error("get_last_peer_connection_cached() can only be called in balancer phase")
-    end
-
-    local r = get_request()
-    if not r then
-        error("no request found")
+local get_last_peer_connection_cached
+
+
+if subsystem == "http" then
+    ffi.cdef[[
+    int ngx_http_lua_kong_ffi_get_last_peer_connection_cached(ngx_http_request_t *r,
+        char **err);
+    ]]
+
+    get_last_peer_connection_cached = function()
+        if get_phase() ~= "balancer" then
+            error("get_last_peer_connection_cached() can only be called in balancer phase")
+        end
+
+        local r = get_request()
+        if not r then
+            error("no request found")
+        end
+
+        local rc = C.ngx_http_lua_kong_ffi_get_last_peer_connection_cached(r, errmsg)
+
+        if rc == NGX_ERROR then
+            error(ffi_str(errmsg[0]), 2)
+        end
+
+        return rc == 1
     end
-
-    local rc = C.ngx_http_lua_kong_ffi_get_last_peer_connection_cached(r, errmsg)
-
-    if rc == NGX_ERROR then
-        error(ffi_str(errmsg[0]), 2)
-    end
-
-    return rc == 1
 end
 
 return {