feature: allow socket override

this allows to fallback on LuaSocket in contexts that do not
support co-sockets.

README.markdown

@@ -134,6 +134,12 @@ It accepts a `opts` table argument. The following options are supported:
 * `no_recurse`
 
 	a boolean flag controls whether to disable the "recursion desired" (RD) flag in the UDP request. Defaults to `false`.
+* `tcp`
+
+  an optional function to create a tcp socket. This allows using the library in contexts where the co-sockets are unavailable.  Defaults to `ngx.socket.tcp`.
+* `udp`
+  an optional function to create a udp socket. This allows using the library in contexts where the co-sockets are unavailable.  Defaults to `ngx.socket.udp`.
+
 
 [Back to TOC](#table-of-contents)
 

lib/resty/dns/resolver.lua

@@ -3,7 +3,6 @@
 
 -- local socket = require "socket"
 local bit = require "bit"
-local udp = ngx.socket.udp
 local rand = math.random
 local char = string.char
 local byte = string.byte
@@ -18,7 +17,6 @@ local lshift = bit.lshift
 local insert = table.insert
 local concat = table.concat
 local re_sub = ngx.re.sub
-local tcp = ngx.socket.tcp
 local log = ngx.log
 local DEBUG = ngx.DEBUG
 local unpack = unpack
@@ -112,6 +110,9 @@ function _M.new(class, opts)
 
     local timeout = opts.timeout or 2000  -- default 2 sec
 
+    local udp = opts.udp or ngx.socket.udp
+    local tcp = opts.tcp or ngx.socket.tcp
+
     local n = #servers
 
     local socks = {}

t/sanity.t

@@ -5,7 +5,7 @@ use Cwd qw(cwd);
 
 repeat_each(2);
 
-plan tests => repeat_each() * (3 * blocks());
+plan tests => repeat_each() * (3 * blocks()) - 2;
 
 my $pwd = cwd();
 
@@ -646,3 +646,50 @@ GET /t
 --- no_error_log
 [error]
 --- no_check_leak
+
+
+
+=== TEST 20: override socket functions
+--- http_config eval: $::HttpConfig
+--- config
+    location /t {
+        content_by_lua '
+            local resolver = require "resty.dns.resolver"
+
+            local r, err =
+                resolver:new {
+                    nameservers = { "$TEST_NGINX_RESOLVER" },
+                    tcp = function(...)
+                      ngx.say("tcp called")
+                      return ngx.socket.tcp(...)
+                    end,
+                    udp = function(...)
+                      ngx.say("udp called")
+                      return ngx.socket.udp(...)
+                    end,
+                }
+            if not r then
+                ngx.say("failed to instantiate resolver: ", err)
+                return
+            end
+
+            local ans, err = r:query("google.com")
+            if not ans then
+                ngx.say("failed to query (udp): ", err)
+                return
+            end
+            local ans, err = r:tcp_query("google.com")
+            if not ans then
+                ngx.say("failed to query (tcp): ", err)
+                return
+            end
+        ';
+    }
+--- request
+GET /t
+--- response
+udp called
+tcp called
+--- no_error_log
+[error]
+--- no_check_leak