Lua /etc/resolv.conf parser and some refactoring

rootfs/etc/nginx/lua/test/util/resolv_conf_test.lua

@@ -0,0 +1,64 @@
+local original_io_open = io.open
+
+describe("resolv_conf", function()
+  after_each(function()
+    package.loaded["util.resolv_conf"] = nil
+    io.open = original_io_open
+  end)
+
+  it("errors when file can not be opened", function()
+    io.open = function(...)
+      return nil, "file does not exist"
+    end
+
+    assert.has_error(function() require("util.resolv_conf") end, "could not open /etc/resolv.conf: file does not exist")
+  end)
+
+  it("opens '/etc/resolv.conf' with mode 'r'", function()
+    io.open = function(path, mode)
+      assert.are.same("/etc/resolv.conf", path)
+      assert.are.same("r", mode)
+
+      return original_io_open(path, mode)
+    end
+
+    assert.has_no.errors(function() require("util.resolv_conf") end)
+  end)
+
+  it("correctly parses resolv.conf", function()
+    local conf = [===[
+# This is a comment
+nameserver 10.96.0.10
+nameserver 10.96.0.99
+search ingress-nginx.svc.cluster.local svc.cluster.local cluster.local
+options ndots:5
+    ]===]
+
+    helpers.with_resolv_conf(conf, function()
+      local resolv_conf = require("util.resolv_conf")
+      assert.are.same({
+        nameservers = { "10.96.0.10", "10.96.0.99" },
+        search = { "ingress-nginx.svc.cluster.local", "svc.cluster.local", "cluster.local" },
+        ndots = 5,
+      }, resolv_conf)
+    end)
+  end)
+
+  it("ignores options that it does not understand", function()
+    local conf = [===[
+nameserver 10.96.0.10
+search example.com
+options debug
+options ndots:3
+    ]===]
+
+    helpers.with_resolv_conf(conf, function()
+      local resolv_conf = require("util.resolv_conf")
+      assert.are.same({
+        nameservers = { "10.96.0.10" },
+        search = { "example.com" },
+        ndots = 3,
+      }, resolv_conf)
+    end)
+  end)
+end)