fix(client) always inject localhost

Treat the localhost name special by always injecting it, according
to RFC 6761: Section 6.3.3

fixes #50

README.md

@@ -42,6 +42,7 @@ Versioning is strictly based on [Semantic Versioning](https://semver.org/)
 - Added: a new option `validTtl` that, if set, will forcefully override the
  `ttl` value of any valid answer received. [Issue 48](https://github.com/Kong/lua-resty-dns-client/issues/48).
 - Fix: remove multiline log entries, now encoded as single-line json. [Issue 52](https://github.com/Kong/lua-resty-dns-client/issues/52).
+- Fix: always inject a `localhost` value, even if not in `/etc/hosts`. [Issue 54](https://github.com/Kong/lua-resty-dns-client/issues/54).
 
 ### 2.1.0 (21-May-2018) Fixes
 

spec/client_spec.lua

@@ -118,6 +118,63 @@ describe("DNS client", function()
  assert.are.equal(#client.getcache(), 0) -- no hosts file record should have been imported
  end)
 
+ describe("inject localhost:", function()
+
+ it("if absent", function()
+ local result, err, record
+ result, err = assert(client.init({
+ nameservers = { "8.8.8.8:53" },
+ resolvConf = {},
+ hosts = {},
+ }))
+ assert.is.True(result)
+ assert.is.Nil(err)
+ record = client.getcache():get("28:localhost")
+ assert.equal("[::1]", record[1].address)
+ record = client.getcache():get("1:localhost")
+ assert.equal("127.0.0.1", record[1].address)
+ end)
+
+ it("not if ipv4 exists", function()
+ local result, err, record
+ result, err = assert(client.init({
+ nameservers = { "8.8.8.8:53" },
+ resolvConf = {},
+ hosts = {"1.2.3.4 localhost"},
+ }))
+ assert.is.True(result)
+ assert.is.Nil(err)
+
+ -- IPv6 is not defined
+ record = client.getcache():get("28:localhost")
+ assert.is_nil(record)
+
+ -- IPv4 is not overwritten
+ record = client.getcache():get("1:localhost")
+ assert.equal("1.2.3.4", record[1].address)
+ end)
+
+ it("not if ipv6 exists", function()
+ local result, err, record
+ result, err = assert(client.init({
+ nameservers = { "8.8.8.8:53" },
+ resolvConf = {},
+ hosts = {"::1:2:3:4 localhost"},
+ }))
+ assert.is.True(result)
+ assert.is.Nil(err)
+
+ -- IPv6 is not overwritten
+ record = client.getcache():get("28:localhost")
+ assert.equal("[::1:2:3:4]", record[1].address)
+
+ -- IPv4 is not defined
+ record = client.getcache():get("1:localhost")
+ assert.is_nil(record)
+ end)
+
+ end)
+
  end)
 
 

src/resty/dns/client.lua

@@ -485,6 +485,14 @@ _M.init = function(options)
  hosts = {}
  end
 
+ -- treat `localhost` special, by always defining it, RFC 6761: Section 6.3.3
+ if not hosts.localhost then
+ hosts.localhost = {
+ ipv4 = "127.0.0.1",
+ ipv6 = "[::1]",
+ }
+ end
+
  -- Populate the DNS cache with the hosts (and aliasses) from the hosts file.
  local ttl = 10*365*24*60*60 -- use ttl of 10 years for hostfile entries
  for name, address in pairs(hosts) do