feat: support _dnslink subdomain specified dnslinks (#1843)

Author: chancehudson

src/core/runtime/dns-nodejs.js

@@ -1,21 +1,51 @@
 'use strict'
 
 const dns = require('dns')
+const _ = require('lodash')
+const errcode = require('err-code')
 
 module.exports = (domain, opts, callback) => {
-  dns.resolveTxt(domain, (err, records) => {
-    if (err) {
-      return callback(err, null)
-    }
+  resolveDnslink(domain)
+    .catch(err => {
+      // If the code is not ENOTFOUND or ERR_DNSLINK_NOT_FOUND then throw the error
+      if (err.code !== 'ENOTFOUND' && err.code !== 'ERR_DNSLINK_NOT_FOUND') throw err
 
-    // TODO: implement recursive option
-
-    for (const record of records) {
-      if (record[0].startsWith('dnslink=')) {
-        return callback(null, record[0].substr(8, record[0].length - 1))
+      if (domain.startsWith('_dnslink.')) {
+        // The supplied domain contains a _dnslink component
+        // Check the non-_dnslink domain
+        const rootDomain = domain.replace('_dnslink.', '')
+        return resolveDnslink(rootDomain)
       }
-    }
+      // Check the _dnslink subdomain
+      const _dnslinkDomain = `_dnslink.${domain}`
+      // If this throws then we propagate the error
+      return resolveDnslink(_dnslinkDomain)
+    })
+    .then(dnslinkRecord => {
+      callback(null, dnslinkRecord.replace('dnslink=', ''))
+    })
+    .catch(callback)
+}
 
-    callback(new Error('domain does not have a txt dnslink entry'))
+function resolveDnslink (domain) {
+  const DNSLINK_REGEX = /^dnslink=.+$/
+  return new Promise((resolve, reject) => {
+    dns.resolveTxt(domain, (err, records) => {
+      if (err) return reject(err)
+      resolve(records)
+    })
   })
+    .then(records => {
+      return _.chain(records).flatten().filter(record => {
+        return DNSLINK_REGEX.test(record)
+      }).value()
+    })
+    .then(dnslinkRecords => {
+      // we now have dns text entries as an array of strings
+      // only records passing the DNSLINK_REGEX text are included
+      if (dnslinkRecords.length === 0) {
+        throw errcode(`No dnslink records found for domain: ${domain}`, 'ERR_DNSLINK_NOT_FOUND')
+      }
+      return dnslinkRecords[0]
+    })
 }

test/cli/dns.js

@@ -19,4 +19,12 @@ describe('dns', () => runOnAndOff((thing) => {
       expect(res.substr(0, 6)).to.eql('/ipns/')
     })
   })
+
+  it('resolve _dnslink.ipfs.io dns', function () {
+    this.timeout(60 * 1000)
+
+    return ipfs('dns _dnslink.ipfs.io').then((res) => {
+      expect(res.substr(0, 6)).to.eql('/ipns/')
+    })
+  })
 }))