Feature: DNS TXT record support for PayID lookup

README.md

@@ -471,6 +471,17 @@ const payId = 'alice$dev.payid.xpring.money'
 // Send XRP to the given PayID.
 const transactionHash = await xpringClient.send(amount, payId, wallet)
 ```
+# PayID-DNS extension
+
+This version of Xpring-JS will attempt to look up PayID information in a DNS TXT record before reverting to http/s protocol.
+
+For example requesting PayID `richard$payid.link` for `xrpl-mainnet` will first attempt to retreive a TXT record at `xrpl-mainnet.richard._payid.payid.link`. 
+
+If a JSON payload is available on that TXT record it will be processed using [PayID-Sign](https://github.com/codetsunami/payid-sign) to check authenticity, and, if verified, will be returned in place of the regular PayID http/s lookup.
+
+This provides an alternative to running a http/s server for seldom changed crypto addresses while maintaining the benefits of PayID as a universal cryptocurrency address-book. It also provides a DDoS resistant way to ensure a PayID is always available.
+
+To generate a JSON payload for your own DNS TXT record PayID please use the tool here: [PayID-Sign Commandline Tool](https://github.com/codetsunami/payid-sign-cmdline)
 
 # Contributing
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "xpring-js",
-  "version": "5.0.0",
+  "version": "5.1.0",
   "description": "XpringJS provides a Javascript based SDK for interacting with the Ripple Ledger.",
   "main": "build/index.js",
   "repository": {
@@ -51,6 +51,7 @@
     "typescript": "^3.9.3"
   },
   "dependencies": {
+    "payid-sign": ">=1.0.2",
     "@grpc/grpc-js": "^1.1.1",
     "axios": "^0.19.2",
     "big-integer": "^1.6.48",

src/PayID/pay-id-client.ts

@@ -2,6 +2,8 @@
 import { PayIdUtils } from 'xpring-common-js'
 import PayIdError, { PayIdErrorType } from './pay-id-error'
 import { Address, DefaultApi, CryptoAddressDetails } from './Generated/api'
+import * as PayIDSign from 'payid-sign'
+import * as dns from 'dns'
 
 const PAYID_API_VERSION = '1.0'
 
@@ -66,13 +68,33 @@ export default class PayIdClient {
     return this.addressesForPayIdAndNetwork(payId, 'payid')
   }
 
+  /**
+   * Look up a DNS txt record and return as a promise
+   *
+   * @param domain the domain name to look up for example arthur._payid.mydomain.com
+   */
+  private async lookupDnsTxt(
+    domain:string
+  ): Promise<string> {
+    return new Promise((resolve, reject) => {
+        dns.resolveTxt(domain, (err: any | null, addresses: string[][]) => {
+            if(err) reject(err)
+            try {
+                resolve(addresses[0].join(''))
+            } catch (error) {
+                reject('no txt record')
+            }
+        })
+    })
+  }
+
   /**
    * Return an array of {@link Address}es that match the inputs.
    *
    * @param payId The PayID to resolve.
    * @param network The network to resolve on.
    */
-  private async addressesForPayIdAndNetwork(
+  public async addressesForPayIdAndNetwork(
     payId: string,
     network: string,
   ): Promise<Array<Address>> {
@@ -84,6 +106,24 @@ export default class PayIdClient {
     // Swagger API adds the leading '/' in path automatically because it is part of the endpoint.
     const path = payIdComponents.path.substring(1)
 
+    // First check if there is a DNS entry for this PayID, and use it preferentially if there is
+    const identifier = path.replace(/\+.+$/,'')
+    const domain = network + "." + identifier + "._payid." + payIdComponents.host
+    try {
+        const payload = await this.lookupDnsTxt(domain);
+        // execution to here is a DNS hit so process the DNS txt payload
+        if (PayIDSign.verify_signed_payid( identifier + '$' + payIdComponents.host, payload )) {
+            // if the DNS payload is not verified we will fall through to regular protocol,
+            // however if it is verified we will now return based on the DNS payload
+            var ret = JSON.parse(payload)
+            delete ret['signature'] 
+            delete ret['publicKey']
+            return [ret]
+        } 
+    } catch (error) {
+        // this is a DNS miss, so continue executing along the normal path
+    }
+
     const api = new DefaultApi(undefined, basePath)
 
     const options = PayIdClient.makeOptionsWithAcceptTypes(