From cfe4ca0d87af67986af8c503fe44545435d1ff93 Mon Sep 17 00:00:00 2001
From: Karol Wypchlo <kwypchlo@gmail.com>
Date: Fri, 8 Apr 2022 13:56:20 +0200
Subject: [PATCH] add skynet-sponsor-key dnslink functionality

---
 docker/nginx/conf.d/server/server.dnslink | 17 ++++++++++---
 packages/dnslink-api/src/index.js         | 29 +++++++++++++++++++----
 2 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/docker/nginx/conf.d/server/server.dnslink b/docker/nginx/conf.d/server/server.dnslink
index cf385a1d..139196ef 100644
--- a/docker/nginx/conf.d/server/server.dnslink
+++ b/docker/nginx/conf.d/server/server.dnslink
@@ -5,6 +5,7 @@ location / {
     set $path $uri;
 
     rewrite_by_lua_block {
+        local cjson = require("cjson")
         local cache = ngx.shared.dnslink
         local cache_value = cache:get(ngx.var.host)
 
@@ -28,13 +29,23 @@ location / {
                     ngx.exit(ngx.status)
                 end
             else
-                ngx.var.skylink = res.body
+                local resolved = cjson.decode(res.body)
+
+                ngx.var.skylink = resolved.skylink
+                if resolved.sponsor then
+                    ngx.req.set_header("Skynet-Api-Key", resolved.sponsor)
+                end
 
                 local cache_ttl = 300 -- 5 minutes cache expire time
-                cache:set(ngx.var.host, ngx.var.skylink, cache_ttl)
+                cache:set(ngx.var.host, res.body, cache_ttl)
             end
         else
-            ngx.var.skylink = cache_value
+            local resolved = cjson.decode(cache_value)
+
+            ngx.var.skylink = resolved.skylink
+            if resolved.sponsor then
+                ngx.req.set_header("Skynet-Api-Key", resolved.sponsor)
+            end
         end
 
         ngx.var.skylink = require("skynet.skylink").parse(ngx.var.skylink)
diff --git a/packages/dnslink-api/src/index.js b/packages/dnslink-api/src/index.js
index 300277c2..8ea0aeec 100644
--- a/packages/dnslink-api/src/index.js
+++ b/packages/dnslink-api/src/index.js
@@ -8,12 +8,14 @@ const port = Number(process.env.DNSLINK_API_PORT) || 3100;
 const server = express();
 
 const dnslinkNamespace = "skynet-ns";
+const sponsorNamespace = "skynet-sponsor-key";
 const dnslinkRegExp = new RegExp(`^dnslink=/${dnslinkNamespace}/.+$`);
+const sponsorRegExp = new RegExp(`^${sponsorNamespace}=[a-zA-Z0-9]+$`);
 const dnslinkSkylinkRegExp = new RegExp(`^dnslink=/${dnslinkNamespace}/([a-zA-Z0-9_-]{46}|[a-z0-9]{55})`);
 const hint = `valid example: dnslink=/${dnslinkNamespace}/3ACpC9Umme41zlWUgMQh1fw0sNwgWwyfDDhRQ9Sppz9hjQ`;
 
 server.get("/dnslink/:name", async (req, res) => {
-  const success = (skylink) => res.send(skylink);
+  const success = (response) => res.json(response);
   const failure = (message) => res.status(400).send(message);
 
   if (!isValidDomain(req.params.name)) {
@@ -22,7 +24,7 @@ server.get("/dnslink/:name", async (req, res) => {
 
   const lookup = `_dnslink.${req.params.name}`;
 
-  dns.resolveTxt(lookup, (error, records) => {
+  dns.resolveTxt(lookup, (error, addresses) => {
     if (error) {
       if (error.code === "ENOTFOUND") {
         return failure(`ENOTFOUND: ${lookup} TXT record doesn't exist`);
@@ -35,11 +37,12 @@ server.get("/dnslink/:name", async (req, res) => {
       return failure(`Failed to fetch ${lookup} TXT record: ${error.message}`);
     }
 
-    if (records.length === 0) {
+    if (addresses.length === 0) {
       return failure(`No TXT record found for ${lookup}`);
     }
 
-    const dnslinks = records.flat().filter((record) => dnslinkRegExp.test(record));
+    const records = addresses.flat();
+    const dnslinks = records.filter((record) => dnslinkRegExp.test(record));
 
     if (dnslinks.length === 0) {
       return failure(`TXT records for ${lookup} found but none of them contained valid skynet dnslink - ${hint}`);
@@ -58,9 +61,25 @@ server.get("/dnslink/:name", async (req, res) => {
 
     const skylink = matchSkylink[1];
 
+    // check if _dnslink records contain skynet-sponsor-key entries
+    const sponsors = records.filter((record) => sponsorRegExp.test(record));
+
+    if (sponsors.length > 1) {
+      return failure(`Multiple TXT records with valid sponsor key found for ${lookup}, only one allowed`);
+    }
+
+    if (sponsors.length === 1) {
+      // extract just the key part from the record
+      const sponsor = sponsors[0].substring(sponsors[0].indexOf("=") + 1);
+
+      console.log(`${req.params.name} => ${skylink} | sponsor: ${sponsor}`);
+
+      return success({ skylink, sponsor });
+    }
+
     console.log(`${req.params.name} => ${skylink}`);
 
-    return success(skylink);
+    return success({ skylink });
   });
 });