From 997e6a6f43cf64817be9cb57333f5d8b66b4d8fa Mon Sep 17 00:00:00 2001
From: Thaddee Tyl <thaddee.tyl@gmail.com>
Date: Thu, 23 Jun 2016 19:28:56 +0200
Subject: [PATCH] GitHub auth: maintain rate limit reset information, track
 token with highest remaining requests

---
 lib/github-auth.js | 62 ++++++++++++++++++++++++++++++++--------------
 1 file changed, 43 insertions(+), 19 deletions(-)

diff --git a/lib/github-auth.js b/lib/github-auth.js
index 52b02f5..eed29c4 100644
--- a/lib/github-auth.js
+++ b/lib/github-auth.js
@@ -115,36 +115,60 @@ function sendTokenToAllServers(token) {
 
 // Track rate limit requests remaining.
 
-var reqRemaining = new Map();
-var lowestReqRemaining = Infinity, lowestReqRemainingToken;
+var reqRemaining = new Map();  // From token to requests remaining.
+var reqReset = new Map();  // From token to timestamp.
+var highestReqRemaining = 0, highestReqRemainingToken;
 
-// Set lowestReqRemaining* variables if the token / requests remaining
-// combination passed as a parameter is lower than previously registered.
-function setLowestReqRemaining(token, reqs) {
-  if (reqs <= lowestReqRemaining) {
-    lowestReqRemaining = reqs;
-    lowestReqRemainingToken = token;
+// Set highestReqRemaining* variables if the token / requests remaining
+// combination passed as a parameter is higher than previously registered.
+function setHighestReqRemaining(token, reqs) {
+  // Equality is allowed to ensure that we have a token set as
+  // highestReqRemainingToken (or else there are no user tokens given).
+  if (reqs >= highestReqRemaining) {
+    highestReqRemaining = reqs;
+    highestReqRemainingToken = token;
   }
 }
 
 // token: client token as a string.
 // reqs: number of requests remaining.
-function setReqRemaining(token, reqs) {
-  setLowestReqRemaining(token, reqs);
+// reset: timestamp when the number of remaining requests is reset.
+function setReqRemaining(token, reqs, reset) {
+  setHighestReqRemaining(token, reqs);
   reqRemaining.set(token, reqs);
+  reqReset.set(token, reset);
+}
+
+// Retrieve a user token if there is one for which we believe there are requests
+// remaining. Return undefined if we could not find one.
+function getReqRemainingToken() {
+  if (highestReqRemaining > 0) {
+    return highestReqRemainingToken;
+  } else {
+    // Go through the user tokens, keep the first one which has reset.
+    var now = +new Date();
+    for (var token of reqReset.keys()) {
+      if (reqReset.get(token) < now) {
+        // We are past the rate limit reset.
+        highestReqRemainingToken = token;
+        return highestReqRemainingToken
+      }
+    }
+  }
 }
 
 function rmReqRemaining(token) {
   reqRemaining.delete(token);
-  if (lowestReqRemainingToken === token) {
-    lowestReqRemaining = Infinity;
-    lowestReqRemainingToken = undefined;
-    reqRemaining.forEach(setLowestReqRemaining);
+  reqReset.delete(token);
+  if (highestReqRemainingToken === token) {
+    highestReqRemaining = 0;
+    highestReqRemainingToken = undefined;
+    reqRemaining.forEach(setHighestReqRemaining);
   }
 }
 
 function addGithubToken(token) {
-  setReqRemaining(token, Infinity);
+  setReqRemaining(token, 0, +new Date());
   // Insert it only if it is not registered yet.
   if (githubUserTokens.data.indexOf(token) === -1) {
     githubUserTokens.data.push(token);
@@ -177,10 +201,9 @@ function githubRequest(request, url, query, cb) {
     'User-Agent': 'Shields.io',
     'Accept': 'application/vnd.github.v3+json',
   };
-  var githubToken;
+  var githubToken = getReqRemainingToken();
 
-  if (lowestReqRemainingToken != null && lowestReqRemaining > 0) {
-    githubToken = lowestReqRemainingToken;
+  if (githubToken != null) {
     headers['Authorization'] = 'token ' + githubToken;
   } else if (serverSecrets && serverSecrets.gh_client_id) {
     // Using our OAuth App secret grants us 5000 req/hour
@@ -197,7 +220,8 @@ function githubRequest(request, url, query, cb) {
         rmGithubToken(githubToken);
       } else {
         var remaining = +res.headers['x-ratelimit-remaining'];
-        setReqRemaining(githubToken, remaining);
+        var reset = +res.headers['x-ratelimit-reset'];
+        setReqRemaining(githubToken, remaining, reset);
       }
     }
     cb(err, res, buffer);