Use GitHub proxy fallback for update checker (#4818)

Author: mdcfe

Essentials/src/main/java/com/earth2me/essentials/updatecheck/UpdateChecker.java

@@ -1,7 +1,6 @@
 package com.earth2me.essentials.updatecheck;
 
 import com.earth2me.essentials.Essentials;
-import com.google.common.base.Charsets;
 import com.google.gson.Gson;
 import com.google.gson.JsonObject;
 import com.google.gson.JsonSyntaxException;
@@ -13,6 +12,7 @@
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
+import java.text.MessageFormat;
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import java.util.stream.Collectors;
@@ -23,6 +23,12 @@ public final class UpdateChecker {
     private static final String REPO = "EssentialsX/Essentials";
     private static final String BRANCH = "2.x";
 
+    private static final String LATEST_RELEASE_URL = "https://api.github.com/repos/" + REPO + "/releases/latest";
+    private static final String LATEST_RELEASE_PROXY_URL = "https://webapi.essentialsx.net/api/v1/github/essx-v2/releases/latest";
+    // 0 = base for comparison, 1 = head for comparison - *not* the same as what this class calls them
+    private static final String DISTANCE_URL = "https://api.github.com/repos/EssentialsX/Essentials/compare/{0}...{1}";
+    private static final String DISTANCE_PROXY_URL = "https://webapi.essentialsx.net/api/v1/github/essx-v2/compare/{0}/{1}";
+
     private final Essentials ess;
     private final String versionIdentifier;
     private final String versionBranch;
@@ -89,8 +95,7 @@ public CompletableFuture<RemoteVersion> fetchLatestRelease() {
             new Thread(() -> {
                 catchBlock:
                 try {
-                    final HttpURLConnection connection = (HttpURLConnection) new URL("https://api.github.com/repos/" + REPO + "/releases/latest").openConnection();
-                    connection.connect();
+                    final HttpURLConnection connection = tryRequestWithFallback(LATEST_RELEASE_URL, LATEST_RELEASE_PROXY_URL);
 
                     if (connection.getResponseCode() == HttpURLConnection.HTTP_NOT_FOUND) {
                         // Locally built?
@@ -102,7 +107,7 @@ public CompletableFuture<RemoteVersion> fetchLatestRelease() {
                         break catchBlock;
                     }
 
-                    try (BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream(), Charsets.UTF_8))) {
+                    try (BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream(), StandardCharsets.UTF_8))) {
                         latestRelease = new Gson().fromJson(reader, JsonObject.class).get("tag_name").getAsString();
                         pendingReleaseFuture.complete(cachedRelease = fetchDistance(latestRelease, getVersionIdentifier()));
                     } catch (JsonSyntaxException | NumberFormatException e) {
@@ -137,10 +142,54 @@ public String getLatestRelease() {
         return latestRelease;
     }
 
-    private RemoteVersion fetchDistance(final String head, final String hash) {
+    private HttpURLConnection tryRequestWithFallback(final String githubUrl, final String fallbackUrl) throws IOException {
+        HttpURLConnection connection = (HttpURLConnection) new URL(githubUrl).openConnection();
         try {
-            final HttpURLConnection connection = (HttpURLConnection) new URL("https://api.github.com/repos/" + REPO + "/compare/" + head + "..." + hash).openConnection();
             connection.connect();
+            if (connection.getResponseCode() != HttpURLConnection.HTTP_INTERNAL_ERROR && connection.getResponseCode() != HttpURLConnection.HTTP_FORBIDDEN) {
+                // Connection succeeded without any errors from GitHub's side.
+                return connection;
+            }
+        } catch (IOException ignored) {
+        }
+
+        // Connection failed, GitHub's down or we hit a ratelimit, so use the fallback URL
+        // If the fallback fails, let the exception or error status bubble up
+        connection = (HttpURLConnection) new URL(fallbackUrl).openConnection();
+        connection.connect();
+
+        return connection;
+    }
+
+    private RemoteVersion tryProcessDistance(final HttpURLConnection connection) throws IOException {
+        try (BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream(), StandardCharsets.UTF_8))) {
+            final JsonObject obj = new Gson().fromJson(reader, JsonObject.class);
+            switch (obj.get("status").getAsString()) {
+                case "identical": {
+                    return new RemoteVersion(BranchStatus.IDENTICAL, 0);
+                }
+                case "ahead": {
+                    return new RemoteVersion(BranchStatus.AHEAD, 0);
+                }
+                case "behind": {
+                    return new RemoteVersion(BranchStatus.BEHIND, obj.get("behind_by").getAsInt());
+                }
+                case "diverged": {
+                    return new RemoteVersion(BranchStatus.DIVERGED, obj.get("behind_by").getAsInt());
+                }
+                default: {
+                    return new RemoteVersion(BranchStatus.UNKNOWN);
+                }
+            }
+        } catch (JsonSyntaxException | NumberFormatException e) {
+            e.printStackTrace();
+            return new RemoteVersion(BranchStatus.ERROR);
+        }
+    }
+
+    private RemoteVersion fetchDistance(final String head, final String hash) {
+        try {
+            final HttpURLConnection connection = tryRequestWithFallback(MessageFormat.format(DISTANCE_URL, head, hash), MessageFormat.format(DISTANCE_PROXY_URL, head, hash));
 
             if (connection.getResponseCode() == HttpURLConnection.HTTP_NOT_FOUND) {
                 // Locally built?
@@ -150,29 +199,7 @@ private RemoteVersion fetchDistance(final String head, final String hash) {
                 return new RemoteVersion(BranchStatus.ERROR);
             }
 
-            try (BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream(), Charsets.UTF_8))) {
-                final JsonObject obj = new Gson().fromJson(reader, JsonObject.class);
-                switch (obj.get("status").getAsString()) {
-                    case "identical": {
-                        return new RemoteVersion(BranchStatus.IDENTICAL, 0);
-                    }
-                    case "ahead": {
-                        return new RemoteVersion(BranchStatus.AHEAD, 0);
-                    }
-                    case "behind": {
-                        return new RemoteVersion(BranchStatus.BEHIND, obj.get("behind_by").getAsInt());
-                    }
-                    case "diverged": {
-                        return new RemoteVersion(BranchStatus.DIVERGED, obj.get("behind_by").getAsInt());
-                    }
-                    default: {
-                        return new RemoteVersion(BranchStatus.UNKNOWN);
-                    }
-                }
-            } catch (JsonSyntaxException | NumberFormatException e) {
-                e.printStackTrace();
-                return new RemoteVersion(BranchStatus.ERROR);
-            }
+            return tryProcessDistance(connection);
         } catch (IOException e) {
             e.printStackTrace();
             return new RemoteVersion(BranchStatus.ERROR);