Feat[downloader]: Implement checksum downloading

app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/mirrors/DownloadMirror.java

@@ -87,6 +87,29 @@ public class DownloadMirror {
         }
     }
 
+    /**
+     * Download a file as a string from the current mirror. If the file does not exist on the mirror
+     * or the mirror returns an invalid string, request the file from the original source
+     * @param downloadClass Class of the download. Can either be DOWNLOAD_CLASS_LIBRARIES,
+     *                      DOWNLOAD_CLASS_METADATA or DOWNLOAD_CLASS_ASSETS
+     * @param urlInput The original (Mojang) URL for the download
+     * @return the contents of the downloaded file as a String.
+     */
+    public static String downloadStringMirrored(int downloadClass, String urlInput) throws IOException{
+        String resultString = null;
+        try {
+            resultString = DownloadUtils.downloadString(getMirrorMapping(downloadClass,urlInput));
+        }catch (FileNotFoundException e) {
+            Log.w("DownloadMirror", "Failed to download string from mirror", e);
+        }
+        if(Tools.isValidString(resultString)) {
+            return resultString;
+        }else {
+            Log.w("DownloadMirror", "Downloaded string is invalid, falling back to default");
+        }
+        return DownloadUtils.downloadString(urlInput);
+    }
+
     /**
      * Check if the current download source is a mirror and not an official source.
      * @return true if the source is a mirror, false otherwise

app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/tasks/MinecraftDownloader.java

@@ -368,6 +368,8 @@ public class MinecraftDownloader {
         mSourceJarFile = clientJar;
     }
 
+
+
     private static byte[] getLocalBuffer() {
         byte[] tlb = sThreadLocalDownloadBuffer.get();
         if(tlb != null) return tlb;
@@ -395,6 +397,40 @@ public class MinecraftDownloader {
             this.mSkipIfFailed = skipIfFailed;
         }
 
+        private String downloadSha1() throws IOException {
+            String downloadedHash = DownloadMirror.downloadStringMirrored(
+                    mDownloadClass, mTargetUrl + ".sha1"
+            );
+            if(!Tools.isValidString(downloadedHash)) return null;
+            // Ensure that we don't have leading/trailing whitespaces before checking hash length
+            downloadedHash = downloadedHash.trim();
+            // SHA1 is made up of 20 bytes, which means 40 hexadecimal digits, which means 40 chars
+            if(downloadedHash.length() != 40) return null;
+            return downloadedHash;
+        }
+
+        /**
+         * Maven repositories usually have the hash of a library near it, like:
+         * .../libraryName-1.0.jar
+         * .../libraryName.1.0.jar.sha1
+         * Since Minecraft libraries are stored in maven repositories, try to use
+         * this when downloading libraries without hashes in the json.
+         */
+        private void tryGetLibrarySha1() {
+            String resultHash = null;
+            try {
+                resultHash = downloadSha1();
+            }catch (IOException e) {
+                Log.i("MinecraftDownloader", "Failed to download hash", e);
+            }
+            if(resultHash != null) {
+                Log.i("MinecraftDownloader", "Got hash: "+resultHash+ " for "+FileUtils.getFileName(mTargetUrl));
+                mTargetSha1 = resultHash;
+            }
+            // The hash is a 40-byte download.
+            mInternetUsageCounter.getAndAdd(40);
+        }
+
         @Override
         public void run() {
             try {
@@ -405,6 +441,10 @@ public class MinecraftDownloader {
         }
 
         private void runCatching() throws Exception {
+            if(mDownloadClass == DownloadMirror.DOWNLOAD_CLASS_LIBRARIES && !Tools.isValidString(mTargetSha1)) {
+                // If we're downloading a library, try to get sha1 since it might be available as a file
+                tryGetLibrarySha1();
+            }
             if(Tools.isValidString(mTargetSha1)) {
                 verifyFileSha1();
             }else {