fabric: properly retry download when fabric installer is invalid (#620)

Author: itzg

src/main/java/me/itzg/helpers/fabric/FabricMetaClient.java

@@ -1,7 +1,8 @@
 package me.itzg.helpers.fabric;
 
-import java.io.BufferedReader;
 import java.io.IOException;
+import java.io.InputStream;
+import java.nio.ByteBuffer;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.time.Duration;
@@ -16,6 +17,7 @@
 import me.itzg.helpers.http.FileDownloadStatusHandler;
 import me.itzg.helpers.http.SharedFetch;
 import me.itzg.helpers.http.UriBuilder;
+import org.apache.commons.codec.binary.Hex;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import reactor.core.publisher.Mono;
@@ -155,52 +157,59 @@ public Mono<Path> downloadLauncher(
             .handleStatus(statusHandler)
             .assemble()
             .retryWhen(Retry.backoff(downloadRetryMaxAttempts, downloadRetryMinBackoff).filter(IOException.class::isInstance))
-            .flatMap(path -> skipValidation ? Mono.just(path) : validateLauncherJar(path))
-            .doOnError(InvalidContentException.class, e -> log.warn("Invalid launcher jar, will try again", e))
+            .flatMap(path -> skipValidation ?
+                Mono.just(path)
+                : validateLauncherJar(path).subscribeOn(Schedulers.boundedElastic())
+            )
+            .doOnError(InvalidContentException.class, e ->
+                log.warn("Invalid launcher jar, will try again: {}", e.getMessage())
+            )
             .retryWhen(Retry.backoff(downloadRetryMaxAttempts, downloadRetryMinBackoff).filter(InvalidContentException.class::isInstance))
             .checkpoint("downloadLauncher");
     }
 
     private Mono<Path> validateLauncherJar(Path path) {
-        return Mono.fromCallable(() -> {
-                log.debug("Validating Fabric launcher file {}", path);
+        return Mono.create(sink -> {
+            log.debug("Validating Fabric launcher file {}", path);
 
-                if (!path.toFile().isFile()) {
-                    throw new InvalidContentException("Downloaded launcher jar is not a file");
-                }
-                try {
-                    final Properties installProperties = IoStreams.readFileFromZip(path, "install.properties", in -> {
-                            Properties p = new Properties();
-                            p.load(in);
-                            return p;
-                        }
-                    );
-                    if (installProperties == null) {
-                        debugDownloadedContent(path);
-                        throw new InvalidContentException("Downloaded launcher jar does not contain an install.properties");
-                    }
-                    if (!installProperties.containsKey("game-version")) {
-                        debugDownloadedContent(path);
-                        throw new InvalidContentException("Downloaded launcher jar does not contain a valid install.properties");
+            if (!path.toFile().isFile()) {
+                sink.error(new InvalidContentException("Downloaded launcher jar is not a file"));
+            }
+            try {
+                final Properties installProperties = IoStreams.readFileFromZip(path, "install.properties", in -> {
+                        Properties p = new Properties();
+                        p.load(in);
+                        return p;
                     }
-                } catch (IOException e) {
+                );
+                if (installProperties == null) {
                     debugDownloadedContent(path);
-                    throw new InvalidContentException("Downloaded launcher jar could not be read as a jar/zip", e);
+                    sink.error(new InvalidContentException("Does not contain an install.properties"));
                 }
+                else if (!installProperties.containsKey("game-version")) {
+                    debugDownloadedContent(path);
+                    sink.error(new InvalidContentException("Does not contain a valid install.properties"));
+                }
+            } catch (IOException e) {
+                debugDownloadedContent(path);
+                sink.error(new InvalidContentException("Could not be read as a jar/zip", e));
+            }
 
-                return path;
-            })
-            .subscribeOn(Schedulers.boundedElastic());
+            sink.success(path);
+        });
     }
 
     private static void debugDownloadedContent(Path path) {
         if (log.isDebugEnabled()) {
-            try (BufferedReader reader = Files.newBufferedReader(path)) {
-                final char[] buf = new char[100];
-                final int amount = reader.read(buf);
-                log.debug("Downloaded launcher jar content starts with: {}", new String(buf, 0, amount));
+            try (InputStream in = Files.newInputStream(path)) {
+                final byte[] buf = new byte[100];
+                final int amount = in.read(buf);
+
+                log.debug("Downloaded launcher jar content starts with: {}",
+                    Hex.encodeHexString(ByteBuffer.wrap(buf, 0, amount))
+                );
             } catch (IOException e) {
-                throw new GenericException("Failed to read downloaded launcher jar for debugging", e);
+                log.warn("Failed to debug content of launcher jar", e);
             }
         }
     }