Merge pull request #477 from danthe1st/preserve-attachments

preserve attachments of logged messages via HTTP request

Author: jasonlessenich

src/main/java/net/discordjug/javabot/data/h2db/message_cache/MessageCache.java

@@ -20,6 +20,10 @@
 
 import java.io.ByteArrayInputStream;
 import java.io.InputStream;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse.BodyHandlers;
 import java.nio.charset.StandardCharsets;
 import java.time.Instant;
 import java.time.ZoneOffset;
@@ -137,9 +141,23 @@ public void sendDeletedMessageToLog(Guild guild, MessageChannel channel, CachedM
 				action.addFiles(FileUpload.fromData(buildDeletedMessageFile(author, message), message.getMessageId() + ".txt"));
 			}
 			action.queue();
+			requestMessageAttachments(message);
 		});
 	}
 
+	/**
+	 * Requests each attachment from Discord's CDN.
+	 * This is done in order to prevent Discord from deleting the attachment too quickly.
+	 * @param message the cached message
+	 */
+	private void requestMessageAttachments(CachedMessage message) {
+		HttpClient client = HttpClient.newHttpClient();
+		for (String attachment : message.getAttachments()) {
+			HttpRequest request = HttpRequest.newBuilder(URI.create(attachment)).build();
+			client.sendAsync(request, BodyHandlers.discarding());
+		}
+	}
+
 	private EmbedBuilder buildMessageCacheEmbed(MessageChannel channel, User author, CachedMessage before) {
 		long epoch = IdCalculatorCommand.getTimestampFromId(before.getMessageId()) / 1000;
 		return new EmbedBuilder()