Extract zips while reading the chunks, instead reading them to memory first

src/main/java/com/sheepit/client/ChunkInputStream.java

@@ -0,0 +1,53 @@
+package com.sheepit.client;
+
+import lombok.NonNull;
+
+import java.io.BufferedInputStream;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.file.Path;
+import java.util.ArrayDeque;
+import java.util.List;
+import java.util.NoSuchElementException;
+
+public class ChunkInputStream extends InputStream {
+	
+	@NonNull private final ArrayDeque<Path> chunkPaths;
+	@NonNull private BufferedInputStream currentStream;
+	
+	/**
+	 * Given a list of chunk paths, provides an InputStream that reads the contents of these files in the order they were provided in.
+	 * @param chunkPaths Non-empty, ordered list of paths
+	 * @throws IOException If the first chunk could not be found. Errors with other chunk will be thrown during calls to read()
+	 */
+	public ChunkInputStream(List<Path> chunkPaths) throws IOException {
+		this.chunkPaths = new ArrayDeque<>(chunkPaths);
+		
+		/// Setup the first chunk for reading
+		prepareNextChunk();
+	}
+	
+	private void prepareNextChunk() throws FileNotFoundException, NoSuchElementException {
+		currentStream = new BufferedInputStream(new FileInputStream(chunkPaths.removeFirst().toFile()));
+	}
+	
+	@Override public int read() throws IOException {
+		int result = currentStream.read();
+		
+		if (result == -1) {
+			/// Finished reading from this chunk, continue with the next if possible
+			try {
+				prepareNextChunk();
+			}
+			catch (NoSuchElementException e) {
+				/// This was the last chunk
+				return -1;
+			}
+			result = currentStream.read();
+		}
+		
+		return result;
+	}
+}

src/main/java/com/sheepit/client/Utils.java

@@ -45,6 +45,7 @@ import java.util.Map;
 import java.util.TimeZone;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
+import java.util.stream.Collectors;
 
 /**
  * Provides various general utility methods for the SheepIt client codebase
@@ -105,18 +106,11 @@ public class Utils {
 	 */
 	public static int unzipChunksIntoDirectory(List<String> full_path_chunks, String destinationDirectory, char[] password, Log log) {
 		try {
-			// STEP 1: assemble the chunks into an actual zip (in RAM)
+			// STEP 1: Create a ChunkInputStream, which will read the chunks' contents in order
-			ByteArrayOutputStream unzippedData = new ByteArrayOutputStream();
+			ChunkInputStream chunkInputStream = new ChunkInputStream(full_path_chunks.stream().map(Paths::get).collect(Collectors.toList()));
-			
-			for (String full_path_chunk: full_path_chunks) {
-				byte[] data = Files.readAllBytes(Paths.get(full_path_chunk));
-				
-				unzippedData.write(data);
-			}
-			byte[] full_data = unzippedData.toByteArray();
 			
 			// STEP 2: unzip the zip like before
-			ZipInputStream zipInputStream = new ZipInputStream(new ByteArrayInputStream(full_data));
+			ZipInputStream zipInputStream = new ZipInputStream(chunkInputStream);
 			if (password != null) {
 				zipInputStream.setPassword(password);
 			}