Create a "unified-diff" patch using java-diff-utils instead of including the entire modified file. I still need to test how well this works with binary files.

src/main/java/org/qortal/arbitrary/ArbitraryDataDiff.java

@@ -1,13 +1,17 @@
 package org.qortal.arbitrary;
 
+import com.github.difflib.DiffUtils;
+import com.github.difflib.UnifiedDiffUtils;
+import com.github.difflib.patch.Patch;
+import org.apache.commons.io.FileUtils;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.qortal.arbitrary.metadata.ArbitraryDataMetadataPatch;
 import org.qortal.crypto.Crypto;
 import org.qortal.settings.Settings;
 
-import java.io.File;
+import java.io.*;
-import java.io.IOException;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.*;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.util.ArrayList;
@@ -133,9 +137,14 @@ public class ArbitraryDataDiff {
                         wasModified = true;
                     }
 
-                    if (wasAdded | wasModified) {
+                    if (wasAdded) {
                         ArbitraryDataDiff.copyFilePathToBaseDir(after, diffPathAbsolute, filePathAfter);
                     }
+                    if (wasModified) {
+                        // Create patch using java-diff-utils
+                        Path destination = Paths.get(diffPathAbsolute.toString(), filePathAfter.toString());
+                        ArbitraryDataDiff.createAndCopyDiffUtilsPatch(filePathBefore, after, destination);
+                    }
 
                     return FileVisitResult.CONTINUE;
                 }
@@ -159,7 +168,7 @@ public class ArbitraryDataDiff {
         }
     }
 
-    private void findRemovedFiles() {
+    private void findRemovedFiles() throws IOException {
         try {
             final Path pathBeforeAbsolute = this.pathBefore.toAbsolutePath();
             final Path pathAfterAbsolute = this.pathAfter.toAbsolutePath();
@@ -219,7 +228,7 @@ public class ArbitraryDataDiff {
 
             });
         } catch (IOException e) {
-            LOGGER.info("IOException when walking through file tree: {}", e.getMessage());
+            throw new IOException(String.format("IOException when walking through file tree: %s", e.getMessage()));
         }
     }
 
@@ -231,6 +240,7 @@ public class ArbitraryDataDiff {
 
     private void writeMetadata() throws IOException {
         ArbitraryDataMetadataPatch metadata = new ArbitraryDataMetadataPatch(this.diffPath);
+        metadata.setPatchType("unified-diff");
         metadata.setAddedPaths(this.addedPaths);
         metadata.setModifiedPaths(this.modifiedPaths);
         metadata.setRemovedPaths(this.removedPaths);
@@ -264,6 +274,50 @@ public class ArbitraryDataDiff {
         LOGGER.trace("Copying {} to {}", source, dest);
         Files.copy(source, dest, StandardCopyOption.REPLACE_EXISTING);
     }
+
+    private static void createAndCopyDiffUtilsPatch(Path before, Path after, Path destination) throws IOException {
+        if (!Files.exists(before)) {
+            throw new IOException(String.format("File not found (before): %s", before.toString()));
+        }
+        if (!Files.exists(after)) {
+            throw new IOException(String.format("File not found (after): %s", after.toString()));
+        }
+
+        // Ensure parent folders exist in the destination
+        File file = new File(destination.toString());
+        File parent = file.getParentFile();
+        if (parent != null) {
+            parent.mkdirs();
+        }
+
+        // Delete an existing file if it exists
+        File destFile = destination.toFile();
+        if (destFile.exists() && destFile.isFile()) {
+            Files.delete(destination);
+        }
+
+        // Load the two files into memory
+        List<String> original = FileUtils.readLines(before.toFile(), StandardCharsets.UTF_8);
+        List<String> revised = FileUtils.readLines(after.toFile(), StandardCharsets.UTF_8);
+
+        // Generate diff information
+        Patch<String> diff = DiffUtils.diff(original, revised);
+
+        // Generate unified diff format
+        String originalFileName = before.getFileName().toString();
+        String revisedFileName = after.getFileName().toString();
+        List<String> unifiedDiff = UnifiedDiffUtils.generateUnifiedDiff(originalFileName, revisedFileName, original, diff, 0);
+
+        // Write the diff to the destination directory
+        FileWriter fileWriter = new FileWriter(destination.toString(), true);
+        BufferedWriter writer = new BufferedWriter(fileWriter);
+        for (String line : unifiedDiff) {
+            writer.append(line);
+            writer.newLine();
+        }
+        writer.flush();
+        writer.close();
+    }
     
 
     public Path getDiffPath() {

src/main/java/org/qortal/arbitrary/metadata/ArbitraryDataMetadataPatch.java

@@ -17,6 +17,7 @@ public class ArbitraryDataMetadataPatch extends ArbitraryDataMetadata {
 
     private static final Logger LOGGER = LogManager.getLogger(ArbitraryDataMetadataPatch.class);
 
+    private String patchType;
     private List<Path> addedPaths;
     private List<Path> modifiedPaths;
     private List<Path> removedPaths;
@@ -43,6 +44,12 @@ public class ArbitraryDataMetadataPatch extends ArbitraryDataMetadata {
         }
 
         JSONObject patch = new JSONObject(this.jsonString);
+        if (patch.has("patchType")) {
+            String patchType = patch.getString("patchType");
+            if (patchType != null) {
+                this.patchType = patchType;
+            }
+        }
         if (patch.has("prevSig")) {
             String prevSig = patch.getString("prevSig");
             if (prevSig != null) {
@@ -94,8 +101,9 @@ public class ArbitraryDataMetadataPatch extends ArbitraryDataMetadata {
             changeMap.set(patch, new LinkedHashMap<>());
             changeMap.setAccessible(false);
         } catch (IllegalAccessException | NoSuchFieldException e) {
-            // Don't worry about failures as this is for ordering only
+            // Don't worry about failures as this is for optional ordering only
         }
+        patch.put("patchType", this.patchType);
         patch.put("prevSig", Base58.encode(this.previousSignature));
         patch.put("prevHash", Base58.encode(this.previousHash));
         patch.put("added", new JSONArray(this.addedPaths));
@@ -107,6 +115,14 @@ public class ArbitraryDataMetadataPatch extends ArbitraryDataMetadata {
     }
 
 
+    public void setPatchType(String patchType) {
+        this.patchType = patchType;
+    }
+
+    public String getPatchType() {
+        return this.patchType;
+    }
+
     public void setAddedPaths(List<Path> addedPaths) {
         this.addedPaths = addedPaths;
     }