Preserve binary markers when formatting Git patches

README.md

@@ -137,7 +137,7 @@ jsdiff's diff functions all take an old text and a new text and perform three st
 
     `patch` may be either a single structured patch object (as returned by `structuredPatch`) or an array of them (as returned by `parsePatch`). The optional `headerOptions` argument behaves the same as the `headerOptions` option of `createTwoFilesPatch`, except that it is ignored for Git patches (i.e. patches where `isGit` is `true`).
 
-    When a patch has `isGit: true`, `formatPatch` output is changed to more closely match Git's output: it emits a `diff --git` header, emits Git extended headers as appropriate based on properties like `isRename`, `isCreate`, `newMode`, etc, and always emits `---`/`+++` file headers when hunks are present but omits them when there are no hunks (e.g. renames without content changes). The `headerOptions` parameter has no effect on Git patches since the header format is fully determined by the Git extended header properties.
+    When a patch has `isGit: true`, `formatPatch` output is changed to more closely match Git's output: it emits a `diff --git` header, emits Git extended headers as appropriate based on properties like `isRename`, `isCreate`, `newMode`, etc, and always emits `---`/`+++` file headers when hunks are present but omits them when there are no hunks (e.g. renames without content changes). The `headerOptions` parameter has no effect on Git patches since the header format is fully determined by the Git extended header properties. Binary patches retain a `Binary files ... differ` marker; the formatted patch does not contain the binary file data.
 
 * `structuredPatch(oldFileName, newFileName, oldStr, newStr[, oldHeader[, newHeader[, options]]])` - returns an object with an array of hunk objects.
 

src/patch/create.ts

@@ -411,6 +411,11 @@ export function formatPatch(patch: StructuredPatch | StructuredPatch[], headerOp
       ret.push('copy from ' + quoteFileNameIfNeeded((patch.oldFileName ?? '').replace(/^a\//, '')));
       ret.push('copy to ' + quoteFileNameIfNeeded((patch.newFileName ?? '').replace(/^b\//, '')));
     }
+    if (patch.isBinary) {
+      const oldName = patch.isCreate ? '/dev/null' : patch.oldFileName;
+      const newName = patch.isDelete ? '/dev/null' : patch.newFileName;
+      ret.push('Binary files ' + quoteFileNameIfNeeded(oldName) + ' and ' + quoteFileNameIfNeeded(newName) + ' differ');
+    }
   } else {
     if (headerOptions.includeIndex && patch.oldFileName == patch.newFileName && patch.oldFileName !== undefined) {
       ret.push('Index: ' + quoteFileNameIfNeeded(patch.oldFileName));

test/patch/create.js

@@ -1354,6 +1354,60 @@ describe('patch/create', function() {
         expect(formatPatch(patches, OMIT_HEADERS)).to.equal(expected);
       });
 
+      describe('binary Git patches', function() {
+        const fixtures = [
+          ['modification',
+            'diff --git a/old.bin b/new.bin\n' +
+            'Binary files a/old.bin and b/new.bin differ\n'],
+          ['creation',
+            'diff --git a/new.bin b/new.bin\n' +
+            'new file mode 100644\n' +
+            'Binary files /dev/null and b/new.bin differ\n'],
+          ['deletion',
+            'diff --git a/old.bin b/old.bin\n' +
+            'deleted file mode 100644\n' +
+            'Binary files a/old.bin and /dev/null differ\n'],
+          ['rename',
+            'diff --git a/old.bin b/new.bin\n' +
+            'rename from old.bin\n' +
+            'rename to new.bin\n' +
+            'Binary files a/old.bin and b/new.bin differ\n'],
+          ['copy',
+            'diff --git a/old.bin b/new.bin\n' +
+            'copy from old.bin\n' +
+            'copy to new.bin\n' +
+            'Binary files a/old.bin and b/new.bin differ\n'],
+          ['quoted filename',
+            'diff --git "a/caf\\303\\251\\timage.bin" "b/caf\\303\\251\\timage.bin"\n' +
+            'Binary files "a/caf\\303\\251\\timage.bin" and "b/caf\\303\\251\\timage.bin" differ\n']
+        ];
+
+        for (const [name, text] of fixtures) {
+          it(`should preserve a binary ${name} when formatting`, function() {
+            const parsed = parsePatch(text);
+            expect(parsed[0].isBinary).to.equal(true);
+            expect(formatPatch(parsed)).to.equal(text);
+            expect(parsePatch(formatPatch(parsed))).to.deep.equal(parsed);
+          });
+        }
+
+        it('should preserve binary flags in a mixed multi-file patch', function() {
+          const text = fixtures[0][1] +
+            '\n' +
+            'diff --git a/text.txt b/text.txt\n' +
+            '--- a/text.txt\n' +
+            '+++ b/text.txt\n' +
+            '@@ -1,1 +1,1 @@\n' +
+            '-before\n' +
+            '+after\n' +
+            '\n' + fixtures[1][1];
+          const parsed = parsePatch(text);
+          expect(parsed).to.have.length(3);
+          expect(parsed.map(patch => patch.isBinary)).to.deep.equal([true, undefined, true]);
+          expect(parsePatch(formatPatch(parsed))).to.deep.equal(parsed);
+        });
+      });
+
       it('should emit rename headers for patches with isGit and isRename', function() {
         const patch = {
           oldFileName: 'a/old.txt',