Expose PNG metadata comments (#4157)

docs/api-input.md

@@ -42,6 +42,7 @@ A `Promise` is returned when `callback` is not provided.
 - `xmp`: Buffer containing raw XMP data, if present
 - `tifftagPhotoshop`: Buffer containing raw TIFFTAG_PHOTOSHOP data, if present
 - `formatMagick`: String containing format for images loaded via *magick
+- `comments`:  Array of keyword/text pairs representing PNG text blocks, if present.
 
 
 

lib/index.d.ts

@@ -1108,6 +1108,8 @@ declare namespace sharp {
         resolutionUnit?: 'inch' | 'cm' | undefined;
         /** String containing format for images loaded via *magick */
         formatMagick?: string | undefined;
+        /** Array of keyword/text pairs representing PNG text blocks, if present. */
+        comments?: CommentsMetadata[] | undefined;
     }
 
     interface LevelMetadata {
@@ -1115,6 +1117,11 @@ declare namespace sharp {
         height: number;
     }
 
+    interface CommentsMetadata {
+        keyword: string;
+        text: string;
+    }
+
     interface Stats {
         /** Array of channel statistics for each channel in the image. */
         channels: ChannelStats[];

lib/input.js

@@ -450,6 +450,7 @@ function _isStreamInput () {
  * - `xmp`: Buffer containing raw XMP data, if present
  * - `tifftagPhotoshop`: Buffer containing raw TIFFTAG_PHOTOSHOP data, if present
  * - `formatMagick`: String containing format for images loaded via *magick
+ * - `comments` Array of keyword/text pairs representing PNG text blocks, if present.
  *
  * @example
  * const metadata = await sharp(input).metadata();

src/metadata.cc

@@ -10,6 +10,8 @@
 #include "common.h"
 #include "metadata.h"
 
+static void* readPNGComment(VipsImage *image, const char *field, GValue *value, void *p);
+
 class MetadataWorker : public Napi::AsyncWorker {
  public:
   MetadataWorker(Napi::Function callback, MetadataBaton *baton, Napi::Function debuglog) :
@@ -131,6 +133,8 @@ class MetadataWorker : public Napi::AsyncWorker {
         memcpy(baton->tifftagPhotoshop, tifftagPhotoshop, tifftagPhotoshopLength);
         baton->tifftagPhotoshopLength = tifftagPhotoshopLength;
       }
+      // PNG comments
+      vips_image_map(image.get_image(), readPNGComment, &baton->comments);
     }
 
     // Clean up
@@ -246,6 +250,17 @@ class MetadataWorker : public Napi::AsyncWorker {
           Napi::Buffer<char>::NewOrCopy(env, baton->tifftagPhotoshop,
             baton->tifftagPhotoshopLength, sharp::FreeCallback));
       }
+      if (baton->comments.size() > 0) {
+        int i = 0;
+        Napi::Array comments = Napi::Array::New(env, baton->comments.size());
+        for (auto &c : baton->comments) {
+          Napi::Object comment = Napi::Object::New(env);
+          comment.Set("keyword", c.first);
+          comment.Set("text", c.second);
+          comments.Set(i++, comment);
+        }
+        info.Set("comments", comments);
+      }
       Callback().Call(Receiver().Value(), { env.Null(), info });
     } else {
       Callback().Call(Receiver().Value(), { Napi::Error::New(env, sharp::TrimEnd(baton->err)).Value() });
@@ -285,3 +300,21 @@ Napi::Value metadata(const Napi::CallbackInfo& info) {
 
   return info.Env().Undefined();
 }
+
+const char *PNG_COMMENT_START = "png-comment-";
+const int PNG_COMMENT_START_LEN = strlen(PNG_COMMENT_START);
+
+static void* readPNGComment(VipsImage *image, const char *field, GValue *value, void *p) {
+  MetadataComments *comments = static_cast<MetadataComments *>(p);
+
+  if (vips_isprefix(PNG_COMMENT_START, field)) {
+    const char *keyword = strchr(field + PNG_COMMENT_START_LEN, '-');
+    const char *str;
+    if (keyword != NULL && !vips_image_get_string(image, field, &str)) {
+      keyword++;  // Skip the hyphen
+      comments->push_back(std::make_pair(keyword, str));
+    }
+  }
+
+  return NULL;
+}

src/metadata.h

@@ -9,6 +9,8 @@
 
 #include "./common.h"
 
+typedef std::vector<std::pair<std::string, std::string>> MetadataComments;
+
 struct MetadataBaton {
   // Input
   sharp::InputDescriptor *input;
@@ -47,6 +49,7 @@ struct MetadataBaton {
   size_t xmpLength;
   char *tifftagPhotoshop;
   size_t tifftagPhotoshopLength;
+  MetadataComments comments;
   std::string err;
 
   MetadataBaton():

test/unit/metadata.js

@@ -154,6 +154,31 @@ describe('Image metadata', function () {
     });
   });
 
+  it('PNG with comment', function (done) {
+    sharp(fixtures.inputPngTestJoinChannel).metadata(function (err, metadata) {
+      if (err) throw err;
+      assert.strictEqual('png', metadata.format);
+      assert.strictEqual('undefined', typeof metadata.size);
+      assert.strictEqual(320, metadata.width);
+      assert.strictEqual(240, metadata.height);
+      assert.strictEqual('b-w', metadata.space);
+      assert.strictEqual(1, metadata.channels);
+      assert.strictEqual('uchar', metadata.depth);
+      assert.strictEqual(72, metadata.density);
+      assert.strictEqual('undefined', typeof metadata.chromaSubsampling);
+      assert.strictEqual(false, metadata.isProgressive);
+      assert.strictEqual(false, metadata.hasProfile);
+      assert.strictEqual(false, metadata.hasAlpha);
+      assert.strictEqual('undefined', typeof metadata.orientation);
+      assert.strictEqual('undefined', typeof metadata.exif);
+      assert.strictEqual('undefined', typeof metadata.icc);
+      assert.strictEqual(1, metadata.comments.length);
+      assert.strictEqual('Comment', metadata.comments[0].keyword);
+      assert.strictEqual('Created with GIMP', metadata.comments[0].text);
+      done();
+    });
+  });
+
   it('Transparent PNG', function (done) {
     sharp(fixtures.inputPngWithTransparency).metadata(function (err, metadata) {
       if (err) throw err;