Handle non-empty resource names in IPTC resource block

#459
mattiasw · Jan 26, 2025 · 386c8ec · 386c8ec
1 parent a4a8fc4
commit 386c8ec
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Showing 4 changed files with 29 additions and 10 deletions.
diff --git a/dist/exif-reader.js b/dist/exif-reader.js
diff --git a/dist/exif-reader.js.map b/dist/exif-reader.js.map
diff --git a/src/iptc-tags.js b/src/iptc-tags.js
@@ -7,8 +7,12 @@ import TagDecoder from './tag-decoder.js';
 
 const BYTES_8BIM = 0x3842494d;
 const BYTES_8BIM_SIZE = 4;
-const RESOURCE_BLOCK_HEADER_SIZE = BYTES_8BIM_SIZE + 8;
-const NAA_RESOURCE_BLOCK_TYPE = 0x0404;
+const RESOURCE_ID_SIZE = 2;
+const RESOURCE_NAME_SIZE_SIZE = 1;
+const RESOURCE_NAME_MIN_SIZE = 2;
+const RESOURCE_SIZE_SIZE = 4;
+const RESOURCE_BLOCK_MIN_HEADER_SIZE = BYTES_8BIM_SIZE + RESOURCE_ID_SIZE + RESOURCE_NAME_MIN_SIZE + RESOURCE_SIZE_SIZE;
+const NAA_RESOURCE_BLOCK_TYPE = 0x0404; // Sometimes called resource ID.
 const TAG_HEADER_SIZE = 5;
 
 export default {
@@ -28,26 +32,29 @@ function read(dataView, dataOffset, includeUnknown) {
 }
 
 function getNaaResourceBlock(dataView, dataOffset) {
-    while (dataOffset + RESOURCE_BLOCK_HEADER_SIZE <= dataView.byteLength) {
+    while (dataOffset + RESOURCE_BLOCK_MIN_HEADER_SIZE <= dataView.byteLength) {
         const resourceBlock = getResourceBlock(dataView, dataOffset);
         if (isNaaResourceBlock(resourceBlock)) {
-            return {naaBlock: resourceBlock, dataOffset: dataOffset + RESOURCE_BLOCK_HEADER_SIZE};
+            return {naaBlock: resourceBlock, dataOffset: dataOffset + resourceBlock.headerSize};
         }
-        dataOffset += RESOURCE_BLOCK_HEADER_SIZE + resourceBlock.size + getBlockPadding(resourceBlock);
+        dataOffset += resourceBlock.headerSize + resourceBlock.size + getBlockPadding(resourceBlock);
     }
     throw new Error('No IPTC NAA resource block.');
 }
 
 function getResourceBlock(dataView, dataOffset) {
-    const RESOURCE_BLOCK_SIZE_OFFSET = 10;
-
     if (dataView.getUint32(dataOffset, false) !== BYTES_8BIM) {
         throw new Error('Not an IPTC resource block.');
     }
 
+    // We currently do not use the resource name for anything, we just need to know the size.
+    const resourceNameSize = dataView.getUint8(dataOffset + BYTES_8BIM_SIZE + RESOURCE_ID_SIZE);
+    const resourceNameTotalSize = (resourceNameSize % 2 === 0 ? resourceNameSize + 1 : resourceNameSize) + RESOURCE_NAME_SIZE_SIZE;
+
     return {
+        headerSize: BYTES_8BIM_SIZE + RESOURCE_ID_SIZE + resourceNameTotalSize + RESOURCE_SIZE_SIZE,
         type: dataView.getUint16(dataOffset + BYTES_8BIM_SIZE),
-        size: dataView.getUint16(dataOffset + RESOURCE_BLOCK_SIZE_OFFSET)
+        size: dataView.getUint32(dataOffset + BYTES_8BIM_SIZE + RESOURCE_ID_SIZE + resourceNameTotalSize),
     };
 }
 

diff --git a/test/unit/iptc-tags-spec.js b/test/unit/iptc-tags-spec.js
@@ -49,6 +49,18 @@ describe('iptc-tags', function () {
         expect(naaBlock['size']).to.equal(0x42);
     });
 
+    it('should find the IPTC NAA resource block with non-empty resource name (without padding)', () => {
+        const dataView = getDataView('8BIM\x04\x04\x05aname\x00\x00\x00\x42');
+        const {naaBlock} = getNaaResourceBlock(dataView, 0);
+        expect(naaBlock['size']).to.equal(0x42);
+    });
+
+    it('should find the IPTC NAA resource block with non-empty resource name (with padding)', () => {
+        const dataView = getDataView('8BIM\x04\x04\x04name\x00\x00\x00\x00\x42');
+        const {naaBlock} = getNaaResourceBlock(dataView, 0);
+        expect(naaBlock['size']).to.equal(0x42);
+    });
+
     it('should fail for IPTC header with no NAA resource block', () => {
         const dataView = getDataView('8BIM\x04\x05\x00\x00\x00\x00\x00\x42');
         expect(() => getNaaResourceBlock(dataView, 0)).to.throw(/No IPTC NAA resource block./);