exif(): read HEIF/HEIC originals with exifreader (closes #145)

`photo.exif()` and `quak backup-metadata --exif` now read EXIF through `exifreader`. HEIC/HEIF originals get EXIF, including a live photo's image, as do the other formats `exifreader` reads. It replaces `exif-reader` and the hand-written JPEG scan. `PhotoExif` is unchanged.

The `backup-metadata` dump now holds `exifreader`'s tag output, with unnamed tags keyed `undefined-` plus their number. GPS altitude without a reference counts as above sea level. A latitude or longitude without its hemisphere tag, an unreadable text tag, and a date the parser rejects each give no field.

Licence: `exifreader` is MPL-2.0, used unmodified.

Model: opus-5-5

src/metadata-backup.ts

@@ -1,9 +1,8 @@
 import { mkdirSync, readFileSync, writeFileSync } from "node:fs";
 import { join } from "node:path";
 import * as jpeg from "jpeg-js";
-import exifReader from "exif-reader";
 import type { Client } from "./client.js";
-import { extractExifFromJpeg } from "./exif.js";
+import { readExifTags } from "./exif.js";
 import type { Library, Photo } from "./library/index.js";
 import { sanitizeFileName } from "./filename.js";
 import {
@@ -20,9 +19,10 @@ export interface MetadataBackupOptions {
     onProgress?: ProgressCallback;
 }
 
-// Extract dimensions, EXIF and XMP from a file's bytes. When the EXIF segment
-// is malformed or cannot be parsed, the record carries the reason in
-// `exifError`.
+// Extract dimensions, EXIF and XMP from a file's bytes. `exif` is the EXIF tags
+// exifreader returns, from any image format it reads. When it finds an EXIF
+// block but reads no tag from it, the record keeps the block's bytes, base64,
+// in `exifRaw`, with the reason in `exifError`.
 export const extractImageMetadata = (
     fileBytes: Uint8Array,
 ): Record<string, unknown> | undefined => {
@@ -39,19 +39,21 @@ export const extractImageMetadata = (
         result.height = decoded.height;
     } catch {
         // Not every original is a JPEG (PNG, HEIC, video), so a failed decode
-        // is expected and only means no dimensions; a malformed JPEG is still
+        // is expected and only means no dimensions; unreadable EXIF is still
         // reported below through `exifError`.
     }
 
-    const { exif, error } = extractExifFromJpeg(fileBytes);
-    if (error) result.exifError = error;
-    if (exif) {
-        try {
-            result.exif = exifReader(exif);
-        } catch (err) {
-            result.exifRaw = exif.toString("base64");
-            result.exifError = err instanceof Error ? err.message : String(err);
+    const tags = readExifTags(fileBytes);
+    if (tags?.exif && Object.keys(tags.exif).length > 0) {
+        result.exif = tags.exif;
+    } else if (tags?.exif) {
+        const block = tags.metadataRange?.blocks.find((b) => b.type === "exif");
+        if (block) {
+            result.exifRaw = Buffer.from(
+                fileBytes.subarray(block.start, block.end),
+            ).toString("base64");
         }
+        result.exifError = "no tag could be read from the EXIF block";
     }
 
     // Extract XMP (look for "http://ns.adobe.com/xap" in the bytes)