PngExifReader.php: add internal debugging error codes

inc/Data/Driver/Metadata/PngExifReader.php

@@ -1,5 +1,5 @@
 <?php
-namespace Vichan\Data\Driver;
+namespace Vichan\Data\Driver\Metadata;
 
 
 class PngExifReader implements ExifReader {
@@ -9,11 +9,23 @@ class PngExifReader implements ExifReader {
 	// Exif data type identifier.
 	private const TYPE_SHORT = 0x3;
 
+	// Errors, mostly for debugging.
+	private const ERR_BAD_EXIF = -1;
+	private const ERR_BAD_ENDIAN = -2;
+	private const ERR_BAD_MARK = -2;
+	private const ERR_BAD_OFFSET_TO_IFD = -3;
+	private const ERR_BAD_OFFSET_TO_DIR_ENTRY = -4;
+	private const ERR_BAD_ORIENTATION_NOT_FOUND = -5;
+	private const ERR_NOT_A_PNG = -6;
+	private const ERR_EOF = -7;
+	private const ERR_COULD_NOT_OPEN = -8;
 
-	private static function tryReadExifChunk(string $chunk_blob): ?int {
+
+	private static function tryReadExifChunk(string $chunk_blob): int {
 		// Ensure the chunk starts with "Exif" (EXIF header).
-		if (\substr($chunk_blob, 0, 6) !== "Exif\0\0") {
+		$a = \substr($chunk_blob, 0, 6);
-			return null;
+		if ($a !== "Exif\0\0") {
+			return self::ERR_BAD_EXIF;
 		}
 
 		// Remove the "Exif\0\0" header.
@@ -27,18 +39,18 @@ class PngExifReader implements ExifReader {
 		} elseif ($byte_order === 'MM') {
 			$little_endian = false;
 		} else {
-			return null;
+			return self::ERR_BAD_ENDIAN;
 		}
 
 		// Verify tag mark.
 		$tag_mark = \substr($tiff_data, 2, 4);
 		if ($little_endian) {
 			if ($tag_mark !== "*\0") {
-				return null;
+				return self::ERR_BAD_MARK;
 			}
 		} else {
 			if ($tag_mark !== "\0*") {
-				return null;
+				return self::ERR_BAD_MARK;
 			}
 		}
 
@@ -48,7 +60,7 @@ class PngExifReader implements ExifReader {
 		// Offset to the first IFD.
 		$current_offset = \unpack($unpack_fmt, \substr($tiff_data, 4, 2))[1];
 		if ($current_offset > \strlen($chunk_blob)) {
-			return null;
+			return self::ERR_BAD_OFFSET_TO_IFD;
 		}
 
 		while ($current_offset > 0) {
@@ -57,7 +69,7 @@ class PngExifReader implements ExifReader {
 			$current_offset += 2;
 
 			if ($current_offset + $num_entries * 12 > \strlen($chunk_blob)) {
-				return null;
+				return self::ERR_BAD_OFFSET_TO_DIR_ENTRY;
 			}
 
 			for ($i = 0; $i < $num_entries; $i++) {
@@ -84,18 +96,16 @@ class PngExifReader implements ExifReader {
 			$current_offset = \unpack($unpack_fmt, \substr($tiff_data, $current_offset + ($num_entries * 12), 4))[1];
 		}
 
-		return null;
+		return self::ERR_BAD_ORIENTATION_NOT_FOUND;
 	}
 
 	// Mostly adapted from https://stackoverflow.com/a/2190438
-	private static function tryReadPngChunks(mixed $fd): ?int {
+	private static function tryReadPngChunks(mixed $fd): int {
-		$text_chunks = [];
-
 		// Read the magic bytes and verify.
 		$header = \fread($fd, 8);
 
 		if ($header != "\x89PNG\x0d\x0a\x1a\x0a") {
-			return null;
+			return self::ERR_NOT_A_PNG;
 		}
 
 		// Loop through the PNG's chunks. Byte 0-3 is length, Byte 4-7 is type.
@@ -105,17 +115,12 @@ class PngExifReader implements ExifReader {
 			// Extract length and type from binary data.
 			$chunk = @\unpack('Nsize/a4type', $chunkHeader);
 
-			// Store position into internal array.
-			if (!isset($text_chunks[$chunk['type']])) {
-				$text_chunks[$chunk['type']] = [];
-			}
-
 			if ($chunk['type'] === 'tEXt') {
 				if ($chunk['size'] > 0 && $chunk['size'] < self::MAX_CHUNK_SIZE) {
 					$size = $chunk['size'];
 					$chunk_blob = \fread($fd, $size);
 					$ret = self::tryReadExifChunk($chunk_blob);
-					if ($ret !== null) {
+					if ($ret < 1) {
 						return $ret;
 					}
 				}
@@ -128,18 +133,18 @@ class PngExifReader implements ExifReader {
 			$chunkHeader = \fread($fd, 8);
 		}
 
-		return null;
+		return self::ERR_EOF;
 	}
 
 	public function getOrientation(string $file): ?int {
 		// Open the file.
 		$fd = \fopen($file, 'r');
 		if ($fd === false) {
-			return null;
+			return self::ERR_COULD_NOT_OPEN;
 		}
-		$ret = self::tryReadPngChunks($fd);
+		return self::tryReadPngChunks($fd);
 		\fclose($fd);
-		if ($ret === null || $ret > 9) {
+		if ($ret < 1 || $ret > 9) {
 			return null;
 		} else {
 			return $ret;