Add getLabel() to retrieve filesystem label

Change-type: minor
Signed-off-by: Ken Bannister <[email protected]>

lib/index.ts

@@ -223,10 +223,60 @@ export async function getLabel(
 	disk: Disk,
 	partition: partitioninfo.GPTPartition | partitioninfo.MBRPartition,
 ): Promise<string> {
-	let buf = Buffer.alloc(1024);
-	// Read buf.length bytes into buf starting at the beginning of the filesystem.
-	await disk.read(buf, 0, buf.length, partition.offset);
+	// If GPT, can we just read the protective MBR?
+	// Is there a more Typescript native way to determine partition table type? 
+	// const isGpt = 'guid' in partition;
 
-	const label = buf.toString('utf8', 0x2B, 0x2B+11).trim();
+	// Linux native FS, expecting ext2+, so skip to superblock for metadata.
+	let metadataOffset = 0;
+	if (partition.type === 0x83) {
+		metadataOffset += 0x400;
+	}
+
+	// Read filesystem metadata
+	let buf = Buffer.alloc(0x100);
+	await disk.read(buf, 0, buf.length, partition.offset + metadataOffset);
+
+	let labelOffset = 0;
+	let maxLength = 0;
+	// First verify magic signature to determine metadata layout for label offset.
+	const fatTypes = [0xB, 0xC, 0xE];
+	if (fatTypes.some(ptype => partition.type === ptype)) {
+		maxLength = 11;
+		// FAT16
+		if (buf.readUInt8(0x26) === 0x29) {
+			labelOffset = 0x2B;
+		// FAT32
+		} else if (buf.readUInt8(0x42) === 0x29) {
+			labelOffset = 0x47;
+		} else {
+			return '';
+		}
+	} else if (partition.type === 0x83) {
+		maxLength = 16;
+		if (buf.readUInt16LE(0x38) === 0xEF53) {
+			labelOffset = 0x78;
+		} else {
+			return '';
+		}
+	// Unexpected partition type
+	} else {
+		return '';
+	}
+
+	// Identify and exclude trailing /0 bytes to stringify.
+	let i = 0;
+	for (; i <= maxLength; i++) {
+		// If label fills available space, no need to test. We just need i
+		// to have the expected value for Buffer.toString() call below.
+		if (i == maxLength) {
+			break;
+		}
+		if (buf.readUInt8(labelOffset + i) == 0) {
+			break;
+		}
+	}
+
+	const label = buf.toString('utf8', labelOffset, labelOffset + i).trim();
 	return label;
 }

tests/fsLabel.ts

@@ -8,6 +8,7 @@ import * as partitioninfo from 'partitioninfo';
 import * as imagefs from '../lib';
 
 const RASPBERRYPI = Path.join(__dirname, 'images', 'raspberrypi.img');
+const MBR_FAT32 = Path.join(__dirname, 'images', 'mbr-fat32.img');
 
 async function tmpFile(): Promise<{ path: string; cleanup: () => void }> {
 	return await new Promise((resolve, reject) => {
@@ -52,7 +53,10 @@ function testWithFileCopy(
 function testFileDisk(
 	title: string,
 	image: { image: string; partition: number },
-	fn: (label: string) => Promise<void>,
+	fn: (
+		disk: FileDisk,
+		partition: partitioninfo.GPTPartition | partitioninfo.MBRPartition,
+	) => Promise<void>,
 ) {
 	testWithFileCopy(
 		`${title} (filedisk)`,
@@ -61,19 +65,53 @@ function testFileDisk(
 			await withOpenFile(fileCopy, 'r+', async (handle) => {
 				const disk = new FileDisk(handle);
 				const partition = await partitioninfo.get(disk, image.partition);
-				await fn(await imagefs.getLabel(disk, partition));
+				await fn(disk, partition);
 			});
 		},
 	);
 }
 
 testFileDisk(
-	'should find label in MBR with FAT16 partition',
+	'should find label in MBR with FAT16 (0xB) partition',
 	{
 		image: RASPBERRYPI,
 		partition: 1,
 	},
-	async (label: string) => {
+	async (
+		disk: FileDisk,
+		partition: partitioninfo.GPTPartition | partitioninfo.MBRPartition,
+	) => {
+		const label = await imagefs.getLabel(disk, partition);
 		deepEqual(label, 'RESIN-BOOT');
 	},
 );
+
+testFileDisk(
+	'should find label in MBR with FAT32 (0xC) partition',
+	{
+		image: MBR_FAT32,
+		partition: 1,
+	},
+	async (
+		disk: FileDisk,
+		partition: partitioninfo.GPTPartition | partitioninfo.MBRPartition,
+	) => {
+		const label = await imagefs.getLabel(disk, partition);
+		deepEqual(label, 'resin-boot');
+	},
+);
+
+testFileDisk(
+	'should find label in MBR with ext4 (0x83) partition',
+	{
+		image: MBR_FAT32,
+		partition: 6,
+	},
+	async (
+		disk: FileDisk,
+		partition: partitioninfo.GPTPartition | partitioninfo.MBRPartition,
+	) => {
+		const label = await imagefs.getLabel(disk, partition);
+		deepEqual(label, 'resin-data');
+	},
+);