From: Chris Duncan <chris@zoso.dev>
Date: Thu, 13 Aug 2026 04:27:52 +0000 (-0700)
Subject: Use type guard to enable direct use of typechecked output buffer.
X-Git-Url: https://git.codecow.com/?a=commitdiff_plain;h=86e01f1831b929af74be98c896f0085e47222944;p=nano25519.git

Use type guard to enable direct use of typechecked output buffer.
---

diff --git a/src/lib/nano25519.ts b/src/lib/nano25519.ts
index 4d86043..61fa85f 100644
--- a/src/lib/nano25519.ts
+++ b/src/lib/nano25519.ts
@@ -72,7 +72,7 @@ const nano25519_init = (bytes: number[]): { derive: typeof derive, sign: typeof
 		let buffer = new DataView(exports.memory.buffer)
 		try {
 			out ??= new Uint8Array(32)
-			if (!(out instanceof Uint8Array && out.buffer instanceof ArrayBuffer && out.byteLength === 32)) {
+			if (!(isBytes(out) && out.byteLength === 32)) {
 				throw new TypeError('Derive output buffer must be 32-byte Uint8Array<ArrayBuffer>')
 			}
 			privateKey.set(normalize('private key', 32, 32, k))
@@ -83,20 +83,19 @@ const nano25519_init = (bytes: number[]): { derive: typeof derive, sign: typeof
 			privateKey.fill(0)
 			exports.derive()
 			const outPtr = exports.getOutputPointer()
-			const publicKey = new Uint8Array(out.buffer)
 			buffer = new DataView(exports.memory.buffer)
 			for (let i = 0; i < 32; i++) {
-				publicKey[i] = buffer.getUint8(outPtr + i + 32)
+				out[i] = buffer.getUint8(outPtr + i + 32)
 			}
 			clear(buffer)
 			if (typeof k === 'string') {
 				let hex = ''
-				for (const byte of publicKey) {
+				for (const byte of out) {
 					hex += byte.toString(16).padStart(2, '0')
 				}
 				return hex
 			} else {
-				return publicKey
+				return out
 			}
 		} finally {
 			privateKey.fill(0)
@@ -120,18 +119,17 @@ const nano25519_init = (bytes: number[]): { derive: typeof derive, sign: typeof
 		exports.sign(message.byteLength)
 		const outPtr = exports.getOutputPointer()
 		s ??= new Uint8Array(64)
-		if (!(s instanceof Uint8Array && s.buffer instanceof ArrayBuffer && s.byteLength === 64)) {
+		if (!(isBytes(s) && s.byteLength === 64)) {
 			throw new TypeError('Sign output buffer must be 64-byte Uint8Array<ArrayBuffer>')
 		}
-		const signature = new Uint8Array(s.buffer)
 		buffer = new DataView(exports.memory.buffer)
 		for (let i = 0; i < 64; i++) {
-			signature[i] = buffer.getUint8(outPtr + i)
+			s[i] = buffer.getUint8(outPtr + i)
 		}
 		clear(buffer)
 		return typeof k === 'string'
-			? [...signature].map(b => b.toString(16).padStart(2, '0')).join('')
-			: signature
+			? [...s].map(b => b.toString(16).padStart(2, '0')).join('')
+			: s
 	}
 
 	function verify (s: unknown, m: unknown, k: unknown): boolean {
@@ -169,6 +167,10 @@ const nano25519_init = (bytes: number[]): { derive: typeof derive, sign: typeof
 		}
 	}
 
+	function isBytes (a: unknown): a is Uint8Array<ArrayBuffer> {
+		return a instanceof Uint8Array && a.buffer instanceof ArrayBuffer
+	}
+
 	function normalize (name: string, byteLengthMin: number, byteLengthMax: number, value: unknown): Uint8Array<ArrayBuffer> {
 		if (typeof name !== 'string') {
 			throw new TypeError(`Invalid name ${name}`)