chore: pointer info building & formatting helpers

src/pointers.ts

@@ -1,4 +1,8 @@
 import path from 'path';
+import { toHex } from './util';
+
+
+const SPEC_URL = 'https://git-lfs.github.com/spec/v1';
 
 
 export interface PointerInfo {
@@ -58,3 +62,21 @@ export function readPointer({ dir, gitdir = path.join(dir, '.git'), content }: P
 
   return { info, objectPath };
 }
+
+
+/** Formats given PointerInfo for writing in Git tree. */
+export function formatPointerInfo(info: PointerInfo): Buffer {
+  const lines = [
+    `version ${SPEC_URL}`,
+    `oid sha256:${info.oid}`,
+    `size ${info.size}`,
+  ];
+  return Buffer.from(lines.join('\n'));
+}
+
+
+export async function buildPointerInfo(content: Buffer): Promise<PointerInfo> {
+  const size = Buffer.byteLength(content);
+  const hash = await crypto.subtle.digest('SHA-1', content);
+  return { oid: toHex(hash), size };
+}

src/util.ts

@@ -74,3 +74,14 @@ export async function bodyToBuffer(body: Uint8Array[]): Promise<Buffer> {
   }
   return Buffer.from(result.buffer);
 }
+
+
+// Borrowed from Isomorphic Git core, it is not importable.
+export function toHex(buffer: ArrayBuffer): string {
+  let hex = ''
+  for (const byte of new Uint8Array(buffer)) {
+    if (byte < 16) hex += '0'
+    hex += byte.toString(16)
+  }
+  return hex
+}