chore: convert more files to TypeScript (#18820)

lib/common/buffer-utils.ts

@@ -0,0 +1,71 @@
+import { Buffer } from 'buffer'
+
+const typedArrays: Record<string, Function> = {
+  Buffer,
+  ArrayBuffer,
+  Int8Array,
+  Uint8Array,
+  Uint8ClampedArray,
+  Int16Array,
+  Uint16Array,
+  Int32Array,
+  Uint32Array,
+  Float32Array,
+  Float64Array
+}
+
+type BufferLike = Buffer | ArrayBuffer | ArrayBufferView
+
+function getType (value: BufferLike) {
+  for (const type of Object.keys(typedArrays)) {
+    if (value instanceof typedArrays[type]) {
+      return type
+    }
+  }
+  throw new Error('Invalid buffer')
+}
+
+function getBuffer (value: BufferLike) {
+  if (value instanceof Buffer) {
+    return value
+  } else if (value instanceof ArrayBuffer) {
+    return Buffer.from(value)
+  } else {
+    return Buffer.from(value.buffer, value.byteOffset, value.byteLength)
+  }
+}
+
+export function isBuffer (value: BufferLike) {
+  return ArrayBuffer.isView(value) || value instanceof ArrayBuffer
+}
+
+interface BufferMeta {
+  type: keyof typeof typedArrays;
+  data: Buffer;
+  length: number | undefined;
+}
+
+export function bufferToMeta (value: BufferLike): BufferMeta {
+  return {
+    type: getType(value),
+    data: getBuffer(value),
+    // NB. We only use length when decoding Int8Array and friends.
+    // For other buffer-like types this is expected to be undefined.
+    length: (value as Buffer).length
+  }
+}
+
+export function metaToBuffer (value: BufferMeta) {
+  const constructor = typedArrays[value.type]
+  const data = getBuffer(value.data)
+
+  if (constructor === Buffer) {
+    return data
+  } else if (constructor === ArrayBuffer) {
+    return data.buffer
+  } else if (constructor) {
+    return new (constructor as any)(data.buffer, data.byteOffset, value.length)
+  } else {
+    return data
+  }
+}