1 files changed, 46 insertions, 0 deletions
diff --git a/packages/server/src/helpers/cbor.ts b/packages/server/src/helpers/cbor.ts
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+++ b/packages/server/src/helpers/cbor.ts
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+/* eslint-disable @typescript-eslint/ban-ts-comment */
+import * as cborx from 'cbor-x';
+
+/**
+ * This encoder should keep CBOR data the same length when data is re-encoded
+ *
+ * MOST CRITICALLY, this means the following needs to be true of whatever CBOR library we use:
+ * - CBOR Map type values MUST decode to JavaScript Maps
+ * - CBOR tag 64 (uint8 Typed Array) MUST NOT be used when encoding Uint8Arrays back to CBOR
+ *
+ * So long as these requirements are maintained, then CBOR sequences can be encoded and decoded
+ * freely while maintaining their lengths for the most accurate pointer movement across them.
+ */
+const encoder = new cborx.Encoder({ mapsAsObjects: false, tagUint8Array: false });
+
+/**
+ * Decode and return the first item in a sequence of CBOR-encoded values
+ *
+ * @param input The CBOR data to decode
+ * @param asObject (optional) Whether to convert any CBOR Maps into JavaScript Objects. Defaults to
+ * `false`
+ */
+export function decodeFirst<Type>(input: Uint8Array): Type {
+  const decoded = encoder.decodeMultiple(input) as undefined | Type[];
+
+  if (decoded === undefined) {
+    throw new Error('CBOR input data was empty');
+  }
+
+  /**
+   * Typing on `decoded` is `void | []` which causes TypeScript to think that it's an empty array,
+   * and thus you can't destructure it. I'm ignoring that because the code works fine in JS, and
+   * so this should be a valid operation.
+   */
+  // @ts-ignore 2493
+  const [first] = decoded;
+
+  return first;
+}
+
+/**
+ * Encode data to CBOR
+ */
+export function encode(input: any): Uint8Array {
+  return encoder.encode(input);
+}