From 4f49cb5c9eed78c5894b6e53f7a6cb64887dc9f5 Mon Sep 17 00:00:00 2001
From: Kyle Peacock <kylpeacock@gmail.com>
Date: Mon, 18 Sep 2023 10:44:54 -0700
Subject: [PATCH] wip: bigint decoding

---
 packages/agent/src/cbor.test.ts | 40 +++++++++++++++++++++++++++++++++
 packages/agent/src/cbor.ts      | 25 +++++++++++++++++----
 2 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/packages/agent/src/cbor.test.ts b/packages/agent/src/cbor.test.ts
index b36c8bfa6..035ed1454 100644
--- a/packages/agent/src/cbor.test.ts
+++ b/packages/agent/src/cbor.test.ts
@@ -60,3 +60,43 @@ function buf2hex(buffer: Uint8Array) {
   // join the elements.
   return Array.prototype.map.call(buffer, x => ('00' + x.toString(16)).slice(-2)).join('');
 }
+
+describe('encode + decode numbers', () => {
+  it('should handle 0', () => {
+    expect(decode(encode(0))).toBe(0);
+  });
+  it('should handle 1', () => {
+    expect(decode(encode(1))).toBe(1);
+  });
+  it('should handle -1', () => {
+    expect(decode(encode(-1))).toBe(-1);
+  });
+  it('should handle 255', () => {
+    expect(decode(encode(255))).toBe(255);
+  });
+  it('should handle 256', () => {
+    expect(decode(encode(256))).toBe(256);
+  });
+  it('should handle 65535', () => {
+    expect(decode(encode(65535))).toBe(65535);
+  });
+  it('should handle 65536', () => {
+    expect(decode(encode(65536))).toBe(65536);
+  });
+  it('should handle 4294967295', () => {
+    expect(decode(encode(4294967295))).toBe(4294967295);
+  });
+  it('should handle 4294967296', () => {
+    expect(decode(encode(4294967296))).toBe(4294967296);
+  });
+  it('should handle 18446744073709551615n', () => {
+    expect(decode(encode(BigInt('18446744073709551615')))).toBe(BigInt('18446744073709551615'));
+  });
+  it('should encode 0n', () => {
+    expect(decode(encode(0n))).toBe(0n);
+  });
+  it('should encode 1n', () => {
+    // Is this valid?
+    expect(decode(encode(1n))).toBe(1);
+  });
+});
diff --git a/packages/agent/src/cbor.ts b/packages/agent/src/cbor.ts
index fec1a7d66..e59ac4eaf 100644
--- a/packages/agent/src/cbor.ts
+++ b/packages/agent/src/cbor.ts
@@ -50,7 +50,7 @@ class BufferEncoder implements CborEncoder<ArrayBuffer> {
   }
 }
 
-class BigIntEncoder implements CborEncoder<BigInt> {
+class BigIntEncoder implements CborEncoder<bigint> {
   public get name() {
     return 'BigInt';
   }
@@ -64,13 +64,30 @@ class BigIntEncoder implements CborEncoder<BigInt> {
   }
 
   public encode(v: bigint): cbor.CborValue {
-    // Always use a bigint encoding.
-    if (v > BigInt(0)) {
+    // Use a bigint encoding for large values
+    if (v > BigInt(Number.MAX_SAFE_INTEGER)) {
       return cbor.value.tagged(2, cbor.value.bytes(fromHex(v.toString(16))));
-    } else {
+    }
+    // If zero, use the zero encoding.
+    else if (v === BigInt(0)) {
+      return cbor.value.tagged(2, cbor.value.bytes(new Uint8Array([])));
+    }
+    // Use Number serialization for safe numbers
+    else if (v >= BigInt(-1 * Number.MAX_SAFE_INTEGER) && v <= BigInt(Number.MAX_SAFE_INTEGER)) {
+      const serialized = serializer.serialize(Number(v)) as cbor.CborValue;
+      // Add CBOR tag
+      Object.defineProperty(serialized, '__brand', { value: 'CBOR' });
+
+      return serialized;
+    } else if (v < BigInt(Number.MAX_SAFE_INTEGER)) {
       return cbor.value.tagged(3, cbor.value.bytes(fromHex((BigInt('-1') * v).toString(16))));
+    } else {
+      this.#never();
     }
   }
+  #never(): never {
+    throw new Error('Should never happen');
+  }
 }
 
 const serializer = SelfDescribeCborSerializer.withDefaultEncoders(true);