Remove error checks when decoding VLQ

Author: szuend

src/vlq.test.ts

@@ -0,0 +1,63 @@
+// Copyright 2025 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import { describe, it } from "jsr:@std/testing/bdd";
+import { TokenIterator } from "./vlq.ts";
+import { assertFalse, assertStrictEquals } from "jsr:@std/assert";
+
+describe("TokenIterator", () => {
+  describe("nextUnsignedVLQ", () => {
+    it("returns zero when no more characters are available", () => {
+      const iter = new TokenIterator("");
+      assertFalse(iter.hasNext());
+
+      assertStrictEquals(iter.nextUnsignedVLQ(), 0);
+    });
+
+    it("treats unknown characters as 0", () => {
+      const iter = new TokenIterator("h,C"); // 'h' has the continuation bit set. ',' is treated as 0 so we stop decoding.
+
+      assertStrictEquals(iter.nextUnsignedVLQ(), 1);
+      assertStrictEquals(iter.peek(), "C");
+    });
+
+    it("treats unknown unicode characters as 0", () => {
+      const iter = new TokenIterator("hæC"); // 'h' has the continuation bit set. 'æ' falls outside the array so has 'undefined as its digit value.
+
+      assertStrictEquals(iter.nextUnsignedVLQ(), 1);
+      assertStrictEquals(iter.peek(), "C");
+    });
+  });
+
+  describe("nextSignedVLQ", () => {
+    it("returns zero when no more characters are available", () => {
+      const iter = new TokenIterator("");
+      assertFalse(iter.hasNext());
+
+      assertStrictEquals(iter.nextSignedVLQ(), 0);
+    });
+
+    it("treats unknown characters as 0", () => {
+      const iter = new TokenIterator("i,C"); // 'i' has the continuation bit set. ',' is treated as 0 so we stop decoding.
+
+      assertStrictEquals(iter.nextSignedVLQ(), 1);
+      assertStrictEquals(iter.peek(), "C");
+    });
+
+    it("treats unknown unicode characters as 0", () => {
+      const iter = new TokenIterator("iæC"); // 'i' has the continuation bit set. 'æ' falls outside the array so has 'undefined as its digit value.
+
+      assertStrictEquals(iter.nextSignedVLQ(), 1);
+      assertStrictEquals(iter.peek(), "C");
+    });
+  });
+
+  describe("current", () => {
+    it("returns the empty string when calling it without advancing the iterator", () => {
+      const iter = new TokenIterator("CCCC");
+
+      assertStrictEquals(iter.currentChar(), "");
+    });
+  });
+});

src/vlq.ts

@@ -85,26 +85,15 @@ export class TokenIterator {
     let shift = 0;
     let digit: number = VLQ_CONTINUATION_MASK;
     while (digit & VLQ_CONTINUATION_MASK) {
-      if (!this.hasNext()) {
-        throw new Error("Unexpected end of input while decodling VLQ number!");
-      }
       const charCode = this.nextCharCode();
       digit = BASE64_CODES[charCode];
-      if (charCode !== 65 /* 'A' */ && digit === 0) {
-        throw new Error(
-          `Unexpected char '${
-            String.fromCharCode(charCode)
-          }' encountered while decoding`,
-        );
-      }
       result += (digit & VLQ_BASE_MASK) << shift;
       shift += VLQ_BASE_SHIFT;
     }
     return result;
   }
 
   currentChar(): string {
-    if (this.#position === 0) throw new Error("Move the iterator first!");
     return this.#string.charAt(this.#position - 1);
   }
 }