fix encoding exact 255-length strings. closes #216

Author: endel

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@colyseus/schema",
-  "version": "4.0.8",
+  "version": "4.0.9",
   "description": "Binary state serializer with delta encoding for games",
   "type": "module",
   "bin": {

src/encoding/encode.ts

@@ -192,7 +192,7 @@ function string(bytes: BufferLike, value: string, it: Iterator) {
   // str 8
   else if (length < 0x100) {
     bytes[it.offset++] = 0xd9;
-    bytes[it.offset++] = length % 255;
+    bytes[it.offset++] = length;
     size = 2;
   }
   // str 16

test/Schema.test.ts

@@ -299,6 +299,26 @@ describe("Type: Schema", () => {
             assert.strictEqual(decoded.longstring, longstring);
         });
 
+        it("string with exactly 255 UTF-8 bytes", () => {
+            class Data extends Schema {
+                @type("string") str: string;
+                @type("number") num: number;
+            }
+
+            // Create a string that is exactly 255 UTF-8 bytes
+            const str255 = "a".repeat(255);
+            assert.strictEqual(Buffer.byteLength(str255, "utf8"), 255);
+
+            let data = new Data();
+            data.str = str255;
+            data.num = 42;
+
+            const decoded = new Data();
+            decoded.decode(data.encode());
+            assert.strictEqual(decoded.str, str255);
+            assert.strictEqual(decoded.num, 42);
+        });
+
         it("bigints", () => {
             class Data extends Schema {
                 @type("biguint64") u64: bigint;