initial commit

lib/varint.js

@@ -0,0 +1,90 @@
+// https://wiki.vg/Data_types
+
+const varint = {
+    encodeInt: (val) => {
+        // "constInts are never longer than 5 bytes"
+        // https://wiki.vg/Data_types#constInt_and_constLong
+        const buf = Buffer.alloc(5);
+        let written = 0;
+
+        while (true) {
+            if ((val & 0xFFFFFF80) === 0) {
+                buf.writeUInt8(val, written++);
+                break;
+            } else {
+                buf.writeUInt8(val & 0x7F | 0x80, written++);
+                val >>>= 7;
+            }
+        }
+
+        return buf.slice(0, written);
+    },
+
+    encodeString: (val) => {
+        return Buffer.from(val, 'utf-8');
+    },
+
+    encodeUShort: (val) => {
+        return Buffer.from([val >> 8, val & 0xFF]);
+    },
+
+    concat: (chunks) => {
+        let length = 0;
+
+        for (const chunk of chunks) {
+            length += chunk.length;
+        }
+
+        const buffer = [
+            varint.encodeInt(length),
+            ...chunks
+        ];
+
+        return Buffer.concat(buffer);
+    },
+
+    decodeInt: (buffer, offset) => {
+        let val = 0;
+        let count = 0;
+
+        while (true) {
+            const b = buffer.readUInt8(offset++);
+
+            val |= (b & 0x7F) << count++ * 7;
+
+            if ((b & 0x80) != 128) {
+                break;
+            }
+        }
+
+        return val;
+    },
+
+    // The number of bytes that the last .decodeInt() call had to use to decode.
+    decodeLength: (val) => {
+        const N1 = Math.pow(2, 7);
+        const N2 = Math.pow(2, 14);
+        const N3 = Math.pow(2, 21);
+        const N4 = Math.pow(2, 28);
+        const N5 = Math.pow(2, 35);
+        const N6 = Math.pow(2, 42);
+        const N7 = Math.pow(2, 49);
+        const N8 = Math.pow(2, 56);
+        const N9 = Math.pow(2, 63);
+
+        return (
+            val < N1 ? 1
+                : val < N2 ? 2
+                    : val < N3 ? 3
+                        : val < N4 ? 4
+                            : val < N5 ? 5
+                                : val < N6 ? 6
+                                    : val < N7 ? 7
+                                        : val < N8 ? 8
+                                            : val < N9 ? 9
+                                                : 10
+        );
+    }
+};
+
+export default varint;