Use LEB128 encoding for all integer values in ALiS

asciinema · Jan 28, 2025 · 6163d02 · 6163d02
1 parent 5dab60d
commit 6163d02
Showing 1 changed file with 27 additions and 49 deletions.
diff --git a/src/driver/websocket/alis.js b/src/driver/websocket/alis.js
@@ -17,16 +17,16 @@ function alisHandler(logger) {
   }
 
   function parseInitFrame(buffer) {
-    const view = new DataViewReader(new DataView(buffer));
+    const view = new BinaryReader(new DataView(buffer));
     const type = view.getUint8();
 
     if (type !== 0x01) throw `expected init (0x01) frame, got ${type}`;
 
-    let time = decodeRelTime(view);
+    let time = view.decodeVarUint();
     lastEventTime = time;
     time = time / ONE_SEC_IN_USEC;
-    const cols = view.getUint16();
-    const rows = view.getUint16();
+    const cols = view.decodeVarUint();
+    const rows = view.decodeVarUint();
     const themeFormat = view.getUint8();
     let theme;
 
@@ -44,7 +44,7 @@ function alisHandler(logger) {
       return;
     }
 
-    const initLen = view.getUint32();
+    const initLen = view.decodeVarUint();
 
     let init;
 
@@ -65,38 +65,38 @@ function alisHandler(logger) {
   }
 
   function parseEventFrame(buffer) {
-    const view = new DataViewReader(new DataView(buffer));
+    const view = new BinaryReader(new DataView(buffer));
     const type = view.getUint8();
 
     if (type === 0x6f) {
       // 'o' - output
-      const relTime = decodeRelTime(view);
+      const relTime = view.decodeVarUint();
       lastEventTime += relTime;
-      const len = view.getUint32();
+      const len = view.decodeVarUint();
       const text = outputDecoder.decode(new Uint8Array(buffer, view.offset, len));
 
       return [lastEventTime / ONE_SEC_IN_USEC, "o", text];
     } else if (type === 0x69) {
       // 'i' - input
-      const relTime = decodeRelTime(view);
+      const relTime = view.decodeVarUint();
       lastEventTime += relTime;
-      const len = view.getUint32();
+      const len = view.decodeVarUint();
       const text = inputDecoder.decode(new Uint8Array(buffer, view.offset, len));
 
       return [lastEventTime / ONE_SEC_IN_USEC, "i", text];
     } else if (type === 0x72) {
       // 'r' - resize
-      const relTime = decodeRelTime(view);
+      const relTime = view.decodeVarUint();
       lastEventTime += relTime;
-      const cols = view.getUint16();
-      const rows = view.getUint16();
+      const cols = view.decodeVarUint();
+      const rows = view.decodeVarUint();
 
       return [lastEventTime / ONE_SEC_IN_USEC, "r", { cols, rows }];
     } else if (type === 0x6d) {
       // 'm' - marker
-      const relTime = decodeRelTime(view);
+      const relTime = view.decodeVarUint();
       lastEventTime += relTime;
-      const len = view.getUint32();
+      const len = view.decodeVarUint();
       const decoder = new TextDecoder();
       const text = decoder.decode(new Uint8Array(buffer, view.offset, len));
 
@@ -115,22 +115,6 @@ function alisHandler(logger) {
   };
 }
 
-function decodeRelTime(view) {
-  const size = view.getUint8();
-
-  if (size === 1) {
-    return view.getUint8();
-  } else if (size === 2) {
-    return view.getUint16();
-  } else if (size === 4) {
-    return view.getUint32();
-  } else if (size === 8) {
-    return Number(view.getBigUint64());
-  } else {
-    throw `alis: invalid relative time size: ${size}`;
-  }
-}
-
 function parseTheme(arr) {
   const colorCount = arr.length / 3;
   const foreground = hexColor(arr[0], arr[1], arr[2]);
@@ -152,7 +136,7 @@ function byteToHex(value) {
   return value.toString(16).padStart(2, "0");
 }
 
-class DataViewReader {
+class BinaryReader {
   constructor(inner, offset = 0) {
     this.inner = inner;
     this.offset = offset;
@@ -169,25 +153,19 @@ class DataViewReader {
     return value;
   }
 
-  getUint16() {
-    const value = this.inner.getUint16(this.offset, true);
-    this.offset += 2;
-
-    return value;
-  }
-
-  getUint32() {
-    const value = this.inner.getUint32(this.offset, true);
-    this.offset += 4;
-
-    return value;
-  }
+  decodeVarUint() {
+    let number = 0;
+    let shift = 0;
+    let byte = this.getUint8();
 
-  getBigUint64() {
-    const value = this.inner.getBigUint64(this.offset, true);
-    this.offset += 8;
+    while (byte > 127) {
+      byte &= 127;
+      number += (byte << shift);
+      shift += 7;
+      byte = this.getUint8();
+    }
 
-    return value;
+    return number + (byte << shift);
   }
 }