fix: Support encoding map-as-arrays

false-spring · false-spring · commit 3cf5d2d77d9d · 2024-04-03T22:22:08.000-07:00
diff --git a/src/Encoder.ts b/src/Encoder.ts
@@ -297,7 +297,19 @@ export class Encoder<ContextType = undefined> {
     if (ext != null) {
       this.encodeExtension(ext);
     } else if (Array.isArray(object)) {
-      this.encodeArray(object, depth);
+      // We need to peek the first element to determine if it's an array or a map.
+      const firstElement = object[0];
+
+      if (
+        firstElement != null &&
+        typeof firstElement === "object" &&
+        "key" in firstElement &&
+        "value" in firstElement
+      ) {
+        this.encodeMapArray(object as [{ key: string | number; value: unknown }], depth);
+      } else {
+        this.encodeArray(object, depth);
+      }
     } else if (ArrayBuffer.isView(object)) {
       this.encodeBinary(object);
     } else if (typeof object === "object") {
@@ -350,18 +362,6 @@ export class Encoder<ContextType = undefined> {
     }
   }
 
-  private countWithoutUndefined(object: Record<string, unknown>, keys: ReadonlyArray<string>): number {
-    let count = 0;
-
-    for (const key of keys) {
-      if (object[key] !== undefined) {
-        count++;
-      }
-    }
-
-    return count;
-  }
-
   private encodeMap(object: Record<string, unknown>, depth: number) {
     const keys = Object.keys(object);
     if (this.sortKeys) {
@@ -395,6 +395,39 @@ export class Encoder<ContextType = undefined> {
     }
   }
 
+  private encodeMapArray(object: [{ key: string | number; value: unknown }], depth: number) {
+    const keys = object.map((pair) => pair.key);
+    if (this.sortKeys) {
+      keys.sort();
+    }
+
+    const size = keys.length;
+
+    if (size < 16) {
+      // fixmap
+      this.writeU8(0x80 + size);
+    } else if (size < 0x10000) {
+      // map 16
+      this.writeU8(0xde);
+      this.writeU16(size);
+    } else if (size < 0x100000000) {
+      // map 32
+      this.writeU8(0xdf);
+      this.writeU32(size);
+    } else {
+      throw new Error(`Too large map object: ${size}`);
+    }
+
+    for (const pair of object) {
+      const value = pair.value;
+
+      if (!(this.ignoreUndefined && value === undefined)) {
+        this.encodeString(pair.key.toString());
+        this.doEncode(value, depth + 1);
+      }
+    }
+  }
+
   private encodeExtension(ext: ExtData) {
     const size = ext.data.length;
     if (size === 1) {
