something is working

node_modules/bson/src/validate_utf8.ts

@@ -0,0 +1,47 @@
+const FIRST_BIT = 0x80;
+const FIRST_TWO_BITS = 0xc0;
+const FIRST_THREE_BITS = 0xe0;
+const FIRST_FOUR_BITS = 0xf0;
+const FIRST_FIVE_BITS = 0xf8;
+
+const TWO_BIT_CHAR = 0xc0;
+const THREE_BIT_CHAR = 0xe0;
+const FOUR_BIT_CHAR = 0xf0;
+const CONTINUING_CHAR = 0x80;
+
+/**
+ * Determines if the passed in bytes are valid utf8
+ * @param bytes - An array of 8-bit bytes. Must be indexable and have length property
+ * @param start - The index to start validating
+ * @param end - The index to end validating
+ */
+export function validateUtf8(
+  bytes: { [index: number]: number },
+  start: number,
+  end: number
+): boolean {
+  let continuation = 0;
+
+  for (let i = start; i < end; i += 1) {
+    const byte = bytes[i];
+
+    if (continuation) {
+      if ((byte & FIRST_TWO_BITS) !== CONTINUING_CHAR) {
+        return false;
+      }
+      continuation -= 1;
+    } else if (byte & FIRST_BIT) {
+      if ((byte & FIRST_THREE_BITS) === TWO_BIT_CHAR) {
+        continuation = 1;
+      } else if ((byte & FIRST_FOUR_BITS) === THREE_BIT_CHAR) {
+        continuation = 2;
+      } else if ((byte & FIRST_FIVE_BITS) === FOUR_BIT_CHAR) {
+        continuation = 3;
+      } else {
+        return false;
+      }
+    }
+  }
+
+  return !continuation;
+}