test: implement dnsname encoder

src/dnsname.ts

@@ -0,0 +1,29 @@
+// Adapted from https://github.com/petejkim/ens-dnsname/blob/master/dnsname.go#L59
+export function encode(name: string): Buffer {
+  const trimmed = name.replace(/^\.+|\.+$/g, "");
+
+  // split name into labels
+  const labels = trimmed.split(".").map((l) => Buffer.from(l, "utf8"));
+
+  const encoded = Buffer.alloc(Buffer.from(trimmed, "utf8").byteLength + 2);
+  let offset = 0;
+
+  for (const label of labels) {
+    const l = label.byteLength;
+
+    // length must be less than 64
+    if (l > 63) {
+      throw new Error("label too long");
+    }
+
+    // write length
+    encoded.writeUInt8(l, offset);
+    offset++;
+
+    // write label
+    label.copy(encoded, offset);
+    offset += l;
+  }
+
+  return encoded;
+}

test/dnsname.test.ts

@@ -0,0 +1,26 @@
+import { expect } from "chai";
+import { encode } from "../src/dnsname";
+
+describe("dnsname", () => {
+  describe("encode", () => {
+    it("encodes a given name in the ens-compatible dns wire format", () => {
+      ["test.eth", ".test.eth", "test.eth.", "..test.eth..."].forEach((name) =>
+        expect(encode(name).toString("hex")).to.equal("04746573740365746800")
+      );
+      [
+        ["pete.test.eth", "047065746504746573740365746800"],
+        ["this.is.test.eth", "047468697302697304746573740365746800"],
+        ["example.xyz", "076578616d706c650378797a00"],
+        ["", "0000"],
+      ].forEach((tc) => expect(encode(tc[0]).toString("hex")).to.equal(tc[1]));
+    });
+
+    it("throws an error if a label has greater than 63 characters", () => {
+      expect(() =>
+        encode(
+          "0000000001000000000200000000030000000004000000000500000000061234.eth"
+        )
+      ).to.throw("label too long");
+    });
+  });
+});

tsconfig.json

@@ -18,5 +18,5 @@
   },
   "exclude": ["node_modules"],
   "files": ["./hardhat.config.ts"],
-  "include": ["tasks/**/*", "test/**/*", "types/**/*"]
+  "include": ["tasks/**/*", "test/**/*", "types/**/*", "src/**/*"]
 }