5 is passing 🎉

5.ts

@@ -0,0 +1,82 @@
+import { BufReader } from "https://deno.land/std@0.157.0/io/buffer.ts";
+import { copy } from "https://deno.land/std@0.156.0/streams/conversion.ts";
+
+const PORT = 5588;
+const PROXY_CHAT_SERVER = "chat.protohackers.com";
+const PROXY_CHAT_PORT = 16963;
+const TONYS_ADDRESS = "7YWHMfk9JZe0LM0g1ZauHuiSxhI";
+
+const tEnc = new TextEncoder();
+
+console.log(`Starting TCP listener on on 0.0.0.0:${PORT}`);
+
+async function chatSession(conn: Deno.Conn) {
+  const proxy = await Deno.connect({
+    hostname: PROXY_CHAT_SERVER,
+    port: PROXY_CHAT_PORT,
+  });
+
+  const closeOnDisconnect = () => {
+    console.warn("Disconnected client");
+    try {
+      proxy.close();
+    } catch (err) {
+      console.error("Error closing proxy connection:", err);
+    }
+    try {
+      conn.close();
+    } catch (err) {
+      console.error("Error closing client connection:", err);
+    }
+  };
+
+  rewriteMessages(conn, proxy).catch((e) => e).finally(closeOnDisconnect);
+  rewriteMessages(proxy, conn).catch((e) => e).finally(closeOnDisconnect);
+}
+
+const chatCommands = (reader: Deno.Conn) => ({
+  async *[Symbol.asyncIterator]() {
+    let s = await BufReader.create(reader).readString("\n");
+    if (!s) return;
+    while (s) {
+      console.log(s);
+      yield s;
+      s = await BufReader.create(reader).readString("\n");
+    }
+  },
+});
+
+async function rewriteMessages(reader: Deno.Conn, writer: Deno.Conn) {
+  try {
+    for await (const rawLine of chatCommands(reader)) {
+      if (!rawLine || !rawLine.endsWith("\n")) throw "incomplete chat command";
+      const line = rawLine.trim();
+      console.debug("Line:", line);
+      await writer.write(tEnc.encode(replaceAddresses(line) + "\n"));
+    }
+  } catch (err) {
+    console.error("Error reading line:", err, { ...err });
+    throw err;
+  }
+}
+
+function replaceAddresses(text: string): string {
+  const result = text.split(" ").map((word) => replaceAddress(word)).join(" ");
+  if (result != text) console.debug("replaced text:", result);
+  return result;
+}
+
+function replaceAddress(word: string): string {
+  const result = word.replace(
+    /^7\w{25,34}$/i,
+    TONYS_ADDRESS,
+  );
+  if (word != result) console.debug("word:", word, "replaced:", result);
+  return result;
+}
+
+for await (const conn of Deno.listen({ port: PORT })) {
+  console.log("Connection established:", conn.remoteAddr);
+  chatSession(conn);
+  console.log("Connection closed:", conn.remoteAddr);
+}