1 files changed, 130 insertions, 0 deletions
diff --git a/deno/mail-relay/dumb-smtp-server.ts b/deno/mail-relay/dumb-smtp-server.ts
new file mode 100644
index 0000000..ac7069c
--- /dev/null
+++ b/deno/mail-relay/dumb-smtp-server.ts
@@ -0,0 +1,130 @@
+import { MailDeliverer } from "./mail.ts";
+
+const CRLF = "\r\n";
+
+function createResponses(host: string, port: number | string) {
+  const serverName = `[${host}]:${port}`;
+  return {
+    serverName,
+    READY: `220 ${serverName} SMTP Ready`,
+    EHLO: `250 ${serverName}`,
+    MAIL: "250 2.1.0 Sender OK",
+    RCPT: "250 2.1.5 Recipient OK",
+    DATA: "354 Start mail input; end with <CRLF>.<CRLF>",
+    QUIT: `211 2.0.0 ${serverName} closing connection`,
+    INVALID: "500 5.5.1 Error: command not recognized",
+  } as const;
+}
+
+const LOG_TAG = "[dumb-smtp]";
+
+export class DumbSmtpServer {
+  #deliverer;
+  #responses: ReturnType<typeof createResponses> = createResponses(
+    "invalid",
+    "invalid",
+  );
+
+  constructor(deliverer: MailDeliverer) {
+    this.#deliverer = deliverer;
+  }
+
+  async #handleConnection(conn: Deno.Conn) {
+    using disposeStack = new DisposableStack();
+    disposeStack.defer(() => {
+      console.info(LOG_TAG, "Close session's tcp connection.");
+      conn.close();
+    });
+
+    console.info(LOG_TAG, "New session's tcp connection established.");
+
+    const writer = conn.writable.getWriter();
+    disposeStack.defer(() => writer.releaseLock());
+    const reader = conn.readable.getReader();
+    disposeStack.defer(() => reader.releaseLock());
+
+    const [decoder, encoder] = [new TextDecoder(), new TextEncoder()];
+    const decode = (data: Uint8Array) => decoder.decode(data);
+    const send = async (s: string) => {
+      console.info(LOG_TAG, "Send line: " + s);
+      await writer.write(encoder.encode(s + CRLF));
+    };
+
+    let buffer: string = "";
+    let rawMail: string | null = null;
+
+    await send(this.#responses["READY"]);
+
+    while (true) {
+      const { value, done } = await reader.read();
+      if (done) break;
+
+      buffer += decode(value);
+
+      while (true) {
+        const eolPos = buffer.indexOf(CRLF);
+        if (eolPos === -1) break;
+
+        const line = buffer.slice(0, eolPos);
+        buffer = buffer.slice(eolPos + CRLF.length);
+
+        if (rawMail == null) {
+          console.info(LOG_TAG, "Received line: " + line);
+          const upperLine = line.toUpperCase();
+          if (upperLine.startsWith("EHLO") || upperLine.startsWith("HELO")) {
+            await send(this.#responses["EHLO"]);
+          } else if (upperLine.startsWith("MAIL FROM:")) {
+            await send(this.#responses["MAIL"]);
+          } else if (upperLine.startsWith("RCPT TO:")) {
+            await send(this.#responses["RCPT"]);
+          } else if (upperLine === "DATA") {
+            await send(this.#responses["DATA"]);
+            console.info(LOG_TAG, "Begin to receive mail data...");
+            rawMail = "";
+          } else if (upperLine === "QUIT") {
+            await send(this.#responses["QUIT"]);
+            return;
+          } else {
+            console.warn(LOG_TAG, "Unrecognized command from client: " + line);
+            await send(this.#responses["INVALID"]);
+            return;
+          }
+        } else {
+          if (line === ".") {
+            try {
+              console.info(LOG_TAG, "Mail data Received, begin to relay...");
+              const { message } = await this.#deliverer.deliverRaw(rawMail);
+              await send(`250 2.6.0 ${message}`);
+              rawMail = null;
+              console.info(LOG_TAG, "Relay succeeded.");
+            } catch (err) {
+              console.error(LOG_TAG, "Relay failed.", err);
+              await send("554 5.3.0 Error: check server log");
+              return;
+            }
+          } else {
+            const dataLine = line.startsWith("..") ? line.slice(1) : line;
+            rawMail += dataLine + CRLF;
+          }
+        }
+      }
+    }
+  }
+
+  async serve(options: { hostname: string; port: number }) {
+    const listener = Deno.listen(options);
+    this.#responses = createResponses(options.hostname, options.port);
+    console.info(
+      LOG_TAG,
+      `Dumb SMTP server starts to listen on ${this.#responses.serverName}.`,
+    );
+
+    for await (const conn of listener) {
+      try {
+        await this.#handleConnection(conn);
+      } catch (cause) {
+        console.error(LOG_TAG, "Tcp connection throws an error.", cause);
+      }
+    }
+  }
+}