1 files changed, 119 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..6c63f5c
--- /dev/null
+++ b/deno/mail-relay/dumb-smtp-server.ts
@@ -0,0 +1,119 @@
+import config from "./config.ts";
+import log from "./log.ts";
+import { MailDeliverer } from "./mail.ts";
+
+const CRLF = "\r\n";
+
+const SERVER_NAME = `[${config.SMTP_HOST}]:${config.SMTP_PORT}`;
+
+const RESPONSES = {
+  "READY": `220 ${SERVER_NAME} SMTP Ready`,
+  "EHLO": `250 ${SERVER_NAME}`,
+  "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 ${SERVER_NAME} closing connection`,
+  "INVALID": "500 5.5.1 Error: command not recognized",
+} as const;
+
+export class DumbSmtpServer {
+  #deliverer: MailDeliverer;
+
+  constructor(deliverer: MailDeliverer) {
+    this.#deliverer = deliverer;
+  }
+
+  async #handleConnection(conn: Deno.Conn) {
+    using disposeStack = new DisposableStack();
+    disposeStack.defer(() => {
+      log.info("Close smtp session tcp connection.");
+      conn.close();
+    });
+    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) =>
+      await writer.write(encoder.encode(s + CRLF));
+
+    let buffer: string = "";
+    let rawMail: string | null = null;
+
+    await send(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) {
+          log.info("Smtp server received line:", line);
+          const upperLine = line.toUpperCase();
+          if (upperLine.startsWith("EHLO") || upperLine.startsWith("HELO")) {
+            await send(RESPONSES["EHLO"]);
+          } else if (upperLine.startsWith("MAIL FROM:")) {
+            await send(RESPONSES["MAIL"]);
+          } else if (upperLine.startsWith("RCPT TO:")) {
+            await send(RESPONSES["RCPT"]);
+          } else if (upperLine === "DATA") {
+            await send(RESPONSES["DATA"]);
+            log.info("Begin to receive mail data...");
+            rawMail = "";
+          } else if (upperLine === "QUIT") {
+            await send(RESPONSES["QUIT"]);
+            return;
+          } else {
+            log.warn("Smtp server command unrecognized:", line);
+            await send(RESPONSES["INVALID"]);
+            return;
+          }
+        } else {
+          if (line === ".") {
+            try {
+              log.info("Done receiving mail data, begin to relay...");
+              const { message } = await this.#deliverer.deliverRaw(rawMail);
+              await send(`250 2.6.0 ${message}`);
+              rawMail = null;
+              log.info("Done SMTP mail session.");
+            } catch (err) {
+              log.info(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() {
+    const listener = Deno.listen({
+      hostname: config.SMTP_HOST,
+      port: config.SMTP_PORT,
+    });
+    listener.unref();
+    log.info(`Dumb SMTP server starts running on port ${config.SMTP_PORT}.`);
+
+    for await (const conn of listener) {
+      try {
+        await this.#handleConnection(conn);
+      } catch (cause) {
+        log.error("One smtp connection session throws an error " + cause);
+      }
+    }
+  }
+}