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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`,
ACTIVE_CLOSE: "421 4.7.0 Please open a new connection to send more emails",
INVALID: "500 5.5.1 Error: command not recognized",
} as const;
}
export class DumbSmtpServer {
#deliverer;
constructor(deliverer: MailDeliverer) {
this.#deliverer = deliverer;
}
async #handleConnection(
logTag: string,
conn: Deno.Conn,
responses: ReturnType<typeof createResponses>,
) {
using disposeStack = new DisposableStack();
disposeStack.defer(() => {
console.info(logTag, "Close tcp connection.");
conn.close();
});
console.info(logTag, "New 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(logTag, "Send line:", s);
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) {
console.info(logTag, "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"]);
console.info(logTag, "Begin to receive mail data...");
rawMail = "";
} else if (upperLine === "QUIT") {
await send(responses["QUIT"]);
return;
} else {
await send(responses["INVALID"]);
return;
}
} else {
if (line === ".") {
try {
console.info(logTag, "Mail data received, begin to relay...");
const { smtpMessage } = await this.#deliverer.deliverRaw(rawMail);
await send(`250 2.6.0 ${smtpMessage}`);
rawMail = null;
} catch (err) {
console.error(logTag, "Relay failed.", err);
await send("554 5.3.0 Error: check server log");
}
await send(responses["ACTIVE_CLOSE"]);
} else {
const dataLine = line.startsWith("..") ? line.slice(1) : line;
rawMail += dataLine + CRLF;
}
}
}
}
}
async serve(options: { hostname: string; port: number }) {
const listener = Deno.listen(options);
const responses = createResponses(options.hostname, options.port);
console.info(
`Dumb SMTP server starts to listen on ${responses.serverName}.`,
);
let counter = 1;
for await (const conn of listener) {
const logTag = `[outbound ${counter++}]`;
try {
await this.#handleConnection(logTag, conn, responses);
} catch (cause) {
console.error(logTag, "A JS error was thrown by handler:", cause);
}
}
}
}
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