1 files changed, 308 insertions, 0 deletions
diff --git a/services/docker/mail-server/relay/mail.ts b/services/docker/mail-server/relay/mail.ts
new file mode 100644
index 0000000..08335ed
--- /dev/null
+++ b/services/docker/mail-server/relay/mail.ts
@@ -0,0 +1,308 @@
+import { encodeBase64 } from "@std/encoding/base64";
+import { parse } from "@std/csv/parse";
+import emailAddresses from "email-addresses";
+
+import { log, warn } from "./logger.ts";
+import { getConfigValue } from "./config.ts";
+
+class MailParseError extends Error {
+  constructor(
+    message: string,
+    public readonly mail: Mail,
+    public readonly lineNumber?: number,
+    options?: ErrorOptions,
+  ) {
+    if (lineNumber != null) message += `(at line ${lineNumber})`;
+    super(message, options);
+  }
+}
+
+interface ParsedMail {
+  sections: {
+    header: string;
+    body: string;
+  };
+  /**
+   * The empty line between headers and body.
+   */
+  sep: string;
+  eol: string;
+}
+
+export class Mail {
+  date?: Date;
+  messageId?: string;
+  deliverMessage?: string;
+
+  constructor(public raw: string) {}
+
+  toUtf8Bytes(): Uint8Array {
+    const utf8Encoder = new TextEncoder();
+    return utf8Encoder.encode(this.raw);
+  }
+
+  toBase64(): string {
+    return encodeBase64(this.raw);
+  }
+
+  simpleParse(): ParsedMail {
+    const twoEolMatch = this.raw.match(/(\r?\n)(\r?\n)/);
+    if (twoEolMatch == null) {
+      throw new MailParseError(
+        "No header/body section separator (2 successive EOLs) found.",
+        this,
+      );
+    }
+
+    const [eol, sep] = [twoEolMatch[1], twoEolMatch[2]];
+
+    if (eol !== sep) {
+      warn("Different EOLs (\\r\\n, \\n) found.");
+    }
+
+    return {
+      sections: {
+        header: this.raw.slice(0, twoEolMatch.index!),
+        body: this.raw.slice(twoEolMatch.index! + eol.length + sep.length),
+      },
+      sep,
+      eol,
+    };
+  }
+
+  simpleParseHeaders(): [key: string, value: string][] {
+    const { sections } = this.simpleParse();
+    const headers: [string, string][] = [];
+
+    let field: string | null = null;
+    let lineNumber = 1;
+
+    const handleField = () => {
+      if (field == null) return;
+      const sepPos = field.indexOf(":");
+      if (sepPos === -1) {
+        throw new MailParseError(
+          "No ':' in the header field.",
+          this,
+          lineNumber,
+        );
+      }
+      headers.push([field.slice(0, sepPos).trim(), field.slice(sepPos + 1)]);
+      field = null;
+    };
+
+    for (const line of sections.header.trimEnd().split(/\r?\n|\r/)) {
+      if (line.match(/^\s/)) {
+        if (field == null) {
+          throw new MailParseError(
+            "Header field starts with a space.",
+            this,
+            lineNumber,
+          );
+        }
+        field += line;
+      } else {
+        handleField();
+        field = line;
+      }
+      lineNumber += 1;
+    }
+
+    handleField();
+
+    return headers;
+  }
+
+  simpleParseDate<T = undefined>(
+    invalidValue: T | undefined = undefined,
+  ): Date | T | undefined {
+    const headers = this.simpleParseHeaders();
+    for (const [key, value] of headers) {
+      if (key.toLowerCase() === "date") {
+        const date = new Date(value);
+        if (isNaN(date.getTime())) {
+          warn(`Invalid date string (${value}) found in header.`);
+          return invalidValue;
+        }
+        return date;
+      }
+    }
+    return undefined;
+  }
+
+  simpleParseReceipts(
+    options?: { domain?: string; headers?: string[] },
+  ): Set<string> {
+    const domain = options?.domain;
+    const headers = options?.headers ?? ["to", "cc", "bcc", "x-original-to"];
+    const receipts = new Set<string>();
+    for (const [key, value] of this.simpleParseHeaders()) {
+      if (headers.includes(key.toLowerCase())) {
+        emailAddresses.parseAddressList(value)?.flatMap((a) =>
+          a.type === "mailbox" ? a.address : a.addresses.map((a) => a.address)
+        )?.forEach((a) => {
+          if (domain == null || a.endsWith(domain)) {
+            receipts.add(a);
+          }
+        });
+      }
+    }
+    return receipts;
+  }
+
+  // TODO: Add folding.
+  appendHeaders(headers: [key: string, value: string][]) {
+    const { sections, sep, eol } = this.simpleParse();
+
+    this.raw = sections.header + eol +
+      headers.map(([k, v]) => `${k}: ${v}`).join(eol) + eol + sep +
+      sections.body;
+  }
+}
+
+export type MailDeliverResultKind = "done" | "fail" | "retry";
+
+export interface MailDeliverReceiptResult {
+  kind: MailDeliverResultKind;
+  message: string;
+  cause?: unknown;
+}
+
+export class MailDeliverResult {
+  readonly receipts: Map<string, MailDeliverReceiptResult> = new Map();
+
+  add(
+    receipt: string,
+    kind: MailDeliverResultKind,
+    message: string,
+    cause?: unknown,
+  ) {
+    this.receipts.set(receipt, { kind, message, cause });
+  }
+
+  set(receipt: string, result: MailDeliverReceiptResult) {
+    this.receipts.set(receipt, result);
+  }
+
+  [Symbol.for("Deno.customInspect")]() {
+    return [
+      ...this.receipts.entries().map(([receipt, result]) =>
+        `${receipt}[${result.kind}]: ${result.message}`
+      ),
+    ].join("\n");
+  }
+}
+
+export class MailDeliverContext {
+  readonly receipts: Set<string> = new Set();
+  readonly result: MailDeliverResult = new MailDeliverResult();
+
+  constructor(public mail: Mail) {}
+}
+
+export interface MailDeliverHook {
+  callback(context: MailDeliverContext): Promise<void>;
+}
+
+export abstract class MailDeliverer {
+  abstract readonly name: string;
+  preHooks: MailDeliverHook[] = [];
+  postHooks: MailDeliverHook[] = [];
+
+  protected abstract doDeliver(
+    mail: Mail,
+    context: MailDeliverContext,
+  ): Promise<void>;
+
+  async deliverRaw(rawMail: string): Promise<Mail> {
+    const mail = new Mail(rawMail);
+    await this.deliver(mail);
+    return mail;
+  }
+
+  async deliver(mail: Mail): Promise<MailDeliverResult> {
+    log(`Begin to deliver mail via ${this.name}...`);
+
+    const context = new MailDeliverContext(mail);
+
+    for (const hook of this.preHooks) {
+      await hook.callback(context);
+    }
+
+    await this.doDeliver(context.mail, context);
+
+    for (const hook of this.postHooks) {
+      await hook.callback(context);
+    }
+
+    log("Deliver result:", context.result);
+
+    if (context.result.receipts.values().some((r) => r.kind !== "done")) {
+      throw new Error("Mail failed to deliver.");
+    }
+
+    return context.result;
+  }
+}
+
+export class ReceiptsFromHeadersHook implements MailDeliverHook {
+  callback(context: MailDeliverContext) {
+    if (context.receipts.size !== 0) {
+      warn("Receipts are already filled. Won't set them with ones in headers.");
+    } else {
+      context.mail.simpleParseReceipts({
+        domain: getConfigValue("mailDomain"),
+      }).forEach((r) => context.receipts.add(r));
+
+      if (context.receipts.size === 0) {
+        warn("No receipts found from mail headers.");
+      }
+    }
+    return Promise.resolve();
+  }
+}
+
+export class FallbackReceiptsHook implements MailDeliverHook {
+  constructor(public fallback: Set<string> = new Set()) {}
+
+  callback(context: MailDeliverContext) {
+    if (context.receipts.size === 0) {
+      log(`No receipts, fill with fallback ${[...this.fallback].join(" ")}.`);
+      this.fallback.forEach((a) => context.receipts.add(a));
+    }
+    return Promise.resolve();
+  }
+}
+
+export class AliasFileMailHook implements MailDeliverHook {
+  #aliasFile;
+
+  constructor(aliasFile: string) {
+    this.#aliasFile = aliasFile;
+  }
+
+  async #parseAliasFile(): Promise<Map<string, string>> {
+    const result = new Map();
+    if ((await Deno.stat(this.#aliasFile)).isFile) {
+      log(`Found receipts alias file: ${this.#aliasFile}.`);
+      const text = await Deno.readTextFile(this.#aliasFile);
+      const csv = parse(text);
+      for (const [real, ...aliases] of csv) {
+        aliases.forEach((a) => result.set(a, real));
+      }
+    }
+    return result;
+  }
+
+  async callback(context: MailDeliverContext) {
+    const aliases = await this.#parseAliasFile();
+    for (const receipt of [...context.receipts]) {
+      const realReceipt = aliases.get(receipt);
+      if (realReceipt != null) {
+        log(`Receipt alias resolved: ${receipt} => ${realReceipt}.`);
+        context.receipts.delete(receipt);
+        context.receipts.add(realReceipt);
+      }
+    }
+  }
+}