1 files changed, 196 insertions, 0 deletions
diff --git a/deno/mail-relay/mail-parsing.ts b/deno/mail-relay/mail-parsing.ts
new file mode 100644
index 0000000..7e76257
--- /dev/null
+++ b/deno/mail-relay/mail-parsing.ts
@@ -0,0 +1,196 @@
+import emailAddresses from "email-addresses";
+
+class MailSimpleParseError extends Error {}
+
+function lazy<T>(calculator: () => T): () => T {
+  const tag = new Object();
+  let cache: typeof tag | T = tag;
+  return () => {
+    if (cache === tag) cache = calculator();
+    return cache as T;
+  };
+}
+
+class MailSimpleParsedHeaders {
+  #headerSection;
+
+  #headers = lazy(() => {
+    const headers = [] as [key: string, value: string][];
+
+    let field: string | null = null;
+    let lineNumber = 1;
+
+    const handleField = () => {
+      if (field == null) return;
+      const sepPos = field.indexOf(":");
+      if (sepPos === -1) {
+        throw new MailSimpleParseError(`No ':' in the header line: ${field}`);
+      }
+      headers.push([field.slice(0, sepPos).trim(), field.slice(sepPos + 1)]);
+      field = null;
+    };
+
+    for (const line of this.#headerSection.trimEnd().split(/\r?\n|\r/)) {
+      if (line.match(/^\s/)) {
+        if (field == null) {
+          throw new MailSimpleParseError("Header section starts with a space.");
+        }
+        field += line;
+      } else {
+        handleField();
+        field = line;
+      }
+      lineNumber += 1;
+    }
+
+    handleField();
+
+    return headers;
+  });
+
+  #messageId = lazy(() => {
+    const messageIdField = this.#getFirst("message-id");
+    if (messageIdField == null) return undefined;
+
+    const match = messageIdField.match(/\<(.*?)\>/);
+    if (match != null) {
+      return match[1];
+    } else {
+      console.warn("Invalid message-id header of mail: " + messageIdField);
+      return undefined;
+    }
+  });
+
+  #date = lazy(() => {
+    const dateField = this.#getFirst("date");
+    if (dateField == null) return undefined;
+
+    const date = new Date(dateField);
+    if (isNaN(date.getTime())) {
+      console.warn(`Invalid date string (${dateField}) found in header.`);
+      return undefined;
+    }
+    return date;
+  });
+
+  #from = lazy(() => {
+    const fromField = this.#getFirst("from");
+    if (fromField == null) return undefined;
+
+    const addr = emailAddresses.parseOneAddress(fromField);
+    return addr?.type === "mailbox" ? addr.address : undefined;
+  });
+
+  #recipients = lazy(() => {
+    const headers = ["to", "cc", "bcc", "x-original-to"];
+    const recipients = new Set<string>();
+    for (const [key, value] of this.#headers()) {
+      if (headers.includes(key.toLowerCase())) {
+        emailAddresses
+          .parseAddressList(value)
+          ?.flatMap((a) => (a.type === "mailbox" ? a : a.addresses))
+          ?.forEach(({ address }) => recipients.add(address));
+      }
+    }
+    return recipients;
+  });
+
+  constructor(headerSection: string) {
+    this.#headerSection = headerSection;
+  }
+
+  #getFirst(fieldKey: string): string | undefined {
+    for (const [key, value] of this.#headers()) {
+      if (key.toLowerCase() === fieldKey.toLowerCase()) return value;
+    }
+    return undefined;
+  }
+
+  get messageId() {
+    return this.#messageId();
+  }
+  get date() {
+    return this.#date();
+  }
+  get from() {
+    return this.#from();
+  }
+  get recipients() {
+    return this.#recipients();
+  }
+
+  toList(): [string, string][] {
+    return [...this.#headers()];
+  }
+}
+
+class MailSimpleParsed {
+  #raw;
+
+  #sections = lazy(() => {
+    const twoEolMatch = this.#raw.match(/(\r?\n)(\r?\n)/);
+    if (twoEolMatch == null) {
+      throw new MailSimpleParseError(
+        "No header/body section separator (2 successive EOLs) found.",
+      );
+    }
+
+    const [eol, sep] = [twoEolMatch[1], twoEolMatch[2]];
+
+    if (eol !== sep) {
+      console.warn("Different EOLs (\\r\\n, \\n) found.");
+    }
+
+    return {
+      header: this.#raw.slice(0, twoEolMatch.index!),
+      body: this.#raw.slice(twoEolMatch.index! + eol.length + sep.length),
+      eol,
+      sep,
+    };
+  });
+
+  #headers = lazy(() => {
+    return new MailSimpleParsedHeaders(this.header);
+  });
+
+  constructor(raw: string) {
+    this.#raw = raw;
+  }
+
+  get header() {
+    return this.#sections().header;
+  }
+  get body() {
+    return this.#sections().body;
+  }
+  get sep() {
+    return this.#sections().sep;
+  }
+  get eol() {
+    return this.#sections().eol;
+  }
+
+  get headers() {
+    return this.#headers();
+  }
+
+  get date() {
+    return this.headers.date;
+  }
+
+  get messageId() {
+    return this.headers.messageId;
+  }
+
+  get from() {
+    return this.headers.from;
+  }
+
+  get recipients() {
+    return this.headers.recipients;
+  }
+}
+
+export function simpleParseMail(raw: string): MailSimpleParsed {
+  return new MailSimpleParsed(raw);
+}