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import emailAddresses from "email-addresses";
function parseHeaderSection(section: string) {
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 Error(`Expect ':' in the header field line: ${field}`);
}
headers.push([field.slice(0, sepPos).trim(), field.slice(sepPos + 1)]);
field = null;
};
for (const line of section.trimEnd().split(/\r?\n|\r/)) {
if (line.match(/^\s/)) {
if (field == null) {
throw new Error("Header section starts with a space.");
}
field += line;
} else {
handleField();
field = line;
}
lineNumber += 1;
}
handleField();
return headers;
}
function findFirst(fields: readonly [string, string][], key: string) {
for (const [k, v] of fields) {
if (key.toLowerCase() === k.toLowerCase()) return v;
}
return undefined;
}
function findMessageId(fields: readonly [string, string][]) {
const messageIdField = findFirst(fields, "message-id");
if (messageIdField == null) return undefined;
const match = messageIdField.match(/\<(.*?)\>/);
if (match != null) {
return match[1];
} else {
console.warn(`Invalid syntax in header 'message-id': ${messageIdField}`);
return undefined;
}
}
function findDate(fields: readonly [string, string][]) {
const dateField = findFirst(fields, "date");
if (dateField == null) return undefined;
const date = new Date(dateField);
if (isNaN(date.getTime())) {
console.warn(`Invalid date string in header 'date': ${dateField}`);
return undefined;
}
return date;
}
function findFrom(fields: readonly [string, string][]) {
const fromField = findFirst(fields, "from");
if (fromField == null) return undefined;
const addr = emailAddresses.parseOneAddress(fromField);
return addr?.type === "mailbox" ? addr.address : undefined;
}
function findRecipients(fields: readonly [string, string][]) {
const headers = ["to", "cc", "bcc", "x-original-to"];
const recipients = new Set<string>();
for (const [key, value] of fields) {
if (headers.includes(key.toLowerCase())) {
emailAddresses
.parseAddressList(value)
?.flatMap((a) => (a.type === "mailbox" ? a : a.addresses))
?.forEach(({ address }) => recipients.add(address));
}
}
return recipients;
}
function parseSections(raw: string) {
const twoEolMatch = raw.match(/(\r?\n)(\r?\n)/);
if (twoEolMatch == null) {
throw new Error(
"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: raw.slice(0, twoEolMatch.index!),
body: raw.slice(twoEolMatch.index! + eol.length + sep.length),
eol,
sep,
};
}
export type ParsedMail = Readonly<{
header: string;
body: string;
sep: string;
eol: string;
headers: readonly [string, string][];
messageId: string | undefined;
date: Date | undefined;
from: string | undefined;
recipients: readonly string[];
}>;
export function simpleParseMail(raw: string): ParsedMail {
const sections = Object.freeze(parseSections(raw));
const headers = Object.freeze(parseHeaderSection(sections.header));
const messageId = findMessageId(headers);
const date = findDate(headers);
const from = findFrom(headers);
const recipients = Object.freeze([...findRecipients(headers)]);
return Object.freeze({
...sections,
headers,
messageId,
date,
from,
recipients,
});
}
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