feat: add custom header support (closes #22) (#23)

* feat: add custom header support (closes #22)

* deno fmt, lint

README.md

@@ -274,11 +274,16 @@ export interface SendConfig {
    * allowes preprocessors to hande different email types
    */
   internalTag?: string | symbol;
+  headers: Record<string, string>;
 }
 ```
 
 All of it should be clear by name except:
 
+#### headers
+
+Add custom headers to the email.
+
 #### mimeContent
 
 There are use cases where you want to do encoding etc. on your own. This option

client/basic/client.ts

@@ -143,6 +143,13 @@ export class SMTPClient {
 
       await this.#connection.writeCmd("Date: ", config.date);
 
+      const obj = Object.entries(config.headers);
+
+      for (let i = 0; i < obj.length; i++) {
+        const [name, value] = obj[i];
+        await this.#connection.writeCmd(name + ": ", value);
+      }
+
       if (config.inReplyTo) {
         await this.#connection.writeCmd("InReplyTo: ", config.inReplyTo);
       }

config/mail/headers.ts

@@ -0,0 +1,13 @@
+export interface Headers {
+  [headerName: string]: string;
+}
+
+export function validateHeaders(
+  headers: Headers,
+) {
+  return !(Object.keys(headers).some((v) =>
+    v.includes("\n") || v.includes("\r")
+  ) || Object.values(headers).some((v) =>
+    v.includes("\n") || v.includes("\r")
+  ));
+}

config/mail/mod.ts

@@ -13,7 +13,7 @@ import {
   validateEmailList,
 } from "./email.ts";
 import { ResolvedClientOptions } from "../client.ts";
-
+import { Headers, validateHeaders } from "./headers.ts";
 /**
  * Config for a mail
  */
@@ -37,6 +37,7 @@ export interface SendConfig {
    * allowes preprocessors to hande different email types
    */
   internalTag?: string | symbol;
+  headers?: Headers;
 }
 
 export interface ResolvedSendConfig {
@@ -53,6 +54,7 @@ export interface ResolvedSendConfig {
   priority?: "high" | "normal" | "low";
   attachments: ResolvedAttachment[];
   internalTag?: string | symbol;
+  headers: Headers;
 }
 
 export function resolveSendConfig(config: SendConfig): ResolvedSendConfig {
@@ -72,6 +74,7 @@ export function resolveSendConfig(config: SendConfig): ResolvedSendConfig {
     priority,
     attachments,
     internalTag,
+    headers,
   } = config;
 
   return {
@@ -94,6 +97,7 @@ export function resolveSendConfig(config: SendConfig): ResolvedSendConfig {
     references,
     priority,
     internalTag,
+    headers: headers ?? ({} as Headers),
   };
 }
 
@@ -160,6 +164,10 @@ export function validateConfig(
     warn.push("You should provide at least html or text content!");
   }
 
+  if (!validateHeaders(config.headers)) {
+    errors.push(`Headers are not allowed to include linebreaks!`);
+  }
+
   if (client.client.warning === "log" && warn.length > 0) {
     console.warn(warn.join("\n"));
   }