Misc. fixes (#267)

* Misc. fixes

- Do not expose 'username' to a potential recipient.
- Make 'from' mandatory, because there is no fallback anymore.
- Validate 'from' to make shure, it contains an email address.
- Avoid namespace pollution: Use let instead of var.

* Suggested changes from codereview

README.md

@@ -39,10 +39,11 @@ Some features:
     password: ${{secrets.MAIL_PASSWORD}}
     # Required mail subject:
     subject: Github Actions job result
-    # Required recipients' addresses:
+    # Optional recipients' addresses:
     to: obiwan@example.com,yoda@example.com
-    # Required sender full name (address can be skipped):
-    from: Luke Skywalker # <user@example.com>
+    # Required sender (Either: "Plain Simple Name <user@doma.in>" or just "user@doma.in" (without the <>))
+    # Important: '<' and '>' are special chars in yaml. Therefore this string should be quoted
+    from: 'Luke Skywalker <user@example.com>'
     # Optional plain body:
     body: Build job of ${{github.repository}} completed successfully!
     # Optional HTML body read from file:

action.yml

@@ -25,7 +25,7 @@ inputs:
     description: Recipients mail addresses (separated with comma)
     required: false
   from:
-    description: Full name of mail sender (might be with an email address specified in <>)
+    description: 'Either a plain email address, or full name of the sender, followed by whitespace, followed by email address enclosed in <>'
     required: true
   body:
     description: Body of mail message (might be a filename prefixed with file:// to read from)

main.js

@@ -23,14 +23,6 @@ function getText(textOrFile, convertMarkdown) {
     return text;
 }
 
-function getFrom(from, username) {
-    if (from.match(/.+ <.+@.+>/)) {
-        return from;
-    }
-
-    return `"${from}" <${username}>`;
-}
-
 async function getAttachments(attachments) {
     const globber = await glob.create(attachments.split(",").join("\n"));
     const files = await globber.glob();
@@ -117,6 +109,12 @@ async function main() {
         const envelopeTo = core.getInput("envelope_to", { required: false });
         const headers = core.getInput("headers", { required: false });
 
+        // Basic check for an email sender address
+        // Either: "Plain Simple Name <user@doma.in>" or just "user@doma.in" (without the <>)
+        if (!(/^([^<>@\s]+\s+)+<[^@\s>]+@[^@\s>]+>$/.test(from) || /^[^<>@\s]+@[^@\s<>]+$/.test(from))) {
+            throw new Error("'from' address is invalid");
+        }
+
         // if neither to, cc or bcc is provided, throw error
         if (!to && !cc && !bcc) {
             throw new Error(
@@ -150,11 +148,11 @@ async function main() {
             proxy: process.env.HTTP_PROXY,
         });
 
-        var i = 1;
+        let i = 1;
         while (true) {
             try {
                 const info = await transport.sendMail({
-                    from: getFrom(from, username),
+                    from: from,
                     to: to,
                     subject: getText(subject, false),
                     cc: cc ? cc : undefined,