Cannot parse messages without a session

[OrangeDog]

Describe the bug
It used to be the case that you could parse MimeMessages without any session, for an application that doesn't need to send or receive email itself.

This ability has been lost at some point in the migration from com.sun.mail to org.eclipse.angus.

To Reproduce
This code works if using com.sun.mail:mailapi:2.0.1:

String text = """
    From: user@example.com\r
    To: user@example.com\r
    Subject: Testing\r
    Date: Thu, 01 Jul 2021 12:11:25 +0000 (UTC)\r
    Content-Type: text/plain\r
    \r
    Best ever test content.\r
    """;
InputStream inputStream = new ByteArrayInputStream(text.getBytes())
MimeMessage mimeMessage = new MimeMessage(null, inputStream);
mimeMessage.getContent();

If using org.eclipse.angus:jakarta.mail:2.0.2 it throws:

jakarta.mail.MessagingException: No inputstream from datasource
;
  nested exception is:
	java.lang.NullPointerException: Cannot invoke "jakarta.mail.Session.getStreamProvider()" because "this.session" is null
	at jakarta.mail.internet.MimeMultipart.parse(MimeMultipart.java:586)
	at jakarta.mail.internet.MimeMessage.getContent(MimeMessage.java:1522)
	at com.example.Test.test(Test.java:28)

Expected behavior
A session only being necessary if connecting to a server of some kind. Code compatibility with older releases.

Additional information

• org.eclipse.angus:jakarta.mail:1.0.0 throws the same exception
• jakarta.mail:jakarta.mail-api:2.1.2 throws java.lang.IllegalStateException: Not provider of jakarta.mail.util.StreamProvider was found [sic]
• jakarta.mail:jakarta.mail-api:2.0.1 throws java.lang.NoClassDefFoundError: com/sun/mail/util/FolderClosedIOException
• com.sun.mail:jakarta.mail:2.0.1 works successfully

[OrangeDog]

Using an "empty" session appears to work. It doesn't appear to try to connect to anything with the example above.

Session session = Session.getInstance(new Properties());

[jmehrens]

For jakarta.mail:jakarta.mail-api:2.1.2 it looks like you are missing the Angus dependencies.

There are 4 jars that have to be added:
angus-activation-XXX.jar,
angus-mail-XXX.jar
jakarta.mail-api-XXX.jar
jakarta.activation-api-XXX.jar

The "java.lang.IllegalStateException: Not provider of jakarta.mail.util.StreamProvider" is usually missing dependencies.
The NullPointerException is a cascading failure. See: jakartaee/mail-api#550 (comment)

If you missing those dependencies in your test case then add them and retest.

[OrangeDog]

you are missing the Angus dependencies

My point there is that in the previous version you did not need those dependencies. mailapi was sufficient to parse MIME messages.

[jmehrens]

@OrangeDog Yes I was able to gather that when I dug deeper into the code. My initial understanding was incorrect. Because of that I fixed this. Thank you for reporting this!