[EMAIL-207] Modify createDataSource method to use AttachmentDataSource

[violetbeach]

Issue

Hello,

OOM occurred in the mail service developed using Apache-commons-email.

I debugged and found that the mail lookup function was wasting memory!

Problem

Below is a test for reproducing the problem.

@Test
void memoryTest() throws Exception {
    InputStream is = new SharedFileInputStream("/test/oom.eml");
    Session session = Session.getInstance(System.getProperties());
    MimeMessage mimeMessage = new MimeMessage(session, is);
    MimeMessageParser parser = new MimeMessageParser(mimeMessage).parse();
}

Below is the memory usage.

I expected to write attachments to the buffer of the output stream when absolutely necessary.

However, it is becoming a problem by putting all bytes[] in memory.

Sugest

So i modified these processes to use AttachmentDataSource.

Attachment DataSource uses InputStream from original DataSource to ensure memory is not wasted.

As a result, i can get a big effect in memory usage.

I worked hard to fix it. Feel free to let me know if you have any advice or lack!

If you need the tested eml file, I will send it to you by email.

Thanks very much. 🙇

[garydgregory]

@violetbeach
Thank you for your PR.

• All new public and protected elements should have a Javadoc comment
• All new and changed code should have a matching unit test

[violetbeach]

• All new public and protected elements should have a Javadoc comment
• All new and changed code should have a matching unit test

Thank very much!

I added Javadoc comments on public and protected elements. And I added a unit test for new class.

But, i could not cover the changed createDataSource method of MimeMessageParser because it is a difficult area to test.
I could only check that all the existing tests worked well.

Please let me know if there's anything missing! Thank you.

[codecov-commenter]

Codecov Report

Merging #159 (cf8417c) into master (b5511b9) will increase coverage by 0.16%.
Report is 30 commits behind head on master.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #159      +/-   ##
============================================
+ Coverage     65.87%   66.03%   +0.16%     
- Complexity      305      309       +4     
============================================
  Files            18       19       +1     
  Lines          1052     1057       +5     
  Branches        138      137       -1     
============================================
+ Hits            693      698       +5     
  Misses          280      280              
  Partials         79       79              

Files	Coverage Δ
...apache/commons/mail/util/AttachmentDataSource.java	100.00% <100.00%> (ø)
...rg/apache/commons/mail/util/MimeMessageParser.java	83.95% <100.00%> (-1.92%)	⬇️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[garydgregory]

Looks like a copy of https://github.com/apache/cxf/blob/main/rt/frontend/jaxrs/src/main/java/org/apache/cxf/jaxrs/ext/multipart/InputStreamDataSource.java ?

[violetbeach]

Oh! It's almost the same.

[garydgregory]

Hello @violetbeach
This issue has been handled slightly differently in git master. You are credited in changes.xml.

[violetbeach]

Hello @garydgregory

I've verified that the issue has been solved!

Memory is much cleaner, and the parser no longer puts the entire data in the file into memory.

Thank you. 👍

[garydgregory]

@violetbeach 👍