[issue41145] EmailMessage.as_string is altering the message state and actually fix bugs

[R. David Murray]

R. David Murray  added the comment:

The as_strings docs say:

"Flattening the message may trigger changes to the Message if defaults need to 
be filled in to complete the transformation to a string (for example, MIME 
boundaries may be generated or modified)."

So, while this is indeed an API design bug, it isn't an actual bug in the code 
but rather is expected behavior, currently.  The historical reason for this is 
that the generator code looks at the entire message to make sure the boundary 
string is unique.  My long term plan for email included plans to rewrite the 
generator, and I was going to fix this issue at that point.  My life got too 
busy to be able to continue with email development work, though, so that never 
happened.

It has been *years* since I've looked at the code.  Thinking about it now, I'm 
wondering if it would be possible to use a GUID technique to generate the 
boundary and thus do exactly as you say: have make_alternative (and anything 
else that causes a boundary to be needed) pre-create the boundary.  That, I 
think, would mean we wouldn't need to change the generator, even though it 
would still be doing its (inefficient) check that the boundary was unique.  I'm 
not sure if it would work, though; it's been too long since I've looked at the 
relevant code.

--
type: resource usage -> behavior

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[issue41145] EmailMessage.as_string is altering the message state and actually fix bugs

[Eric V. Smith]

Change by Eric V. Smith :


--
components: +email
nosy: +barry, r.david.murray

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[issue41145] EmailMessage.as_string is altering the message state and actually fix bugs

[Guillaume Gauvrit]

New submission from Guillaume Gauvrit :

I am currently refactoring code and use the EmailMessage api
to build message.

I encountered weird behavior while building an email.
The `as_string()` method is fixing the `make_alternative` method.

So, to me their is two bug here: a `as_string` method should not mutate 
internal state,
and the `make_alternative` should create a correct internal state.


It may be resume in the following program:


```
흿 python
Python 3.8.3 (default, May 17 2020, 18:15:42)
[GCC 10.1.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import email
>>> from email.message import EmailMessage, MIMEPart
>>>
>>> msg = EmailMessage()
>>> msg.make_alternative()
>>> print(msg.get_boundary())
None
>>> print(msg._headers)
[('Content-Type', 'multipart/alternative')]
>>> _ = msg.as_string()
>>> print(msg.get_boundary())
===3171625413581695247==
>>> print(msg._headers)
[('Content-Type', 'multipart/alternative; 
boundary="===3171625413581695247=="')]
```

--
files: bug.py
messages: 372508
nosy: mardiros
priority: normal
severity: normal
status: open
title: EmailMessage.as_string is altering the message state and actually fix 
bugs
type: resource usage
versions: Python 3.7, Python 3.8
Added file: https://bugs.python.org/file49271/bug.py

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