fix: catch exceptions due to failure to create XML from text

[joanise]

I don't know what causes this, but we got a few 5xx errors from the Heroku logs with this trace:

   File "/app/readalongs/web_api.py", line 209, in assemble
     parsed = parse_xml(
              ^^^^^^^^^^
   File "/app/readalongs/text/util.py", line 138, in parse_xml
     return etree.fromstring(
            ^^^^^^^^^^^^^^^^^
 lxml.etree.XMLSyntaxError: PCDATA invalid Char value 3, line 8, column 26

While it makes no sense we should fail to parse XML we just generated in this broader block:

    parsed = parse_xml(
        create_ras_from_text(
            (request.input_text or "").splitlines(keepends=True),
            text_languages=request.text_languages,
        )
    )

let's just put a try/except in there since we saw it live on Heroku.

Whatever the error in the input is, though I cannot reproduce it, should generate a 422 HTTP code.

PR Goal?

Fix the 5xx errors we saw on Heroku today.

Feedback sought?

sanity check

Priority?

high

Tests added?

can't reproduce, so none

How to test?

beats me, I can't figure out what caused this to happen on Heroku in the first place.

Confidence?

high, because it's a safe patch: there's no risk in adding a try/except block that should never get triggered.

I still wish I could reproduce it, though, and thus unit test it.

Version change?

no

[semanticdiff-com]

Review changes with SemanticDiff.

Analyzed 1 of 1 files.

Overall, the semantic diff is 62% smaller than the GitHub diff.

	Filename	Status
✔️	readalongs/web_api.py	61.79% smaller

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 87.90%. Comparing base (791e0b9) to head (1eea719).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
readalongs/web_api.py	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #242      +/-   ##
==========================================
+ Coverage   87.21%   87.90%   +0.69%     
==========================================
  Files          21       21              
  Lines        1783     1786       +3     
  Branches      323      323              
==========================================
+ Hits         1555     1570      +15     
+ Misses        189      179      -10     
+ Partials       39       37       -2     

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[roedoejet]

looks good. Maybe ask the user to send us the text?

[joanise]

I guess it's unlikely the user would see the actual text of the error message, but I guess it would not hurt.