Sideloader: no line breaks in base64 content

[plexus]

Currently we are sending sideloaded resources as line-wrapped base64. The extra
newlines confuse the nREPL sideloader, turning the result into binary garbage.

I think in this case we should be both more conservative in what we send (this
patch) and more lenient in what we receive (nREPL should sanitize the input and
drop any characters that aren't valid base64).

Part of #3037

---

• The commits are consistent with our contribution guidelines
• You've added tests (if possible) to cover your change(s)
• All tests are passing (eldev test)
• All code passes the linter (eldev lint) which is based on elisp-lint and includes
  • byte-compilation, checkdoc, check-declare, packaging metadata, indentation, and trailing whitespace checks.
• You've updated the changelog (if adding/changing user-visible functionality)
• You've updated the user manual (if adding/changing user-visible functionality)

[plexus]

The linter does not currently pass for me on master, but this PR does not introduce any new linting warnings. This PR does not add user visible functionality that needs to be mentioned in the manual.

[plexus]

Seems the linting does pass on CI. I installed eldev as per https://github.com/doublep/eldev#installation , and eldev lint gives me a bunch of warnings like

cider-doc.el:123:0 (checkdoc)    First sentence should end with punctuation
cider-doc.el:129:0 (checkdoc)    First sentence should end with punctuation
cider-doc.el:135:0 (checkdoc)    First sentence should end with punctuation
cider-doc.el:141:0 (checkdoc)    First sentence should end with punctuation
cider-doc.el:191:0 (checkdoc)    First line is not a complete sentence
Found 5 warnings in file ‘cider-doc.el’

cider-popup.el:30:0 (checkdoc)   First sentence should end with punctuation
Found 1 warning in file ‘cider-popup.el’

cider-scratch.el:74:0 (checkdoc) Lisp symbol ‘clojure-mode’ should appear in quotes
Found 1 warning in file ‘cider-scratch.el’

cider-stacktrace.el:89:0 (checkdoc) First sentence should end with punctuation
cider-stacktrace.el:95:0 (checkdoc) First sentence should end with punctuation
cider-stacktrace.el:101:0 (checkdoc) First sentence should end with punctuation
cider-stacktrace.el:107:0 (checkdoc) First sentence should end with punctuation
cider-stacktrace.el:113:0 (checkdoc) First sentence should end with punctuation
cider-stacktrace.el:119:0 (checkdoc) First sentence should end with punctuation
cider-stacktrace.el:125:0 (checkdoc) First sentence should end with punctuation
Found 7 warnings in file ‘cider-stacktrace.el’

is there some linter config I'm missing?

[bbatsov]

Good catch, and good point about doing input sanitization on nREPL's side.

You can ignore the checkdoc warnings.