Never generate empty filename for download

[christopher-dG]

Ran into a strange error when I was trying HTTP.download, it tried to save the file to /tmp/, which obviously is not a valid path for a file. Found out that the Content-Disposition header listed an empty filename which is... odd.

julia> using HTTP

julia> resp = HTTP.get("https://pretalx.com/media/juliacon2020/images/9A8DCP/logo_kafyqWH.png");

julia> println(HTTP.header(resp, "Content-Disposition"))
attachment; filename=""

I could add this to the test suite but I'm afraid of the URL not being very permanent. Thoughts on that?

[codecov-commenter]

Codecov Report

Merging #561 into master will decrease coverage by 0.09%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #561      +/-   ##
==========================================
- Coverage   77.52%   77.43%   -0.10%     
==========================================
  Files          37       37              
  Lines        2096     2096              
==========================================
- Hits         1625     1623       -2     
- Misses        471      473       +2     

Impacted Files	Coverage Δ
src/download.jl	0.00% <0.00%> (ø)
src/IOExtras.jl	64.28% <0.00%> (-3.58%)	⬇️
src/ConnectionPool.jl	77.63% <0.00%> (-0.43%)	⬇️

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[quinnj]

Unrelated to this PR, but is quoted_filename[1] valid? I don't think that works when doing match, because it returns a RegexMatch object, right? So trying to index it is going to be an error? Am I missing something here?

[pfitzseb]

RegexMatches are indexable:

julia> match(r"(x)(y)", "xyz")[1]
"x"

julia> match(r"(x)(y)", "xyz")[2]
"y"

[quinnj]

Ah, my confusion was missing the match groups in the regex. Thanks.

[StefanKarpinski]

Is it possible that this is because you can open a directory these days and it acts like an empty file? That is a bug: JuliaLang/julia#36605.

[christopher-dG]

I'm guessing it was totally unintentional, having a filename set in Content-Disposition as explicitly empty seems like an edge case.