IOBuffer support

[johnnychen94]

following all the way from JuliaIO/ImageIO.jl#6 and JuliaImages/Images.jl#912, it turns out #14 isn't so generic...

Tracking down with debugger, here's a minimal example that reproduces the issue:

julia> using Base64, ImageCore, PNGFiles

julia> io = Base64EncodePipe(IOBuffer())

julia> img = rand(RGB{N0f8}, 2, 2)

julia> PNGFiles.save(io, img)

The result take!(io.io) is then passed down to VSCode or whatever displayer.

I'm not familiar with libpng and C bindings to fix the issue, but the root problem seems to be

PNGFiles.jl/src/io.jl

Line 298 in 206430f

png_set_write_fn(png_ptr, s.handle, writecallback_c[], C_NULL)

Instead of writing to file handle, here we need to write contents to IO buffer via the Base64 encoder pipe s. I don't know how the pointer of s can be passed to libpng, though. Any guidance would be helpful.

Other related PRs:

• Add missing stream kwargs & functionality for MIME ImageIO.jl#7 to pass mapi keywords
• Base64: add isreadable and iswritable for Base64EncodePipe/Base64DecodePipe JuliaLang/julia#37520 for a more general iswritable. A patch is still needed here for old Julia versions.
• a more general version of dont lock Process #21 as commented in use generic interface instead of accessing fields #19 (comment) to pass through maybe_lock for Base64EncodePipe and IOBuffer types.

[johnnychen94]

closed by #27 and JuliaIO/ImageIO.jl#15