nhentai saves images as the wrong file extension

[RitoPls]

It seems to occur with most or all of the comics I downloaded from nhentai. If you need an example for a test case you could use (NSFW) https://nhentai.net/g/219213/

Win8
Python 3.5
gallery-dl 1.1.1

I open up one of the PNG files it downloaded with infranview and it gives me a warning telling me to rename the file from *.png to *.jpg

It's still viewable as *.png , but the warnings gets annoying in infranview.

[mikf]

nhentai advertises these files as *.png in every way possible:

• Image URLs end in *.png: https://i.nhentai.net/galleries/1164085/4.png
• The Content-Type header says it's a PNG file: Content-Type: image/png
• nhentai's gallery metadata says it's a PNG file: …{"t":"p","w":1280,"h":1854}… (meaning type: png)
• The files inside the download torrent also have *.png as filename extension

It is obviously a `.jpg file, but gallery-dl is only doing what it is being told by nhentai.

A possible solution would be to look at the first few bytes when downloading and see if the file header matches the suggested filename extension, but implementing this properly might take a bit.

[Bfgeshka]

You probably do not have to read bytes and compare them manually, doesn't python have proper mime support?

[mikf]

There are Python wrappers for libmagic, but they are not part of the standard library. There you only have the mimetypes module which maps MIME-types to file extensions and vice versa.

Manually supporting the 3 or 4 most common image types shouldn't be a problem, it's more about how to properly fit this into the current download implementation.