I'm not a stranger to mime types but this is strange. Normally, a text file would have been considered to be of text/plain mime but now, after implementing fileinfo, this type of file is now considered to be "text/x-pascal". I'm a little concerned because I need to be sure that I get the correct mime types set before allowing users to upload with it.
Is there a cheat sheet that will give me all of the "common" mimes as they are interpreted by fileinfo?
Sinan provided a link that lists all of the more common mimes. If you look at this list, you will see that a .txt file is of text/plain mime but in my case, a plain-jane text file is interpreted as text/pascal.
fileinfo is a "best guess". It analyzes only a portion of the file in order to try to figure out what type the file is, and as such it can be fooled easily enough. Perhaps your file starts with a Pascal comment or keyword such as Project or Unit.
Fileinfo is not using the extension of the file to determine which mime-type it is, but (quoting) :
The functions in this module try to guess the content type and encoding of a file by looking for certain magic byte sequences at specific positions within the file.
The idea being that the name à of the file, and its extension, are provided by the users (especially in a case such as yours, where the files are being uploaded by users), and, as such, are less "sure" than the content of the file itself.
Maybe a solution could be to not check on the whole mime-type returned by fileinfo, but to only use the first part of it -- at least in some cases ?
For instance, maybe you could accept all mimetype that are in the text/* and image/* families, and refuse all those look like application/*, except for application/pdf ?
(Just an example -- but you see the point)
I have found that, as of at least version 5.03, the 'file' command can in some circumstances mis-identify a plain text file as a Pascal source file, simply because it contains the word 'program' or 'record'. At least that's how it looks having examined the source (src/names.h). I believe the php fileinfo command uses the same 'magic' engine, so I suspect this is the cause of the problem. If/when I am accepted on the file mailing list, I will notify the maintainers of this issue.
[UPDATE] I asked the question, but got little in the way of a response. Having investigated this issue a bit more throughly, it turns out that identifying text formats is, in general, really difficult. If you get a 'text/*' MIME type back from file, you might want to consider ignoring the result and assuming the resource is just 'text/plain', unless the false negatives (text/html maybe) will cause you difficulties.
There is a chart that shows a list of common MIME types and their corresponding extensions. Here
来源：https://stackoverflow.com/questions/2345899/fileinfo-and-mime-types-ive-never-heard-of