regex pattern base64 data uri according to RFC 2397

data-uri-regex-rfc2397.md

pattern:

^data:((?:\w+\/(?:(?!;).)+)?)((?:;[\w\W]*?[^;])*),(.+)$

test this pattern on regexr: https://regexr.com/4inht

regex pattern to match RFC 2397 data URL

syntax:

dataurl := "data:" [ mediatype ] [ ";base64" ] "," data mediatype := [ type "/" subtype ] *( ";" parameter ) data := *urlchar parameter := attribute "=" value

examples:

example1: simple

data:image/jpeg;base64,UEsDBBQAAAAI

example2: with meta key=value

data:image/jpeg;key=value;base64,UEsDBBQAAAAI

example3: without base64 key name

data:image/jpeg;key=value,UEsDBBQAAAAI

example4: without mime-type

data:;base64;sdfgsdfgsdfasdfa=s,UEsDBBQAAAAI

example5: without mime-type , base64 and meta key=value

data:,UEsDBBQAAAAI

Even in valid URL data is allowed to be empty, so it might be a good idea to replace
,(.+)$ to ,(.*)$

One should perhaps also be humble to admit that one can have own bugs; I would second that example #4 is wrong: data:;base64;sdfgsdfgsdfasdfa=s,UEsDBBQAAAAI is not valid afaik.

The reason for me saying so is that if you look at the standard you posted, you see that:

1. attribute = value is a parameter
2. a parameter is placed after type / subtype as part of media-type
3. a parameter is prefixed by a semi-colon
4. a parameter is optional
5. a media-type is always placed before ";base64"

A valid example according to these statements would be: data:;sdfgsdfgsdfasdfa=s;base64,UEsDBBQAAAAI

I may of course be wrong.. 👍