IsBase64

From EggeWiki

Test to determine if a string is base64 encoded. This check only shows if the string conforms to base64. It's possible that the string conforms, but is not in fact encoded.

	static boolean isBase64(String s) {
		return (s.length() % 4 == 0) && s.matches("^[A-Za-z0-9+/]+[=]{0,2}$");
	}

	@Test
	public void testIsBase64() throws Exception {
		Assert.assertTrue(RssFileUpload.isBase64("bGVhc3VyZS4="));
		Assert.assertTrue(RssFileUpload.isBase64("ZWFzdXJlLg=="));
		Assert.assertTrue(RssFileUpload.isBase64("YXN1cmUu"));
		Assert.assertTrue(RssFileUpload.isBase64("c3VyZS4="));
		Assert.assertFalse(RssFileUpload.isBase64("OMG!"));
	}

Python

The same function in Python:

def isBase64(s):
    return (len(s) % 4 == 0) and re.match('^[A-Za-z0-9+/]+[=]{0,2}$', s)

Regex

In both of the above examples, I check the length, and then apply the regex. I think this makes it a bit more readable. However, it is possible to do the entire check with just a single regex.

^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$