JSON is not recognised

[rickb777]

application/json is widely used in REST APIs, but isn't detected by mimesniffer, nor by the default net/http sniffer.

This would be a useful addition for many people.

Correct sniffing should determine whether the content is valid JSON. If it isn't then the result would be "text/plain". This can be done using encoding/json via the json.Valid function.

[rickb777]

Workaround:

mimesniffer.Register("application/json", func(bs []byte) bool {
    return json.Valid(bs)
})