func AddExtensionType(ext, typ string) error
AddExtensionType sets the MIME type associated with the extension ext to typ. The extension should begin with a leading dot, as in ".html".
func FormatMediaType(t string, param map[string]string) string
FormatMediaType serializes mediatype t and the parameters param as a media type conforming to RFC 2045 and RFC 2616. The type and parameter names are written in lower-case. When any of the arguments result in a standard violation then FormatMediaType returns the empty string.
func ParseMediaType(v string) (mediatype string, params map[string]string, err error)
ParseMediaType parses a media type value and any optional parameters, per RFC 1521. Media types are the values in Content-Type and Content-Disposition headers (RFC 2183). On success, ParseMediaType returns the media type converted to lowercase and trimmed of white space and a non-nil map. The returned map, params, maps from the lowercase attribute to the attribute value with its case preserved.
func TypeByExtension(ext string) string
TypeByExtension returns the MIME type associated with the file extension ext. The extension ext should begin with a leading dot, as in ".html". When ext has no associated type, TypeByExtension returns "".
Extensions are looked up first case-sensitively, then case-insensitively.
The built-in table is small but on unix it is augmented by the local system's mime.types file(s) if available under one or more of these names:
/etc/mime.types /etc/apache2/mime.types /etc/apache/mime.types
On Windows, MIME types are extracted from the registry.
Text types have the charset parameter set to "utf-8" by default.