go-httpaccept/mediarange/mediarange.go

package mediarange

import (
	"errors"
	"strings"
)

var (
	errBadMediaRange = errors.New("bad media-range")
)

// MediaRange represents a "media-range" as defined by IETF RFC-2616 (Hypertext Transfer Protocol — HTTP/1.1) in section 14.1.
//
// Here are some sample media-ranges:
//
//	*/*
//	audio/*
//	image/*
//	text/*
//	video/*
//	application/x-tar
//	audio/wav
//	image/gif
//	image/png
//	text/html
//	text/plain
//	video/mp4
//
// Note that some of these sample media-ranges look like media-types / mime-types:
//
//	application/x-tar
//	audio/wav
//	image/gif
//	image/png
//	text/html
//	text/plain
//	video/mp4
//
// But some of these sample media-ranges are not media-types / mime-types:
//
//	*/*
//	audio/*
//	image/*
//	text/*
//	video/*
//
// These later kinds of media-ranges (that do not look like media-types / mime-types) use the asterisk ("*") as a wild-card symbol.
// So "*/*" represents any media-type / mime-type.
// ANd "image/*" represents "image/gif", "image/png", etc.
type MediaRange struct {
	typ string
	subtyp string
}

// Create creates a MediaRange.
//
// For example:
//
//	// audio/ogg
//	mediarange.Create("audio", "ogg")
//
//	// audio/*
//	mediarange.Create("audio", "*")
//
//	// */*
//	mediarange.Create("*", "*")
//
// Note that an empty string for mediaRangeType or mediaRangeSubType will be treated as a wild-card (i.e., "*").
func Create(mediaRangeType string, mediaRangeSubType string) MediaRange {
	mediaRangeType = strings.TrimSpace(mediaRangeType)
	mediaRangeSubType = strings.TrimSpace(mediaRangeSubType)

	if "*" == mediaRangeType {
		mediaRangeType = ""
	}
	if "*" == mediaRangeSubType {
		mediaRangeSubType = ""
	}

	return MediaRange{
		typ:    strings.ToLower(mediaRangeType),
		subtyp: strings.ToLower(mediaRangeSubType),
	}
}

// Parse parses a string and returns a MediaRange.
//
// For example:
//
//	mr, err := mediarange.Parse("application/activity+json")
func Parse(value string) (MediaRange, error) {

	value = strings.TrimSpace(value)

	parts := strings.SplitN(value, "/", 2)
	if 2 != len(parts) {
		return MediaRange{}, errBadMediaRange
	}

	var typ string = parts[0]

	var subtyp string
	{
		a := strings.SplitN(parts[1], ";", 2)
		{
			length := len(a)
			if 2 != length && 1 != length {
				return MediaRange{}, errBadMediaRange
			}
		}

		subtyp = a[0]
	}

	return Create(typ, subtyp), nil
}

// SubType returns the subtype of the media-range in its canonical form — i.e. lower-case and without spacing.
func (receiver MediaRange) SubType() string {
	var typ string = receiver.typ
	var subtyp string = receiver.subtyp

	if "" == typ || "*" == typ  {
		return "*"
	}

	if "" == subtyp {
		return "*"
	}

	return subtyp
}

// Type returns the type of the media-range in its canonical form — i.e. lower-case and without spacing.
func (receiver MediaRange) Type() string {
	var typ string = receiver.typ

	if "" == typ {
		return "*"
	}

	return typ
}

func (receiver MediaRange) Match(value string) bool {

	var typ string = receiver.Type()
	if "*" == typ {
		return true
	}

	// Since media-types are a sub-set of media-ranges, we can do this.
	var mediatype MediaRange
	{
		var err error

		mediatype, err = Parse(value)
		if nil != err {
			return false
		}
	}

	if mediatype.typ != typ  {
		return false
	}

	var subtyp string = receiver.SubType()
	if "*" == subtyp {
		return true
	}

	if mediatype.subtyp != subtyp {
		return false
	}

	return true
}

// String returns the serialed media-range.
//
// For example:
//
//	"text/html" == mediarange.Create("text", "html").String()
func (receiver MediaRange) String() string {
	var p []byte

	var typ string = receiver.Type()
	p = append(p, typ...)

	p = append(p, '/')

	var subtyp string = receiver.SubType()
	p = append(p, subtyp...)

	return string(p)
}