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|
package http
import (
"fmt"
"mime"
"reflect"
"regexp"
"sort"
"strconv"
"strings"
)
type MediaType struct {
Type string
Subtype string
Parameters map[string]string
Weight float64
originalQ string
}
func ParseMediaType(v string) (*MediaType, error) {
mt, params, err := mime.ParseMediaType(v)
if err != nil {
return nil, err
}
majorMinor := strings.Split(mt, "/")
if len(majorMinor) != 2 {
return nil, fmt.Errorf("Invalid major/minor media type: %s", mt)
}
// No q should be weight 1.0, per spec
q := float64(1)
sq, ok := params["q"]
if ok {
delete(params, "q")
q, err = parseQ(sq)
if err != nil {
return nil, err
}
}
return &MediaType{
Type: majorMinor[0],
Subtype: majorMinor[1],
Parameters: params,
Weight: q,
originalQ: sq,
}, nil
}
func (m MediaType) String() string {
b := strings.Builder{}
b.WriteString(m.Type + "/" + m.Subtype)
params := []string{}
for k, v := range m.Parameters {
params = append(params, fmt.Sprintf("%s=%s", k, v))
}
// Keep them in the same order so they're comparable
sort.Strings(params)
// Q should always be last per RFC9110
if m.originalQ != "" {
params = append(params, fmt.Sprintf("q=%s", m.originalQ))
}
if len(params) > 0 {
b.WriteString(";")
b.WriteString(strings.Join(params, ";"))
}
return b.String()
}
func (m MediaType) Specificity() int {
s := 0
if m.Type != "*" {
s += 1
}
if m.Subtype != "*" {
s += 1
}
if m.Parameters != nil {
s += len(m.Parameters)
}
return s
}
func (m MediaType) Satisfies(v MediaType) bool {
if m.Equal(v) {
return true
}
if m.Type != v.Type && m.Type != "*" && v.Type != "*" {
return false
}
if m.Subtype != v.Subtype && m.Subtype != "*" && v.Subtype != "*" {
return false
}
return reflect.DeepEqual(m.Parameters, v.Parameters)
}
func (m MediaType) Equal(v MediaType) bool {
return m.Type == v.Type &&
m.Subtype == v.Subtype &&
reflect.DeepEqual(m.Parameters, v.Parameters)
}
type AcceptableTypes []*MediaType
func (a AcceptableTypes) Sorted() AcceptableTypes { sort.Stable(sort.Reverse(a)); return a }
func (a AcceptableTypes) Len() int { return len(a) }
func (a AcceptableTypes) Less(i, j int) bool { return a[i].Weight < a[j].Weight }
func (a AcceptableTypes) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
// FindMatch returns the MediaType in the set that has the best match
// for the passed media types as well as the media type that determined
// the match. According to the rules of RFC7231, the most specific match
// wins in order of weight. This function assumes that both values are
// sorted.
func (a AcceptableTypes) FindMatch(values AcceptableTypes) (match *MediaType, matcher *MediaType) {
if len(a) == 0 || len(values) == 0 {
return nil, nil
}
candidates := AcceptableTypes{}
// Return the highest precedence match for the type. If there is no
// exact match then the most specific match with the highest precedence
// should win.
for _, matcher = range values {
for _, match = range a {
if match.Equal(*matcher) {
return match, matcher
}
if match.Satisfies(*matcher) {
candidates = append(candidates, match)
}
}
if len(candidates) != 0 {
break
}
}
if len(candidates) == 0 {
return nil, nil
}
// Sort ascending by specificity
sort.SliceStable(candidates, func(i, j int) bool {
return candidates[i].Specificity() < candidates[j].Specificity()
})
return candidates[len(candidates)-1], matcher
}
// ParseAccept parses a set of Accept headers and scores them per the
// rules in RFC7231, returning a slice of headers in descending order of
// priority. If the Accept header occurs multiple times in the request
// the result of all headers will be combined and scored together as if
// they were all in one header line.
//
// See: https://tools.ietf.org/html/rfc7231#section-5.3.2
func ParseAccept(values []string) (AcceptableTypes, error) {
all := AcceptableTypes{}
for _, l := range values {
t, err := parseAcceptLine(l)
if err != nil {
return nil, err
}
all = append(all, t...)
}
return all.Sorted(), nil
}
func parseAcceptLine(l string) (AcceptableTypes, error) {
out := AcceptableTypes{}
for _, t := range strings.Split(l, ",") {
mt, err := ParseMediaType(t)
if err != nil {
return nil, err
}
out = append(out, mt)
}
return out, nil
}
// https://tools.ietf.org/html/rfc7231#section-5.3.1
var validateQ = regexp.MustCompile(`(0\.[0-9]{1,3}|1\.0{1,3})$`)
func parseQ(v string) (float64, error) {
if !validateQ.Match([]byte(v)) {
return 0.0, fmt.Errorf("Invalid format for Q")
}
f, err := strconv.ParseFloat(v, 64)
if err != nil {
return 0.0, err
}
return f, nil
}
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