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magnet.go
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magnet.go
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package metainfo
import (
"encoding/base32"
"encoding/hex"
"fmt"
"net/url"
"strings"
)
// Magnet link components.
type Magnet struct {
InfoHash Hash
Trackers []string
DisplayName string
}
const xtPrefix = "urn:btih:"
func (m Magnet) String() string {
// net.URL likes to assume //, and encodes ':' on us, so we do most of
// this manually.
ret := "magnet:?xt="
ret += xtPrefix + hex.EncodeToString(m.InfoHash[:])
if m.DisplayName != "" {
ret += "&dn=" + url.QueryEscape(m.DisplayName)
}
for _, tr := range m.Trackers {
ret += "&tr=" + url.QueryEscape(tr)
}
return ret
}
// ParseMagnetURI parses Magnet-formatted URIs into a Magnet instance
func ParseMagnetURI(uri string) (m Magnet, err error) {
u, err := url.Parse(uri)
if err != nil {
err = fmt.Errorf("error parsing uri: %s", err)
return
}
if u.Scheme != "magnet" {
err = fmt.Errorf("unexpected scheme: %q", u.Scheme)
return
}
xt := u.Query().Get("xt")
if !strings.HasPrefix(xt, xtPrefix) {
err = fmt.Errorf("bad xt parameter")
return
}
infoHash := xt[len(xtPrefix):]
// BTIH hash can be in HEX or BASE32 encoding
// will assign apropriate func judging from symbol length
var decode func(dst, src []byte) (int, error)
switch len(infoHash) {
case 40:
decode = hex.Decode
case 32:
decode = base32.StdEncoding.Decode
}
if decode == nil {
err = fmt.Errorf("unhandled xt parameter encoding: encoded length %d", len(infoHash))
return
}
n, err := decode(m.InfoHash[:], []byte(infoHash))
if err != nil {
err = fmt.Errorf("error decoding xt: %s", err)
return
}
if n != 20 {
panic(n)
}
m.DisplayName = u.Query().Get("dn")
m.Trackers = u.Query()["tr"]
return
}