From 890658ef937ffaae4122c19177f5b1059319a021 Mon Sep 17 00:00:00 2001
From: Seth Hoenig <seth.a.hoenig@gmail.com>
Date: Sun, 3 Apr 2016 08:51:46 -0500
Subject: [PATCH] convenience function for creating magnets

---
 cmd/torrent-magnet/main.go | 17 +++-----------
 magnet.go                  | 25 +++++++++++++++++---
 magnet_test.go             | 48 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 73 insertions(+), 17 deletions(-)

diff --git a/cmd/torrent-magnet/main.go b/cmd/torrent-magnet/main.go
index 68bae968..a68cb888 100644
--- a/cmd/torrent-magnet/main.go
+++ b/cmd/torrent-magnet/main.go
@@ -20,18 +20,7 @@ func main() {
 		fmt.Fprintf(os.Stderr, "error reading metainfo from stdin: %s", err)
 		os.Exit(1)
 	}
-	ts := torrent.TorrentSpecFromMetaInfo(mi)
-	m := torrent.Magnet{
-		InfoHash: ts.InfoHash,
-		Trackers: func() (ret []string) {
-			for _, tier := range ts.Trackers {
-				for _, tr := range tier {
-					ret = append(ret, tr)
-				}
-			}
-			return
-		}(),
-		DisplayName: ts.DisplayName,
-	}
-	fmt.Fprintf(os.Stdout, "%s\n", m.String())
+
+	magnet := torrent.Magnetize(mi)
+	fmt.Fprintf(os.Stdout, "%s\n", magnet.String())
 }
diff --git a/magnet.go b/magnet.go
index b326e1fc..e7653625 100644
--- a/magnet.go
+++ b/magnet.go
@@ -6,8 +6,11 @@ import (
 	"fmt"
 	"net/url"
 	"strings"
+
+	"github.com/anacrolix/torrent/metainfo"
 )
 
+// Magnet
 type Magnet struct {
 	InfoHash    [20]byte
 	Trackers    []string
@@ -16,10 +19,10 @@ type Magnet struct {
 
 const xtPrefix = "urn:btih:"
 
-func (m *Magnet) String() (ret string) {
+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 := "magnet:?xt="
 	ret += xtPrefix + hex.EncodeToString(m.InfoHash[:])
 	if m.DisplayName != "" {
 		ret += "&dn=" + url.QueryEscape(m.DisplayName)
@@ -27,7 +30,23 @@ func (m *Magnet) String() (ret string) {
 	for _, tr := range m.Trackers {
 		ret += "&tr=" + url.QueryEscape(tr)
 	}
-	return
+	return ret
+}
+
+// Magnetize creates a Magnet from a MetaInfo
+func Magnetize(mi *metainfo.MetaInfo) Magnet {
+	ts := TorrentSpecFromMetaInfo(mi)
+	trackers := []string{}
+	for _, tier := range ts.Trackers {
+		for _, tracker := range tier {
+			trackers = append(trackers, tracker)
+		}
+	}
+	return Magnet{
+		InfoHash:    ts.InfoHash,
+		Trackers:    trackers,
+		DisplayName: ts.DisplayName,
+	}
 }
 
 // ParseMagnetURI parses Magnet-formatted URIs into a Magnet instance
diff --git a/magnet_test.go b/magnet_test.go
index 52a3abbf..4099c229 100644
--- a/magnet_test.go
+++ b/magnet_test.go
@@ -4,6 +4,8 @@ import (
 	"encoding/hex"
 	"reflect"
 	"testing"
+
+	"github.com/anacrolix/torrent/metainfo"
 )
 
 var (
@@ -66,3 +68,49 @@ func TestParseMagnetURI(t *testing.T) {
 	}
 
 }
+
+func Test_Magnetize(t *testing.T) {
+	mi, err := metainfo.LoadFromFile("testdata/bootstrap.dat.torrent")
+	if err != nil {
+		t.Errorf("Failed to load testdata torrent: %v", err)
+	}
+
+	magnet := Magnetize(mi)
+
+	if magnet.DisplayName != "bootstrap.dat" {
+		t.Errorf("Magnet Dispalyname is incorrect: %s", magnet.DisplayName)
+	}
+
+	ih := [20]byte{
+		54, 113, 155, 162, 206, 207, 159, 59, 215, 197,
+		171, 251, 122, 136, 233, 57, 97, 27, 83, 108,
+	}
+
+	if magnet.InfoHash != ih {
+		t.Errorf("Magnet infohash is incorrect")
+	}
+
+	trackers := []string{
+		"udp://tracker.openbittorrent.com:80",
+		"udp://tracker.openbittorrent.com:80",
+		"udp://tracker.publicbt.com:80",
+		"udp://coppersurfer.tk:6969/announce",
+		"udp://open.demonii.com:1337",
+		"http://bttracker.crunchbanglinux.org:6969/announce",
+	}
+
+	for _, expected := range trackers {
+		if !contains(magnet.Trackers, expected) {
+			t.Errorf("Magnet does not contain expected tracker: %s", expected)
+		}
+	}
+}
+
+func contains(haystack []string, needle string) bool {
+	for _, s := range haystack {
+		if s == needle {
+			return true
+		}
+	}
+	return false
+}