Upgrade from within GUI (fixes #190)

cmd/syncthing/upgrade_common.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"bytes"
+	"strconv"
+	"strings"
+)
+
+type githubRelease struct {
+	Tag      string        `json:"tag_name"`
+	Prelease bool          `json:"prerelease"`
+	Assets   []githubAsset `json:"assets"`
+}
+
+type githubAsset struct {
+	URL  string `json:"url"`
+	Name string `json:"name"`
+}
+
+func compareVersions(a, b string) int {
+	return bytes.Compare(versionParts(a), versionParts(b))
+}
+
+func versionParts(v string) []byte {
+	parts := strings.Split(v, "-")
+	fields := strings.Split(parts[0], ".")
+	res := make([]byte, len(fields))
+	for i, s := range fields {
+		v, _ := strconv.Atoi(s)
+		res[i] = byte(v)
+	}
+	return res
+}