Link refactor (#941)

* Link refactoring

* More refactoring

* More tweaking

* Cleaner shutdowns, UNIX socket support, more tweaks

* Actorise links, remove mutex

* SOCKS support

src/core/link_socks.go

@@ -0,0 +1,52 @@
+package core
+
+import (
+	"fmt"
+	"net"
+	"net/url"
+	"strings"
+
+	"golang.org/x/net/proxy"
+)
+
+type linkSOCKS struct {
+	*links
+}
+
+func (l *links) newLinkSOCKS() *linkSOCKS {
+	lt := &linkSOCKS{
+		links: l,
+	}
+	return lt
+}
+
+func (l *linkSOCKS) dial(url *url.URL, options linkOptions) error {
+	info := linkInfoFor("socks", "", url.Path)
+	if l.links.isConnectedTo(info) {
+		return fmt.Errorf("duplicate connection attempt")
+	}
+	proxyAuth := &proxy.Auth{}
+	proxyAuth.User = url.User.Username()
+	proxyAuth.Password, _ = url.User.Password()
+	dialer, err := proxy.SOCKS5("tcp", url.Host, proxyAuth, proxy.Direct)
+	if err != nil {
+		return fmt.Errorf("failed to configure proxy")
+	}
+	pathtokens := strings.Split(strings.Trim(url.Path, "/"), "/")
+	conn, err := dialer.Dial("tcp", pathtokens[0])
+	if err != nil {
+		return err
+	}
+	return l.handler(url.String(), info, conn, options, false)
+}
+
+func (l *linkSOCKS) handler(name string, info linkInfo, conn net.Conn, options linkOptions, incoming bool) error {
+	return l.links.create(
+		conn,     // connection
+		name,     // connection name
+		info,     // connection info
+		incoming, // not incoming
+		false,    // not forced
+		options,  // connection options
+	)
+}