Perform external queries

2013-12-22 17:13:51 -05:00
parent e48222ada0
commit 31ea72dbb3
4 changed files with 282 additions and 111 deletions
--- a/discover/encoding.go
+++ b/discover/encoding.go
@@ -0,0 +1,160 @@
+package discover
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+)
+
+type packet struct {
+	magic uint32 // AnnouncementMagic or QueryMagic
+	port  uint16 // unset if magic == QueryMagic
+	id    string
+	ip    []byte // zero length in local announcements
+}
+
+var (
+	errBadMagic = errors.New("bad magic")
+	errFormat   = errors.New("incorrect packet format")
+)
+
+func encodePacket(pkt packet) []byte {
+	if l := len(pkt.ip); l != 0 && l != 4 && l != 16 {
+		// bad ip format
+		return nil
+	}
+
+	var idbs = []byte(pkt.id)
+	var l = 4 + 4 + len(idbs) + pad(len(idbs))
+	if pkt.magic == AnnouncementMagic {
+		l += 4 + 4 + len(pkt.ip)
+	}
+
+	var buf = make([]byte, l)
+	var offset = 0
+
+	binary.BigEndian.PutUint32(buf[offset:], pkt.magic)
+	offset += 4
+
+	if pkt.magic == AnnouncementMagic {
+		binary.BigEndian.PutUint16(buf[offset:], uint16(pkt.port))
+		offset += 4
+	}
+
+	binary.BigEndian.PutUint32(buf[offset:], uint32(len(idbs)))
+	offset += 4
+	copy(buf[offset:], idbs)
+	offset += len(idbs) + pad(len(idbs))
+
+	if pkt.magic == AnnouncementMagic {
+		binary.BigEndian.PutUint32(buf[offset:], uint32(len(pkt.ip)))
+		offset += 4
+		copy(buf[offset:], pkt.ip)
+		offset += len(pkt.ip)
+	}
+
+	return buf
+}
+
+func decodePacket(buf []byte) (*packet, error) {
+	var p packet
+	var offset int
+
+	if len(buf) < 4 {
+		// short packet
+		return nil, errFormat
+	}
+	p.magic = binary.BigEndian.Uint32(buf[offset:])
+	offset += 4
+
+	if p.magic != AnnouncementMagic && p.magic != QueryMagic {
+		return nil, errBadMagic
+	}
+
+	if p.magic == AnnouncementMagic {
+		// Port Number
+
+		if len(buf) < offset+4 {
+			// short packet
+			return nil, errFormat
+		}
+		p.port = binary.BigEndian.Uint16(buf[offset:])
+		offset += 2
+		reserved := binary.BigEndian.Uint16(buf[offset:])
+		if reserved != 0 {
+			return nil, errFormat
+		}
+		offset += 2
+	}
+
+	// Node ID
+
+	if len(buf) < offset+4 {
+		// short packet
+		return nil, errFormat
+	}
+	l := binary.BigEndian.Uint32(buf[offset:])
+	offset += 4
+
+	if len(buf) < offset+int(l)+pad(int(l)) {
+		// short packet
+		return nil, errFormat
+	}
+	idbs := buf[offset : offset+int(l)]
+	p.id = string(idbs)
+	offset += int(l) + pad(int(l))
+
+	if p.magic == AnnouncementMagic {
+		// IP
+
+		if len(buf) < offset+4 {
+			// short packet
+			return nil, errFormat
+		}
+		l = binary.BigEndian.Uint32(buf[offset:])
+		offset += 4
+
+		if l != 0 && l != 4 && l != 16 {
+			// weird ip length
+			return nil, errFormat
+		}
+		if len(buf) < offset+int(l) {
+			// short packet
+			return nil, errFormat
+		}
+		if l > 0 {
+			p.ip = buf[offset : offset+int(l)]
+			offset += int(l)
+		}
+	}
+
+	if len(buf[offset:]) > 0 {
+		// extra data
+		return nil, errFormat
+	}
+
+	return &p, nil
+}
+
+func pad(l int) int {
+	d := l % 4
+	if d == 0 {
+		return 0
+	}
+	return 4 - d
+}
+
+func ipStr(ip []byte) string {
+	switch len(ip) {
+	case 4:
+		return fmt.Sprintf("%d.%d.%d.%d", ip[0], ip[1], ip[2], ip[3])
+	case 16:
+		return fmt.Sprintf("%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x",
+			ip[0], ip[1], ip[2], ip[3],
+			ip[4], ip[5], ip[6], ip[7],
+			ip[8], ip[9], ip[10], ip[11],
+			ip[12], ip[13], ip[14], ip[15])
+	default:
+		return ""
+	}
+}