blob: d76fc9561c1b315652688e9d39703e8ea2ac9df5 [file] [log] [blame]
// Copyright 2016 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ble
import (
"bytes"
"errors"
"fmt"
"v.io/v23/discovery"
idiscovery "v.io/x/ref/lib/discovery"
)
const (
// We pack an advertisement except attachments into a few characteristics
// with values up to 512 byte. This makes it simple to handle the limit on
// the maximum size of each characteristic value. And it would be more
// efficient by sending the smaller number of packets.
// The maximum size of a characteristic value is limited to 512 bytes
// by the specification.
//
// See Bluetooth specification 4.2, section 3.2.9:
// https://www.bluetooth.com/specifications/adopted-specifications
maxCharacteristicValueLen = 512
// Format string for packed characteristic uuids.
packedCharacteristicUuidFmt = "31ca10d5-0195-54fa-9344-25fcd7072e%x%x"
// We should allow up to 16 packed characteristics to keep the packed
// characteristic uuids valid. This should be enough since we limit
// the size of advertisement except attachments to 512 bytes.
maxNumPackedServices = 16
maxNumPackedCharacteristicsPerService = 16
)
func cUuid(i, j int) string {
return fmt.Sprintf(packedCharacteristicUuidFmt, i, j)
}
func packToCharacteristics(encoded map[discovery.AdId][]byte) map[string][]byte {
cs := make(map[string][]byte)
i := 0
for _, v := range encoded {
buf := bytes.NewBuffer(v)
for j := 0; buf.Len() > 0; j++ {
cs[cUuid(i, j)] = buf.Next(maxCharacteristicValueLen)
}
i++
}
return cs
}
func encodeAdInfo(adinfo *idiscovery.AdInfo) ([]byte, error) {
// The current encoding format is
//
// <Id>
// <InterfaceName>
// <Addresses encoded using idiscovery.PackAddresses>
// <#Attributes>[<AttributeKey><AttributeValue>...]
// <EncryptionAlgorithm>[<#EncryptionKeys><EncryptionKey>...]
// <Hash>
// <TimestampNs>
// <DirAddrs encoded using idiscovery.PackAddresses>
// <Status>
//
// Any change of this format (except appending new fields) would break decoding.
// We can handle any versioning through different characteristic uuids if needed.
buf := idiscovery.NewEncodingBuffer(nil)
buf.Write(adinfo.Ad.Id[:])
buf.WriteString(adinfo.Ad.InterfaceName)
buf.WriteBytes(idiscovery.PackAddresses(adinfo.Ad.Addresses))
buf.WriteInt(len(adinfo.Ad.Attributes))
for k, v := range adinfo.Ad.Attributes {
buf.WriteString(k)
buf.WriteString(v)
}
buf.WriteInt(int(adinfo.EncryptionAlgorithm))
if adinfo.EncryptionAlgorithm != idiscovery.NoEncryption {
buf.WriteInt(len(adinfo.EncryptionKeys))
for _, key := range adinfo.EncryptionKeys {
buf.WriteBytes(key)
}
}
buf.Write(adinfo.Hash[:])
buf.Write(idiscovery.EncodeTimestamp(adinfo.TimestampNs))
if len(adinfo.Ad.Attachments) == 0 {
buf.WriteBytes(idiscovery.PackAddresses(nil)) // No DirAddrs necessary
buf.WriteInt(int(idiscovery.AdReady))
} else {
buf.WriteBytes(idiscovery.PackAddresses(adinfo.DirAddrs))
buf.WriteInt(int(idiscovery.AdPartiallyReady))
}
if buf.Len() > maxCharacteristicValueLen*maxNumPackedCharacteristicsPerService {
return nil, errors.New("max advertisement size exceeded")
}
return buf.Bytes(), nil
}
func unpackFromCharacteristics(cs map[string][]byte) [][]byte {
var unpacked [][]byte
for i := 0; i < maxNumPackedServices; i++ {
if _, ok := cs[cUuid(i, 0)]; !ok {
break
}
var splitted [][]byte
for j := 0; j < maxNumPackedCharacteristicsPerService; j++ {
c, ok := cs[cUuid(i, j)]
if !ok {
break
}
splitted = append(splitted, c)
}
if len(splitted) == 1 {
// Short-cut for a single characteristic.
unpacked = append(unpacked, splitted[0])
} else {
n := 0
for _, d := range splitted {
n += len(d)
}
merged := make([]byte, n)
i := 0
for _, v := range splitted {
i += copy(merged[i:], v)
}
unpacked = append(unpacked, merged)
}
}
return unpacked
}
func decodeAdInfo(encoded []byte) (*idiscovery.AdInfo, error) {
var (
err error
buf *idiscovery.EncodingBuffer = idiscovery.NewEncodingBuffer(encoded)
read = func(p []byte) {
if err != nil {
return
}
err = buf.Read(p)
}
readInt = func() (x int) {
if err != nil {
return
}
x, err = buf.ReadInt()
return
}
readBytes = func() (p []byte) {
if err != nil {
return
}
p, err = buf.ReadBytes()
return
}
readString = func() (s string) {
if err != nil {
return
}
s, err = buf.ReadString()
return
}
readTimestamp = func() (ts int64) {
if err != nil {
return
}
ts, err = idiscovery.DecodeTimestamp(buf.Next(8))
return
}
)
adinfo := &idiscovery.AdInfo{}
read(adinfo.Ad.Id[:])
adinfo.Ad.InterfaceName = readString()
adinfo.Ad.Addresses, err = idiscovery.UnpackAddresses(readBytes())
if n := readInt(); n > 0 {
adinfo.Ad.Attributes = make(map[string]string, n)
for i := 0; i < n; i++ {
adinfo.Ad.Attributes[readString()] = readString()
}
}
adinfo.EncryptionAlgorithm = idiscovery.EncryptionAlgorithm(readInt())
if adinfo.EncryptionAlgorithm != idiscovery.NoEncryption {
n := readInt()
adinfo.EncryptionKeys = make([]idiscovery.EncryptionKey, n)
for i := 0; i < n; i++ {
adinfo.EncryptionKeys[i] = readBytes()
}
}
read(adinfo.Hash[:])
adinfo.TimestampNs = readTimestamp()
adinfo.DirAddrs, err = idiscovery.UnpackAddresses(readBytes())
adinfo.Status = idiscovery.AdStatus(readInt())
if err != nil {
adinfo = nil
}
return adinfo, nil
}