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server.go
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server.go
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package main
import (
"bufio"
"crypto/rand"
"crypto/subtle"
"encoding/binary"
"io"
"log"
"net"
"sync"
"sync/atomic"
"time"
"golang.org/x/crypto/ed25519"
)
// ClientConnection - A client connection
type ClientConnection struct {
conf Conf
conn net.Conn
reader *bufio.Reader
writer *bufio.Writer
clientVersion byte
}
// StoredContent - Paste buffer
type StoredContent struct {
sync.RWMutex
encryptSkID []byte
ts []byte
signature []byte
ciphertextWithNonce []byte
}
var storedContent StoredContent
var trustedClients TrustedClients
var clientsCount = uint64(0)
func (cnx *ClientConnection) getOperation(h1 []byte, isMove bool) {
conf, reader, writer := cnx.conf, cnx.reader, cnx.writer
rbuf := make([]byte, 32)
if _, err := io.ReadFull(reader, rbuf); err != nil {
log.Print(err)
return
}
h2 := rbuf
opcode := byte('G')
if isMove {
opcode = byte('M')
}
wh2 := auth2get(conf, cnx.clientVersion, h1, opcode)
if subtle.ConstantTimeCompare(wh2, h2) != 1 {
return
}
var encryptSkID, ts, signature, ciphertextWithNonce []byte
if isMove {
storedContent.Lock()
encryptSkID, ts, signature, ciphertextWithNonce =
storedContent.encryptSkID, storedContent.ts,
storedContent.signature, storedContent.ciphertextWithNonce
storedContent.encryptSkID, storedContent.ts, storedContent.signature,
storedContent.ciphertextWithNonce = nil, nil, nil, nil
storedContent.Unlock()
} else {
storedContent.RLock()
encryptSkID, ts, signature, ciphertextWithNonce =
storedContent.encryptSkID, storedContent.ts, storedContent.signature,
storedContent.ciphertextWithNonce
storedContent.RUnlock()
}
cnx.conn.SetDeadline(time.Now().Add(conf.DataTimeout))
h3 := auth3get(conf, cnx.clientVersion, h2, encryptSkID, ts, signature)
writer.Write(h3)
ciphertextWithNonceLen := uint64(len(ciphertextWithNonce))
binary.Write(writer, binary.LittleEndian, ciphertextWithNonceLen)
writer.Write(encryptSkID)
if cnx.clientVersion >= 5 {
writer.Write(ts)
}
writer.Write(signature)
writer.Write(ciphertextWithNonce)
if err := writer.Flush(); err != nil {
log.Print(err)
return
}
}
func (cnx *ClientConnection) storeOperation(h1 []byte) {
conf, reader, writer := cnx.conf, cnx.reader, cnx.writer
var rbuf []byte
if cnx.clientVersion < 5 {
rbuf = make([]byte, 112)
} else {
rbuf = make([]byte, 120)
}
if _, err := io.ReadFull(reader, rbuf); err != nil {
log.Print(err)
return
}
h2 := rbuf[0:32]
ciphertextWithNonceLen := binary.LittleEndian.Uint64(rbuf[32:40])
if conf.MaxLen > 0 && ciphertextWithNonceLen > conf.MaxLen {
log.Printf("%v bytes requested to be stored, but limit set to %v bytes (%v Mb)\n",
ciphertextWithNonceLen, conf.MaxLen, conf.MaxLen/(1024*1024))
return
}
encryptSkID := rbuf[40:48]
var ts, signature []byte
if cnx.clientVersion < 5 {
ts = make([]byte, 8)
binary.LittleEndian.PutUint64(ts, uint64(time.Now().Unix()))
signature = rbuf[48:112]
} else {
ts = rbuf[48:56]
signature = rbuf[56:120]
}
opcode := byte('S')
wh2 := auth2store(conf, cnx.clientVersion, h1, opcode, encryptSkID, ts, signature)
if subtle.ConstantTimeCompare(wh2, h2) != 1 {
return
}
ciphertextWithNonce := make([]byte, ciphertextWithNonceLen)
cnx.conn.SetDeadline(time.Now().Add(conf.DataTimeout))
if _, err := io.ReadFull(reader, ciphertextWithNonce); err != nil {
log.Print(err)
return
}
if ed25519.Verify(conf.SignPk, ciphertextWithNonce, signature) != true {
return
}
h3 := auth3store(conf, h2)
storedContent.Lock()
storedContent.encryptSkID = encryptSkID
storedContent.ts = ts
storedContent.signature = signature
storedContent.ciphertextWithNonce = ciphertextWithNonce
storedContent.Unlock()
writer.Write(h3)
if err := writer.Flush(); err != nil {
log.Print(err)
return
}
}
func handleClientConnection(conf Conf, conn net.Conn) {
defer conn.Close()
reader, writer := bufio.NewReader(conn), bufio.NewWriter(conn)
cnx := ClientConnection{
conf: conf,
conn: conn,
reader: reader,
writer: writer,
}
rbuf := make([]byte, 65)
if _, err := io.ReadFull(reader, rbuf); err != nil {
return
}
cnx.clientVersion = rbuf[0]
if cnx.clientVersion < 4 || cnx.clientVersion > 5 {
log.Print("Unsupported client version - Please run the same version on the server and on the client")
return
}
r := rbuf[1:33]
h0 := rbuf[33:65]
wh0 := auth0(conf, cnx.clientVersion, r)
if subtle.ConstantTimeCompare(wh0, h0) != 1 {
return
}
r2 := make([]byte, 32)
if _, err := rand.Read(r); err != nil {
log.Fatal(err)
}
h1 := auth1(conf, cnx.clientVersion, h0, r2)
writer.Write([]byte{cnx.clientVersion})
writer.Write(r2)
writer.Write(h1)
if err := writer.Flush(); err != nil {
log.Print(err)
return
}
remoteIP := cnx.conn.RemoteAddr().(*net.TCPAddr).IP
addToTrustedIPs(conf, remoteIP)
opcode, err := reader.ReadByte()
if err != nil {
return
}
switch opcode {
case byte('G'):
cnx.getOperation(h1, false)
case byte('M'):
cnx.getOperation(h1, true)
case byte('S'):
cnx.storeOperation(h1)
}
}
// TrustedClients - Clients IPs having recently performed a succesful handshake
type TrustedClients struct {
sync.RWMutex
ips []net.IP
}
func addToTrustedIPs(conf Conf, ip net.IP) {
trustedClients.Lock()
if uint64(len(trustedClients.ips)) >= conf.TrustedIPCount {
trustedClients.ips = append(trustedClients.ips[1:], ip)
} else {
trustedClients.ips = append(trustedClients.ips, ip)
}
trustedClients.Unlock()
}
func isIPTrusted(conf Conf, ip net.IP) bool {
trustedClients.RLock()
defer trustedClients.RUnlock()
if len(trustedClients.ips) == 0 {
return true
}
for _, foundIP := range trustedClients.ips {
if foundIP.Equal(ip) {
return true
}
}
return false
}
func acceptClient(conf Conf, conn net.Conn) {
handleClientConnection(conf, conn)
atomic.AddUint64(&clientsCount, ^uint64(0))
}
func maybeAcceptClient(conf Conf, conn net.Conn) {
conn.SetDeadline(time.Now().Add(conf.Timeout))
remoteIP := conn.RemoteAddr().(*net.TCPAddr).IP
for {
count := atomic.LoadUint64(&clientsCount)
if count >= conf.MaxClients-conf.TrustedIPCount && isIPTrusted(conf, remoteIP) == false {
conn.Close()
return
}
if count >= conf.MaxClients {
conn.Close()
return
} else if atomic.CompareAndSwapUint64(&clientsCount, count, count+1) {
break
}
}
go acceptClient(conf, conn)
}
// RunServer - run a server
func RunServer(conf Conf) {
go handleSignals()
listen, err := net.Listen("tcp", conf.Listen)
if err != nil {
log.Fatal(err)
}
defer listen.Close()
for {
conn, err := listen.Accept()
if err != nil {
log.Fatal(err)
}
maybeAcceptClient(conf, conn)
}
}