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serverEntry.go
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serverEntry.go
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/*
* Copyright (c) 2015, Psiphon Inc.
* All rights reserved.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package protocol
import (
"bytes"
"encoding/hex"
"encoding/json"
"errors"
"fmt"
"net"
"strings"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common"
)
// ServerEntry represents a Psiphon server. It contains information
// about how to establish a tunnel connection to the server through
// several protocols. Server entries are JSON records downloaded from
// various sources.
type ServerEntry struct {
IpAddress string `json:"ipAddress"`
WebServerPort string `json:"webServerPort"` // not an int
WebServerSecret string `json:"webServerSecret"`
WebServerCertificate string `json:"webServerCertificate"`
SshPort int `json:"sshPort"`
SshUsername string `json:"sshUsername"`
SshPassword string `json:"sshPassword"`
SshHostKey string `json:"sshHostKey"`
SshObfuscatedPort int `json:"sshObfuscatedPort"`
SshObfuscatedKey string `json:"sshObfuscatedKey"`
Capabilities []string `json:"capabilities"`
Region string `json:"region"`
MeekServerPort int `json:"meekServerPort"`
MeekCookieEncryptionPublicKey string `json:"meekCookieEncryptionPublicKey"`
MeekObfuscatedKey string `json:"meekObfuscatedKey"`
MeekFrontingHost string `json:"meekFrontingHost"`
MeekFrontingHosts []string `json:"meekFrontingHosts"`
MeekFrontingDomain string `json:"meekFrontingDomain"`
MeekFrontingAddresses []string `json:"meekFrontingAddresses"`
MeekFrontingAddressesRegex string `json:"meekFrontingAddressesRegex"`
MeekFrontingDisableSNI bool `json:"meekFrontingDisableSNI"`
// These local fields are not expected to be present in downloaded server
// entries. They are added by the client to record and report stats about
// how and when server entries are obtained.
LocalSource string `json:"localSource"`
LocalTimestamp string `json:"localTimestamp"`
}
// GetCapability returns the server capability corresponding
// to the protocol.
func GetCapability(protocol string) string {
return strings.TrimSuffix(protocol, "-OSSH")
}
// SupportsProtocol returns true if and only if the ServerEntry has
// the necessary capability to support the specified tunnel protocol.
func (serverEntry *ServerEntry) SupportsProtocol(protocol string) bool {
requiredCapability := GetCapability(protocol)
return common.Contains(serverEntry.Capabilities, requiredCapability)
}
// GetSupportedProtocols returns a list of tunnel protocols supported
// by the ServerEntry's capabilities.
func (serverEntry *ServerEntry) GetSupportedProtocols() []string {
supportedProtocols := make([]string, 0)
for _, protocol := range SupportedTunnelProtocols {
if serverEntry.SupportsProtocol(protocol) {
supportedProtocols = append(supportedProtocols, protocol)
}
}
return supportedProtocols
}
// DisableImpairedProtocols modifies the ServerEntry to disable
// the specified protocols.
// Note: this assumes that protocol capabilities are 1-to-1.
func (serverEntry *ServerEntry) DisableImpairedProtocols(impairedProtocols []string) {
capabilities := make([]string, 0)
for _, capability := range serverEntry.Capabilities {
omit := false
for _, protocol := range impairedProtocols {
requiredCapability := GetCapability(protocol)
if capability == requiredCapability {
omit = true
break
}
}
if !omit {
capabilities = append(capabilities, capability)
}
}
serverEntry.Capabilities = capabilities
}
// SupportsSSHAPIRequests returns true when the server supports
// SSH API requests.
func (serverEntry *ServerEntry) SupportsSSHAPIRequests() bool {
return common.Contains(serverEntry.Capabilities, CAPABILITY_SSH_API_REQUESTS)
}
func (serverEntry *ServerEntry) GetUntunneledWebRequestPorts() []string {
ports := make([]string, 0)
if common.Contains(serverEntry.Capabilities, CAPABILITY_UNTUNNELED_WEB_API_REQUESTS) {
// Server-side configuration quirk: there's a port forward from
// port 443 to the web server, which we can try, except on servers
// running FRONTED_MEEK, which listens on port 443.
if !serverEntry.SupportsProtocol(TUNNEL_PROTOCOL_FRONTED_MEEK) {
ports = append(ports, "443")
}
ports = append(ports, serverEntry.WebServerPort)
}
return ports
}
// EncodeServerEntry returns a string containing the encoding of
// a ServerEntry following Psiphon conventions.
func EncodeServerEntry(serverEntry *ServerEntry) (string, error) {
serverEntryContents, err := json.Marshal(serverEntry)
if err != nil {
return "", common.ContextError(err)
}
return hex.EncodeToString([]byte(fmt.Sprintf(
"%s %s %s %s %s",
serverEntry.IpAddress,
serverEntry.WebServerPort,
serverEntry.WebServerSecret,
serverEntry.WebServerCertificate,
serverEntryContents))), nil
}
// DecodeServerEntry extracts server entries from the encoding
// used by remote server lists and Psiphon server handshake requests.
//
// The resulting ServerEntry.LocalSource is populated with serverEntrySource,
// which should be one of SERVER_ENTRY_SOURCE_EMBEDDED, SERVER_ENTRY_SOURCE_REMOTE,
// SERVER_ENTRY_SOURCE_DISCOVERY, SERVER_ENTRY_SOURCE_TARGET.
// ServerEntry.LocalTimestamp is populated with the provided timestamp, which
// should be a RFC 3339 formatted string. These local fields are stored with the
// server entry and reported to the server as stats (a coarse granularity timestamp
// is reported).
func DecodeServerEntry(
encodedServerEntry, timestamp,
serverEntrySource string) (serverEntry *ServerEntry, err error) {
hexDecodedServerEntry, err := hex.DecodeString(encodedServerEntry)
if err != nil {
return nil, common.ContextError(err)
}
// Skip past legacy format (4 space delimited fields) and just parse the JSON config
fields := bytes.SplitN(hexDecodedServerEntry, []byte(" "), 5)
if len(fields) != 5 {
return nil, common.ContextError(errors.New("invalid encoded server entry"))
}
serverEntry = new(ServerEntry)
err = json.Unmarshal(fields[4], &serverEntry)
if err != nil {
return nil, common.ContextError(err)
}
// NOTE: if the source JSON happens to have values in these fields, they get clobbered.
serverEntry.LocalSource = serverEntrySource
serverEntry.LocalTimestamp = timestamp
return serverEntry, nil
}
// ValidateServerEntry checks for malformed server entries.
// Currently, it checks for a valid ipAddress. This is important since
// handshake requests submit back to the server a list of known server
// IP addresses and the handshake API expects well-formed inputs.
// TODO: validate more fields
func ValidateServerEntry(serverEntry *ServerEntry) error {
ipAddr := net.ParseIP(serverEntry.IpAddress)
if ipAddr == nil {
errMsg := fmt.Sprintf("server entry has invalid IpAddress: '%s'", serverEntry.IpAddress)
return common.ContextError(errors.New(errMsg))
}
return nil
}
// DecodeAndValidateServerEntryList extracts server entries from the list encoding
// used by remote server lists and Psiphon server handshake requests.
// Each server entry is validated and invalid entries are skipped.
// See DecodeServerEntry for note on serverEntrySource/timestamp.
func DecodeAndValidateServerEntryList(
encodedServerEntryList, timestamp,
serverEntrySource string) (serverEntries []*ServerEntry, err error) {
serverEntries = make([]*ServerEntry, 0)
for _, encodedServerEntry := range strings.Split(encodedServerEntryList, "\n") {
if len(encodedServerEntry) == 0 {
continue
}
// TODO: skip this entry and continue if can't decode?
serverEntry, err := DecodeServerEntry(encodedServerEntry, timestamp, serverEntrySource)
if err != nil {
return nil, common.ContextError(err)
}
if ValidateServerEntry(serverEntry) != nil {
// Skip this entry and continue with the next one
// TODO: invoke a logging callback
continue
}
serverEntries = append(serverEntries, serverEntry)
}
return serverEntries, nil
}