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psinet.go
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psinet.go
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/*
* Copyright (c) 2016, 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 psiphon/server/psinet implements psinet database services. The psinet
// database is a JSON-format file containing information about the Psiphon network,
// including sponsors, home pages, stats regexes, available upgrades, and other
// servers for discovery. This package also implements the Psiphon discovery algorithm.
package psinet
import (
"encoding/hex"
"encoding/json"
"fmt"
"math"
"math/rand"
"strconv"
"strings"
"time"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common"
)
// Database serves Psiphon API data requests. It's safe for
// concurrent usage. The Reload function supports hot reloading
// of Psiphon network data while the server is running.
type Database struct {
common.ReloadableFile
Hosts map[string]Host `json:"hosts"`
Servers []Server `json:"servers"`
Sponsors map[string]Sponsor `json:"sponsors"`
Versions map[string][]ClientVersion `json:"client_versions"`
DefaultSponsorID string `json:"default_sponsor_id"`
}
type Host struct {
DatacenterName string `json:"datacenter_name"`
Id string `json:"id"`
IpAddress string `json:"ip_address"`
IsTCS bool `json:"is_TCS"`
MeekCookieEncryptionPublicKey string `json:"meek_cookie_encryption_public_key"`
MeekServerObfuscatedKey string `json:"meek_server_obfuscated_key"`
MeekServerPort int `json:"meek_server_port"`
Region string `json:"region"`
}
type Server struct {
AlternateSshObfuscatedPorts []string `json:"alternate_ssh_obfuscated_ports"`
Capabilities map[string]bool `json:"capabilities"`
DiscoveryDateRange []string `json:"discovery_date_range"`
EgressIpAddress string `json:"egress_ip_address"`
HostId string `json:"host_id"`
Id string `json:"id"`
InternalIpAddress string `json:"internal_ip_address"`
IpAddress string `json:"ip_address"`
IsEmbedded bool `json:"is_embedded"`
IsPermanent bool `json:"is_permanent"`
PropogationChannelId string `json:"propagation_channel_id"`
SshHostKey string `json:"ssh_host_key"`
SshObfuscatedKey string `json:"ssh_obfuscated_key"`
SshObfuscatedPort int `json:"ssh_obfuscated_port"`
SshPassword string `json:"ssh_password"`
SshPort string `json:"ssh_port"`
SshUsername string `json:"ssh_username"`
WebServerCertificate string `json:"web_server_certificate"`
WebServerPort string `json:"web_server_port"`
WebServerSecret string `json:"web_server_secret"`
}
type Sponsor struct {
Banner string
HomePages map[string][]HomePage `json:"home_pages"`
HttpsRequestRegexes []HttpsRequestRegex `json:"https_request_regexes"`
Id string `json:"id"`
MobileHomePages map[string][]HomePage `json:"mobile_home_pages"`
Name string `json:"name"`
PageViewRegexes []PageViewRegex `json:"page_view_regexes"`
WebsiteBanner string `json:"website_banner"`
WebsiteBannerLink string `json:"website_banner_link"`
}
type ClientVersion struct {
Version string `json:"version"`
}
type HomePage struct {
Region string `json:"region"`
Url string `json:"url"`
}
type HttpsRequestRegex struct {
Regex string `json:"regex"`
Replace string `json:"replace"`
}
type MobileHomePage struct {
Region string `json:"region"`
Url string `json:"url"`
}
type PageViewRegex struct {
Regex string `json:"regex"`
Replace string `json:"replace"`
}
// NewDatabase initializes a Database, calling Reload on the specified
// filename.
func NewDatabase(filename string) (*Database, error) {
database := &Database{}
database.ReloadableFile = common.NewReloadableFile(
filename,
func(fileContent []byte) error {
var newDatabase Database
err := json.Unmarshal(fileContent, &newDatabase)
if err != nil {
return common.ContextError(err)
}
// Note: an unmarshal directly into &database would fail
// to reset to zero value fields not present in the JSON.
database.Hosts = newDatabase.Hosts
database.Servers = newDatabase.Servers
database.Sponsors = newDatabase.Sponsors
database.Versions = newDatabase.Versions
database.DefaultSponsorID = newDatabase.DefaultSponsorID
return nil
})
_, err := database.Reload()
if err != nil {
return nil, common.ContextError(err)
}
return database, nil
}
// GetRandomHomepage returns a random home page from a set of home pages
// for the specified sponsor, region, and platform.
func (db *Database) GetRandomHomepage(sponsorID, clientRegion string, isMobilePlatform bool) []string {
homepages := db.GetHomepages(sponsorID, clientRegion, isMobilePlatform)
if len(homepages) > 0 {
index := rand.Intn(len(homepages))
return homepages[index : index+1]
}
return homepages
}
// GetHomepages returns a list of home pages for the specified sponsor,
// region, and platform.
func (db *Database) GetHomepages(sponsorID, clientRegion string, isMobilePlatform bool) []string {
db.ReloadableFile.RLock()
defer db.ReloadableFile.RUnlock()
sponsorHomePages := make([]string, 0)
// Sponsor id does not exist: fail gracefully
sponsor, ok := db.Sponsors[sponsorID]
if !ok {
sponsor, ok = db.Sponsors[db.DefaultSponsorID]
if !ok {
return sponsorHomePages
}
}
homePages := sponsor.HomePages
if isMobilePlatform {
if len(sponsor.MobileHomePages) > 0 {
homePages = sponsor.MobileHomePages
}
}
// Case: lookup succeeded and corresponding homepages found for region
homePagesByRegion, ok := homePages[clientRegion]
if ok {
for _, homePage := range homePagesByRegion {
sponsorHomePages = append(sponsorHomePages, strings.Replace(homePage.Url, "client_region=XX", "client_region="+clientRegion, 1))
}
}
// Case: lookup failed or no corresponding homepages found for region --> use default
if len(sponsorHomePages) == 0 {
defaultHomePages, ok := homePages["None"]
if ok {
for _, homePage := range defaultHomePages {
// client_region query parameter substitution
sponsorHomePages = append(sponsorHomePages, strings.Replace(homePage.Url, "client_region=XX", "client_region="+clientRegion, 1))
}
}
}
return sponsorHomePages
}
// GetUpgradeClientVersion returns a new client version when an upgrade is
// indicated for the specified client current version. The result is "" when
// no upgrade is available. Caller should normalize clientPlatform.
func (db *Database) GetUpgradeClientVersion(clientVersion, clientPlatform string) string {
db.ReloadableFile.RLock()
defer db.ReloadableFile.RUnlock()
// Check lastest version number against client version number
clientVersions, ok := db.Versions[clientPlatform]
if !ok {
return ""
}
if len(clientVersions) == 0 {
return ""
}
// NOTE: Assumes versions list is in ascending version order
lastVersion := clientVersions[len(clientVersions)-1].Version
lastVersionInt, err := strconv.Atoi(lastVersion)
if err != nil {
return ""
}
clientVersionInt, err := strconv.Atoi(clientVersion)
if err != nil {
return ""
}
// Return latest version if upgrade needed
if lastVersionInt > clientVersionInt {
return lastVersion
}
return ""
}
// GetHttpsRequestRegexes returns bytes transferred stats regexes for the
// specified sponsor.
func (db *Database) GetHttpsRequestRegexes(sponsorID string) []map[string]string {
db.ReloadableFile.RLock()
defer db.ReloadableFile.RUnlock()
regexes := make([]map[string]string, 0)
sponsor, ok := db.Sponsors[sponsorID]
if !ok {
sponsor, ok = db.Sponsors[db.DefaultSponsorID]
}
// If neither sponsorID or DefaultSponsorID were found, sponsor will be the
// zero value of the map, an empty Sponsor struct.
for _, sponsorRegex := range sponsor.HttpsRequestRegexes {
regex := make(map[string]string)
regex["replace"] = sponsorRegex.Replace
regex["regex"] = sponsorRegex.Regex
regexes = append(regexes, regex)
}
return regexes
}
// DiscoverServers selects new encoded server entries to be "discovered" by
// the client, using the discoveryValue -- a function of the client's IP
// address -- as the input into the discovery algorithm.
// The server list (db.Servers) loaded from JSON is stored as an array instead of
// a map to ensure servers are discovered deterministically. Each iteration over a
// map in go is seeded with a random value which causes non-deterministic ordering.
func (db *Database) DiscoverServers(discoveryValue int) []string {
db.ReloadableFile.RLock()
defer db.ReloadableFile.RUnlock()
var servers []Server
discoveryDate := time.Now().UTC()
candidateServers := make([]Server, 0)
for _, server := range db.Servers {
var start time.Time
var end time.Time
var err error
// All servers that are discoverable on this day are eligable for discovery
if len(server.DiscoveryDateRange) != 0 {
start, err = time.Parse("2006-01-02T15:04:05", server.DiscoveryDateRange[0])
if err != nil {
continue
}
end, err = time.Parse("2006-01-02T15:04:05", server.DiscoveryDateRange[1])
if err != nil {
continue
}
if discoveryDate.After(start) && discoveryDate.Before(end) {
candidateServers = append(candidateServers, server)
}
}
}
timeInSeconds := int(discoveryDate.Unix())
servers = selectServers(candidateServers, timeInSeconds, discoveryValue)
encodedServerEntries := make([]string, 0)
for _, server := range servers {
encodedServerEntries = append(encodedServerEntries, db.getEncodedServerEntry(server))
}
return encodedServerEntries
}
// Combine client IP address and time-of-day strategies to give out different
// discovery servers to different clients. The aim is to achieve defense against
// enumerability. We also want to achieve a degree of load balancing clients
// and these strategies are expected to have reasonably random distribution,
// even for a cluster of users coming from the same network.
//
// We only select one server: multiple results makes enumeration easier; the
// strategies have a built-in load balancing effect; and date range discoverability
// means a client will actually learn more servers later even if they happen to
// always pick the same result at this point.
//
// This is a blended strategy: as long as there are enough servers to pick from,
// both aspects determine which server is selected. IP address is given the
// priority: if there are only a couple of servers, for example, IP address alone
// determines the outcome.
func selectServers(servers []Server, timeInSeconds, discoveryValue int) []Server {
TIME_GRANULARITY := 3600
if len(servers) == 0 {
return nil
}
// Time truncated to an hour
timeStrategyValue := timeInSeconds / TIME_GRANULARITY
// Divide servers into buckets. The bucket count is chosen such that the number
// of buckets and the number of items in each bucket are close (using sqrt).
// IP address selects the bucket, time selects the item in the bucket.
// NOTE: this code assumes that the range of possible timeStrategyValues
// and discoveryValues are sufficient to index to all bucket items.
bucketCount := calculateBucketCount(len(servers))
buckets := bucketizeServerList(servers, bucketCount)
if len(buckets) == 0 {
return nil
}
bucket := buckets[discoveryValue%len(buckets)]
if len(bucket) == 0 {
return nil
}
server := bucket[timeStrategyValue%len(bucket)]
serverList := make([]Server, 1)
serverList[0] = server
return serverList
}
// Number of buckets such that first strategy picks among about the same number
// of choices as the second strategy. Gives an edge to the "outer" strategy.
func calculateBucketCount(length int) int {
return int(math.Ceil(math.Sqrt(float64(length))))
}
// bucketizeServerList creates nearly equal sized slices of the input list.
func bucketizeServerList(servers []Server, bucketCount int) [][]Server {
// This code creates the same partitions as legacy servers:
// https://bitbucket.org/psiphon/psiphon-circumvention-system/src/03bc1a7e51e7c85a816e370bb3a6c755fd9c6fee/Automation/psi_ops_discovery.py
//
// Both use the same algorithm from:
// http://stackoverflow.com/questions/2659900/python-slicing-a-list-into-n-nearly-equal-length-partitions
// TODO: this partition is constant for fixed Database content, so it could
// be done once and cached in the Database ReloadableFile reloadAction.
buckets := make([][]Server, bucketCount)
division := float64(len(servers)) / float64(bucketCount)
for i := 0; i < bucketCount; i++ {
start := int((division * float64(i)) + 0.5)
end := int((division * (float64(i) + 1)) + 0.5)
buckets[i] = servers[start:end]
}
return buckets
}
// Return hex encoded server entry string for comsumption by client.
// Newer clients ignore the legacy fields and only utilize the extended (new) config.
func (db *Database) getEncodedServerEntry(server Server) string {
host, hostExists := db.Hosts[server.HostId]
if !hostExists {
return ""
}
// TCS web server certificate has PEM headers and newlines, so strip those now
// for legacy format compatibility
webServerCertificate := server.WebServerCertificate
if host.IsTCS {
splitCert := strings.Split(server.WebServerCertificate, "\n")
if len(splitCert) <= 2 {
webServerCertificate = ""
} else {
webServerCertificate = strings.Join(splitCert[1:len(splitCert)-2], "")
}
}
// Double-check that we're not giving our blank server credentials
if len(server.IpAddress) <= 1 || len(server.WebServerPort) <= 1 || len(server.WebServerSecret) <= 1 || len(webServerCertificate) <= 1 {
return ""
}
// Extended (new) entry fields are in a JSON string
var extendedConfig 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"`
}
// NOTE: also putting original values in extended config for easier parsing by new clients
extendedConfig.IpAddress = server.IpAddress
extendedConfig.WebServerPort = server.WebServerPort
extendedConfig.WebServerSecret = server.WebServerSecret
extendedConfig.WebServerCertificate = webServerCertificate
sshPort, err := strconv.Atoi(server.SshPort)
if err != nil {
extendedConfig.SshPort = 0
} else {
extendedConfig.SshPort = sshPort
}
extendedConfig.SshUsername = server.SshUsername
extendedConfig.SshPassword = server.SshPassword
sshHostKeyType, sshHostKey := parseSshKeyString(server.SshHostKey)
if strings.Compare(sshHostKeyType, "ssh-rsa") == 0 {
extendedConfig.SshHostKey = sshHostKey
} else {
extendedConfig.SshHostKey = ""
}
extendedConfig.SshObfuscatedPort = server.SshObfuscatedPort
// Use the latest alternate port unless tunneling through meek
if len(server.AlternateSshObfuscatedPorts) > 0 && !server.Capabilities["UNFRONTED-MEEK"] {
port, err := strconv.Atoi(server.AlternateSshObfuscatedPorts[len(server.AlternateSshObfuscatedPorts)-1])
if err == nil {
extendedConfig.SshObfuscatedPort = port
}
}
extendedConfig.SshObfuscatedKey = server.SshObfuscatedKey
extendedConfig.Region = host.Region
extendedConfig.MeekCookieEncryptionPublicKey = host.MeekCookieEncryptionPublicKey
extendedConfig.MeekServerPort = host.MeekServerPort
extendedConfig.MeekObfuscatedKey = host.MeekServerObfuscatedKey
serverCapabilities := make(map[string]bool, 0)
for capability, enabled := range server.Capabilities {
serverCapabilities[capability] = enabled
}
if serverCapabilities["UNFRONTED-MEEK"] && host.MeekServerPort == 443 {
serverCapabilities["UNFRONTED-MEEK"] = false
serverCapabilities["UNFRONTED-MEEK-HTTPS"] = true
}
for capability, enabled := range serverCapabilities {
if enabled == true {
extendedConfig.Capabilities = append(extendedConfig.Capabilities, capability)
}
}
jsonDump, err := json.Marshal(extendedConfig)
if err != nil {
return ""
}
// Legacy format + extended (new) config
prefixString := fmt.Sprintf("%s %s %s %s ", server.IpAddress, server.WebServerPort, server.WebServerSecret, webServerCertificate)
return hex.EncodeToString(append([]byte(prefixString)[:], []byte(jsonDump)[:]...))
}
// Parse string of format "ssh-key-type ssh-key".
func parseSshKeyString(sshKeyString string) (keyType string, key string) {
sshKeyArr := strings.Split(sshKeyString, " ")
if len(sshKeyArr) != 2 {
return "", ""
}
return sshKeyArr[0], sshKeyArr[1]
}