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remoteServerList.go
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/
remoteServerList.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 psiphon
import (
"context"
"encoding/hex"
"errors"
"fmt"
"os"
"time"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/osl"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/parameters"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/protocol"
)
type RemoteServerListFetcher func(
ctx context.Context, config *Config, attempt int, tunnel *Tunnel, untunneledDialConfig *DialConfig) error
// FetchCommonRemoteServerList downloads the common remote server list from
// config.RemoteServerListURLs. It validates its digital signature using the
// public key config.RemoteServerListSignaturePublicKey and parses the
// data field into ServerEntry records.
// config.RemoteServerListDownloadFilename is the location to store the
// download. As the download is resumed after failure, this filename must
// be unique and persistent.
func FetchCommonRemoteServerList(
ctx context.Context,
config *Config,
attempt int,
tunnel *Tunnel,
untunneledDialConfig *DialConfig) error {
NoticeInfo("fetching common remote server list")
p := config.clientParameters.Get()
publicKey := p.String(parameters.RemoteServerListSignaturePublicKey)
urls := p.DownloadURLs(parameters.RemoteServerListURLs)
downloadTimeout := p.Duration(parameters.FetchRemoteServerListTimeout)
p = nil
downloadURL, canonicalURL, skipVerify := urls.Select(attempt)
newETag, err := downloadRemoteServerListFile(
ctx,
config,
tunnel,
untunneledDialConfig,
downloadTimeout,
downloadURL,
canonicalURL,
skipVerify,
"",
config.RemoteServerListDownloadFilename)
if err != nil {
return fmt.Errorf("failed to download common remote server list: %s", common.ContextError(err))
}
// When the resource is unchanged, skip.
if newETag == "" {
return nil
}
file, err := os.Open(config.RemoteServerListDownloadFilename)
if err != nil {
return fmt.Errorf("failed to open common remote server list: %s", common.ContextError(err))
}
defer file.Close()
serverListPayloadReader, err := common.NewAuthenticatedDataPackageReader(
file, publicKey)
if err != nil {
return fmt.Errorf("failed to read remote server list: %s", common.ContextError(err))
}
err = StreamingStoreServerEntries(
config,
protocol.NewStreamingServerEntryDecoder(
serverListPayloadReader,
common.GetCurrentTimestamp(),
protocol.SERVER_ENTRY_SOURCE_REMOTE),
true)
if err != nil {
return fmt.Errorf("failed to store common remote server list: %s", common.ContextError(err))
}
// Now that the server entries are successfully imported, store the response
// ETag so we won't re-download this same data again.
err = SetUrlETag(canonicalURL, newETag)
if err != nil {
NoticeAlert("failed to set ETag for common remote server list: %s", common.ContextError(err))
// This fetch is still reported as a success, even if we can't store the etag
}
return nil
}
// FetchObfuscatedServerLists downloads the obfuscated remote server lists
// from config.ObfuscatedServerListRootURLs.
// It first downloads the OSL registry, and then downloads each seeded OSL
// advertised in the registry. All downloads are resumable, ETags are used
// to skip both an unchanged registry or unchanged OSL files, and when an
// individual download fails, the fetch proceeds if it can.
// Authenticated package digital signatures are validated using the
// public key config.RemoteServerListSignaturePublicKey.
// config.ObfuscatedServerListDownloadDirectory is the location to store the
// downloaded files. As downloads are resumed after failure, this directory
// must be unique and persistent.
func FetchObfuscatedServerLists(
ctx context.Context,
config *Config,
attempt int,
tunnel *Tunnel,
untunneledDialConfig *DialConfig) error {
NoticeInfo("fetching obfuscated remote server lists")
p := config.clientParameters.Get()
publicKey := p.String(parameters.RemoteServerListSignaturePublicKey)
urls := p.DownloadURLs(parameters.ObfuscatedServerListRootURLs)
downloadTimeout := p.Duration(parameters.FetchRemoteServerListTimeout)
p = nil
rootURL, canonicalRootURL, skipVerify := urls.Select(attempt)
downloadURL := osl.GetOSLRegistryURL(rootURL)
canonicalURL := osl.GetOSLRegistryURL(canonicalRootURL)
downloadFilename := osl.GetOSLRegistryFilename(config.ObfuscatedServerListDownloadDirectory)
cachedFilename := downloadFilename + ".cached"
// If the cached registry is not present, we need to download or resume downloading
// the registry, so clear the ETag to ensure that always happens.
_, err := os.Stat(cachedFilename)
if os.IsNotExist(err) {
SetUrlETag(canonicalURL, "")
}
// failed is set if any operation fails and should trigger a retry. When the OSL registry
// fails to download, any cached registry is used instead; when any single OSL fails
// to download, the overall operation proceeds. So this flag records whether to report
// failure at the end when downloading has proceeded after a failure.
// TODO: should disk-full conditions not trigger retries?
var failed bool
// updateCache is set when modifed registry content is downloaded. Both the cached
// file and the persisted ETag will be updated in this case. The update is deferred
// until after the registry has been authenticated.
updateCache := false
registryFilename := cachedFilename
newETag, err := downloadRemoteServerListFile(
ctx,
config,
tunnel,
untunneledDialConfig,
downloadTimeout,
downloadURL,
canonicalURL,
skipVerify,
"",
downloadFilename)
if err != nil {
failed = true
NoticeAlert("failed to download obfuscated server list registry: %s", common.ContextError(err))
// Proceed with any existing cached OSL registry.
} else if newETag != "" {
updateCache = true
registryFilename = downloadFilename
}
lookupSLOKs := func(slokID []byte) []byte {
// Lookup SLOKs in local datastore
key, err := GetSLOK(slokID)
if err != nil {
NoticeAlert("GetSLOK failed: %s", err)
}
return key
}
registryFile, err := os.Open(registryFilename)
if err != nil {
return fmt.Errorf("failed to read obfuscated server list registry: %s", common.ContextError(err))
}
defer registryFile.Close()
registryStreamer, err := osl.NewRegistryStreamer(
registryFile,
publicKey,
lookupSLOKs)
if err != nil {
// TODO: delete file? redownload if corrupt?
return fmt.Errorf("failed to read obfuscated server list registry: %s", common.ContextError(err))
}
// NewRegistryStreamer authenticates the downloaded registry, so now it would be
// ok to update the cache. However, we defer that until after processing so we
// can close the file first before copying it, avoiding related complications on
// platforms such as Windows.
// Note: we proceed to check individual OSLs even if the directory is unchanged,
// as the set of local SLOKs may have changed.
for {
oslFileSpec, err := registryStreamer.Next()
if err != nil {
failed = true
NoticeAlert("failed to stream obfuscated server list registry: %s", common.ContextError(err))
break
}
if oslFileSpec == nil {
break
}
downloadFilename := osl.GetOSLFilename(
config.ObfuscatedServerListDownloadDirectory, oslFileSpec.ID)
downloadURL := osl.GetOSLFileURL(rootURL, oslFileSpec.ID)
canonicalURL := osl.GetOSLFileURL(canonicalRootURL, oslFileSpec.ID)
hexID := hex.EncodeToString(oslFileSpec.ID)
// Note: the MD5 checksum step assumes the remote server list host's ETag uses MD5
// with a hex encoding. If this is not the case, the sourceETag should be left blank.
sourceETag := fmt.Sprintf("\"%s\"", hex.EncodeToString(oslFileSpec.MD5Sum))
newETag, err := downloadRemoteServerListFile(
ctx,
config,
tunnel,
untunneledDialConfig,
downloadTimeout,
downloadURL,
canonicalURL,
skipVerify,
sourceETag,
downloadFilename)
if err != nil {
failed = true
NoticeAlert("failed to download obfuscated server list file (%s): %s", hexID, common.ContextError(err))
continue
}
// When the resource is unchanged, skip.
if newETag == "" {
continue
}
file, err := os.Open(downloadFilename)
if err != nil {
failed = true
NoticeAlert("failed to open obfuscated server list file (%s): %s", hexID, common.ContextError(err))
continue
}
// Note: don't defer file.Close() since we're in a loop
serverListPayloadReader, err := osl.NewOSLReader(
file,
oslFileSpec,
lookupSLOKs,
publicKey)
if err != nil {
file.Close()
failed = true
NoticeAlert("failed to read obfuscated server list file (%s): %s", hexID, common.ContextError(err))
continue
}
err = StreamingStoreServerEntries(
config,
protocol.NewStreamingServerEntryDecoder(
serverListPayloadReader,
common.GetCurrentTimestamp(),
protocol.SERVER_ENTRY_SOURCE_OBFUSCATED),
true)
if err != nil {
file.Close()
failed = true
NoticeAlert("failed to store obfuscated server list file (%s): %s", hexID, common.ContextError(err))
continue
}
// Now that the server entries are successfully imported, store the response
// ETag so we won't re-download this same data again.
err = SetUrlETag(canonicalURL, newETag)
if err != nil {
file.Close()
NoticeAlert("failed to set ETag for obfuscated server list file (%s): %s", hexID, common.ContextError(err))
continue
// This fetch is still reported as a success, even if we can't store the ETag
}
file.Close()
// Clear the reference to this OSL file streamer and immediately run
// a garbage collection to reclaim its memory before processing the
// next file.
serverListPayloadReader = nil
defaultGarbageCollection()
}
// Now that a new registry is downloaded, validated, and parsed, store
// the response ETag so we won't re-download this same data again. First
// close the file to avoid complications on platforms such as Windows.
if updateCache {
registryFile.Close()
err := os.Rename(downloadFilename, cachedFilename)
if err != nil {
NoticeAlert("failed to set cached obfuscated server list registry: %s", common.ContextError(err))
// This fetch is still reported as a success, even if we can't update the cache
}
err = SetUrlETag(canonicalURL, newETag)
if err != nil {
NoticeAlert("failed to set ETag for obfuscated server list registry: %s", common.ContextError(err))
// This fetch is still reported as a success, even if we can't store the ETag
}
}
if failed {
return errors.New("one or more operations failed")
}
return nil
}
// downloadRemoteServerListFile downloads the source URL to
// the destination file, performing a resumable download. When
// the download completes and the file content has changed, the
// new resource ETag is returned. Otherwise, blank is returned.
// The caller is responsible for calling SetUrlETag once the file
// content has been validated.
func downloadRemoteServerListFile(
ctx context.Context,
config *Config,
tunnel *Tunnel,
untunneledDialConfig *DialConfig,
downloadTimeout time.Duration,
sourceURL string,
canonicalURL string,
skipVerify bool,
sourceETag string,
destinationFilename string) (string, error) {
// All download URLs with the same canonicalURL
// must have the same entity and ETag.
lastETag, err := GetUrlETag(canonicalURL)
if err != nil {
return "", common.ContextError(err)
}
// sourceETag, when specified, is prior knowledge of the
// remote ETag that can be used to skip the request entirely.
// This will be set in the case of OSL files, from the MD5Sum
// values stored in the registry.
if lastETag != "" && sourceETag == lastETag {
// TODO: notice?
return "", nil
}
var cancelFunc context.CancelFunc
ctx, cancelFunc = context.WithTimeout(ctx, downloadTimeout)
defer cancelFunc()
// MakeDownloadHttpClient will select either a tunneled
// or untunneled configuration.
httpClient, err := MakeDownloadHTTPClient(
ctx,
config,
tunnel,
untunneledDialConfig,
skipVerify)
if err != nil {
return "", common.ContextError(err)
}
n, responseETag, err := ResumeDownload(
ctx,
httpClient,
sourceURL,
MakePsiphonUserAgent(config),
destinationFilename,
lastETag)
NoticeRemoteServerListResourceDownloadedBytes(sourceURL, n)
if err != nil {
return "", common.ContextError(err)
}
if responseETag == lastETag {
return "", nil
}
NoticeRemoteServerListResourceDownloaded(sourceURL)
RecordRemoteServerListStat(sourceURL, responseETag)
return responseETag, nil
}