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upgradeDownload.go
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upgradeDownload.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"
"fmt"
"net/http"
"os"
"strconv"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/parameters"
)
// DownloadUpgrade performs a resumable download of client upgrade files.
//
// While downloading/resuming, a temporary file is used. Once the download is complete,
// a notice is issued and the upgrade is available at the destination specified in
// config.UpgradeDownloadFilename.
//
// The upgrade download may be either tunneled or untunneled. As the untunneled case may
// happen with no handshake request response, the downloader cannot rely on having the
// upgrade_client_version output from handshake and instead this logic performs a
// comparison between the config.ClientVersion and the client version recorded in the
// remote entity's UpgradeDownloadClientVersionHeader. A HEAD request is made to check the
// version before proceeding with a full download.
//
// NOTE: This code does not check that any existing file at config.UpgradeDownloadFilename
// is actually the version specified in handshakeVersion.
//
// TODO: This logic requires the outer client to *omit* config.UpgradeDownloadFilename
// when there's already a downloaded upgrade pending. Because the outer client currently
// handles the authenticated package phase, and because the outer client deletes the
// intermediate files (including config.UpgradeDownloadFilename), if the outer client
// does not omit config.UpgradeDownloadFilename then the new version will be downloaded
// repeatedly. Implement a new scheme where tunnel core does the authenticated package phase
// and tracks the the output by version number so that (a) tunnel core knows when it's not
// necessary to re-download; (b) newer upgrades will be downloaded even when an older
// upgrade is still pending install by the outer client.
func DownloadUpgrade(
ctx context.Context,
config *Config,
attempt int,
handshakeVersion string,
tunnel *Tunnel,
untunneledDialConfig *DialConfig) error {
// Note: this downloader doesn't use ETags since many client binaries, with
// different embedded values, exist for a single version.
// Check if complete file already downloaded
if _, err := os.Stat(config.UpgradeDownloadFilename); err == nil {
NoticeClientUpgradeDownloaded(config.UpgradeDownloadFilename)
return nil
}
p := config.clientParameters.Get()
urls := p.DownloadURLs(parameters.UpgradeDownloadURLs)
clientVersionHeader := p.String(parameters.UpgradeDownloadClientVersionHeader)
downloadTimeout := p.Duration(parameters.FetchUpgradeTimeout)
p = nil
var cancelFunc context.CancelFunc
ctx, cancelFunc = context.WithTimeout(ctx, downloadTimeout)
defer cancelFunc()
// Select tunneled or untunneled configuration
downloadURL, _, skipVerify := urls.Select(attempt)
httpClient, err := MakeDownloadHTTPClient(
ctx,
config,
tunnel,
untunneledDialConfig,
skipVerify)
// If no handshake version is supplied, make an initial HEAD request
// to get the current version from the version header.
availableClientVersion := handshakeVersion
if availableClientVersion == "" {
request, err := http.NewRequest("HEAD", downloadURL, nil)
if err != nil {
return common.ContextError(err)
}
request = request.WithContext(ctx)
response, err := httpClient.Do(request)
if err == nil && response.StatusCode != http.StatusOK {
response.Body.Close()
err = fmt.Errorf("unexpected response status code: %d", response.StatusCode)
}
if err != nil {
return common.ContextError(err)
}
defer response.Body.Close()
currentClientVersion, err := strconv.Atoi(config.ClientVersion)
if err != nil {
return common.ContextError(err)
}
// Note: if the header is missing, Header.Get returns "" and then
// strconv.Atoi returns a parse error.
availableClientVersion = response.Header.Get(clientVersionHeader)
checkAvailableClientVersion, err := strconv.Atoi(availableClientVersion)
if err != nil {
// If the header is missing or malformed, we can't determine the available
// version number. This is unexpected; but if it happens, it's likely due
// to a server-side configuration issue. In this one case, we don't
// return an error so that we don't go into a rapid retry loop making
// ineffective HEAD requests (the client may still signal an upgrade
// download later in the session).
NoticeAlert(
"failed to download upgrade: invalid %s header value %s: %s",
clientVersionHeader, availableClientVersion, err)
return nil
}
if currentClientVersion >= checkAvailableClientVersion {
NoticeClientIsLatestVersion(availableClientVersion)
return nil
}
}
// Proceed with download
// An intermediate filename is used since the presence of
// config.UpgradeDownloadFilename indicates a completed download.
downloadFilename := fmt.Sprintf(
"%s.%s", config.UpgradeDownloadFilename, availableClientVersion)
n, _, err := ResumeDownload(
ctx,
httpClient,
downloadURL,
MakePsiphonUserAgent(config),
downloadFilename,
"")
NoticeClientUpgradeDownloadedBytes(n)
if err != nil {
return common.ContextError(err)
}
err = os.Rename(downloadFilename, config.UpgradeDownloadFilename)
if err != nil {
return common.ContextError(err)
}
NoticeClientUpgradeDownloaded(config.UpgradeDownloadFilename)
return nil
}