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userAgentPicker.go
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/
userAgentPicker.go
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/*
* Copyright (c) 2017, 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 (
"net/http"
"sync/atomic"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/parameters"
)
var registeredUserAgentPicker atomic.Value
func RegisterUserAgentPicker(picker func() string) {
registeredUserAgentPicker.Store(picker)
}
func pickUserAgent() string {
picker := registeredUserAgentPicker.Load()
if picker != nil {
return picker.(func() string)()
}
return ""
}
// PickUserAgentIfUnset selects a User-Agent header if one is not set.
func PickUserAgentIfUnset(
p *parameters.ClientParametersSnapshot, headers http.Header) (bool, string) {
if _, ok := headers["User-Agent"]; !ok {
userAgent := ""
if p.WeightedCoinFlip(parameters.PickUserAgentProbability) {
userAgent = pickUserAgent()
}
return true, userAgent
}
return false, ""
}