// selectProtocol is a helper that picks the tunnel protocol
func selectProtocol(
config *Config, serverEntry *protocol.ServerEntry) (selectedProtocol string, err error) {
// TODO: properly handle protocols (e.g. FRONTED-MEEK-OSSH) vs. capabilities (e.g., {FRONTED-MEEK, OSSH})
// for now, the code is simply assuming that MEEK capabilities imply OSSH capability.
if config.TunnelProtocol != "" {
if !serverEntry.SupportsProtocol(config.TunnelProtocol) {
return "", common.ContextError(fmt.Errorf("server does not have required capability"))
}
selectedProtocol = config.TunnelProtocol
} else {
// Pick at random from the supported protocols. This ensures that we'll eventually
// try all possible protocols. Depending on network configuration, it may be the
// case that some protocol is only available through multi-capability servers,
// and a simpler ranked preference of protocols could lead to that protocol never
// being selected.
candidateProtocols := serverEntry.GetSupportedProtocols()
if len(candidateProtocols) == 0 {
return "", common.ContextError(fmt.Errorf("server does not have any supported capabilities"))
}
index, err := common.MakeSecureRandomInt(len(candidateProtocols))
if err != nil {
return "", common.ContextError(err)
}
selectedProtocol = candidateProtocols[index]
}
return selectedProtocol, nil
}
// MakeCompatibleServerEntry provides backwards compatibility with old server entries
// which have a single meekFrontingDomain and not a meekFrontingAddresses array.
// By copying this one meekFrontingDomain into meekFrontingAddresses, this client effectively
// uses that single value as legacy clients do.
func MakeCompatibleServerEntry(serverEntry *protocol.ServerEntry) *protocol.ServerEntry {
if len(serverEntry.MeekFrontingAddresses) == 0 && serverEntry.MeekFrontingDomain != "" {
serverEntry.MeekFrontingAddresses =
append(serverEntry.MeekFrontingAddresses, serverEntry.MeekFrontingDomain)
}
return serverEntry
}