102 lines
2.3 KiB
Go
102 lines
2.3 KiB
Go
package upstream
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import (
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"net"
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"strings"
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"github.com/miekg/dns"
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"golang.org/x/net/context"
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)
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// Detects the upstream type from the specified url and creates a proper Upstream object
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func NewUpstream(url string, bootstrap string) (Upstream, error) {
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proto := "udp"
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prefix := ""
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switch {
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case strings.HasPrefix(url, "tcp://"):
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proto = "tcp"
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prefix = "tcp://"
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case strings.HasPrefix(url, "tls://"):
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proto = "tcp-tls"
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prefix = "tls://"
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case strings.HasPrefix(url, "https://"):
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return NewHttpsUpstream(url, bootstrap)
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}
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hostname := strings.TrimPrefix(url, prefix)
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host, port, err := net.SplitHostPort(hostname)
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if err != nil {
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// Set port depending on the protocol
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switch proto {
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case "udp":
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port = "53"
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case "tcp":
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port = "53"
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case "tcp-tls":
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port = "853"
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}
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// Set host = hostname
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host = hostname
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}
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// Try to resolve the host address (or check if it's an IP address)
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bootstrapResolver := CreateResolver(bootstrap)
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ips, err := bootstrapResolver.LookupIPAddr(context.Background(), host)
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if err != nil || len(ips) == 0 {
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return nil, err
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}
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addr := ips[0].String()
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endpoint := net.JoinHostPort(addr, port)
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tlsServerName := ""
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if proto == "tcp-tls" && host != addr {
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// Check if we need to specify TLS server name
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tlsServerName = host
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}
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return NewDnsUpstream(endpoint, proto, tlsServerName)
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}
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func CreateResolver(bootstrap string) *net.Resolver {
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bootstrapResolver := net.DefaultResolver
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if bootstrap != "" {
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bootstrapResolver = &net.Resolver{
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PreferGo: true,
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Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
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var d net.Dialer
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return d.DialContext(ctx, network, bootstrap)
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},
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}
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}
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return bootstrapResolver
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}
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// Performs a simple health-check of the specified upstream
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func IsAlive(u Upstream) (bool, error) {
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// Using ipv4only.arpa. domain as it is a part of DNS64 RFC and it should exist everywhere
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ping := new(dns.Msg)
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ping.SetQuestion("ipv4only.arpa.", dns.TypeA)
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resp, err := u.Exchange(context.Background(), ping)
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// If we got a header, we're alright, basically only care about I/O errors 'n stuff.
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if err != nil && resp != nil {
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// Silly check, something sane came back.
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if resp.Rcode != dns.RcodeServerFailure {
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err = nil
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}
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}
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return err == nil, err
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}
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