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package listen
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import (
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	"fmt"
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	"net"
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	"strings"
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)
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type IPVersion int
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const (
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	IPAny IPVersion = iota
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	IPV4
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	IPV6
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)
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const (
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	// FlyGlobalServicesHost is a special-cased hostname used by Fly.io's
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	// anycast load balancer. UDP traffic is only delivered on IPv4, even if
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	// AAAA records exist, so we force an IPv4 bind when this host is used.
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	FlyGlobalServicesHost = "fly-global-services"
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)
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type Address struct {
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	Address string
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	Host    string
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	Network string
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	Version IPVersion
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}
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// ParseAddresses normalizes listen addresses and expands per-family networks.
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// baseAddrs is the shared list (e.g. listen-addr). If overrides are provided
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// and non-empty after trimming, they replace the base list.
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func ParseAddresses(proto string, baseAddrs []string, overrides []string) ([]Address, error) {
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	addrs := coalesceAddrs(baseAddrs)
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	if trimmed := coalesceAddrs(overrides); len(trimmed) > 0 {
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		addrs = trimmed
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	}
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	if len(addrs) == 0 {
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		return nil, fmt.Errorf("no listen addresses provided for %s", proto)
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	}
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	seen := make(map[string]struct{}, len(addrs))
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	out := make([]Address, 0, len(addrs))
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	for _, a := range addrs {
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		if _, ok := seen[a]; ok {
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			continue
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		}
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		host, _, err := net.SplitHostPort(a)
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		if err != nil {
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			return nil, err
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		}
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		if host != "" && net.ParseIP(host) == nil && host != FlyGlobalServicesHost {
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			return nil, fmt.Errorf("listen host must be an IP address (got %q)", host)
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		}
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		seen[a] = struct{}{}
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		version := overrideHostIPVersion(host, ClassifyIPVersion(host))
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		out = append(out, Address{
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			Address: a,
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			Host:    host,
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			Version: version,
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			Network: NetworkForVersion(proto, version),
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		})
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	}
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	return out, nil
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}
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// coalesceAddrs trims whitespace and drops empties.
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func coalesceAddrs(addrs []string) []string {
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	out := make([]string, 0, len(addrs))
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	for _, a := range addrs {
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		v := strings.TrimSpace(a)
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		if v == "" {
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			continue
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		}
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		out = append(out, v)
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	}
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	return out
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}
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func ClassifyIPVersion(host string) IPVersion {
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	ip := net.ParseIP(host)
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	if ip == nil {
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		return IPAny
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	}
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	if ip.To4() != nil {
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		return IPV4
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	}
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	return IPV6
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}
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// overrideHostIPVersion applies known host-specific IP family constraints.
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func overrideHostIPVersion(host string, version IPVersion) IPVersion {
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	if host == FlyGlobalServicesHost {
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		// Fly UDP proxy is IPv4-only; force v4 even if the hostname resolves to v6.
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		return IPV4
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	}
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	return version
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}
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func NetworkForVersion(proto string, version IPVersion) string {
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	switch version {
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	case IPV4:
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		return proto + "4"
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	case IPV6:
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		return proto + "6"
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	default:
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		return proto
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	}
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}