ginuerzh
0522ae8155
When no custom resolver or host mapper is configured, xnet.Resolve now resolves hostnames via Go's native pure-Go resolver (PreferGo: true) instead of returning the hostname unchanged. Previously, the unresolved hostname would reach net.Dialer.DialContext, which on CGO_ENABLED=1 builds used cgo-based DNS — blocking a dedicated OS thread per concurrent lookup. At scale (1000+ listeners), this exhausted Go's 10000-thread limit. Fixes go-gost/gost#550
75 lines
2.0 KiB
Go
75 lines
2.0 KiB
Go
package net
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import (
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"context"
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"fmt"
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"net"
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"github.com/go-gost/core/hosts"
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"github.com/go-gost/core/logger"
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"github.com/go-gost/core/resolver"
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ctxvalue "github.com/go-gost/x/ctx"
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)
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// Resolve resolves addr to a concrete IP address. If hosts is non-nil, it is
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// consulted first. If r is non-nil and no host mapping matched, the resolver
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// is used. If neither is available, Go's native pure-Go resolver is used as a
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// fallback to avoid cgo-based DNS lookups that would block OS threads.
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func Resolve(ctx context.Context, network, addr string, r resolver.Resolver, hosts hosts.HostMapper, log logger.Logger) (string, error) {
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if addr == "" {
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return addr, nil
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}
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host, port, _ := net.SplitHostPort(addr)
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if host == "" {
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return addr, nil
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}
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if log == nil {
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log = logger.Default()
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}
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log = log.WithFields(map[string]any{
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"sid": ctxvalue.SidFromContext(ctx),
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})
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if hosts != nil {
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if ips, _ := hosts.Lookup(ctx, network, host); len(ips) > 0 {
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log.Debugf("hit host mapper: %s -> %s", host, ips)
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return net.JoinHostPort(ips[0].String(), port), nil
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}
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}
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if r != nil {
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ips, err := r.Resolve(ctx, network, host)
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if err != nil {
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if err == resolver.ErrInvalid {
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return addr, nil
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}
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log.Error(err)
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}
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if len(ips) == 0 {
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return "", fmt.Errorf("resolver: domain %s does not exist", host)
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}
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return net.JoinHostPort(ips[0].String(), port), nil
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}
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// A literal IP address needs no resolution.
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if net.ParseIP(host) != nil {
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return addr, nil
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}
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// Fallback to Go's native (pure-Go) resolver when no custom resolver or
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// host mapper is configured. This avoids cgo-based DNS lookups in
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// downstream net.Dialer.DialContext which would block OS threads and
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// cause thread exhaustion under high connection concurrency.
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lr := &net.Resolver{PreferGo: true}
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ips, err := lr.LookupIP(ctx, "ip", host)
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if err != nil {
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return "", err
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}
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if len(ips) == 0 {
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return "", fmt.Errorf("resolver: domain %s does not exist", host)
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}
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return net.JoinHostPort(ips[0].String(), port), nil
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}
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