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refactor(resolver): extract preference constants and shouldReturn helper

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Replace 10 raw "ipv4"/"ipv6" string literals with preferIPv4/preferIPv6
constants, extract the duplicated fallback-condition check (repeated 4x
across resolve and lookupCache) into shouldReturn, and fix a misleading
doc comment on resolvePreference's default return.
This commit is contained in:
ginuerzh
2026-05-25 21:54:54 +08:00
parent 039bcc9af9
commit f20e151cfa
1 changed files with 26 additions and 14 deletions
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resolver/resolver.go
+26 -14
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@@ -56,7 +56,12 @@ func LoggerOption(logger logger.Logger) Option {
} }
} }
const maxAsyncRefresh = 32 // max concurrent background refresh goroutines const (
maxAsyncRefresh = 32 // max concurrent background refresh goroutines
preferIPv4 = "ipv4"
preferIPv6 = "ipv6"
)
// localResolver resolves hostnames via DNS using configured nameservers and a cache. // localResolver resolves hostnames via DNS using configured nameservers and a cache.
type localResolver struct { type localResolver struct {
@@ -101,11 +106,11 @@ func NewResolver(nameservers []NameServer, opts ...Option) (resolver.Resolver, e
switch server.Only { switch server.Only {
case "ip4", "ipv4": case "ip4", "ipv4":
server.Only = "ipv4" server.Only = preferIPv4
server.Prefer = "ipv4" server.Prefer = preferIPv4
case "ip6", "ipv6": case "ip6", "ipv6":
server.Only = "ipv6" server.Only = preferIPv6
server.Prefer = "ipv6" server.Prefer = preferIPv6
default: default:
server.Only = "" server.Only = ""
} }
@@ -130,9 +135,9 @@ func NewResolver(nameservers []NameServer, opts ...Option) (resolver.Resolver, e
func callerNetworkPref(network string) string { func callerNetworkPref(network string) string {
switch network { switch network {
case "ip4": case "ip4":
return "ipv4" return preferIPv4
case "ip6": case "ip6":
return "ipv6" return preferIPv6
default: default:
return "" return ""
} }
@@ -183,7 +188,14 @@ func resolvePreference(server *NameServer, callerPref string) string {
if server.Prefer != "" { if server.Prefer != "" {
return server.Prefer return server.Prefer
} }
return "" // default: ipv4-first return ""
}
// shouldReturn reports whether results from the given address family should be
// accepted without falling back to the other family. Returns true when results
// were found, or when a hard constraint (Only or caller network) pins to this family.
func shouldReturn(ips []net.IP, server *NameServer, callerPref, family string) bool {
return len(ips) > 0 || server.Only == family || callerPref == family
} }
func (r *localResolver) resolve(ctx context.Context, server *NameServer, host string, callerPref string) (ips []net.IP, err error) { func (r *localResolver) resolve(ctx context.Context, server *NameServer, host string, callerPref string) (ips []net.IP, err error) {
@@ -193,14 +205,14 @@ func (r *localResolver) resolve(ctx context.Context, server *NameServer, host st
pref := resolvePreference(server, callerPref) pref := resolvePreference(server, callerPref)
if pref == "ipv6" { if pref == preferIPv6 {
if ips, err = r.resolve6(ctx, server, host); len(ips) > 0 || server.Only == "ipv6" || callerPref == "ipv6" { if ips, err = r.resolve6(ctx, server, host); shouldReturn(ips, server, callerPref, preferIPv6) {
return return
} }
return r.resolve4(ctx, server, host) return r.resolve4(ctx, server, host)
} }
if ips, err = r.resolve4(ctx, server, host); len(ips) > 0 || server.Only == "ipv4" || callerPref == "ipv4" { if ips, err = r.resolve4(ctx, server, host); shouldReturn(ips, server, callerPref, preferIPv4) {
return return
} }
return r.resolve6(ctx, server, host) return r.resolve6(ctx, server, host)
@@ -242,9 +254,9 @@ func (r *localResolver) lookupCache(ctx context.Context, server *NameServer, hos
pref := resolvePreference(server, callerPref) pref := resolvePreference(server, callerPref)
if pref == "ipv6" { if pref == preferIPv6 {
ips, ttl, ok = lookup(dns.TypeAAAA, host) ips, ttl, ok = lookup(dns.TypeAAAA, host)
if len(ips) > 0 || server.Only == "ipv6" || callerPref == "ipv6" { if shouldReturn(ips, server, callerPref, preferIPv6) {
return return
} }
ips, ttl, ok = lookup(dns.TypeA, host) ips, ttl, ok = lookup(dns.TypeA, host)
@@ -252,7 +264,7 @@ func (r *localResolver) lookupCache(ctx context.Context, server *NameServer, hos
} }
ips, ttl, ok = lookup(dns.TypeA, host) ips, ttl, ok = lookup(dns.TypeA, host)
if len(ips) > 0 || server.Only == "ipv4" || callerPref == "ipv4" { if shouldReturn(ips, server, callerPref, preferIPv4) {
return return
} }
return lookup(dns.TypeAAAA, host) return lookup(dns.TypeAAAA, host)