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resolver.go
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resolver.go
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package ara
import (
"context"
"net"
"net/http/httptrace"
)
// A Resolver looks up hosts.
type Resolver interface {
LookupHost(ctx context.Context, host string) ([]string, error)
}
type resolver struct {
hosts map[string][]string
}
// NewCustomResolver returns a resolver that will give priority
// to given host/ip mappings on lookups.
//
// If a host is not part of the given mapping, it will use the
// net.DefaultResolver.
//
// hosts is a map of addresses for a host name, like map[host][]address.
func NewCustomResolver(hosts map[string][]string) Resolver {
return &resolver{
hosts: hosts,
}
}
func handleClientTrace(t *httptrace.ClientTrace, host string, records []string) {
if t.DNSStart != nil {
t.DNSStart(httptrace.DNSStartInfo{
Host: host,
})
}
if t.DNSDone != nil {
var addrs []net.IPAddr
for _, rec := range records {
ip := net.ParseIP(rec)
if ip != nil {
addrs = append(addrs, net.IPAddr{
IP: ip,
})
}
}
t.DNSDone(httptrace.DNSDoneInfo{
Addrs: addrs,
})
}
}
func (r *resolver) LookupHost(ctx context.Context, host string) ([]string, error) {
records := r.hosts[host]
if records != nil && len(records) != 0 {
t := httptrace.ContextClientTrace(ctx)
if t != nil {
handleClientTrace(t, host, records)
}
return records, nil
}
return net.DefaultResolver.LookupHost(ctx, host)
}