mem-resolver
memresolver is an in-memory golang resolver that allows to override current golang Lookup func literals
How to use it
Create your custom Lookup function, is it common to overwrite LookupIP, that is the one used by the Dialer so we can redirect custom domains, per example.
func myLookupIP(ctx context.Context, network, host string) ([]net.IP, error) {
// fqdn appends a dot
if "mycustom.mydomain" == strings.TrimSuffix(host, ".") {
return []net.IP{net.ParseIP("127.0.0.1")}, nil
}
return net.DefaultResolver.LookupIP(ctx, network, host)
}
Once we have our cusotm Lookup function we create a custom net.Resolver
f := &MemResolver{
LookupIP: myLookupIP,
}
// override lookupIP
resolver := NewMemoryResolver(f)
This custom resolver implements a Dial function that can be used to override the net.Dialer resolver.
tr := &http.Transport{
Proxy: http.ProxyFromEnvironment,
DialContext: (&net.Dialer{
Timeout: 30 * time.Second,
KeepAlive: 30 * time.Second,
Resolver: resolver,
}).DialContext,
}
client := &http.Client{
Transport: tr,
}
Check example_test.go for a full example.
