go-mockdns

Boilerplate for testing of code involving DNS lookups, including ~~unholy~~ hacks to redirect net.Lookup* calls.

Example

Trivial mock resolver, for cases where tested code supports custom resolvers:

r := mockdns.Resolver{
    Zones: map[string]mockdns.Zone{
        "example.org.": {
            A: []string{"1.2.3.4"},
        },
    },
}

addrs, err := r.LookupHost(context.Background(), "example.org")
fmt.Println(addrs, err)

// Output:
// [1.2.3.4] <nil>

~~Unholy~~ hack for cases where it doesn't:

srv, _ := mockdns.NewServer(map[string]mockdns.Zone{
    "example.org.": {
        A: []string{"1.2.3.4"},
    },
}, false)
defer srv.Close()

srv.PatchNet(net.DefaultResolver)
defer mockdns.UnpatchNet(net.DefaultResolver)

addrs, err := net.LookupHost("example.org")
fmt.Println(addrs, err)

// Output:
// [1.2.3.4] <nil>

Note, if you need to replace net.Dial calls and tested code supports custom net.Dial, patch the resolver object inside it instead of net.DefaultResolver. If tested code supports Dialer-like objects - use Resolver itself, it implements Dial and DialContext methods.