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feat(substituter): add substituter middleware and `MIDDLEWARE_SUBSTIT…
…UTER_SUBSTITUTIONS`
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,85 @@ | ||
| package substituter | ||
|
|
||
| import ( | ||
| "fmt" | ||
|
|
||
| "github.com/miekg/dns" | ||
| ) | ||
|
|
||
| type Middleware struct { | ||
| mapping map[questionKey][]dns.RR | ||
| } | ||
|
|
||
| func New(settings Settings) (middleware *Middleware, err error) { | ||
| settings.SetDefaults() | ||
| err = settings.Validate() | ||
| if err != nil { | ||
| return nil, fmt.Errorf("validating settings: %w", err) | ||
| } | ||
|
|
||
| mapping := make(map[questionKey][]dns.RR, len(settings.Substitutions)) | ||
| for _, substitution := range settings.Substitutions { | ||
| substitution.setDefaults() | ||
| question := substitution.toQuestion() | ||
| key := makeKey(question) | ||
| mapping[key] = substitution.toRRs() | ||
| } | ||
|
|
||
| return &Middleware{ | ||
| mapping: mapping, | ||
| }, nil | ||
| } | ||
|
|
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| func (m *Middleware) String() string { return "substituter" } | ||
|
|
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| // Wrap wraps the DNS handler with the middleware. | ||
| func (m *Middleware) Wrap(next dns.Handler) dns.Handler { //nolint:ireturn | ||
| if len(m.mapping) == 0 { | ||
| return next | ||
| } | ||
| return &handler{ | ||
| mapping: m.mapping, | ||
| next: next, | ||
| } | ||
| } | ||
|
|
||
| func (m *Middleware) Stop() (err error) { | ||
| return nil | ||
| } | ||
|
|
||
| type handler struct { | ||
| mapping map[questionKey][]dns.RR | ||
| next dns.Handler | ||
| } | ||
|
|
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| func (h *handler) ServeDNS(w dns.ResponseWriter, r *dns.Msg) { | ||
| for _, question := range r.Question { | ||
| key := makeKey(question) | ||
| rrs, found := h.mapping[key] | ||
| if !found { | ||
| continue | ||
| } | ||
| response := &dns.Msg{ | ||
| Answer: rrs, | ||
| } | ||
| response.SetReply(r) | ||
| _ = w.WriteMsg(response) | ||
| return | ||
| } | ||
|
|
||
| h.next.ServeDNS(w, r) | ||
| } | ||
|
|
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| func makeKey(question dns.Question) (key questionKey) { | ||
| return questionKey{ | ||
| Name: question.Name, | ||
| Qtype: question.Qtype, | ||
| Qclass: question.Qclass, | ||
| } | ||
| } | ||
|
|
||
| type questionKey struct { | ||
| Name string | ||
| Qtype uint16 | ||
| Qclass uint16 | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,141 @@ | ||
| package substituter | ||
|
|
||
| import ( | ||
| net "net" | ||
| "net/netip" | ||
| "testing" | ||
|
|
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| "github.com/golang/mock/gomock" | ||
| "github.com/miekg/dns" | ||
| "github.com/stretchr/testify/assert" | ||
| "github.com/stretchr/testify/require" | ||
| ) | ||
|
|
||
| func Test_New(t *testing.T) { | ||
| t.Parallel() | ||
|
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| settings := Settings{ | ||
| Substitutions: []Substitution{ | ||
| {Name: "github.com", IPs: []netip.Addr{netip.MustParseAddr("1.2.3.4")}}, | ||
| }, | ||
| } | ||
|
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| middleware, err := New(settings) | ||
| require.NoError(t, err) | ||
|
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| expectedMiddleware := &Middleware{ | ||
| mapping: map[questionKey][]dns.RR{ | ||
| { | ||
| Name: "github.com.", | ||
| Qtype: dns.TypeA, | ||
| Qclass: dns.ClassINET, | ||
| }: {&dns.A{ | ||
| Hdr: dns.RR_Header{ | ||
| Name: "github.com.", | ||
| Rrtype: dns.TypeA, | ||
| Class: dns.ClassINET, | ||
| Ttl: 300, | ||
| }, | ||
| A: net.IP{1, 2, 3, 4}, | ||
| }}, | ||
| }, | ||
| } | ||
| assert.Equal(t, expectedMiddleware, middleware) | ||
|
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| next := dns.HandlerFunc(func(rw dns.ResponseWriter, m *dns.Msg) {}) | ||
| handler := middleware.Wrap(next) | ||
|
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| request := &dns.Msg{Question: []dns.Question{ | ||
| {Name: "github.com.", Qtype: dns.TypeA, Qclass: dns.ClassINET}, | ||
| }} | ||
|
|
||
| ctrl := gomock.NewController(t) | ||
| writer := NewMockResponseWriter(ctrl) | ||
| substitutedResponse := &dns.Msg{ | ||
| Answer: []dns.RR{ | ||
| &dns.A{ | ||
| Hdr: dns.RR_Header{ | ||
| Name: "github.com.", | ||
| Rrtype: dns.TypeA, | ||
| Class: dns.ClassINET, | ||
| Ttl: 300, | ||
| }, | ||
| A: net.IP{1, 2, 3, 4}, | ||
| }, | ||
| }, | ||
| } | ||
| substitutedResponse.SetReply(request) | ||
|
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| writer.EXPECT().WriteMsg(substitutedResponse) | ||
|
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| handler.ServeDNS(writer, request) | ||
|
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| err = middleware.Stop() | ||
| require.NoError(t, err) | ||
| } | ||
|
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| func Test_handler_ServeDNS(t *testing.T) { | ||
| t.Parallel() | ||
|
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| request := &dns.Msg{ | ||
| Question: []dns.Question{ | ||
| {Name: "github.com.", Qtype: dns.TypeA, Qclass: dns.ClassINET}, | ||
| }, | ||
| } | ||
| response := &dns.Msg{ | ||
| Answer: []dns.RR{&dns.A{ | ||
| Hdr: dns.RR_Header{ | ||
| Name: "github.com.", | ||
| Rrtype: dns.TypeA, | ||
| Class: dns.ClassINET, | ||
| Ttl: 300, | ||
| }, | ||
| A: net.IP{1, 2, 3, 4}, | ||
| }, | ||
| }, | ||
| } | ||
| response.SetReply(request) | ||
|
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| testCases := map[string]struct { | ||
| settings Settings | ||
| responseWriterBuilder func(ctrl *gomock.Controller) dns.ResponseWriter | ||
| }{ | ||
| "no_substitution": { | ||
| responseWriterBuilder: func(ctrl *gomock.Controller) dns.ResponseWriter { | ||
| return NewMockResponseWriter(ctrl) | ||
| }, | ||
| }, | ||
| "substitution": { | ||
| settings: Settings{ | ||
| Substitutions: []Substitution{ | ||
| {Name: "github.com", IPs: []netip.Addr{netip.MustParseAddr("1.2.3.4")}}, | ||
| }, | ||
| }, | ||
| responseWriterBuilder: func(ctrl *gomock.Controller) dns.ResponseWriter { | ||
| writer := NewMockResponseWriter(ctrl) | ||
| writer.EXPECT().WriteMsg(response).Return(nil) | ||
| return writer | ||
| }, | ||
| }, | ||
| } | ||
|
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| for name, testCase := range testCases { | ||
| testCase := testCase | ||
| t.Run(name, func(t *testing.T) { | ||
| t.Parallel() | ||
| ctrl := gomock.NewController(t) | ||
|
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| middleware, err := New(testCase.settings) | ||
| require.NoError(t, err) | ||
|
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| next := dns.HandlerFunc(func(rw dns.ResponseWriter, m *dns.Msg) { | ||
| assert.Equal(t, request, m) | ||
| }) | ||
| handler := middleware.Wrap(next) | ||
|
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| responseWriter := testCase.responseWriterBuilder(ctrl) | ||
|
|
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| handler.ServeDNS(responseWriter, request) | ||
| }) | ||
| } | ||
| } |
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