refactor: start refactoring session resolver (#807)

This diff addresses the following points of https://github.com/ooni/probe/issues/2135:

- [x] the `childResolver` type is useless and we can use `model.Resolver` directly;
- [x] we should use `model/mocks` instead of custom fakes;
- [x] we should not use `log.Log` rather we should use `model.DiscardLogger`;
- [x] make `timeLimitedLookup` easier to test with a `-short` tests;
- [x] ensure `timeLimitedLookup` returns as soon as its context expires regardless of the child resolver;

Subsequent diffs will address more points mentioned in there.

internal/engine/internal/sessionresolver/childresolver.go

@@ -3,25 +3,46 @@ package sessionresolver
 import (
 	"context"
 	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/model"
 )
 
-// childResolver is the DNS client that this package uses
-// to perform individual domain name resolutions.
-type childResolver interface {
-	// LookupHost performs a DNS lookup.
-	LookupHost(ctx context.Context, domain string) ([]string, error)
-
-	// CloseIdleConnections closes idle connections.
-	CloseIdleConnections()
-}
-
-// timeLimitedLookup performs a time-limited lookup using the given re.
-func (r *Resolver) timeLimitedLookup(ctx context.Context, re childResolver, hostname string) ([]string, error) {
-	// Algorithm similar to Firefox TRR2 mode. See:
+// defaultTimeLimitedLookupTimeout is the default timeout the code should
+// pass to the timeLimitedLookup function.
+//
+// This algorithm is similar to Firefox using TRR2 mode. See:
 // https://wiki.mozilla.org/Trusted_Recursive_Resolver#DNS-over-HTTPS_Prefs_in_Firefox
+//
 // We use a higher timeout than Firefox's timeout (1.5s) to be on the safe side
 // and therefore see to use DoH more often.
-	ctx, cancel := context.WithTimeout(ctx, 4*time.Second)
-	defer cancel()
-	return re.LookupHost(ctx, hostname)
+const defaultTimeLimitedLookupTimeout = 4 * time.Second
+
+// timeLimitedLookup performs a time-limited lookup using the given re.
+func timeLimitedLookup(ctx context.Context, re model.Resolver, hostname string) ([]string, error) {
+	return timeLimitedLookupWithTimeout(ctx, re, hostname, defaultTimeLimitedLookupTimeout)
+}
+
+// timeLimitedLookupResult is the result of a timeLimitedLookup
+type timeLimitedLookupResult struct {
+	addrs []string
+	err   error
+}
+
+// timeLimitedLookupWithTimeout is like timeLimitedLookup but with explicit timeout.
+func timeLimitedLookupWithTimeout(ctx context.Context, re model.Resolver,
+	hostname string, timeout time.Duration) ([]string, error) {
+	outch := make(chan *timeLimitedLookupResult, 1) // buffer
+	ctx, cancel := context.WithTimeout(ctx, timeout)
+	defer cancel()
+	go func() {
+		out := &timeLimitedLookupResult{}
+		out.addrs, out.err = re.LookupHost(ctx, hostname)
+		outch <- out
+	}()
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	case out := <-outch:
+		return out.addrs, out.err
+	}
 }

internal/engine/internal/sessionresolver/childresolver_test.go

@@ -8,51 +8,35 @@ import (
 	"time"
 
 	"github.com/google/go-cmp/cmp"
+	"github.com/ooni/probe-cli/v3/internal/model/mocks"
 )
 
-type FakeResolver struct {
-	Closed bool
-	Data   []string
-	Err    error
-	Sleep  time.Duration
-}
-
-func (r *FakeResolver) LookupHost(ctx context.Context, hostname string) ([]string, error) {
-	select {
-	case <-time.After(r.Sleep):
-		return r.Data, r.Err
-	case <-ctx.Done():
-		return nil, ctx.Err()
-	}
-}
-
-func (r *FakeResolver) CloseIdleConnections() {
-	r.Closed = true
-}
-
 func TestTimeLimitedLookupSuccess(t *testing.T) {
-	reso := &Resolver{}
-	re := &FakeResolver{
-		Data: []string{"8.8.8.8", "8.8.4.4"},
+	expected := []string{"8.8.8.8", "8.8.4.4"}
+	re := &mocks.Resolver{
+		MockLookupHost: func(ctx context.Context, domain string) ([]string, error) {
+			return expected, nil
+		},
 	}
 	ctx := context.Background()
-	out, err := reso.timeLimitedLookup(ctx, re, "dns.google")
+	out, err := timeLimitedLookup(ctx, re, "dns.google")
 	if err != nil {
 		t.Fatal(err)
 	}
-	if diff := cmp.Diff(re.Data, out); diff != "" {
+	if diff := cmp.Diff(expected, out); diff != "" {
 		t.Fatal(diff)
 	}
 }
 
 func TestTimeLimitedLookupFailure(t *testing.T) {
-	reso := &Resolver{}
-	re := &FakeResolver{
-		Err: io.EOF,
+	re := &mocks.Resolver{
+		MockLookupHost: func(ctx context.Context, domain string) ([]string, error) {
+			return nil, io.EOF
+		},
 	}
 	ctx := context.Background()
-	out, err := reso.timeLimitedLookup(ctx, re, "dns.google")
-	if !errors.Is(err, re.Err) {
+	out, err := timeLimitedLookup(ctx, re, "dns.google")
+	if !errors.Is(err, io.EOF) {
 		t.Fatal("not the error we expected", err)
 	}
 	if out != nil {
@@ -61,20 +45,23 @@ func TestTimeLimitedLookupFailure(t *testing.T) {
 }
 
 func TestTimeLimitedLookupWillTimeout(t *testing.T) {
-	if testing.Short() {
-		t.Skip("skip test in short mode")
-	}
-	reso := &Resolver{}
-	re := &FakeResolver{
-		Err:   io.EOF,
-		Sleep: 20 * time.Second,
+	done := make(chan bool)
+	block := make(chan bool)
+	re := &mocks.Resolver{
+		MockLookupHost: func(ctx context.Context, domain string) ([]string, error) {
+			defer close(done)
+			<-block
+			return nil, io.EOF
+		},
 	}
 	ctx := context.Background()
-	out, err := reso.timeLimitedLookup(ctx, re, "dns.google")
+	out, err := timeLimitedLookupWithTimeout(ctx, re, "dns.google", 10*time.Millisecond)
 	if !errors.Is(err, context.DeadlineExceeded) {
 		t.Fatal("not the error we expected", err)
 	}
 	if out != nil {
 		t.Fatal("expected nil here")
 	}
+	close(block)
+	<-done
 }

internal/engine/internal/sessionresolver/clientmaker.go

@@ -1,11 +1,14 @@
 package sessionresolver
 
-import "github.com/ooni/probe-cli/v3/internal/engine/netx"
+import (
+	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/model"
+)
 
 // dnsclientmaker makes a new resolver.
 type dnsclientmaker interface {
 	// Make makes a new resolver.
-	Make(config netx.Config, URL string) (childResolver, error)
+	Make(config netx.Config, URL string) (model.Resolver, error)
 }
 
 // clientmaker returns a valid dnsclientmaker
@@ -20,6 +23,6 @@ func (r *Resolver) clientmaker() dnsclientmaker {
 type defaultDNSClientMaker struct{}
 
 // Make implements dnsclientmaker.Make.
-func (*defaultDNSClientMaker) Make(config netx.Config, URL string) (childResolver, error) {
+func (*defaultDNSClientMaker) Make(config netx.Config, URL string) (model.Resolver, error) {
 	return netx.NewDNSClient(config, URL)
 }

internal/engine/internal/sessionresolver/clientmaker_test.go

@@ -7,16 +7,17 @@ import (
 	"testing"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/model"
 )
 
 type fakeDNSClientMaker struct {
-	reso        childResolver
+	reso        model.Resolver
 	err         error
 	savedConfig netx.Config
 	savedURL    string
 }
 
-func (c *fakeDNSClientMaker) Make(config netx.Config, URL string) (childResolver, error) {
+func (c *fakeDNSClientMaker) Make(config netx.Config, URL string) (model.Resolver, error) {
 	c.savedConfig = config
 	c.savedURL = URL
 	return c.reso, c.err

internal/engine/internal/sessionresolver/resolvermaker.go

@@ -5,7 +5,6 @@ import (
 	"strings"
 	"time"
 
-	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/bytecounter"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 	"github.com/ooni/probe-cli/v3/internal/model"
@@ -71,15 +70,12 @@ func (r *Resolver) byteCounter() *bytecounter.Counter {
 
 // logger returns the configured logger or a default
 func (r *Resolver) logger() model.Logger {
-	if r.Logger != nil {
-		return r.Logger
-	}
-	return log.Log
+	return model.ValidLoggerOrDefault(r.Logger)
 }
 
 // newresolver creates a new resolver with the given config and URL. This is
 // where we expand http3 to https and set the h3 options.
-func (r *Resolver) newresolver(URL string) (childResolver, error) {
+func (r *Resolver) newresolver(URL string) (model.Resolver, error) {
 	h3 := strings.HasPrefix(URL, "http3://")
 	if h3 {
 		URL = strings.Replace(URL, "http3://", "https://", 1)
@@ -95,7 +91,7 @@ func (r *Resolver) newresolver(URL string) (childResolver, error) {
 
 // getresolver returns a resolver with the given URL. This function caches
 // already allocated resolvers so we only allocate them once.
-func (r *Resolver) getresolver(URL string) (childResolver, error) {
+func (r *Resolver) getresolver(URL string) (model.Resolver, error) {
 	defer r.mu.Unlock()
 	r.mu.Lock()
 	if re, found := r.res[URL]; found {
@@ -106,7 +102,7 @@ func (r *Resolver) getresolver(URL string) (childResolver, error) {
 		return nil, err // config err?
 	}
 	if r.res == nil {
-		r.res = make(map[string]childResolver)
+		r.res = make(map[string]model.Resolver)
 	}
 	r.res[URL] = re
 	return re, nil

internal/engine/internal/sessionresolver/resolvermaker_test.go

@@ -5,8 +5,9 @@ import (
 	"strings"
 	"testing"
 
-	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/bytecounter"
+	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/model/mocks"
 )
 
 func TestDefaultByteCounter(t *testing.T) {
@@ -18,18 +19,33 @@ func TestDefaultByteCounter(t *testing.T) {
 }
 
 func TestDefaultLogger(t *testing.T) {
-	logger := &log.Logger{}
+	t.Run("when using a different logger", func(t *testing.T) {
+		logger := &mocks.Logger{}
 		reso := &Resolver{Logger: logger}
 		lo := reso.logger()
 		if lo != logger {
-		t.Fatal("expected another logger here counter")
+			t.Fatal("expected another logger here")
 		}
+	})
+
+	t.Run("when no logger is set", func(t *testing.T) {
+		reso := &Resolver{Logger: nil}
+		lo := reso.logger()
+		if lo != model.DiscardLogger {
+			t.Fatal("expected another logger here")
+		}
+	})
 }
 
 func TestGetResolverHTTPSStandard(t *testing.T) {
 	bc := bytecounter.New()
 	URL := "https://dns.google"
-	re := &FakeResolver{}
+	var closed bool
+	re := &mocks.Resolver{
+		MockCloseIdleConnections: func() {
+			closed = true
+		},
+	}
 	cmk := &fakeDNSClientMaker{reso: re}
 	reso := &Resolver{dnsClientMaker: cmk, ByteCounter: bc}
 	out, err := reso.getresolver(URL)
@@ -47,7 +63,7 @@ func TestGetResolverHTTPSStandard(t *testing.T) {
 		t.Fatal("not the result we expected")
 	}
 	reso.closeall()
-	if re.Closed != true {
+	if closed != true {
 		t.Fatal("was not closed")
 	}
 	if cmk.savedURL != URL {
@@ -62,7 +78,7 @@ func TestGetResolverHTTPSStandard(t *testing.T) {
 	if cmk.savedConfig.HTTP3Enabled != false {
 		t.Fatal("unexpected HTTP3Enabled")
 	}
-	if cmk.savedConfig.Logger != log.Log {
+	if cmk.savedConfig.Logger != model.DiscardLogger {
 		t.Fatal("unexpected Log")
 	}
 }
@@ -70,7 +86,12 @@ func TestGetResolverHTTPSStandard(t *testing.T) {
 func TestGetResolverHTTP3(t *testing.T) {
 	bc := bytecounter.New()
 	URL := "http3://dns.google"
-	re := &FakeResolver{}
+	var closed bool
+	re := &mocks.Resolver{
+		MockCloseIdleConnections: func() {
+			closed = true
+		},
+	}
 	cmk := &fakeDNSClientMaker{reso: re}
 	reso := &Resolver{dnsClientMaker: cmk, ByteCounter: bc}
 	out, err := reso.getresolver(URL)
@@ -88,7 +109,7 @@ func TestGetResolverHTTP3(t *testing.T) {
 		t.Fatal("not the result we expected")
 	}
 	reso.closeall()
-	if re.Closed != true {
+	if closed != true {
 		t.Fatal("was not closed")
 	}
 	if cmk.savedURL != strings.Replace(URL, "http3://", "https://", 1) {
@@ -103,7 +124,7 @@ func TestGetResolverHTTP3(t *testing.T) {
 	if cmk.savedConfig.HTTP3Enabled != true {
 		t.Fatal("unexpected HTTP3Enabled")
 	}
-	if cmk.savedConfig.Logger != log.Log {
+	if cmk.savedConfig.Logger != model.DiscardLogger {
 		t.Fatal("unexpected Log")
 	}
 }

internal/engine/internal/sessionresolver/sessionresolver.go

@@ -95,7 +95,7 @@ type Resolver struct {
 	// res maps a URL to a child resolver. We will
 	// construct child resolvers just once and we
 	// will track them into this field.
-	res map[string]childResolver
+	res map[string]model.Resolver
 }
 
 // CloseIdleConnections closes the idle connections, if any. This
@@ -169,7 +169,7 @@ func (r *Resolver) lookupHost(ctx context.Context, ri *resolverinfo, hostname st
 		ri.Score = 0 // this is a hard error
 		return nil, err
 	}
-	addrs, err := r.timeLimitedLookup(ctx, re, hostname)
+	addrs, err := timeLimitedLookup(ctx, re, hostname)
 	if err == nil {
 		r.logger().Infof("sessionresolver: %s... %v", ri.URL, model.ErrorToStringOrOK(nil))
 		ri.Score = ewma*1.0 + (1-ewma)*ri.Score // increase score

internal/engine/internal/sessionresolver/sessionresolver_test.go

@@ -11,6 +11,7 @@ import (
 	"github.com/google/go-cmp/cmp"
 	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/kvstore"
+	"github.com/ooni/probe-cli/v3/internal/model/mocks"
 	"github.com/ooni/probe-cli/v3/internal/multierror"
 )
 
@@ -85,7 +86,11 @@ func TestTypicalUsageWithSuccess(t *testing.T) {
 	reso := &Resolver{
 		KVStore: &kvstore.Memory{},
 		dnsClientMaker: &fakeDNSClientMaker{
-			reso: &FakeResolver{Data: expected},
+			reso: &mocks.Resolver{
+				MockLookupHost: func(ctx context.Context, domain string) ([]string, error) {
+					return expected, nil
+				},
+			},
 		},
 	}
 	addrs, err := reso.LookupHost(ctx, "dns.google")
@@ -117,7 +122,11 @@ func TestLittleLLookupHostWithSuccess(t *testing.T) {
 	expected := []string{"8.8.8.8", "8.8.4.4"}
 	reso := &Resolver{
 		dnsClientMaker: &fakeDNSClientMaker{
-			reso: &FakeResolver{Data: expected},
+			reso: &mocks.Resolver{
+				MockLookupHost: func(ctx context.Context, domain string) ([]string, error) {
+					return expected, nil
+				},
+			},
 		},
 	}
 	ctx := context.Background()
@@ -138,7 +147,11 @@ func TestLittleLLookupHostWithFailure(t *testing.T) {
 	errMocked := errors.New("mocked error")
 	reso := &Resolver{
 		dnsClientMaker: &fakeDNSClientMaker{
-			reso: &FakeResolver{Err: errMocked},
+			reso: &mocks.Resolver{
+				MockLookupHost: func(ctx context.Context, domain string) ([]string, error) {
+					return nil, errMocked
+				},
+			},
 		},
 	}
 	ctx := context.Background()