feat(enginenetx): support getting stats on a domain endpoint (#1311)

We need this functionality to ask the stats questions like "what are all
the available tactics for www.example.com:443 along with their stats?".
In turn, this information is needed to implement a new policy that uses
existing stats to choose what to do.

While there, rename files to make it clear which files contain policies
and which contain state trackers. Useful because upcoming changes will
add files containing state-based policy.

While there, stop being paranoid about cloning a nil map to a nil map,
acknowledge this is not important and making it round trip correctly
would require more code we don't need, and simply adjust tests to accept
nil and empty map as equal.

Part of ooni/probe#2531

internal/enginenetx/stats.go → internal/enginenetx/statstracker.go

@@ -10,6 +10,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"net"
 	"sync"
 	"time"
 
@@ -87,10 +88,8 @@ type statsTactic struct {
 }
 
 func statsCloneMapStringInt64(input map[string]int64) (output map[string]int64) {
+	output = make(map[string]int64)
 	for key, value := range input {
-		if output == nil {
-			output = make(map[string]int64) // the idea here is to clone a nil map to a nil map
-		}
 		output[key] = value
 	}
 	return
@@ -401,3 +400,20 @@ func (mt *statsManager) Close() error {
 	// write updated stats into the underlying key-value store
 	return mt.kvStore.Set(statsKey, runtimex.Try1(json.Marshal(mt.container)))
 }
+
+// LookupTacticsStats returns stats about tactics for a given domain and port. The returned
+// list is a clone of the one stored by [*statsManager] so, it can easily be modified.
+func (mt *statsManager) LookupTactics(domain string, port string) []*statsTactic {
+	out := []*statsTactic{}
+
+	// get exclusive access
+	defer mt.mu.Unlock()
+	mt.mu.Lock()
+
+	// return a copy of each entry
+	domainEpnts := mt.container.DomainEndpoints[net.JoinHostPort(domain, port)]
+	for _, entry := range domainEpnts.Tactics {
+		out = append(out, entry.Clone())
+	}
+	return out
+}

internal/enginenetx/stats_test.go → internal/enginenetx/statstracker_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"sort"
 	"testing"
 	"time"
 
@@ -746,6 +747,7 @@ func TestStatsManagerCallbacks(t *testing.T) {
 			// make sure the stats are the ones we expect
 			diffOptions := []cmp.Option{
 				cmpopts.IgnoreFields(statsTactic{}, "LastUpdated"),
+				cmpopts.EquateEmpty(),
 			}
 			if diff := cmp.Diff(tc.expectRoot, root, diffOptions...); diff != "" {
 				t.Fatal(diff)
@@ -758,3 +760,112 @@ func TestStatsManagerCallbacks(t *testing.T) {
 		})
 	}
 }
+
+// Make sure that we can safely obtain statistics for a domain and a port.
+func TestStatsManagerLookupTacticsStats(t *testing.T) {
+
+	// prepare the content of the stats
+	twentyMinutesAgo := time.Now().Add(-20 * time.Minute)
+
+	expectTactics := []*statsTactic{{
+		CountStarted:               5,
+		CountTCPConnectError:       0,
+		CountTCPConnectInterrupt:   0,
+		CountTLSHandshakeError:     0,
+		CountTLSHandshakeInterrupt: 0,
+		CountTLSVerificationError:  0,
+		CountSuccess:               5,
+		HistoTCPConnectError:       map[string]int64{},
+		HistoTLSHandshakeError:     map[string]int64{},
+		HistoTLSVerificationError:  map[string]int64{},
+		LastUpdated:                twentyMinutesAgo,
+		Tactic: &httpsDialerTactic{
+			Address:        "162.55.247.208",
+			InitialDelay:   0,
+			Port:           "443",
+			SNI:            "www.repubblica.it",
+			VerifyHostname: "api.ooni.io",
+		},
+	}, {
+		CountStarted:               1,
+		CountTCPConnectError:       0,
+		CountTCPConnectInterrupt:   0,
+		CountTLSHandshakeError:     0,
+		CountTLSHandshakeInterrupt: 0,
+		CountTLSVerificationError:  0,
+		CountSuccess:               1,
+		HistoTCPConnectError:       map[string]int64{},
+		HistoTLSHandshakeError:     map[string]int64{},
+		HistoTLSVerificationError:  map[string]int64{},
+		LastUpdated:                twentyMinutesAgo,
+		Tactic: &httpsDialerTactic{
+			Address:        "162.55.247.208",
+			InitialDelay:   0,
+			Port:           "443",
+			SNI:            "www.kernel.org",
+			VerifyHostname: "api.ooni.io",
+		},
+	}, {
+		CountStarted:               3,
+		CountTCPConnectError:       0,
+		CountTCPConnectInterrupt:   0,
+		CountTLSHandshakeError:     0,
+		CountTLSHandshakeInterrupt: 0,
+		CountTLSVerificationError:  0,
+		CountSuccess:               3,
+		HistoTCPConnectError:       map[string]int64{},
+		HistoTLSHandshakeError:     map[string]int64{},
+		HistoTLSVerificationError:  map[string]int64{},
+		LastUpdated:                twentyMinutesAgo,
+		Tactic: &httpsDialerTactic{
+			Address:        "162.55.247.208",
+			InitialDelay:   0,
+			Port:           "443",
+			SNI:            "theconversation.com",
+			VerifyHostname: "api.ooni.io",
+		},
+	}}
+
+	expectContainer := &statsContainer{
+		DomainEndpoints: map[string]*statsDomainEndpoint{
+			"api.ooni.io:443": {
+				Tactics: map[string]*statsTactic{},
+			},
+		},
+		Version: statsContainerVersion,
+	}
+
+	for _, tactic := range expectTactics {
+		expectContainer.DomainEndpoints["api.ooni.io:443"].Tactics[tactic.Tactic.tacticSummaryKey()] = tactic
+	}
+
+	// configure the initial value of the stats
+	kvStore := &kvstore.Memory{}
+	if err := kvStore.Set(statsKey, runtimex.Try1(json.Marshal(expectContainer))); err != nil {
+		t.Fatal(err)
+	}
+
+	// create the stats manager
+	stats := newStatsManager(kvStore, log.Log)
+
+	// obtain tactics
+	tactics := stats.LookupTactics("api.ooni.io", "443")
+	if len(tactics) != 3 {
+		t.Fatal("unexpected tactics length")
+	}
+
+	// sort obtained tactics lexicographically
+	sort.SliceStable(tactics, func(i, j int) bool {
+		return tactics[i].Tactic.tacticSummaryKey() < tactics[j].Tactic.tacticSummaryKey()
+	})
+
+	// sort the initial tactics as well
+	sort.SliceStable(expectTactics, func(i, j int) bool {
+		return expectTactics[i].Tactic.tacticSummaryKey() < expectTactics[j].Tactic.tacticSummaryKey()
+	})
+
+	// compare once we have sorted
+	if diff := cmp.Diff(expectTactics, tactics); diff != "" {
+		t.Fatal(diff)
+	}
+}