mobile: derive the encryption context as the maintainer's core does

The core now picks the KDF context with pickSessionContext: --url, else
the URL of the highest-priority transport, leaving out cupsonline (its
room list only exists once the exit is up) and the "http://#" placeholder,
else "http://#". The bridge still let cupsonline in, and a classic channel
without a document (oneme, direct) fell back to the transport's name, so
the phone and a CLI peer derived different keys.

mobile/mobile.go

@@ -152,11 +152,11 @@ func classicTransport(transportType, documentURL, encryptionSecret, codec, maxTo
 		appendLog("[ANDROID] Шифрование транспорта отключено (ключ не задан)")
 		return inner, nil
 	}
-	// Same fallback as the CLI: the KDF context is the document URL, or
-	// the transport name when there isn't one (oneme). Both peers must
-	// derive the same context or the encrypted channel just won't work.
+	// Same context as the core: the document URL, or "http://#" when there
+	// isn't one (oneme, direct). Both peers must derive the same context or
+	// the encrypted channel just won't work.
 	encrypted, err := transport.NewEncryptedTransport(inner, encryptionSecret,
-		classicContext(transportType, documentURL), exit)
+		classicContext(documentURL), exit)
 	if err != nil {
 		return nil, err
 	}

mobile/session.go

@@ -3,7 +3,6 @@ package mobile
 import (
 	"encoding/json"
 	"fmt"
-	"sort"
 
 	"openflux/transport"
 	"openflux/transport/manager"
@@ -121,16 +120,27 @@ func buildSessionWith(specsJSON, secret string, exit bool) (transport.Transport,
 	return demux, sess, nil
 }
 
-// sessionContext is the encryption context. The exit derives it from its
-// --url, so it is the document URL of the highest-priority transport that
-// has one; "http://#" matches the CLI's --url default when none has.
+// sessionContext is the encryption context, derived as the core's
+// pickSessionContext does for an exit without --url: the document URL of the
+// highest-priority transport that has one, cupsonline aside (its room list
+// only exists once the exit is up), else "http://#". Equal priorities keep
+// the first transport, as the core does.
 func sessionContext(specs []sessionSpec) string {
-	sorted := append([]sessionSpec(nil), specs...)
-	sort.SliceStable(sorted, func(i, j int) bool { return sorted[i].Priority > sorted[j].Priority })
-	for _, s := range sorted {
-		if s.URL != "" {
-			return s.URL
+	best := -1
+	for i, s := range specs {
+		if s.Type == "cupsonline" || s.URL == "" || s.URL == placeholderURL {
+			continue
+		}
+		if best < 0 || s.Priority > specs[best].Priority {
+			best = i
 		}
 	}
-	return "http://#"
+	if best >= 0 {
+		return specs[best].URL
+	}
+	return placeholderURL
 }
+
+// placeholderURL is the core's --url default, the context of a channel that
+// has no document URL.
+const placeholderURL = "http://#"

mobile/session_test.go

@@ -77,3 +77,27 @@ func TestSessionContextPrefersHighestPriorityURL(t *testing.T) {
 		t.Fatalf("context without URLs = %q", got)
 	}
 }
+
+// The exit creates the cupsonline room list only when it starts, so the
+// core leaves it out of the context; the phone must too.
+func TestSessionContextSkipsCupsonline(t *testing.T) {
+	specs := []sessionSpec{
+		{Name: "cupsonline", Type: "cupsonline", URL: "room-list", Priority: 100},
+		{Name: "yandex", Type: "yandex", URL: "https://docs.example/d", Priority: 50},
+	}
+	if got := sessionContext(specs); got != "https://docs.example/d" {
+		t.Fatalf("context = %q", got)
+	}
+	if got := sessionContext(specs[:1]); got != "http://#" {
+		t.Fatalf("context of a cupsonline-only session = %q", got)
+	}
+}
+
+func TestClassicContextFallsBackToPlaceholder(t *testing.T) {
+	if got := classicContext(""); got != "http://#" {
+		t.Fatalf("context without a document = %q", got)
+	}
+	if got := classicContext("https://docs.example/d"); got != "https://docs.example/d" {
+		t.Fatalf("context = %q", got)
+	}
+}

mobile/share.go

@@ -56,7 +56,7 @@ func ExitShareLink(host, name string) (string, error) {
 func exitShareClassic(transportType, documentURL, secret, codec string) *share.Config {
 	c := &share.Config{
 		Secret:     secret,
-		Context:    classicContext(transportType, documentURL),
+		Context:    classicContext(documentURL),
 		Transports: []share.Transport{{Type: transportType, URL: documentURL}},
 	}
 	if codec == "legacy" {
@@ -96,14 +96,12 @@ func exitShareSession(specsJSON, secret string) *share.Config {
 	return c
 }
 
-// classicContext is the classic mode's encryption context, as the CLI and
-// classicTransport derive it.
-func classicContext(transportType, documentURL string) string {
-	if documentURL != "" {
-		return documentURL
+// classicContext is the classic mode's encryption context, as the core
+// derives it for --transport with --url: the document URL, or "http://#"
+// when there is none (oneme, direct).
+func classicContext(documentURL string) string {
+	if documentURL == "" {
+		return placeholderURL
 	}
-	if transportType == "" {
-		return "yandex"
-	}
-	return transportType
+	return documentURL
 }