add a version TXT record to adb secure mdns services
In the context of secure connect, allows adbd and host adb to reject
each other based on incompatible versions without even having to
actually connect (since it is a DNS TXT).
Bug: 111434128, 119490749
Test: N/A
Exempt-From-Owner-Approval: already approved
Change-Id: I54312d8b67370c397ba81ecdbca1b27e3ee58572
diff --git a/adb_mdns.h b/adb_mdns.h
index cc22581..6b37355 100644
--- a/adb_mdns.h
+++ b/adb_mdns.h
@@ -27,12 +27,62 @@
const int kADBSecurePairingServiceRefIndex = 1;
const int kADBSecureConnectServiceRefIndex = 2;
+// Each ADB Secure service advertises with a TXT record indicating the version
+// using a key/value pair per RFC 6763 (https://tools.ietf.org/html/rfc6763).
+//
+// The first key/value pair is always the version of the protocol.
+// There may be more key/value pairs added after.
+//
+// The version is purposely represented as the single letter "v" due to the
+// need to minimize DNS traffic. The version starts at 1. With each breaking
+// protocol change, the version is incremented by 1.
+//
+// Newer adb clients/daemons need to recognize and either reject
+// or be backward-compatible with older verseions if there is a mismatch.
+//
+// Relevant sections:
+//
+// """
+// 6.4. Rules for Keys in DNS-SD Key/Value Pairs
+//
+// The key MUST be at least one character. DNS-SD TXT record strings
+// beginning with an '=' character (i.e., the key is missing) MUST be
+// silently ignored.
+//
+// ...
+//
+// 6.5. Rules for Values in DNS-SD Key/Value Pairs
+//
+// If there is an '=' in a DNS-SD TXT record string, then everything
+// after the first '=' to the end of the string is the value. The value
+// can contain any eight-bit values including '='.
+// """
+
+#define ADB_SECURE_SERVICE_VERSION_TXT_RECORD(ver) ("v=" #ver)
+
+// Client/service versions are initially defined to be matching,
+// but may go out of sync as different clients and services
+// try to talk to each other.
+#define ADB_SECURE_SERVICE_VERSION 1
+#define ADB_SECURE_CLIENT_VERSION ADB_SECURE_SERVICE_VERSION
+
+const char* kADBSecurePairingServiceTxtRecord =
+ ADB_SECURE_SERVICE_VERSION_TXT_RECORD(ADB_SECURE_SERVICE_VERSION);
+const char* kADBSecureConnectServiceTxtRecord =
+ ADB_SECURE_SERVICE_VERSION_TXT_RECORD(ADB_SECURE_SERVICE_VERSION);
+
const char* kADBDNSServices[] = {
kADBServiceType,
kADBSecurePairingServiceType,
kADBSecureConnectServiceType,
};
+const char* kADBDNSServiceTxtRecords[] = {
+ nullptr,
+ kADBSecurePairingServiceTxtRecord,
+ kADBSecureConnectServiceTxtRecord,
+};
+
const int kNumADBDNSServices = arraysize(kADBDNSServices);
#endif