libstore: derive legacy-tunneled rpc id from package version

this way each git revision trivially gets its own rpc protocol version.

Change-Id: I066c58ebff697e534479db5d02271dac1ea71709

lix/libstore/daemon.capnp

@@ -28,10 +28,6 @@ interface Protocol {
   # TODO maybe add information or something
 }
 
-# legacy boot protocol. EXPLICITLY UNSTABLE, this id will change frequently and without notice.
-# every change to the experimental tunneling protocol may also change this protocol identifier.
-const unstableLegacyTunneled :Text = "lix/legacy/ba3153c5-4153-4d66-91ec-a258c02e9a3c";
-
 interface LegacyBoot extends(Protocol) $T.throws(T.v1Errors) {
   enum Trust {
     unknown @0;

lix/libstore/daemon.cc

@@ -32,6 +32,8 @@
 #include <kj/memory.h>
 #include <sstream>
 
+const std::string nix::rpc::daemon::UNSTABLE_LEGACY_TUNNELED = "lix/legacy/" PACKAGE_VERSION;
+
 namespace nix::daemon {
 
 Sink & operator << (Sink & sink, const Logger::Fields & fields)

lix/libstore/daemon.hh

@@ -6,6 +6,12 @@
 #include "lix/libstore/store-api.hh"
 #include <kj/async-io.h>
 
+namespace nix::rpc::daemon {
+// legacy boot protocol. EXPLICITLY UNSTABLE, this id will change frequently and without notice.
+// every change to the experimental tunneling protocol may also change this protocol identifier.
+extern const std::string UNSTABLE_LEGACY_TUNNELED;
+}
+
 namespace nix::daemon {
 
 void processLegacyConnection(

lix/libstore/uds-remote-store.cc

@@ -20,6 +20,7 @@
 #include <exception>
 #include <kj/async.h>
 #include <kj/encoding.h>
+#include <string_view>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/socket.h>
@@ -184,7 +185,7 @@ try {
         auto supportedProtos = supported.getProtocols();
         debug("remote advertised %s", supported.toString().flatten().cStr());
         if (supportedProtos.size() != 1
-            && supportedProtos[0].getId() != rpc::daemon::UNSTABLE_LEGACY_TUNNELED)
+            && rpc::to<std::string_view>(supportedProtos[0].getId()) != rpc::daemon::UNSTABLE_LEGACY_TUNNELED)
         {
             co_return false;
         }
@@ -201,7 +202,7 @@ try {
 
     auto bootstrapReq = bootstrap.requestRequest();
     bootstrapReq.setClientInfo(PACKAGE_STRING);
-    bootstrapReq.setProtocol(rpc::daemon::UNSTABLE_LEGACY_TUNNELED);
+    RPC_FILL(bootstrapReq, setProtocol, rpc::daemon::UNSTABLE_LEGACY_TUNNELED);
     auto legacyBoot =
         TRY_AWAIT_RPC_NOEXCEPT(bootstrapReq.send()).getResult().castAs<rpc::daemon::LegacyBoot>();
     auto initReq = legacyBoot.initRequest();