detect old DB versions that need to upgrade

golpe.yaml

@@ -1,6 +1,6 @@
 appName: strfry
-
 quadrable: true
+onAppStartup: true
 
 flatBuffers: |
     include "../fbs/nostr-index.fbs";
@@ -11,6 +11,15 @@ includes: |
     }
 
 tables:
+  ## DB meta-data. Single entry, with id = 1
+  Meta:
+    tableId: 2
+
+    fields:
+      - name: dbVersion
+      - name: endianness
+
+  ## Stored nostr events
   Event:
     tableId: 1
 

src/onAppStartup.cpp

@@ -0,0 +1,49 @@
+#include "golpe.h"
+
+const size_t CURR_DB_VERSION = 1;
+
+void onAppStartup(lmdb::txn &txn, const std::string &cmd) {
+    auto dbTooOld = [&](uint64_t ver) {
+        LE << "Database version too old: " << ver << ". Expected version " << CURR_DB_VERSION;
+        LE << "You should 'strfry export' your events, delete (or move) the DB files, and 'strfry import' them";
+        throw herr("aborting: DB too old");
+    };
+
+    auto dbTooNew = [&](uint64_t ver) {
+        LE << "Database version too new: " << ver << ". Expected version " << CURR_DB_VERSION;
+        LE << "You should upgrade your version of 'strfry'";
+        throw herr("aborting: DB too new");
+    };
+
+    auto s = env.lookup_Meta(txn, 1);
+
+    if (!s) {
+        {
+            // The first version of the DB didn't use a Meta entry -- we consider this version 0
+
+            bool eventFound = false;
+
+            env.foreach_Event(txn, [&](auto &ev){
+                eventFound = true;
+                return false;
+            });
+
+            if (cmd == "export") return;
+            if (eventFound) dbTooOld(0);
+        }
+
+        env.insert_Meta(txn, CURR_DB_VERSION, 1);
+        return;
+    }
+
+    if (s->endianness() != 1) throw herr("DB was created on a machine with different endianness");
+
+    if (s->dbVersion() < CURR_DB_VERSION) {
+        if (cmd == "export") return;
+        dbTooOld(s->dbVersion());
+    }
+
+    if (s->dbVersion() > CURR_DB_VERSION) {
+        dbTooNew(s->dbVersion());
+    }
+}