mapsize: try to shrink mapsize until init works

On some systems like windows and iOS, the mapsize can be an issue.
This continually decreases the mapsize until we find one that works.

Will-Fix: damus-io/notedeck#491

src/config.rs

@@ -1,5 +1,6 @@
 use crate::bindings;
 
+#[derive(Copy, Clone)]
 pub struct Config {
     pub config: bindings::ndb_config,
 }

src/ndb.rs

@@ -10,6 +10,7 @@ use std::os::raw::c_int;
 use std::path::Path;
 use std::sync::Arc;
 use tokio::task; // Make sure to import the task module
+use tracing::debug;
 
 #[derive(Debug)]
 struct NdbRef {
@@ -51,7 +52,28 @@ impl Ndb {
             let _ = fs::create_dir_all(path);
         }
 
-        let result = unsafe { bindings::ndb_init(&mut ndb, db_dir_cstr.as_ptr(), config.as_ptr()) };
+        let min_mapsize = 1024 * 1024 * 512;
+        let mut mapsize = config.config.mapsize;
+        let mut config = *config;
+
+        let result = loop {
+            let result =
+                unsafe { bindings::ndb_init(&mut ndb, db_dir_cstr.as_ptr(), config.as_ptr()) };
+
+            if result == 0 {
+                mapsize /= 2;
+                config = config.set_mapsize(mapsize);
+                debug!("ndb init failed, reducing mapsize to {}", mapsize);
+
+                if mapsize > min_mapsize {
+                    continue;
+                } else {
+                    break 0;
+                }
+            } else {
+                break result;
+            }
+        };
 
         if result == 0 {
             return Err(Error::DbOpenFailed);
@@ -448,4 +470,43 @@ mod tests {
             assert_eq!(note.kind(), 1);
         }
     }
+
+    #[test]
+    #[cfg(target_os = "windows")]
+    fn test_windows_large_mapsize() {
+        use std::{fs, path::Path};
+
+        let db = "target/testdbs/windows_large_mapsize";
+        test_util::cleanup_db(&db);
+
+        {
+            // 32 TiB should be way too big for CI
+            let config =
+                Config::new().set_mapsize(1024usize * 1024usize * 1024usize * 1024usize * 32usize);
+
+            // in this case, nostrdb should try to keep resizing to
+            // smaller mapsizes until success
+
+            let ndb = Ndb::new(db, &config);
+
+            assert!(ndb.is_ok());
+        }
+
+        let file_len = fs::metadata(Path::new(db).join("data.mdb"))
+            .expect("metadata")
+            .len();
+
+        assert!(file_len > 0);
+
+        if cfg!(target_os = "windows") {
+            // on windows the default mapsize will be 1MB when we fail
+            // to open it
+            assert_ne!(file_len, 1048576);
+        } else {
+            assert!(file_len < 1024u64 * 1024u64);
+        }
+
+        // we should definitely clean this up... especially on windows
+        test_util::cleanup_db(&db);
+    }
 }