From 6f1cbf4710f47256f03b834837a33e21ae6dd173 Mon Sep 17 00:00:00 2001
From: Tim Underwood <timunderwood@gmail.com>
Date: Tue, 28 May 2024 10:23:16 -0700
Subject: [PATCH] Add Env::max_key_size() method to determine the max supported
 key length.

This calls the LMDB mdb_env_get_maxkeysize function.
---
 heed/src/env.rs          | 25 +++++++++++++++++++++++++
 heed/src/mdb/lmdb_ffi.rs |  2 +-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/heed/src/env.rs b/heed/src/env.rs
index 21fbcf68..d52e8a83 100644
--- a/heed/src/env.rs
+++ b/heed/src/env.rs
@@ -901,6 +901,14 @@ impl Env {
         mdb_result(unsafe { ffi::mdb_env_set_mapsize(self.env_mut_ptr(), new_size) })
             .map_err(Into::into)
     }
+
+    /// Get the maximum size of keys and MDB_DUPSORT data we can write.
+    ///
+    /// Depends on the compile-time constant MDB_MAXKEYSIZE. Default 511
+    pub fn max_key_size(&self) -> usize {
+        let maxsize: i32 = unsafe{ ffi::mdb_env_get_maxkeysize(self.env_mut_ptr()) };
+        maxsize as usize
+    }
 }
 
 /// Contains information about the environment.
@@ -1251,4 +1259,21 @@ mod tests {
             env.prepare_for_closing().wait();
         }
     }
+
+    #[test]
+    fn max_key_size() {
+        let dir = tempfile::tempdir().unwrap();
+        let env = unsafe { EnvOpenOptions::new().open(dir.path().join(dir.path())).unwrap() };
+        let maxkeysize = env.max_key_size();
+
+        eprintln!("maxkeysize: {}", maxkeysize);
+
+        if cfg!(feature = "longer-keys") {
+            // Should be larger than the default of 511
+            assert!(maxkeysize > 511);
+        } else {
+            // Should be the default of 511
+            assert_eq!(maxkeysize, 511);
+        }
+    }
 }
diff --git a/heed/src/mdb/lmdb_ffi.rs b/heed/src/mdb/lmdb_ffi.rs
index 1aa03d56..b1058964 100644
--- a/heed/src/mdb/lmdb_ffi.rs
+++ b/heed/src/mdb/lmdb_ffi.rs
@@ -3,7 +3,7 @@ use std::ptr;
 pub use ffi::{
     mdb_cursor_close, mdb_cursor_del, mdb_cursor_get, mdb_cursor_open, mdb_cursor_put,
     mdb_dbi_open, mdb_del, mdb_drop, mdb_env_close, mdb_env_copyfd2, mdb_env_create,
-    mdb_env_get_fd, mdb_env_get_flags, mdb_env_info, mdb_env_open, mdb_env_set_flags,
+    mdb_env_get_fd, mdb_env_get_flags, mdb_env_get_maxkeysize, mdb_env_info, mdb_env_open, mdb_env_set_flags,
     mdb_env_set_mapsize, mdb_env_set_maxdbs, mdb_env_set_maxreaders, mdb_env_stat, mdb_env_sync,
     mdb_filehandle_t, mdb_get, mdb_put, mdb_reader_check, mdb_set_compare, mdb_stat, mdb_txn_abort,
     mdb_txn_begin, mdb_txn_commit, mdb_version, MDB_cursor, MDB_dbi, MDB_env, MDB_stat, MDB_txn,