add lmdb.next and pairs(db)

2 files changed, 56 insertions, 3 deletions

diff --git a/README.md b/README.md
index dd0fdef..b63c4e3 100644
--- a/README.md
+++ b/README.md
@@ -19,6 +19,9 @@ create a new environment handle and open the database at the `path`. returns the
 ### `lmdb.version()`
 returns the LMDB version as `major, minor, patch`.
 
+### `lmdb.next(db, key)`
+returns the next key-value pair after `key` in the database handle `db`, or the first key-value pair if `key` is `nil`. keys are ordered lexicographically. unlike `next`, this function does not work for traversal if, during traversal, keys are set to `nil`. (TODO: fix this somehow)
+
 ### `env:txn_begin(write_enabled)`
 create a new transaction in the environment. if `write_enabled` is true, then the transaction may make modifications to the database. returns the transaction handle (`txn`) on success.
 
@@ -32,9 +35,7 @@ flush buffers to disk. if `force` is `true`, a synchronous flush is performed ev
 close the environment.
 
 ### `txn:open(name, create)`
-open a database in the environment. if multiple databases are to be used in the environment, `name` is the name of the database to open. otherwise, it should not be supplied. if `create` is true, the database is created if it does not exist. returns a database handle on success.
-
-the database handle behaves as a table that may be indexed with string keys and contains string values, read from the database. any changes made will be saved to the database when the transaction is committed.
+open a database in the environment. if multiple databases are to be used in the environment, `name` is the name of the database to open. otherwise, it should not be supplied. if `create` is true, the database is created if it does not exist. returns a database handle (`db`) on success.
 
 ### `txn:drop(name)`
 delete the database `name` from the environment. (or clear the database, if `name` is not supplied)
@@ -47,3 +48,12 @@ commit all operations of the transaction into the database.
 
 ### `txn:txn_begin()`
 create a nested transaction in the parent transaction.
+
+### `db[key]`
+read the value of `key` from the database.
+
+### `db[key] = value`
+write `value` as the value of `key` into the database.
+
+### `pairs(db)`
+returns `lmdb.next, db, nil`.
diff --git a/lmdb.c b/lmdb.c
index 7e562c0..d85ce4f 100644
--- a/lmdb.c
+++ b/lmdb.c
@@ -276,6 +276,47 @@ static int db_put(lua_State *L) {
 	return 0;
 }
 
+static int db_next(lua_State *L) {
+	lua_settop(L, 2);
+	MDB_dbi dbi = *(MDB_dbi *) luaL_checkudata(L, 1, "lmdb.db");
+	check_env(L, 1);
+	luaL_argcheck(
+		L, lua_isnil(L, 2) || lua_isstring(L, 2), 2, "expected string or nil");
+
+	lua_getuservalue(L, 1);
+	struct handle *tud = lua_touserdata(L, -1);
+	MDB_cursor *curs;
+	asserr(mdb_cursor_open(tud->obj, dbi, &curs));
+
+	MDB_val key;
+	MDB_val data;
+	int result;
+	if (!lua_isnil(L, 2)) {
+		key = toval(L, 2);
+		asserr(mdb_cursor_get(curs, &key, &data, MDB_SET));
+		result = mdb_cursor_get(curs, &key, &data, MDB_NEXT);
+	} else
+		result = mdb_cursor_get(curs, &key, &data, MDB_FIRST);
+	if (result == MDB_NOTFOUND) {
+		lua_pushnil(L);
+		return 1;
+	} else asserr(result);
+
+	fromval(L, key);
+	fromval(L, data);
+	mdb_cursor_close(curs);
+	return 2;
+}
+
+static int db_pairs(lua_State *L) {
+	lua_settop(L, 1);
+	luaL_checkudata(L, 1, "lmdb.db");
+	lua_pushcfunction(L, db_next);
+	lua_pushvalue(L, 1);
+	lua_pushnil(L);
+	return 3;
+}
+
 static int db_drop(lua_State *L) {
 	lua_settop(L, 2);
 	struct handle *ud = luaL_checkudata(L, 1, "lmdb.txn");
@@ -294,6 +335,7 @@ static int db_drop(lua_State *L) {
 static const struct luaL_Reg lmdb[] = {
 	{"open", env_open},
 	{"version", version},
+	{"next", db_next},
 	{NULL, NULL},
 };
 
@@ -322,6 +364,7 @@ static const struct luaL_Reg lmdb_txn[] = {
 static const struct luaL_Reg lmdb_db[] = {
 	{"__index", db_get},
 	{"__newindex", db_put},
+	{"__pairs", db_pairs},
 	{NULL, NULL},
 };