WIP Sqlite backend

This doesn't cursors or any of the optional features. It also
only has a connection pool of size 1 which limits reader parallelism.

It has to do a bit of gymnastics to implement some of the LMDBisms
of the API

Cargo.toml

@@ -67,6 +67,12 @@ serde_derive = "1.0"
 thiserror = "1.0"
 url = "2.0"
 uuid = "1.0"
+elsa = "1.10.0"
+crossbeam-channel = "0.5.12"
+
+[dependencies.rusqlite]
+version = "0.26.1"
+features = ["bundled"]
 
 [dev-dependencies]
 byteorder = "1"

src/backend.rs

@@ -12,6 +12,7 @@ mod common;
 #[cfg(feature = "lmdb")]
 mod impl_lmdb;
 mod impl_safe;
+mod impl_sqlite;
 mod traits;
 
 pub use common::*;
@@ -38,3 +39,14 @@ pub use impl_safe::{
     RwTransactionImpl as SafeModeRwTransaction, StatImpl as SafeModeStat,
     WriteFlagsImpl as SafeModeWriteFlags,
 };
+
+pub use impl_sqlite::{
+    DatabaseFlagsImpl as SqliteDatabaseFlags, DatabaseImpl as SqliteDatabase,
+    EnvironmentBuilderImpl as Sqlite, EnvironmentFlagsImpl as SqliteEnvironmentFlags,
+    EnvironmentImpl as SqliteEnvironment, ErrorImpl as SqliteError, InfoImpl as SqliteInfo,
+    IterImpl as SqliteIter, RoCursorImpl as SqliteRoCursor,
+    RoTransactionImpl as SqliteRoTransaction, RwCursorImpl as SqliteRwCursor,
+    RwTransactionImpl as SqliteRwTransaction, StatImpl as SqliteStat,
+    WriteFlagsImpl as SqliteWriteFlags,
+};
+

src/backend/impl_sqlite.rs

@@ -0,0 +1,31 @@
+// Copyright 2018-2019 Mozilla
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
+// this file except in compliance with the License. You may obtain a copy of the
+// License at http://www.apache.org/licenses/LICENSE-2.0
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+
+mod cursor;
+mod database;
+mod environment;
+mod error;
+mod flags;
+mod info;
+mod iter;
+mod stat;
+mod transaction;
+
+
+pub use cursor::{RoCursorImpl, RwCursorImpl};
+pub use database::DatabaseImpl;
+pub use environment::{EnvironmentBuilderImpl, EnvironmentImpl};
+pub use error::ErrorImpl;
+pub use flags::{DatabaseFlagsImpl, EnvironmentFlagsImpl, WriteFlagsImpl};
+pub use info::InfoImpl;
+pub use iter::IterImpl;
+pub use stat::StatImpl;
+pub use transaction::{RoTransactionImpl, RwTransactionImpl};