Simplify error type and create a database connection.

Cargo.lock

 version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
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+
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+
 [[package]]
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 version = "0.2.71"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
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+
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+
 [[package]]
 name = "log"
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  "cfg-if 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
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 [[package]]
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 [[package]]
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 [[package]]
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 ]
 
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Cargo.toml

 url = "*"
 range-set = "*"
 fslock = "0.1"
+rusqlite = "0.23"
+thiserror = "1.0"
 
 [dev-dependencies]
 criterion = "0.3"

src/client_side_sync.rs

 use tokio::sync::{mpsc, oneshot, Mutex};
 
 use super::file_tree::{FileTree, NewVersionSource};
-use super::{Error, SynchronizationError};
+use super::SynchronizationError;
 
 pub struct ClientSideSync {
     state_send: mpsc::Sender<(StateChange, oneshot::Sender<()>)>,

src/database.rs

 use std::ffi::OsString;
 
+use rusqlite::Connection;
+
 pub struct Database {
+    db: Connection,
     // TODO
 }
 
 impl Database {
-    pub fn create_or_open(_path: &str) -> Result<Database, crate::Error> {
+    pub fn create_or_open(path: &str) -> Result<Database, crate::Error> {
+        let db = Connection::open(&path)?;
+
+        // We need to create the tables if they do not exist (likely, we just created the
+        // database).
+        //db.execute("CREATE TABLE IF NOT EXISTS synchronized_directories ( );", &[]);
         // TODO
-        Ok(Database {})
+
+        Ok(Database { db })
     }
 
     pub fn synchronized_directories(&self) -> Vec<OsString> {

src/lib.rs

 use std::ffi::OsString;
 use std::io;
 
+use thiserror::Error;
+
 mod client_side_sync;
 mod database;
 mod file_system_watcher;
     pub error: Error,
 }
 
-#[derive(Debug)]
+#[derive(Error, Debug)]
 pub enum Error {
-    Io(std::io::Error),
-    Json(serde_json::error::Error),
+    #[error("input/output error")]
+    Io(#[from] std::io::Error),
+    #[error("JSON serialization error")]
+    Json(#[from] serde_json::error::Error),
+    #[error("database error")]
+    Sqlite(#[from] rusqlite::Error),
+    #[error("directory removed")]
     DirectoryRemoved,
 }
 
-impl From<serde_json::error::Error> for Error {
-    fn from(e: serde_json::error::Error) -> Error {
-        Error::Json(e)
-    }
-}
-
-impl From<io::Error> for Error {
-    fn from(e: io::Error) -> Error {
-        Error::Io(e)
-    }
-}
-
 impl From<fswatcher::Error> for Error {
     fn from(e: fswatcher::Error) -> Error {
         match e {