Properly handle object cleanup errors

Destructors now fail and there's a finish method returning an error.

Author: sfackler

src/lib.rs

@@ -189,6 +189,14 @@ macro_rules! check_desync(
     )
 )
 
+macro_rules! fail_unless_failing(
+    ($($t:tt)*) => (
+        if !task::failing() {
+            fail!($($t)*)
+        }
+    )
+)
+
 static DEFAULT_PORT: Port = 5432;
 
 /// Trait for types that can handle Postgres notice messages
@@ -363,11 +371,18 @@ struct InnerPostgresConnection {
     cancel_data: PostgresCancelData,
     unknown_types: HashMap<Oid, ~str>,
     desynchronized: bool,
+    finished: bool,
 }
 
 impl Drop for InnerPostgresConnection {
     fn drop(&mut self) {
-        let _ = self.write_messages([Terminate]);
+        if !self.finished {
+            match self.finish_inner() {
+                Ok(()) => {}
+                Err(err) =>
+                    fail_unless_failing!("Error dropping connection: {}", err)
+            }
+        }
     }
 }
 
@@ -409,6 +424,7 @@ impl InnerPostgresConnection {
             cancel_data: PostgresCancelData { process_id: 0, secret_key: 0 },
             unknown_types: HashMap::new(),
             desynchronized: false,
+            finished: false,
         };
 
         args.push((~"client_encoding", ~"UTF8"));
@@ -598,10 +614,15 @@ impl InnerPostgresConnection {
             name: stmt_name,
             param_types: param_types,
             result_desc: result_desc,
-            next_portal_id: Cell::new(0)
+            next_portal_id: Cell::new(0),
+            finished: Cell::new(false),
         })
     }
 
+    fn is_desynchronized(&self) -> bool {
+        self.desynchronized
+    }
+
     fn get_type_name(&mut self, oid: Oid) -> Result<~str, PostgresError> {
         match self.unknown_types.find(&oid) {
             Some(name) => return Ok(name.clone()),
@@ -623,6 +644,7 @@ impl InnerPostgresConnection {
 
     fn quick_query(&mut self, query: &str)
             -> Result<~[~[Option<~str>]], PostgresError> {
+        check_desync!(self);
         if_ok_pg!(self.write_messages([Query { query: query }]));
 
         let mut result = ~[];
@@ -640,6 +662,11 @@ impl InnerPostgresConnection {
         }
         Ok(result)
     }
+
+    fn finish_inner(&mut self) -> Result<(), PostgresError> {
+        check_desync!(self);
+        Ok(if_ok_pg!(self.write_messages([Terminate])))
+    }
 }
 
 /// A connection to a Postgres database.
@@ -736,7 +763,8 @@ impl PostgresConnection {
         Ok(PostgresTransaction {
             conn: self,
             commit: Cell::new(true),
-            nested: false
+            nested: false,
+            finished: false,
         })
     }
 
@@ -790,10 +818,23 @@ impl PostgresConnection {
     /// If this has occurred, all further queries will immediately return an
     /// error.
     pub fn is_desynchronized(&self) -> bool {
-        self.conn.with(|conn| conn.desynchronized)
+        self.conn.with(|conn| conn.is_desynchronized())
     }
 
-    fn quick_query(&self, query: &str) -> Result<~[~[Option<~str>]], PostgresError> {
+    /// Consumes the connection, closing it.
+    ///
+    /// Functionally equivalent to the `Drop` implementation for
+    /// `PostgresConnection` except that it returns any error encountered to
+    /// the caller.
+    pub fn finish(self) -> Result<(), PostgresError> {
+        self.conn.with_mut(|conn| {
+            conn.finished = true;
+            conn.finish_inner()
+        })
+    }
+
+    fn quick_query(&self, query: &str)
+            -> Result<~[~[Option<~str>]], PostgresError> {
         self.conn.with_mut(|conn| conn.quick_query(query))
     }
 
@@ -824,25 +865,39 @@ pub enum SslMode {
 pub struct PostgresTransaction<'conn> {
     priv conn: &'conn PostgresConnection,
     priv commit: Cell<bool>,
-    priv nested: bool
+    priv nested: bool,
+    priv finished: bool,
 }
 
 #[unsafe_destructor]
 impl<'conn> Drop for PostgresTransaction<'conn> {
     fn drop(&mut self) {
+        if !self.finished {
+            match self.finish_inner() {
+                Ok(()) => {}
+                Err(err) =>
+                    fail_unless_failing!("Error dropping transaction: {}", err)
+            }
+        }
+    }
+}
+
+impl<'conn> PostgresTransaction<'conn> {
+    fn finish_inner(&mut self) -> Result<(), PostgresError> {
         if task::failing() || !self.commit.get() {
             if self.nested {
-                self.conn.quick_query("ROLLBACK TO sp");
+                if_ok!(self.conn.quick_query("ROLLBACK TO sp"));
             } else {
-                self.conn.quick_query("ROLLBACK");
+                if_ok!(self.conn.quick_query("ROLLBACK"));
             }
         } else {
             if self.nested {
-                self.conn.quick_query("RELEASE sp");
+                if_ok!(self.conn.quick_query("RELEASE sp"));
             } else {
-                self.conn.quick_query("COMMIT");
+                if_ok!(self.conn.quick_query("COMMIT"));
             }
         }
+        Ok(())
     }
 }
 
@@ -884,7 +939,8 @@ impl<'conn> PostgresTransaction<'conn> {
         Ok(PostgresTransaction {
             conn: self.conn,
             commit: Cell::new(true),
-            nested: true
+            nested: true,
+            finished: false,
         })
     }
 
@@ -920,6 +976,15 @@ impl<'conn> PostgresTransaction<'conn> {
     pub fn set_rollback(&self) {
         self.commit.set(false);
     }
+
+    /// Consumes the transaction, commiting or rolling it back as appropriate.
+    ///
+    /// Functionally equivalent to the `Drop` implementation of
+    /// `PostgresTransaction` except that it returns any error to the caller.
+    pub fn finish(mut self) -> Result<(), PostgresError> {
+        self.finished = true;
+        self.finish_inner()
+    }
 }
 
 /// A trait containing methods that can be called on a prepared statement.
@@ -974,6 +1039,12 @@ pub trait PostgresStatement {
             Err(err) => fail!("Error executing query:\n{}", err.to_str())
         }
     }
+
+    /// Consumes the statement, clearing it from the Postgres session.
+    ///
+    /// Functionally identical to the `Drop` implementation of the
+    /// `PostgresStatement` except that it returns any error to the caller.
+    fn finish(self) -> Result<(), PostgresError>;
 }
 
 /// A statement prepared outside of a transaction.
@@ -982,29 +1053,42 @@ pub struct NormalPostgresStatement<'conn> {
     priv name: ~str,
     priv param_types: ~[PostgresType],
     priv result_desc: ~[ResultDescription],
-    priv next_portal_id: Cell<uint>
+    priv next_portal_id: Cell<uint>,
+    priv finished: Cell<bool>,
 }
 
 #[unsafe_destructor]
 impl<'conn> Drop for NormalPostgresStatement<'conn> {
     fn drop(&mut self) {
-        let _ = self.conn.write_messages([
+        if !self.finished.get() {
+            match self.finish_inner() {
+                Ok(()) => {}
+                Err(err) =>
+                    fail_unless_failing!("Error dropping statement: {}", err)
+            }
+        }
+    }
+}
+
+impl<'conn> NormalPostgresStatement<'conn> {
+    fn finish_inner(&mut self) -> Result<(), PostgresError> {
+        check_desync!(self.conn);
+        if_ok_pg!(self.conn.write_messages([
             Close {
                 variant: 'S' as u8,
                 name: self.name.as_slice()
             },
-            Sync]);
+            Sync]));
         loop {
-            match self.conn.read_message() {
-                Ok(ReadyForQuery { .. }) => break,
-                Err(_) => break,
+            // TODO forward db errors
+            match if_ok_pg!(self.conn.read_message()) {
+                ReadyForQuery { .. } => break,
                 _ => {}
             }
         }
+        Ok(())
     }
-}
 
-impl<'conn> NormalPostgresStatement<'conn> {
     fn execute(&self, portal_name: &str, row_limit: uint, params: &[&ToSql])
             -> Result<(), PostgresError> {
         let mut formats = ~[];
@@ -1059,9 +1143,10 @@ impl<'conn> NormalPostgresStatement<'conn> {
             name: portal_name,
             data: RingBuf::new(),
             row_limit: row_limit,
-            more_rows: true
+            more_rows: true,
+            finished: false,
         };
-        result.read_rows();
+        if_ok!(result.read_rows())
 
         Ok(result)
     }
@@ -1114,6 +1199,11 @@ impl<'conn> PostgresStatement for NormalPostgresStatement<'conn> {
         check_desync!(self.conn);
         self.try_lazy_query(0, params)
     }
+
+    fn finish(mut self) -> Result<(), PostgresError> {
+        self.finished.set(true);
+        self.finish_inner()
+    }
 }
 
 /// Information about a column of the result of a query.
@@ -1161,6 +1251,10 @@ impl<'conn> PostgresStatement for TransactionalPostgresStatement<'conn> {
             -> Result<PostgresResult<'a>, PostgresError> {
         self.stmt.try_query(params)
     }
+
+    fn finish(self) -> Result<(), PostgresError> {
+        self.stmt.finish()
+    }
 }
 
 impl<'conn> TransactionalPostgresStatement<'conn> {
@@ -1201,28 +1295,42 @@ pub struct PostgresResult<'stmt> {
     priv name: ~str,
     priv data: RingBuf<~[Option<~[u8]>]>,
     priv row_limit: uint,
-    priv more_rows: bool
+    priv more_rows: bool,
+    priv finished: bool,
 }
 
 #[unsafe_destructor]
 impl<'stmt> Drop for PostgresResult<'stmt> {
     fn drop(&mut self) {
-        let _ = self.stmt.conn.write_messages([
+        if !self.finished {
+            match self.finish_inner() {
+                Ok(()) => {}
+                Err(err) =>
+                    fail_unless_failing!("Error dropping result: {}", err)
+            }
+        }
+    }
+}
+
+impl<'stmt> PostgresResult<'stmt> {
+    fn finish_inner(&mut self) -> Result<(), PostgresError> {
+        check_desync!(self.stmt.conn);
+        if_ok_pg!(self.stmt.conn.write_messages([
             Close {
                 variant: 'P' as u8,
                 name: self.name.as_slice()
             },
-            Sync]);
+            Sync]));
         loop {
-            match self.stmt.conn.read_message() {
-                Ok(ReadyForQuery { .. }) => break,
+            // TODO forward PG errors
+            match if_ok_pg!(self.stmt.conn.read_message()) {
+                ReadyForQuery { .. } => break,
                 _ => {}
             }
         }
+        Ok(())
     }
-}
 
-impl<'stmt> PostgresResult<'stmt> {
     fn read_rows(&mut self) -> Result<(), PostgresError> {
         loop {
             match if_ok_pg!(self.stmt.conn.read_message()) {
@@ -1253,18 +1361,40 @@ impl<'stmt> PostgresResult<'stmt> {
     }
 }
 
-impl<'stmt> Iterator<PostgresRow<'stmt>> for PostgresResult<'stmt> {
-    fn next(&mut self) -> Option<PostgresRow<'stmt>> {
+impl<'stmt> PostgresResult<'stmt> {
+    /// Consumes the `PostgresResult`, cleaning up associated state.
+    ///
+    /// Functionally identical to the `Drop` implementation on
+    /// `PostgresResult` except that it returns any error to the caller.
+    pub fn finish(mut self) -> Result<(), PostgresError> {
+        self.finished = true;
+        self.finish_inner()
+    }
+
+    /// Like `PostgresResult::next` except that it returns any errors to the
+    /// caller instead of failing.
+    pub fn try_next(&mut self)
+            -> Result<Option<PostgresRow<'stmt>>, PostgresError> {
         if self.data.is_empty() && self.more_rows {
-            self.execute();
+            if_ok!(self.execute());
         }
 
-        self.data.pop_front().map(|row| {
+        let row = self.data.pop_front().map(|row| {
             PostgresRow {
                 stmt: self.stmt,
                 data: row
             }
-        })
+        });
+        Ok(row)
+    }
+}
+
+impl<'stmt> Iterator<PostgresRow<'stmt>> for PostgresResult<'stmt> {
+    fn next(&mut self) -> Option<PostgresRow<'stmt>> {
+        match self.try_next() {
+            Ok(ok) => ok,
+            Err(err) => fail!("Error fetching rows: {}", err)
+        }
     }
 
     fn size_hint(&self) -> (uint, Option<uint>) {
@@ -1344,3 +1474,4 @@ impl<'a> RowIndex for &'a str {
         fail!("there is no column with name {}", *self);
     }
 }
+