Enable passing nil context

.gitignore

@@ -1,2 +1,3 @@
 .envrc
 vendor/
+.vscode

doc.go

@@ -23,6 +23,9 @@ Context Support
 All potentially blocking operations take a context.Context. If a context is canceled while the method is in progress the
 method immediately returns. In most circumstances, this will close the underlying connection.
 
+A nil context can be passed for convenience. This has the same effect as passing context.Background() with an additional
+slight performance increase, if you don't need the operation to be cancellable.
+
 The CancelRequest method may be used to request the PostgreSQL server cancel an in-progress query without forcing the
 client to abort.
 */

pgconn.go

@@ -116,6 +116,10 @@ func ConnectConfig(ctx context.Context, config *Config) (pgConn *PgConn, err err
 		panic("config must be created by ParseConfig")
 	}
 
+	if ctx == nil {
+		ctx = context.Background()
+	}
+
 	// Simplify usage by treating primary config and fallbacks the same.
 	fallbackConfigs := []*FallbackConfig{
 		{
@@ -362,6 +366,7 @@ func (pgConn *PgConn) SendBytes(ctx context.Context, buf []byte) error {
 	}
 	defer pgConn.unlock()
 
+	if ctx != nil {
 		select {
 		case <-ctx.Done():
 			return &contextAlreadyDoneError{err: ctx.Err()}
@@ -369,6 +374,7 @@ func (pgConn *PgConn) SendBytes(ctx context.Context, buf []byte) error {
 		}
 		pgConn.contextWatcher.Watch(ctx)
 		defer pgConn.contextWatcher.Unwatch()
+	}
 
 	n, err := pgConn.conn.Write(buf)
 	if err != nil {
@@ -392,6 +398,7 @@ func (pgConn *PgConn) ReceiveMessage(ctx context.Context) (pgproto3.BackendMessa
 	}
 	defer pgConn.unlock()
 
+	if ctx != nil {
 		select {
 		case <-ctx.Done():
 			return nil, &contextAlreadyDoneError{err: ctx.Err()}
@@ -399,6 +406,7 @@ func (pgConn *PgConn) ReceiveMessage(ctx context.Context) (pgproto3.BackendMessa
 		}
 		pgConn.contextWatcher.Watch(ctx)
 		defer pgConn.contextWatcher.Unwatch()
+	}
 
 	msg, err := pgConn.receiveMessage()
 	if err != nil {
@@ -489,8 +497,10 @@ func (pgConn *PgConn) Close(ctx context.Context) error {
 
 	defer pgConn.conn.Close()
 
+	if ctx != nil {
 		pgConn.contextWatcher.Watch(ctx)
 		defer pgConn.contextWatcher.Unwatch()
+	}
 
 	// Ignore any errors sending Terminate message and waiting for server to close connection.
 	// This mimics the behavior of libpq PQfinish. It calls closePGconn which calls sendTerminateConn which purposefully
@@ -586,6 +596,7 @@ func (pgConn *PgConn) Prepare(ctx context.Context, name, sql string, paramOIDs [
 	}
 	defer pgConn.unlock()
 
+	if ctx != nil {
 		select {
 		case <-ctx.Done():
 			return nil, &contextAlreadyDoneError{err: ctx.Err()}
@@ -593,6 +604,7 @@ func (pgConn *PgConn) Prepare(ctx context.Context, name, sql string, paramOIDs [
 		}
 		pgConn.contextWatcher.Watch(ctx)
 		defer pgConn.contextWatcher.Unwatch()
+	}
 
 	buf := pgConn.wbuf
 	buf = (&pgproto3.Parse{Name: name, Query: sql, ParameterOIDs: paramOIDs}).Encode(buf)
@@ -673,18 +685,24 @@ func (pgConn *PgConn) CancelRequest(ctx context.Context) error {
 	// the connection config. This is important in high availability configurations where fallback connections may be
 	// specified or DNS may be used to load balance.
 	serverAddr := pgConn.conn.RemoteAddr()
-	cancelConn, err := pgConn.config.DialFunc(ctx, serverAddr.Network(), serverAddr.String())
+	_ctx := ctx
+	if _ctx == nil {
+		_ctx = context.Background()
+	}
+	cancelConn, err := pgConn.config.DialFunc(_ctx, serverAddr.Network(), serverAddr.String())
 	if err != nil {
 		return err
 	}
 	defer cancelConn.Close()
 
+	if ctx != nil {
 		contextWatcher := ctxwatch.NewContextWatcher(
 			func() { cancelConn.SetDeadline(time.Date(1, 1, 1, 1, 1, 1, 1, time.UTC)) },
 			func() { cancelConn.SetDeadline(time.Time{}) },
 		)
 		contextWatcher.Watch(ctx)
 		defer contextWatcher.Unwatch()
+	}
 
 	buf := make([]byte, 16)
 	binary.BigEndian.PutUint32(buf[0:4], 16)
@@ -712,6 +730,7 @@ func (pgConn *PgConn) WaitForNotification(ctx context.Context) error {
 	}
 	defer pgConn.unlock()
 
+	if ctx != nil {
 		select {
 		case <-ctx.Done():
 			return ctx.Err()
@@ -720,6 +739,7 @@ func (pgConn *PgConn) WaitForNotification(ctx context.Context) error {
 
 		pgConn.contextWatcher.Watch(ctx)
 		defer pgConn.contextWatcher.Unwatch()
+	}
 
 	for {
 		msg, err := pgConn.receiveMessage()
@@ -752,7 +772,7 @@ func (pgConn *PgConn) Exec(ctx context.Context, sql string) *MultiResultReader {
 		ctx:    ctx,
 	}
 	multiResult := &pgConn.multiResultReader
-
+	if ctx != nil {
 		select {
 		case <-ctx.Done():
 			multiResult.closed = true
@@ -762,6 +782,9 @@ func (pgConn *PgConn) Exec(ctx context.Context, sql string) *MultiResultReader {
 		default:
 		}
 		pgConn.contextWatcher.Watch(ctx)
+	} else {
+		pgConn.multiResultReader.ctx = context.Background()
+	}
 
 	buf := pgConn.wbuf
 	buf = (&pgproto3.Query{String: sql}).Encode(buf)
@@ -808,7 +831,7 @@ func (pgConn *PgConn) ExecParams(ctx context.Context, sql string, paramValues []
 	buf = (&pgproto3.Parse{Query: sql, ParameterOIDs: paramOIDs}).Encode(buf)
 	buf = (&pgproto3.Bind{ParameterFormatCodes: paramFormats, Parameters: paramValues, ResultFormatCodes: resultFormats}).Encode(buf)
 
-	pgConn.execExtendedSuffix(ctx, buf, result)
+	pgConn.execExtendedSuffix(buf, result)
 
 	return result
 }
@@ -834,7 +857,7 @@ func (pgConn *PgConn) ExecPrepared(ctx context.Context, stmtName string, paramVa
 	buf := pgConn.wbuf
 	buf = (&pgproto3.Bind{PreparedStatement: stmtName, ParameterFormatCodes: paramFormats, Parameters: paramValues, ResultFormatCodes: resultFormats}).Encode(buf)
 
-	pgConn.execExtendedSuffix(ctx, buf, result)
+	pgConn.execExtendedSuffix(buf, result)
 
 	return result
 }
@@ -845,6 +868,9 @@ func (pgConn *PgConn) execExtendedPrefix(ctx context.Context, paramValues [][]by
 		ctx:    ctx,
 	}
 	result := &pgConn.resultReader
+	if ctx == nil {
+		pgConn.resultReader.ctx = context.Background()
+	}
 
 	if err := pgConn.lock(); err != nil {
 		result.concludeCommand(nil, err)
@@ -859,6 +885,7 @@ func (pgConn *PgConn) execExtendedPrefix(ctx context.Context, paramValues [][]by
 		return result
 	}
 
+	if ctx != nil {
 		select {
 		case <-ctx.Done():
 			result.concludeCommand(nil, &contextAlreadyDoneError{err: ctx.Err()})
@@ -868,11 +895,12 @@ func (pgConn *PgConn) execExtendedPrefix(ctx context.Context, paramValues [][]by
 		default:
 		}
 		pgConn.contextWatcher.Watch(ctx)
+	}
 
 	return result
 }
 
-func (pgConn *PgConn) execExtendedSuffix(ctx context.Context, buf []byte, result *ResultReader) {
+func (pgConn *PgConn) execExtendedSuffix(buf []byte, result *ResultReader) {
 	buf = (&pgproto3.Describe{ObjectType: 'P'}).Encode(buf)
 	buf = (&pgproto3.Execute{}).Encode(buf)
 	buf = (&pgproto3.Sync{}).Encode(buf)
@@ -893,6 +921,7 @@ func (pgConn *PgConn) CopyTo(ctx context.Context, w io.Writer, sql string) (Comm
 		return nil, err
 	}
 
+	if ctx != nil {
 		select {
 		case <-ctx.Done():
 			pgConn.unlock()
@@ -901,6 +930,7 @@ func (pgConn *PgConn) CopyTo(ctx context.Context, w io.Writer, sql string) (Comm
 		}
 		pgConn.contextWatcher.Watch(ctx)
 		defer pgConn.contextWatcher.Unwatch()
+	}
 
 	// Send copy to command
 	buf := pgConn.wbuf
@@ -952,6 +982,7 @@ func (pgConn *PgConn) CopyFrom(ctx context.Context, r io.Reader, sql string) (Co
 	}
 	defer pgConn.unlock()
 
+	if ctx != nil {
 		select {
 		case <-ctx.Done():
 			return nil, &contextAlreadyDoneError{err: ctx.Err()}
@@ -959,6 +990,7 @@ func (pgConn *PgConn) CopyFrom(ctx context.Context, r io.Reader, sql string) (Co
 		}
 		pgConn.contextWatcher.Watch(ctx)
 		defer pgConn.contextWatcher.Unwatch()
+	}
 
 	// Send copy to command
 	buf := pgConn.wbuf
@@ -1344,7 +1376,7 @@ func (pgConn *PgConn) ExecBatch(ctx context.Context, batch *Batch) *MultiResultR
 		ctx:    ctx,
 	}
 	multiResult := &pgConn.multiResultReader
-
+	if ctx != nil {
 		select {
 		case <-ctx.Done():
 			multiResult.closed = true
@@ -1354,6 +1386,9 @@ func (pgConn *PgConn) ExecBatch(ctx context.Context, batch *Batch) *MultiResultR
 		default:
 		}
 		pgConn.contextWatcher.Watch(ctx)
+	} else {
+		pgConn.multiResultReader.ctx = context.Background()
+	}
 
 	batch.buf = (&pgproto3.Sync{}).Encode(batch.buf)