use settings function in interface, let QueryContext handle context cancellation

Author: kminehart

datasource.go

@@ -7,7 +7,6 @@ import (
 	"fmt"
 	"net/http"
 	"sync"
-	"time"
 
 	"github.com/grafana/grafana-plugin-sdk-go/backend"
 	"github.com/grafana/grafana-plugin-sdk-go/backend/instancemgmt"
@@ -18,10 +17,11 @@ import (
 type sqldatasource struct {
 	Completable
 
-	db       *sql.DB
-	c        Driver
-	settings backend.DataSourceInstanceSettings
-	timeout  time.Duration
+	db *sql.DB
+	c  Driver
+
+	driverSettings DriverSettings
+	settings       backend.DataSourceInstanceSettings
 
 	backend.CallResourceHandler
 	CustomRoutes map[string]func(http.ResponseWriter, *http.Request)
@@ -43,7 +43,7 @@ func (ds *sqldatasource) NewDatasource(settings backend.DataSourceInstanceSettin
 	}
 
 	ds.CallResourceHandler = httpadapter.New(mux)
-	ds.timeout = ds.c.Timeout(settings)
+	ds.driverSettings = ds.c.Settings(settings)
 
 	return ds, nil
 }
@@ -103,13 +103,13 @@ func (ds *sqldatasource) handleQuery(ctx context.Context, req backend.DataQuery)
 	}
 
 	// Apply the default FillMode, overwritting it if the query specifies it
-	fillMode := ds.c.FillMode()
+	fillMode := ds.driverSettings.FillMode
 	if q.FillMissing != nil {
 		fillMode = q.FillMissing
 	}
 
-	if ds.timeout != 0 {
-		tctx, cancel := context.WithTimeout(ctx, ds.timeout)
+	if ds.driverSettings.Timeout != 0 {
+		tctx, cancel := context.WithTimeout(ctx, ds.driverSettings.Timeout)
 		defer cancel()
 
 		ctx = tctx
@@ -119,15 +119,13 @@ func (ds *sqldatasource) handleQuery(ctx context.Context, req backend.DataQuery)
 	//  * Some datasources (snowflake) expire connections or have an authentication token that expires if not used in 1 or 4 hours.
 	//    Because the datasource driver does not include an option for permanent connections, we retry the connection
 	//    if the query fails. NOTE: this does not include some errors like "ErrNoRows"
-
-	// This function will return an "ErrorTimeout" if the context's done channel receives data
-	res, err := queryContext(ctx, ds.db, ds.c.Converters(), fillMode, q)
+	res, err := query(ctx, ds.db, ds.c.Converters(), fillMode, q)
 	if err == nil {
 		return res, nil
 	}
 
 	if errors.Is(err, ErrorNoResults) {
-		return nil, nil
+		return res, nil
 	}
 
 	if errors.Is(err, ErrorQuery) {
@@ -136,7 +134,7 @@ func (ds *sqldatasource) handleQuery(ctx context.Context, req backend.DataQuery)
 			return nil, err
 		}
 
-		return queryContext(ctx, ds.db, ds.c.Converters(), fillMode, q)
+		return query(ctx, ds.db, ds.c.Converters(), fillMode, q)
 	}
 
 	return nil, err

driver.go

@@ -9,14 +9,18 @@ import (
 	"github.com/grafana/grafana-plugin-sdk-go/data/sqlutil"
 )
 
+type DriverSettings struct {
+	Timeout  time.Duration
+	FillMode *data.FillMissing
+}
+
 // Driver is a simple interface that defines how to connect to a backend SQL datasource
 // Plugin creators will need to implement this in order to create a managed datasource
 type Driver interface {
 	// Connect connects to the database. It does not need to call `db.Ping()`
 	Connect(backend.DataSourceInstanceSettings) (*sql.DB, error)
-	Timeout(backend.DataSourceInstanceSettings) time.Duration
-	FillMode() *data.FillMissing
+	// Settings are read whenever the plugin is initialized, or after the data source settings are updated
+	Settings(backend.DataSourceInstanceSettings) DriverSettings
 	Macros() Macros
 	Converters() []sqlutil.Converter
-	// Timeout is used when sending a query to the backing data source. If the timeout is exceeded, the QueryData function will return an error.
 }

macros_test.go

@@ -7,7 +7,6 @@ import (
 	"time"
 
 	"github.com/grafana/grafana-plugin-sdk-go/backend"
-	"github.com/grafana/grafana-plugin-sdk-go/data"
 	"github.com/grafana/grafana-plugin-sdk-go/data/sqlutil"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -19,7 +18,7 @@ func (h *MockDB) Connect(backend.DataSourceInstanceSettings) (db *sql.DB, err er
 	return
 }
 
-func (h *MockDB) FillMode() (mode *data.FillMissing) {
+func (h *MockDB) Settings(backend.DataSourceInstanceSettings) (settings DriverSettings) {
 	return
 }
 

query.go

@@ -91,28 +91,6 @@ func getErrorFrameFromQuery(query *Query) data.Frames {
 	return frames
 }
 
-func queryContext(ctx context.Context, db *sql.DB, converters []sqlutil.Converter, fillMode *data.FillMissing, q *Query) (data.Frames, error) {
-	var (
-		done = make(chan bool)
-		res  = data.Frames{}
-		err  error
-	)
-
-	go func() {
-		res, err = query(ctx, db, converters, fillMode, q)
-		done <- true
-	}()
-
-	select {
-	case <-done:
-		// The done channel will receive data if the query funciton has completed
-		return res, err
-	case <-ctx.Done():
-		// The context's done channel will receive data if the timeout is exceeded
-		return nil, ErrorTimeout
-	}
-}
-
 // query sends the query to the sql.DB and converts the rows to a dataframe.
 func query(ctx context.Context, db *sql.DB, converters []sqlutil.Converter, fillMode *data.FillMissing, query *Query) (data.Frames, error) {
 	// Query the rows from the database
@@ -140,7 +118,7 @@ func query(ctx context.Context, db *sql.DB, converters []sqlutil.Converter, fill
 	// Convert the response to frames
 	res, err := getFrames(rows, -1, converters, fillMode, query)
 	if err != nil {
-		return nil, fmt.Errorf("%w: %s", err, "Could not process SQL results")
+		return getErrorFrameFromQuery(query), fmt.Errorf("%w: %s", err, "Could not process SQL results")
 	}
 
 	return res, nil

query_test.go

@@ -0,0 +1,33 @@
+package sqlds
+
+import (
+	"database/sql"
+	"time"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	"github.com/grafana/grafana-plugin-sdk-go/data"
+	"github.com/grafana/grafana-plugin-sdk-go/data/sqlutil"
+)
+
+type MockTimeoutDriver struct{}
+
+// Connect connects to the database. It does not need to call `db.Ping()`
+func (m *MockTimeoutDriver) Connect(_ backend.DataSourceInstanceSettings) (*sql.DB, error) {
+	return nil, nil
+}
+
+func (m *MockTimeoutDriver) FillMode() *data.FillMissing {
+	return nil
+}
+
+func (m *MockTimeoutDriver) Macros() Macros {
+	return nil
+}
+
+func (m *MockTimeoutDriver) Converters() []sqlutil.Converter {
+	return nil
+}
+
+func (m *MockTimeoutDriver) Timeout(backend.DataSourceInstanceSettings) time.Duration {
+	return time.Second
+}