Godriver 1657 pass interface to cursor.all (#431)

Author: KritiRav

mongo/cursor.go

@@ -9,6 +9,7 @@ package mongo
 import (
 	"context"
 	"errors"
+	"fmt"
 	"io"
 	"reflect"
 
@@ -186,10 +187,18 @@ func (c *Cursor) Close(ctx context.Context) error {
 func (c *Cursor) All(ctx context.Context, results interface{}) error {
 	resultsVal := reflect.ValueOf(results)
 	if resultsVal.Kind() != reflect.Ptr {
-		return errors.New("results argument must be a pointer to a slice")
+		return fmt.Errorf("results argument must be a pointer to a slice, but was a %s", resultsVal.Kind())
 	}
 
 	sliceVal := resultsVal.Elem()
+	if sliceVal.Kind() == reflect.Interface {
+		sliceVal = sliceVal.Elem()
+	}
+
+	if sliceVal.Kind() != reflect.Slice {
+		return fmt.Errorf("results argument must be a pointer to a slice, but was a pointer to %s", sliceVal.Kind())
+	}
+
 	elementType := sliceVal.Type().Elem()
 	var index int
 	var err error

mongo/cursor_test.go

@@ -157,5 +157,25 @@ func TestCursor(t *testing.T) {
 			assert.Nil(t, err, "All error: %v", err)
 			assert.True(t, tbc.closed, "expected batch cursor to be closed but was not")
 		})
+
+		t.Run("does not error given interface as parameter", func(t *testing.T) {
+			var docs interface{} = []bson.D{}
+
+			cursor, err := newCursor(newTestBatchCursor(1, 5), nil)
+			assert.Nil(t, err, "newCursor error: %v", err)
+
+			err = cursor.All(context.Background(), &docs)
+			assert.Nil(t, err, "expected Nil, got error: %v", err)
+			assert.Equal(t, 5, len(docs.([]bson.D)), "expected 5 documents, got %v", len(docs.([]bson.D)))
+		})
+		t.Run("errors when not given pointer to slice", func(t *testing.T) {
+			var docs interface{} = "test"
+
+			cursor, err := newCursor(newTestBatchCursor(1, 5), nil)
+			assert.Nil(t, err, "newCursor error: %v", err)
+
+			err = cursor.All(context.Background(), &docs)
+			assert.NotNil(t, err, "expected error, got: %v", err)
+		})
 	})
 }