Fix null value crash in postgresql_extensible input (#4689)

plugins/inputs/postgresql_extensible/postgresql_extensible.go

@@ -19,13 +19,7 @@ type Postgresql struct {
 	postgresql.Service
 	Databases      []string
 	AdditionalTags []string
-	Query          []struct {
+	Query          query
-		Sqlquery    string
-		Version     int
-		Withdbname  bool
-		Tagvalue    string
-		Measurement string
-	}
 	Debug          bool
 }
 
@@ -127,7 +121,6 @@ func (p *Postgresql) Gather(acc telegraf.Accumulator) error {
 	)
 
 	// Retreiving the database version
-
 	query = `select substring(setting from 1 for 3) as version from pg_settings where name='server_version_num'`
 	if err = p.DB.QueryRow(query).Scan(&db_version); err != nil {
 		db_version = 0
@@ -135,7 +128,6 @@ func (p *Postgresql) Gather(acc telegraf.Accumulator) error {
 
 	// We loop in order to process each query
 	// Query is not run if Database version does not match the query version.
-
 	for i := range p.Query {
 		sql_query = p.Query[i].Sqlquery
 		tag_value = p.Query[i].Tagvalue
@@ -221,9 +213,14 @@ func (p *Postgresql) accRow(meas_name string, row scanner, acc telegraf.Accumula
 		return err
 	}
 
-	if columnMap["datname"] != nil {
+	if c, ok := columnMap["datname"]; ok && *c != nil {
 		// extract the database name from the column map
-		dbname.WriteString((*columnMap["datname"]).(string))
+		switch datname := (*c).(type) {
+		case string:
+			dbname.WriteString(datname)
+		default:
+			dbname.WriteString("postgres")
+		}
 	} else {
 		dbname.WriteString("postgres")
 	}

plugins/inputs/postgresql_extensible/postgresql_extensible_test.go

@@ -1,6 +1,7 @@
 package postgresql_extensible
 
 import (
+	"errors"
 	"fmt"
 	"testing"
 
@@ -223,3 +224,41 @@ func TestPostgresqlIgnoresUnwantedColumns(t *testing.T) {
 		assert.False(t, acc.HasMeasurement(col))
 	}
 }
+
+func TestAccRow(t *testing.T) {
+	p := Postgresql{}
+	var acc testutil.Accumulator
+	columns := []string{"datname", "cat"}
+
+	testRows := []fakeRow{
+		{fields: []interface{}{1, "gato"}},
+		{fields: []interface{}{nil, "gato"}},
+		{fields: []interface{}{"name", "gato"}},
+	}
+	for i := range testRows {
+		err := p.accRow("pgTEST", testRows[i], &acc, columns)
+		if err != nil {
+			t.Fatalf("Scan failed: %s", err)
+		}
+	}
+}
+
+type fakeRow struct {
+	fields []interface{}
+}
+
+func (f fakeRow) Scan(dest ...interface{}) error {
+	if len(f.fields) != len(dest) {
+		return errors.New("Nada matchy buddy")
+	}
+
+	for i, d := range dest {
+		switch d.(type) {
+		case (*interface{}):
+			*d.(*interface{}) = f.fields[i]
+		default:
+			return fmt.Errorf("Bad type %T", d)
+		}
+	}
+	return nil
+}