add support for boolean data types as metrics

This is useful if your database uses true/false for state and want to make prometheus alerts based on that. Before, booleans were not able to be parsed. See issue prometheus-community#201

Author: miguelHx

cmd/postgres_exporter/postgres_exporter.go

@@ -647,6 +647,11 @@ func dbToFloat64(t interface{}) (float64, bool) {
 return math.NaN(), false
 }
 return result, true
+case bool:
+if v {
+return 1.0, true
+}
+return 0.0, true
 case nil:
 return math.NaN(), true
 default:
@@ -670,6 +675,11 @@ func dbToString(t interface{}) (string, bool) {
 return string(v), true
 case string:
 return v, true
+case bool:
+if v {
+return "true", true
+}
+return "false", true
 default:
 return "", false
 }

cmd/postgres_exporter/postgres_exporter_test.go

@@ -265,3 +265,39 @@ func UnsetEnvironment(c *C, d string) {
 err := os.Unsetenv(d)
 c.Assert(err, IsNil)
 }
+
+// test boolean metric type gets converted to float
+func (s *FunctionalSuite) TestBooleanConversionToValueAndString(c *C) {
+
+type TestCase struct {
+input interface{}
+expectedString string
+expectedValue float64
+expectedOK bool
+}
+
+cases := []TestCase{
+{
+input: true,
+expectedString: "true",
+expectedValue: 1.0,
+expectedOK: true,
+},
+{
+input: false,
+expectedString: "false",
+expectedValue: 0.0,
+expectedOK: true,
+},
+}
+
+for _, cs := range cases {
+value, ok := dbToFloat64(cs.input)
+c.Assert(value, Equals, cs.expectedValue)
+c.Assert(ok, Equals, cs.expectedOK)
+
+str, ok := dbToString(cs.input)
+c.Assert(str, Equals, cs.expectedString)
+c.Assert(ok, Equals, cs.expectedOK)
+}
+}