Templates: keep large numeric params parseable (#32528)

Co-authored-by: Dennis Klipp <6085348+DennisKlipp@users.noreply.github.com>

util/templates/formatvalue_test.go

@@ -0,0 +1,38 @@
+package templates
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// JSON numbers arrive as float64. Large integers must not be rendered in
+// exponential notation, which would no longer parse as an integer.
+func TestFormatValue(t *testing.T) {
+	for _, tc := range []struct {
+		in   any
+		want string
+	}{
+		{float64(3), "3"},
+		{float64(8899), "8899"},
+		{float64(3493601102), "3493601102"}, // ten digit device serial
+		{float64(1.5), "1.5"},
+		{int(42), "42"},
+		{"text", "text"},
+	} {
+		assert.Equal(t, tc.want, formatValue(tc.in))
+	}
+}
+
+// end-to-end: a required int param supplied as a JSON number must satisfy the
+// required check, e.g. a ten digit device serial
+func TestRequiredLargeNumber(t *testing.T) {
+	tmpl := &Template{
+		Params: []Param{{Name: "serial", Type: TypeInt, Required: true}},
+	}
+
+	_, _, err := tmpl.RenderResult(RenderModeUnitTest, map[string]any{
+		"serial": float64(3493601102),
+	})
+	assert.NoError(t, err, "large serial supplied as JSON number")
+}

util/templates/template.go

@@ -274,6 +274,8 @@ func (t *Template) RenderProxyWithValues(values map[string]any, lang string) ([]
 				t.Params[index].Value = p.yamlQuote(v)
 			case int:
 				t.Params[index].Value = strconv.Itoa(v)
+			case float64, float32:
+				t.Params[index].Value = formatValue(v)
 			}
 		}
 	}
@@ -308,6 +310,20 @@ func (t *Template) RenderProxyWithValues(values map[string]any, lang string) ([]
 	return bytes.TrimSpace(out.Bytes()), err
 }
 
+// formatValue renders a parameter value for yaml. JSON numbers arrive as float64,
+// which %v would render in exponential notation for large values, e.g. a ten digit
+// serial number. Those are no longer parseable as integers.
+func formatValue(val any) string {
+	switch v := val.(type) {
+	case float64:
+		return strconv.FormatFloat(v, 'f', -1, 64)
+	case float32:
+		return strconv.FormatFloat(float64(v), 'f', -1, 32)
+	default:
+		return fmt.Sprintf("%v", val)
+	}
+}
+
 // RenderResult renders the result template to instantiate the proxy
 func (t *Template) RenderResult(renderMode int, other map[string]any) ([]byte, map[string]any, error) {
 	values := t.Defaults(renderMode)
@@ -383,7 +399,7 @@ func (t *Template) RenderResult(renderMode int, other map[string]any) ([]byte, m
 				// prevent rendering nil interfaces as "<nil>" string
 				var s string
 				if val != nil {
-					s = p.yamlQuote(fmt.Sprintf("%v", val))
+					s = p.yamlQuote(formatValue(val))
 				}
 
 				// validate required fields from yaml