Support JSON double values being reencoded.

When the JSON value 2 is decoded, it is a Double, so arithmetic on it returns doubles.

It can be cast into an integer value which make it slightly easier to
read.

With further illustrative tests and documentation.

docs/cel_expressions.md

@@ -7,7 +7,67 @@ In addition to the custom function extension listed below, you can craft any
 valid CEL expression as defined by the
 [cel-spec language definition](https://github.com/google/cel-spec/blob/master/doc/langdef.md)
 
-### List of extensions
+
+## Notes
+
+One thing to be aware of is how numeric values are treated in CEL expressions, JSON numbers are decoded to [CEL double](https://github.com/google/cel-spec/blob/master/doc/langdef.md#values) values.
+
+For example:
+
+```json
+{
+  "count": 2,
+  "measure": 1.7
+}
+```
+
+In the JSON above, both numbers are parsed as floating point values.
+
+This means that if you want to do integer arithmetic, you'll need to [use explicit conversion functions](https://github.com/google/cel-spec/blob/master/doc/langdef.md#numeric-values).
+
+From the CEL specification:
+
+> Note that currently there are no automatic arithmetic conversions for the numeric types (int, uint, and double).
+
+You can either explicitly convert the number, or add another double value e.g.
+
+```yaml
+interceptors:
+  - cel:
+      overlays:
+      - key: count_plus_1
+        expression: "body.count + 1.0"
+      - key: count_plus_2
+        expression: "int(body.count) + 2"
+      - key: measure_times_3
+        expression: "body.measure * 3.0"
+```
+
+These will be serialised back to JSON appropriately:
+
+```json
+{
+  "count_plus_1": 2,
+  "count_plus_2": 3,
+  "measure_times_3": 5.1
+}
+```
+
+### Error messages in conversions
+
+The following example will generate an error with the JSON example.
+
+```yaml
+interceptors:
+  - cel:
+      overlays:
+      - key: bad_measure_times_3
+        expression: "body.measure * 3"
+```
+
+**bad_measure_times_3** will fail with `failed to evaluate overlay expression 'body.measure * 3': no such overload` because there's no automatic conversion.
+
+## List of extensions
 
 The body from the `http.Request` value is decoded to JSON and exposed, and the
 headers are also available.
@@ -59,7 +119,7 @@ type Header map[string][]string
 i.e. the header is a mapping of strings, to arrays of strings, see the `match`
 function on headers below for an extension that makes looking up headers easier.
 
-### List of extension functions
+## List of extension functions
 
 This lists custom functions that can be used from CEL expressions in the CEL
 interceptor.

pkg/interceptors/cel/cel.go

@@ -103,6 +103,17 @@ func (w *Interceptor) ExecuteTrigger(request *http.Request) (*http.Response, err
 			if err == nil {
 				b, err = json.Marshal(raw.(*structpb.Value).GetStringValue())
 			}
+		case types.Double:
+			raw, err = val.ConvertToNative(reflect.TypeOf(&structpb.Value{}))
+			if err == nil {
+				b, err = json.Marshal(raw.(*structpb.Value).GetNumberValue())
+			}
+		case types.Int:
+			raw, err = val.ConvertToNative(reflect.TypeOf(&structpb.Value{}))
+			if err == nil {
+				b, err = json.Marshal(raw.(*structpb.Value).GetNumberValue())
+			}
+
 		default:
 			raw, err = val.ConvertToNative(reflect.TypeOf([]byte{}))
 			b = raw.([]byte)

pkg/interceptors/cel/cel_test.go

@@ -122,6 +122,19 @@ func TestInterceptor_ExecuteTrigger(t *testing.T) {
 			payload: nil,
 			want:    []byte(`{}`),
 		},
+		{
+			name: "incrementing an integer value",
+			CEL: &triggersv1.CELInterceptor{
+				Overlays: []triggersv1.CELOverlay{
+					{Key: "val1", Expression: "body.count + 1.0"},
+					{Key: "val2", Expression: "int(body.count) + 3"},
+					{Key: "val3", Expression: "body.count + 3.5"},
+					{Key: "val4", Expression: "body.measure * 3.0"},
+				},
+			},
+			payload: ioutil.NopCloser(bytes.NewBufferString(`{"count":1,"measure":1.7}`)),
+			want:    []byte(`{"val4":5.1,"val3":4.5,"val2":4,"val1":2,"count":1,"measure":1.7}`),
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -243,9 +256,12 @@ func TestExpressionEvaluation(t *testing.T) {
 	testSHA := "ec26c3e57ca3a959ca5aad62de7213c562f8c821"
 	testRef := "refs/heads/master"
 	jsonMap := map[string]interface{}{
-		"value":    "testing",
-		"sha":      testSHA,
-		"ref":      testRef,
+		"value": "testing",
+		"sha":   testSHA,
+		"ref":   testRef,
+		"pull_request": map[string]interface{}{
+			"commits": 2,
+		},
 		"b64value": "ZXhhbXBsZQ==",
 	}
 	refParts := strings.Split(testRef, "/")
@@ -307,9 +323,9 @@ func TestExpressionEvaluation(t *testing.T) {
 			want: types.Bytes("example"),
 		},
 		{
-			name: "decode a base64 value",
-			expr: "decodeb64(body.b64value)",
-			want: types.Bytes("example"),
+			name: "increment an integer",
+			expr: "body.pull_request.commits + 1",
+			want: types.Int(3),
 		},
 	}
 	for _, tt := range tests {
@@ -337,9 +353,12 @@ func TestExpressionEvaluation_Error(t *testing.T) {
 	jsonMap := map[string]interface{}{
 		"value": "testing",
 		"sha":   testSHA,
+		"pull_request": map[string]interface{}{
+			"commits": []string{},
+		},
 	}
 	header := http.Header{}
-	evalEnv := map[string]interface{}{"body": jsonMap, "headers": header}
+	evalEnv := map[string]interface{}{"body": jsonMap, "header": header}
 	env, err := makeCelEnv()
 	if err != nil {
 		t.Fatal(err)