Support slices in event.GetObjValue and add tests

event.go

@@ -3,6 +3,7 @@ package stripe
 import (
 	"encoding/json"
 	"fmt"
+	"strconv"
 )
 
 // Event is the resource representing a Stripe event.
@@ -82,7 +83,28 @@ func getValue(m map[string]interface{}, keys []string) string {
 	node := m[keys[0]]
 
 	for i := 1; i < len(keys); i++ {
-		node = node.(map[string]interface{})[keys[i]]
+		key := keys[i]
+
+		sliceNode, ok := node.([]interface{})
+		if ok {
+			intKey, err := strconv.Atoi(key)
+			if err != nil {
+				panic(fmt.Sprintf(
+					"Cannot access nested slice element with non-integer key: %s",
+					key))
+			}
+			node = sliceNode[intKey]
+			continue
+		}
+
+		mapNode, ok := node.(map[string]interface{})
+		if ok {
+			node = mapNode[key]
+			continue
+		}
+
+		panic(fmt.Sprintf(
+			"Cannot descend into non-map non-slice object with key: %s", key))
 	}
 
 	if node == nil {

event_test.go

@@ -0,0 +1,55 @@
+package stripe
+
+import (
+	"testing"
+
+	assert "github.com/stretchr/testify/require"
+)
+
+func TestGetObjValue(t *testing.T) {
+	event := &Event{
+		Data: &EventData{
+			Obj: map[string]interface{}{
+				"top_level_key": "top_level",
+				"integer_key":   123,
+				"map": map[string]interface{}{
+					"nested_key": "nested",
+				},
+				"slice": []interface{}{
+					"index-0",
+					"index-1",
+					"index-2",
+				},
+				"slice_of_maps": []interface{}{
+					map[string]interface{}{
+						"slice_nested_key": "slice_nested",
+					},
+				},
+			},
+		},
+	}
+
+	assert.Equal(t, "top_level", event.GetObjValue("top_level_key"))
+
+	// Check that it coerces non-string values into strings (this behavior is
+	// somewhat questionable, but I'm going with how it already works)
+	assert.Equal(t, "123", event.GetObjValue("integer_key"))
+
+	assert.Equal(t, "nested", event.GetObjValue("map", "nested_key"))
+	assert.Equal(t, "index-1", event.GetObjValue("slice", "1"))
+	assert.Equal(t, "slice_nested",
+		event.GetObjValue("slice_of_maps", "0", "slice_nested_key"))
+
+	// By design a `nil` just returns an empty string
+	assert.Equal(t, "", event.GetObjValue("bad_key"))
+
+	// Panic conditions. Usually the function tries to just return a value is
+	// fairly forgiving, but it does panic under certain obviously impossible
+	// cases.
+	assert.Panicsf(t, func() {
+		event.GetObjValue("slice", "string_key")
+	}, "Cannot access nested slice element with non-integer key: %s", "bad_key")
+	assert.Panicsf(t, func() {
+		event.GetObjValue("top_level_key", "bad_key")
+	}, "Cannot descend into non-map non-slice object with key: %s", "bad_key")
+}