chore: add unknown usage event type error (#19436)

- Adds `usagetypes.UnknownEventTypeError` type, which is returned by
`ParseEventWithType`
- Changes `ParseEvent` to not be a generic function since it doesn't
really need it
- Adds `User-Agent` to tallyman requests

coderd/usage/usagetypes/events.go

@@ -13,6 +13,7 @@ package usagetypes
 import (
 	"bytes"
 	"encoding/json"
+	"fmt"
 	"strings"
 
 	"golang.org/x/xerrors"
@@ -22,6 +23,10 @@ import (
 // type `usage_event_type`.
 type UsageEventType string
 
+// All event types.
+//
+// When adding a new event type, ensure you add it to the Valid method and the
+// ParseEventWithType function.
 const (
 	UsageEventTypeDCManagedAgentsV1 UsageEventType = "dc_managed_agents_v1"
 )
@@ -43,38 +48,56 @@ func (e UsageEventType) IsHeartbeat() bool {
 	return e.Valid() && strings.HasPrefix(string(e), "hb_")
 }
 
-// ParseEvent parses the raw event data into the specified Go type. It fails if
-// there is any unknown fields or extra data after the event. The returned event
-// is validated.
-func ParseEvent[T Event](data json.RawMessage) (T, error) {
+// ParseEvent parses the raw event data into the provided event. It fails if
+// there is any unknown fields or extra data at the end of the JSON. The
+// returned event is validated.
+func ParseEvent(data json.RawMessage, out Event) error {
 	dec := json.NewDecoder(bytes.NewReader(data))
 	dec.DisallowUnknownFields()
 
-	var event T
-	err := dec.Decode(&event)
+	err := dec.Decode(out)
 	if err != nil {
-		return event, xerrors.Errorf("unmarshal %T event: %w", event, err)
+		return xerrors.Errorf("unmarshal %T event: %w", out, err)
 	}
 	if dec.More() {
-		return event, xerrors.Errorf("extra data after %T event", event)
+		return xerrors.Errorf("extra data after %T event", out)
 	}
-	err = event.Valid()
+	err = out.Valid()
 	if err != nil {
-		return event, xerrors.Errorf("invalid %T event: %w", event, err)
+		return xerrors.Errorf("invalid %T event: %w", out, err)
 	}
 
-	return event, nil
+	return nil
+}
+
+// UnknownEventTypeError is returned by ParseEventWithType when an unknown event
+// type is encountered.
+type UnknownEventTypeError struct {
+	EventType string
+}
+
+var _ error = UnknownEventTypeError{}
+
+// Error implements error.
+func (e UnknownEventTypeError) Error() string {
+	return fmt.Sprintf("unknown usage event type: %q", e.EventType)
 }
 
 // ParseEventWithType parses the raw event data into the specified Go type. It
 // fails if there is any unknown fields or extra data after the event. The
 // returned event is validated.
+//
+// If the event type is unknown, UnknownEventTypeError is returned.
 func ParseEventWithType(eventType UsageEventType, data json.RawMessage) (Event, error) {
 	switch eventType {
 	case UsageEventTypeDCManagedAgentsV1:
-		return ParseEvent[DCManagedAgentsV1](data)
+		var event DCManagedAgentsV1
+		if err := ParseEvent(data, &event); err != nil {
+			return nil, err
+		}
+		return event, nil
 	default:
-		return nil, xerrors.Errorf("unknown event type: %s", eventType)
+		return nil, UnknownEventTypeError{EventType: string(eventType)}
 	}
 }
 

coderd/usage/usagetypes/events_test.go

@@ -13,29 +13,34 @@ func TestParseEvent(t *testing.T) {
 
 	t.Run("ExtraFields", func(t *testing.T) {
 		t.Parallel()
-		_, err := usagetypes.ParseEvent[usagetypes.DCManagedAgentsV1]([]byte(`{"count": 1, "extra": "field"}`))
-		require.ErrorContains(t, err, "unmarshal usagetypes.DCManagedAgentsV1 event")
+		var event usagetypes.DCManagedAgentsV1
+		err := usagetypes.ParseEvent([]byte(`{"count": 1, "extra": "field"}`), &event)
+		require.ErrorContains(t, err, "unmarshal *usagetypes.DCManagedAgentsV1 event")
 	})
 
 	t.Run("ExtraData", func(t *testing.T) {
 		t.Parallel()
-		_, err := usagetypes.ParseEvent[usagetypes.DCManagedAgentsV1]([]byte(`{"count": 1}{"count": 2}`))
-		require.ErrorContains(t, err, "extra data after usagetypes.DCManagedAgentsV1 event")
+		var event usagetypes.DCManagedAgentsV1
+		err := usagetypes.ParseEvent([]byte(`{"count": 1}{"count": 2}`), &event)
+		require.ErrorContains(t, err, "extra data after *usagetypes.DCManagedAgentsV1 event")
 	})
 
 	t.Run("DCManagedAgentsV1", func(t *testing.T) {
 		t.Parallel()
 
-		event, err := usagetypes.ParseEvent[usagetypes.DCManagedAgentsV1]([]byte(`{"count": 1}`))
+		var event usagetypes.DCManagedAgentsV1
+		err := usagetypes.ParseEvent([]byte(`{"count": 1}`), &event)
 		require.NoError(t, err)
 		require.Equal(t, usagetypes.DCManagedAgentsV1{Count: 1}, event)
 		require.Equal(t, map[string]any{"count": uint64(1)}, event.Fields())
 
-		_, err = usagetypes.ParseEvent[usagetypes.DCManagedAgentsV1]([]byte(`{"count": "invalid"}`))
-		require.ErrorContains(t, err, "unmarshal usagetypes.DCManagedAgentsV1 event")
+		event = usagetypes.DCManagedAgentsV1{}
+		err = usagetypes.ParseEvent([]byte(`{"count": "invalid"}`), &event)
+		require.ErrorContains(t, err, "unmarshal *usagetypes.DCManagedAgentsV1 event")
 
-		_, err = usagetypes.ParseEvent[usagetypes.DCManagedAgentsV1]([]byte(`{}`))
-		require.ErrorContains(t, err, "invalid usagetypes.DCManagedAgentsV1 event: count must be greater than 0")
+		event = usagetypes.DCManagedAgentsV1{}
+		err = usagetypes.ParseEvent([]byte(`{}`), &event)
+		require.ErrorContains(t, err, "invalid *usagetypes.DCManagedAgentsV1 event: count must be greater than 0")
 	})
 }
 
@@ -45,7 +50,9 @@ func TestParseEventWithType(t *testing.T) {
 	t.Run("UnknownEvent", func(t *testing.T) {
 		t.Parallel()
 		_, err := usagetypes.ParseEventWithType(usagetypes.UsageEventType("fake"), []byte(`{}`))
-		require.ErrorContains(t, err, "unknown event type: fake")
+		var unknownEventTypeError usagetypes.UnknownEventTypeError
+		require.ErrorAs(t, err, &unknownEventTypeError)
+		require.Equal(t, "fake", unknownEventTypeError.EventType)
 	})
 
 	t.Run("DCManagedAgentsV1", func(t *testing.T) {