feat: Allow setting state->open to unknown via DELETE

The schema defines the absence of state->open to represent the unknown
state. Previously it was not possible to explicitly set this state via
the HTTP endpoints.

types.SpaceAPIState.Open is now an enum which is either unknown, closed,
or open. Custom IsZero() and MarshalJSON() methods on the type ensure
marshaling the value yields a boolean for open/closed and an empty byte
slice for unknown (resulting in the field being absent from the final
response).

The handlers.StateOpenDELETE() function has been added to expose this
behavior.

Switching to encoding/json/v2 required raising the minimum Go version in
go.mod to 1.27.

Closes: CCCHH/spaceapid!37
Fixes:  CCCHH/spaceapid#38

types/v15.go

@@ -1,5 +1,9 @@
 package types
 
+import (
+	"encoding/json/v2"
+)
+
 const CurrentMessageVersion = "15"
 
 // SpaceAPIResponse represents the contents of the SpaceAPI message
@@ -114,19 +118,50 @@ type SpaceAPILocationAreas struct {
 	SquareMeters float64 `json:"square_meters"` // REQUIRED
 }
 
+type SpaceAPIStateOpen int
+
+const (
+	SpaceAPIStateOpenIsUnknown = iota
+	SpaceAPIStateOpenIsClosed
+	SpaceAPIStateOpenIsOpen
+)
+
+func (state SpaceAPIStateOpen) MarshalJSON() ([]byte, error) {
+	switch state {
+	case SpaceAPIStateOpenIsClosed:
+		return json.Marshal(false)
+	case SpaceAPIStateOpenIsOpen:
+		return json.Marshal(true)
+	default:
+		return []byte{}, nil
+	}
+}
+
+func (state SpaceAPIStateOpen) IsZero() bool {
+	return state == SpaceAPIStateOpenIsUnknown
+}
+
 type SpaceAPIState struct {
-	Open          bool   `json:"open,omitempty"`
-	LastChange    int64  `json:"lastchange,omitempty"`
-	TriggerPerson string `json:"trigger_person,omitempty"`
-	Message       string `json:"message,omitempty"`
+	Open          SpaceAPIStateOpen `json:"open,omitzero"`
+	LastChange    int64             `json:"lastchange,omitempty"`
+	TriggerPerson string            `json:"trigger_person,omitempty"`
+	Message       string            `json:"message,omitempty"`
 	Icon          struct {
 		Open   string `json:"open,omitempty"`   // REQUIRED
 		Closed string `json:"closed,omitempty"` // REQUIRED
 	} `json:"icon,omitzero"`
 }
 
-func (s *SpaceAPIState) FromPersistentSpaceState(ps PersistentSpaceState) {
-	s.Open = ps.State.Open
+func (s *SpaceAPIState) FromPersistentSpaceState(ps PersistentState) {
+	if ps.State.IsUnknown {
+		s.Open = SpaceAPIStateOpenIsUnknown
+	} else {
+		if ps.State.Open {
+			s.Open = SpaceAPIStateOpenIsOpen
+		} else {
+			s.Open = SpaceAPIStateOpenIsClosed
+		}
+	}
 	s.LastChange = ps.State.LastChange
 	s.Message = ps.State.Message
 }
@@ -147,15 +182,18 @@ type EnvironmentSensor struct {
 	LastChange  int64   `json:"lastchange,omitempty"`
 }
 
-type PersistentSpaceState struct {
-	State struct {
-		Open       bool   `json:"open"`
-		LastChange int64  `json:"lastchange"`
-		Message    string `json:"message,omitempty"`
-	} `json:"state"`
+type PersistentState struct {
+	State   PersistentSpaceState                     `json:"state"`
 	Sensors map[string][]PersistentEnvironmentSensor `json:"sensors,omitempty"`
 }
 
+type PersistentSpaceState struct {
+	Open       bool   `json:"open"`
+	IsUnknown  bool   `json:"is_unknown"`
+	LastChange int64  `json:"lastchange"`
+	Message    string `json:"message,omitempty"`
+}
+
 type PersistentEnvironmentSensor struct {
 	Value      float64 `json:"value"`
 	Location   string  `json:"location,omitempty"`