types: make unmarshalExtensionArg into a generic constructor function

Signed-off-by: Patrick Jakubowski <[email protected]>

types/datetime.go

@@ -250,15 +250,11 @@ func (a Datetime) String() string {
 // - { "fn": "datetime", "arg": "1970-01-01" }
 // - "1970-01-01"
 func (a *Datetime) UnmarshalJSON(b []byte) error {
-	arg, err := unmarshalExtensionArg(b, "datetime")
+	aa, err := unmarshalExtensionValue(b, "datetime", ParseDatetime)
 	if err != nil {
 		return err
 	}
 
-	aa, err := ParseDatetime(arg)
-	if err != nil {
-		return err
-	}
 	*a = aa
 	return nil
 }

types/decimal.go

@@ -160,17 +160,19 @@ func (d Decimal) String() string {
 	return res[:right]
 }
 
+// UnmarshalJSON implements encoding/json.Unmarshaler for Decimal
+//
+// It is capable of unmarshaling 3 different representations supported by Cedar
+// - { "__extn": { "fn": "decimal", "arg": "1234.5678" }}
+// - { "fn": "decimal", "arg": "1234.5678" }
+// - "1234.5678"
 func (d *Decimal) UnmarshalJSON(b []byte) error {
-	arg, err := unmarshalExtensionArg(b, "decimal")
+	dd, err := unmarshalExtensionValue(b, "decimal", ParseDecimal)
 	if err != nil {
 		return err
 	}
 
-	vv, err := ParseDecimal(arg)
-	if err != nil {
-		return err
-	}
-	*d = vv
+	*d = dd
 	return nil
 }
 

types/duration.go

@@ -218,15 +218,11 @@ func (v Duration) String() string {
 // - { "fn": "duration", "arg": "1h10m" }
 // - "1h10m"
 func (v *Duration) UnmarshalJSON(b []byte) error {
-	arg, err := unmarshalExtensionArg(b, "duration")
+	vv, err := unmarshalExtensionValue(b, "duration", ParseDuration)
 	if err != nil {
 		return err
 	}
 
-	vv, err := ParseDuration(arg)
-	if err != nil {
-		return err
-	}
 	*v = vv
 	return nil
 }

types/ipaddr.go

@@ -103,16 +103,18 @@ func (c IPAddr) Contains(o IPAddr) bool {
 	return c.Prefix().Contains(o.Addr()) && c.Prefix().Bits() <= o.Prefix().Bits()
 }
 
+// UnmarshalJSON implements encoding/json.Unmarshaler for IPAddr
+//
+// It is capable of unmarshaling 3 different representations supported by Cedar
+// - { "__extn": { "fn": "ip", "arg": "12.34.56.78" }}
+// - { "fn": "ip", "arg": "12.34.56.78" }
+// - "12.34.56.78"
 func (v *IPAddr) UnmarshalJSON(b []byte) error {
-	arg, err := unmarshalExtensionArg(b, "ip")
+	vv, err := unmarshalExtensionValue(b, "ip", ParseIPAddr)
 	if err != nil {
 		return err
 	}
 
-	vv, err := ParseIPAddr(arg)
-	if err != nil {
-		return err
-	}
 	*v = vv
 	return nil
 }

types/json.go

@@ -127,35 +127,41 @@ func UnmarshalJSON(b []byte, v *Value) error {
 	return nil
 }
 
-func unmarshalExtensionArg(b []byte, extName string) (string, error) {
+func unmarshalExtensionValue[T any](b []byte, extName string, parse func(string) (T, error)) (T, error) {
+	var zeroT T
 	var arg string
 	if len(b) > 0 && b[0] == '"' {
 		if err := json.Unmarshal(b, &arg); err != nil {
-			return "", errors.Join(errJSONDecode, err)
+			return zeroT, errors.Join(errJSONDecode, err)
 		}
 	} else {
 		var res extValueJSON
 		if err := json.Unmarshal(b, &res); err != nil {
-			return "", errors.Join(errJSONDecode, err)
+			return zeroT, errors.Join(errJSONDecode, err)
 		}
 		if res.Extn == nil {
 			// If we didn't find an Extn, maybe it's just an extn.
 			var res2 extn
 			_ = json.Unmarshal(b, &res2)
 			// We've tried Ext.Fn and Fn, so no good.
 			if res2.Fn == "" {
-				return "", errJSONExtNotFound
+				return zeroT, errJSONExtNotFound
 			}
 			if res2.Fn != extName {
-				return "", errJSONExtFnMatch
+				return zeroT, errJSONExtFnMatch
 			}
 			arg = res2.Arg
 		} else if res.Extn.Fn != extName {
-			return "", errJSONExtFnMatch
+			return zeroT, errJSONExtFnMatch
 		} else {
 			arg = res.Extn.Arg
 		}
 	}
 
-	return arg, nil
+	v, err := parse(arg)
+	if err != nil {
+		return zeroT, err
+	}
+
+	return v, nil
 }