feat(server/apierror): typed Error + sentinels for /api/* envelope

internal/apierror/apierror.go

@@ -0,0 +1,65 @@
+package apierror
+
+import (
+	"errors"
+	"fmt"
+)
+
+type Error struct {
+	Status  int
+	Code    string
+	Message string
+	Cause   error
+}
+
+func (e *Error) Error() string {
+	if e.Cause != nil {
+		return fmt.Sprintf("%s: %v", e.Message, e.Cause)
+	}
+	return e.Message
+}
+
+func (e *Error) Unwrap() error { return e.Cause }
+
+// From returns err as *Error if it (or anything in its chain) is one;
+// otherwise wraps err in an Internal.
+func From(err error) *Error {
+	if err == nil {
+		return nil
+	}
+	var apiErr *Error
+	if errors.As(err, &apiErr) {
+		return apiErr
+	}
+	return Internal(err)
+}
+
+func NotFound(what string) *Error {
+	return &Error{Status: 404, Code: what + "_not_found", Message: what + " not found"}
+}
+
+func BadRequest(code, message string) *Error {
+	return &Error{Status: 400, Code: code, Message: message}
+}
+
+func Conflict(code, message string) *Error {
+	return &Error{Status: 409, Code: code, Message: message}
+}
+
+func Forbidden(code, message string) *Error {
+	return &Error{Status: 403, Code: code, Message: message}
+}
+
+func Unauthorized(code, message string) *Error {
+	return &Error{Status: 401, Code: code, Message: message}
+}
+
+func Internal(cause error) *Error {
+	return &Error{Status: 500, Code: "server_error", Message: "internal server error", Cause: cause}
+}
+
+var (
+	ErrNotFound     = &Error{Status: 404, Code: "not_found", Message: "not found"}
+	ErrForbidden    = &Error{Status: 403, Code: "forbidden", Message: "forbidden"}
+	ErrUnauthorized = &Error{Status: 401, Code: "unauthorized", Message: "authentication required"}
+)