refactor: backend

common/error.go

@@ -0,0 +1,100 @@
+package common
+
+import (
+	"errors"
+)
+
+// Code is the error code.
+type Code int
+
+// Application error codes.
+const (
+	// 0 ~ 99 general error
+	Ok             Code = 0
+	Internal       Code = 1
+	NotAuthorized  Code = 2
+	Invalid        Code = 3
+	NotFound       Code = 4
+	Conflict       Code = 5
+	NotImplemented Code = 6
+
+	// 101 ~ 199 db error
+	DbConnectionFailure    Code = 101
+	DbStatementSyntaxError Code = 102
+	DbExecutionError       Code = 103
+
+	// 201 db migration error
+	// Db migration is a core feature, so we separate it from the db error
+	MigrationSchemaMissing   Code = 201
+	MigrationAlreadyApplied  Code = 202
+	MigrationOutOfOrder      Code = 203
+	MigrationBaselineMissing Code = 204
+
+	// 301 task error
+	TaskTimingNotAllowed Code = 301
+
+	// 10001 advisor error code
+	CompatibilityDropDatabase  Code = 10001
+	CompatibilityRenameTable   Code = 10002
+	CompatibilityDropTable     Code = 10003
+	CompatibilityRenameColumn  Code = 10004
+	CompatibilityDropColumn    Code = 10005
+	CompatibilityAddPrimaryKey Code = 10006
+	CompatibilityAddUniqueKey  Code = 10007
+	CompatibilityAddForeignKey Code = 10008
+	CompatibilityAddCheck      Code = 10009
+	CompatibilityAlterCheck    Code = 10010
+	CompatibilityAlterColumn   Code = 10011
+)
+
+// Error represents an application-specific error. Application errors can be
+// unwrapped by the caller to extract out the code & message.
+//
+// Any non-application error (such as a disk error) should be reported as an
+// Internal error and the human user should only see "Internal error" as the
+// message. These low-level internal error details should only be logged and
+// reported to the operator of the application (not the end user).
+type Error struct {
+	// Machine-readable error code.
+	Code Code
+
+	// Embedded error.
+	Err error
+}
+
+// Error implements the error interface. Not used by the application otherwise.
+func (e *Error) Error() string {
+	return e.Err.Error()
+}
+
+// ErrorCode unwraps an application error and returns its code.
+// Non-application errors always return EINTERNAL.
+func ErrorCode(err error) Code {
+	var e *Error
+	if err == nil {
+		return Ok
+	} else if errors.As(err, &e) {
+		return e.Code
+	}
+	return Internal
+}
+
+// ErrorMessage unwraps an application error and returns its message.
+// Non-application errors always return "Internal error".
+func ErrorMessage(err error) string {
+	var e *Error
+	if err == nil {
+		return ""
+	} else if errors.As(err, &e) {
+		return e.Err.Error()
+	}
+	return "Internal error."
+}
+
+// Errorf is a helper function to return an Error with a given code and error.
+func Errorf(code Code, err error) *Error {
+	return &Error{
+		Code: code,
+		Err:  err,
+	}
+}