Add api exception mode

[duet3d]

Add api exception mode

[mfs12]

This is how a solution could look like for python:

class DsfException(Exception):
    """Base class for all DSF exceptions"""
    def __init__(self, message):
        super().__init__(message)


class InternalServerException(DsfException):
    """Exception returned by the server for an arbitrary problem"""

    def __init__(self):
        super().__init__("Internal Server Exception")


class ErrorResponseException(DsfException):
    """Exception returned if an Error Response is received"""

    def __init__(self, error_type: str, error_message: str):
        super().__init__("{}: {}".format(error_type, error_message))

This is an incomplete overview of found errors

• NotImplementedError Error: M3: Command is not supported in machine mode FFF
• NotImplementedError Error: Operation is not supported
• NotImplementedError Error: M260: I2C not available
• MissingParameter Error: M42: missing parameter 'P' or Error: M118: missing parameter 'S' or Error: M307: missing parameter 'H' or Error: M581: missing parameter 'T' or Error: M591: missing parameter 'D'
• OutOfRangeError Error: M593: parameter 'F' too low
• DeprecationWarning Error: M305: M305 has been replaced by M308 and M950 in RepRapFirmware 3
• FileNotFoundError Error: M24: Cannot print, because no file is selected!
• AlreadyStopped Error: M25: Cannot pause print, because no file is being printed!
• SHA1Error Error: M38: Could not compute SHA1 checksum for file F a l s e: Could not find file '/F a l s e'.
• FileNotFound Error: M375: Failed to load height map from file heightmap.csv: Could not find file '/opt/dsf/sd/sys/heightmap.csv'.
• DirectoryNotFound Error: M470: Missing directory name
• RenamingError Error: M471: Failed to rename file or directory to : Value cannot be null. (Parameter 'input')
• NetworkError Error: M540: Network-related commands are not supported when using an attached Single Board Computer
• InvalidStateError Error: M585: a axis has not been homed

[wilriker]

Clarification is needed here for go language as well.
Go uses instances of struct error for error handling. You can either return an generic error message by creating it via ```
errors.New("error message")

or create pseudo-static instances like

var ErrSomeDecriptiveName = errors.New("error message")

and then the user can compare against this instance.

AFAIR the Go impl already returns errors where appropriate.