[Qemu-devel] Re: [FOR 0.12 PATCH 18/18] QMP: add human-readable description to error response

[Luiz Capitulino <lcapitulino@redhat.com>]

On Mon,  7 Dec 2009 21:37:16 +0100
Markus Armbruster <armbru@redhat.com> wrote:

> -{ "error": { "class": json-string, "data": json-value }, "id": json-value }
> +{ "error": { "class": json-string, "data": json-value, "desc": json-string },
> +  "id": json-value }
>  
>   Where,
>  
>  - The "class" member contains the error class name (eg. "ServiceUnavailable")
>  - The "data" member contains specific error data and is defined in a
>    per-command basis, it will be an empty json-object if the error has no data
> +- The "desc" member is a human-readable error message.  Clients should
> +  not attempt to parse this message.
>  - The "id" member contains the transaction identification associated with
>    the command execution (if issued by the Client)

 As we've talked on irc, I don't agree with this change.

 Basically, adding 'desc' to the standard error message introduces all
the problems we've discussed about free-form English strings.

 I feel that QError is becoming the worst of all proposals.

 I agree with you that it's not as easy as it should be to report errors,
but as we're targeting on Clients I was convinced that we could not have the
best API internally but offer a good interface for Clients.

 Now, having 'desc' as part of the standard protocol is like not having
the best API internally and offering a bad interface for Clients.

 Not to mention that those strings can't be modified when the protocol
becomes stable and we're probably talking about dozens if not a hundred
of strings. Ok, there isn't a reason to change them often, but it's
still one more thing to maintain.

 Having said that, I would agree to have 'desc' as part of debug
information. I have patches in my tree which adds CONFIG_DEBUG_QMP,
if one enables it information about the error location will also
be part of the error message. I would agree having 'desc' there
too.