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dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:60772 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kcPlw-0008BU-R1 for qemu-devel@archiver.kernel.org; Tue, 10 Nov 2020 04:17:04 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:48228) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kcPkO-0007UA-Un for qemu-devel@nongnu.org; Tue, 10 Nov 2020 04:15:28 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:34957) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kcPkJ-0005Jx-8e for qemu-devel@nongnu.org; Tue, 10 Nov 2020 04:15:28 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1604999722; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=IGDk6ydEz7ioGmRPkhe96shIANMCzQtDVRUfM2yTyEg=; b=Nj1he4RRu6UeHQOz6nxol2YzmQHi0IjXhbwNmYXcA3QtyvLPXstF4cgGdTr6YkAmzkXH1u 1BNuAsXbJ2C/NMu+CzVs3+qZYK77Cv7rTE7OLGJMQ+o3Dq24olBU31uoxT/tudhdUISU5Y fBMagYi277GjUXHbmF0dmPOAi4iUCB0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-35-zXVT5FuYPzKuZ4FxliTkjQ-1; Tue, 10 Nov 2020 04:15:18 -0500 X-MC-Unique: zXVT5FuYPzKuZ4FxliTkjQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EBDE5192CC4A for ; Tue, 10 Nov 2020 09:15:16 +0000 (UTC) Received: from redhat.com (ovpn-115-68.ams2.redhat.com [10.36.115.68]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BB65710013DB; Tue, 10 Nov 2020 09:15:15 +0000 (UTC) Date: Tue, 10 Nov 2020 09:15:12 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Subject: Re: QMP and the 'id' parameter Message-ID: <20201110091512.GA866671@redhat.com> References: <62700620-5228-f1cc-f0df-751c0d9f1f82@redhat.com> <87361h20kd.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87361h20kd.fsf@dusky.pond.sub.org> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/10 02:00:53 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: John Snow , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Nov 10, 2020 at 07:22:26AM +0100, Markus Armbruster wrote: > John Snow writes: > > > The QMP specification states: > > > >> NOTE: Some errors can occur before the Server is able to read the "id" > >> member, in these cases the "id" member will not be part of the error > >> response, even if provided by the client. > > > > I am assuming this case ONLY occurs for Parse errors: > > > > {'class': 'GenericError', 'desc': 'JSON parse error, expecting value'} > > There are more "desc" possible, actually. > > The JSON parser gets fed chunks of input, and calls a callback for every > full JSON value, and on parse error. > > QMP's callback is handle_qmp_command(). Parameter @req is the parsed > JSON value, parameter @err is the (parse) error object, and exactly one > of them is non-null. > > 1. Parse error > > If @err, we send an error response for it. It never has "id". See > qmp_error_response() caller monitor_qmp_dispatcher_co(). The possible > @err are: > > $ grep error_setg qobject/json-*[ch] > qobject/json-parser.c: error_setg(&ctxt->err, "JSON parse error, %s", message); > > This is a syntax error. > > Search for parse_error() to see the possible @message patterns. > > qobject/json-streamer.c: error_setg(&err, "JSON parse error, stray '%s'", input->str); > > This is a lexical error. > > qobject/json-streamer.c: error_setg(&err, "JSON token size limit exceeded"); > qobject/json-streamer.c: error_setg(&err, "JSON token count limit exceeded"); > qobject/json-streamer.c: error_setg(&err, "JSON nesting depth limit exceeded"); > > These are (intentional) parser limits. > > 2. Successful parse > > If @req, it's a successful parse. > > If @req is not a JSON object, there is no "id". qmp_dispatch() reports > > error_setg(&err, "QMP input must be a JSON object"); > > If @req is a JSON object, it has "id" exactly when the client supplied > one. The response mirrors @req's "id". See qmp_error_response() caller > qmp_dispatch(). > > > And I am assuming, in the context of a client that /always/ sets an > > 'id' for its execute statements, that this means that any error > > response we receive without an 'id' field *must* be associated with > > the most-recently-sent command. > > Only if the client keeps no more than one command in flight. > > Command responses get sent strictly in order (even parse errors), except > for commands executed out-of-band. With out of band commands, how much runs in the background ? Is the JSON parsing still in the foreground, such that we can expect that even for OOB commands, a error response without a "id" is still received strictly in order. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|