Attachment 49392 Details for Bug 39450 – [PATCH 2/5] spec: define unicast messages and broadcast signals, and explicitly allow unicast signals

[patch] [PATCH 2/5] spec: define unicast messages and broadcast signals, and explicitly allow unicast signals

0002-spec-define-unicast-messages-and-broadcast-signals-a.patch (text/plain), 2.67 KB, created by Simon McVittie on 2011-07-21 09:08:21 UTC

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Creator: Simon McVittie

Created: 2011-07-21 09:08:21 UTC

Size: 2.67 KB

patch

obsolete

>From 0ca865284b28ff15d251a6c7a76fa11da548ba55 Mon Sep 17 00:00:00 2001
>From: Simon McVittie <simon.mcvittie@collabora.co.uk>
>Date: Thu, 21 Jul 2011 16:17:35 +0100
>Subject: [PATCH 2/5] spec: define unicast messages and broadcast signals, and
> explicitly allow unicast signals
>
>I believe that the wording of the spec has always allowed unicast signals,
>but most bindings assume that signals are broadcasts, so it seems worth
>saying specifically that this feature exists and can be useful.
>---
> doc/dbus-specification.xml |   24 +++++++++++++++++++++---
> 1 files changed, 21 insertions(+), 3 deletions(-)
>
>diff --git a/doc/dbus-specification.xml b/doc/dbus-specification.xml
>index 459f46a..2abe799 100644
>--- a/doc/dbus-specification.xml
>+++ b/doc/dbus-specification.xml
>@@ -3375,7 +3375,8 @@
> 
>       <para>
>         Messages may have a <literal>DESTINATION</literal> field (see <xref
>-        linkend="message-protocol-header-fields"/>).  If the
>+          linkend="message-protocol-header-fields"/>), resulting in a
>+        <firstterm>unicast message</firstterm>.  If the
>         <literal>DESTINATION</literal> field is present, it specifies a message
>         recipient by name. Method calls and replies normally specify this field.
>         The message bus must send messages (of any type) with the
>@@ -3385,9 +3386,26 @@
>       </para>
> 
>       <para>
>-        Signals normally do not specify a destination; they are sent to all
>+        When the message bus receives a signal, if the
>+        <literal>DESTINATION</literal> field is absent, it is considered to
>+        be a <firstterm>broadcast signal</firstterm>, and is sent to all
>         applications with <firstterm>message matching rules</firstterm> that
>-        match the message.
>+        match the message. Most signal messages are broadcasts.
>+      </para>
>+
>+      <para>
>+        Unicast signal messages (those with a <literal>DESTINATION</literal>
>+        field) are not commonly used, but they are treated like any unicast
>+        message: they are delivered to the specified receipient,
>+        regardless of its match rules.  One use for unicast signals is to
>+        avoid a race condition in which a signal is emitted before the intended
>+        recipient can call <xref linkend="bus-messages-add-match"/> to
>+        receive that signal: if the signal is sent directly to that recipient
>+        using a unicast message, it does not need to add a match rule at all,
>+        and there is no race condition.  Another use for unicast signals,
>+        on message buses whose security policy prevents eavesdropping, is to
>+        send sensitive information which should only be visible to one
>+        recipient.
>       </para>
> 
>       <para>
>-- 
>1.7.5.4
>

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