[master] acea9eb33 whats-new: First pass on changes

[Dridi Boukelmoune]

commit acea9eb33675441f5c3c7d49fa2e5c01bd4a54c6
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Mon Mar 6 12:56:25 2023 +0100

    whats-new: First pass on changes

diff --git a/doc/sphinx/whats-new/changes-trunk.rst b/doc/sphinx/whats-new/changes-trunk.rst
index fbda9d6b9..9fddc2441 100644
--- a/doc/sphinx/whats-new/changes-trunk.rst
+++ b/doc/sphinx/whats-new/changes-trunk.rst
@@ -25,9 +25,33 @@ Parameters
 
 **XXX changes in -p parameters**
 
+There is a new parameter ``transit_buffer`` disabled by default to limit the
+amount of storage used for uncacheable responses. This is useful in situations
+where slow clients may consume large but uncacheable objects, to prevent them
+from filling up storage too fast at the expense of cacheable resources. When
+transit buffer is enabled, a client request will effectively hold its backend
+connection open until the client response delivery completes.
+
 Other changes in varnishd
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 
+In addition to classic Unix-domain sockets, abstract sockets can now be used
+on Linux. Instead of an absolute path, the syntax ``-a @name`` can be used to
+bind the abstract socket called ``name``.
+
+Weak ``Last-Modified`` headers are no longer candidates for revalidation. This
+means that a subsequent fetch will not, when such a stale object is available,
+include an ``If-Modified-Since`` header. A weak ``Last-Modified`` header does
+not prevent ``Etag`` revalidation.
+
+A cache hit on an object being streamed no longer prevents delivery of partial
+responses (status code 206) to range requests.
+
+Response status codes other than 200 and 204 are now considered errors for ESI
+fragments. The default behavior was changed, errors are no longer delivered by
+default. The feature flag ``esi_include_onerror`` can be raised to allow a
+backend to specify whether to continue.
+
 Changes to VCL
 ==============
 
@@ -36,9 +60,44 @@ VCL variables
 
 **XXX new, deprecated or removed variables, or changed semantics**
 
+The variables ``req.xid``, ``bereq.xid`` and ``sess.xid`` are now integers
+instead of strings, but should remain usable without a VCL change in a string
+context.
+
+Transit buffer can be controlled per fetch with the ``beresp.transit_buffer``
+variable.
+
 Other changes to VCL
 ~~~~~~~~~~~~~~~~~~~~
 
+Backends have a new ``.via`` attribute referencing another backend::
+
+    backend detour {
+        .host = "...";
+    }
+
+    backend destination {
+        .host = "...";
+        .via = detour;
+    }
+
+Attempting a connection for ``destination`` connects to ``detour`` with a
+PROXYv2 protocol header targeting ``destination``'s address. Optionally, the
+``destination`` backend could use the other new ``.authority`` attribute to
+define an authority TLV in the PROXYv2 header.
+
+Backends can connect to abstract sockets on linux::
+
+    backend abstract {
+        .path = "@name";
+    }
+
+This is the same syntax as the ``varnishd -a`` command line option.
+
+Probes have a new ``.expect_close`` attribute defaulting to ``true``, matching
+the current behavior. Setting it to ``false`` will defer final checks until
+after the probe times out.
+
 VMODs
 =====
 
@@ -49,11 +108,27 @@ varnishlog
 
 **XXX changes concerning varnishlog(1) and/or vsl(7)**
 
+The in-memory and on-disk format of VSL records changed to allow 64bit VXID
+numbers. The new binary format is not compatible with previous versions, and
+log dumps performed with a previous Varnish release are no longer readable
+from now on.
+
+The VXID range is limited to ``VRT_INTEGER`` to fit in VCL the variables
+``req.xid``, ``bereq.xid`` and ``sess.xid``.
+
+A ``ReqStart`` record is emitted for bad requests, allowing ``varnishncsa`` to
+find the client IP address.
+
 varnishadm
 ==========
 
 **XXX changes concerning varnishadm(1) and/or varnish-cli(7)**
 
+The ``debug.xid`` command generally used by ``varnishtest`` used to set up the
+current VXID. As the intent usually is to set up the next VXID, this forced to
+set an off-by-one value. To simplify its usage it now sets up the next VXID
+directly.
+
 varnishstat
 ===========
 
@@ -64,10 +139,29 @@ varnishtest
 
 **XXX changes concerning varnishtest(1) and/or vtc(7)**
 
+It is now possible to send special keys NPAGE, PPAGE, HOME and END to a
+process.
+
+The ``-nolen`` option is implied for ``txreq`` and ``txresp`` when either
+``Content-Length`` or ``Transfer-Encoding`` headers are present.
+
+A new ``stream.peer_window`` variable similar to ``stream.window`` is
+available for HTTP/2 checks.
+
 Changes for developers and VMOD authors
 =======================================
 
 **XXX changes concerning VRT, the public APIs, source code organization,
 builds etc.**
 
+There is a new convenience macro ``WS_TASK_ALLOC_OBJ()`` to allocate objects
+from the current tasks' workspace.
+
+The ``NO_VXID`` macro can be used to explicitly log records outside of a
+transaction.
+
+Custom backend implementations are now in charge of printing headers, which
+avoids duplicates when a custom implementation relied on ``http_*()`` that
+would also log the headers being set up.
+
 *eof*