Doc patch for Logical Replication Message Formats (PG14)

[Brar Piening]

Hello Hackers,
while amending Npgsql to account for the Logical Streaming Replication
Protocol changes in PostgreSQL 14 I stumbled upon two documentation
inaccuracies in the Logical Replication Message Formats documentation
(https://www.postgresql.org/docs/devel/protocol-logicalrep-message-formats.html)
that have been introduced (or rather omitted) with the recent changes to
allow pgoutput to send logical decoding messages
(https://github.com/postgres/postgres/commit/ac4645c0157fc5fcef0af8ff571512aa284a2cec)
and to allow logical replication to transfer data in binary format
(https://github.com/postgres/postgres/commit/9de77b5453130242654ff0b30a551c9c862ed661).


1. The content of the logical decoding message in the 'Message' message
   is prefixed with a length field (Int32) which isn't documented yet.
   See
   
https://github.com/postgres/postgres/blob/69a58bfe4ab05567a8fab8bdce7f3095ed06b99c/src/backend/replication/logical/proto.c#L388
2. The TupleData may now contain the byte 'b' as indicator for binary
   data which isn't documented yet. See
   
https://github.com/postgres/postgres/blob/69a58bfe4ab05567a8fab8bdce7f3095ed06b99c/src/include/replication/logicalproto.h#L83
   and
   
https://github.com/postgres/postgres/blob/69a58bfe4ab05567a8fab8bdce7f3095ed06b99c/src/backend/replication/logical/proto.c#L558.

The attached documentation patch fixes both.

Best regards,

Brar


diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index bc2a2feb0b..53b3f1f651 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -6498,6 +6498,18 @@ Message
 </para>
 </listitem>
 </varlistentry>
+
+<varlistentry>
+<term>
+        Int32
+</term>
+<listitem>
+<para>
+                Length of the content.
+</para>
+</listitem>
+</varlistentry>
+
 <varlistentry>
 <term>
         Byte<replaceable>n</replaceable>
@@ -7430,6 +7442,19 @@ TupleData
 </para>
 </listitem>
 </varlistentry>
+</variablelist>
+        Or
+<variablelist>
+<varlistentry>
+<term>
+        Byte1('b')
+</term>
+<listitem>
+<para>
+                Identifies the data as binary value.
+</para>
+</listitem>
+</varlistentry>
 <varlistentry>
 <term>
         Int32