<para>
      A null-terminated string (C-style string).  There is no
      specific length limitation on strings.
      If <replaceable>s</replaceable> is specified it is the exact
      value that will appear, otherwise the value is variable.
      Eg. String, String("user").
     </para>

     <note>
      <para>
       <emphasis>There is no predefined limit</emphasis> on the length of a string
       that can be returned by the backend.  Good coding strategy for a frontend
       is to use an expandable buffer so that anything that fits in memory can be
       accepted.  If that's not feasible, read the full string and discard trailing
       characters that don't fit into your fixed-size buffer.
      </para>
     </note>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term>Byte<replaceable>n</replaceable>(<replaceable>c</replaceable>)</term>
    <listitem>
     <para>
      Exactly <replaceable>n</replaceable> bytes.  If the field
      width <replaceable>n</replaceable> is not a constant, it is
      always determinable from an earlier field in the message.
      If <replaceable>c</replaceable> is specified it is the exact
      value.  Eg. Byte2, Byte1('\n').
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </sect1>

 <sect1 id="protocol-message-formats">
  <title>Message Formats</title>

  <para>
   This section describes the detailed format of each message.  Each is marked to
   indicate that it can be sent by a frontend (F), a backend (B), or both
   (F &amp; B).
   Notice that although each message includes a byte count at the beginning,
   most messages are defined so that the message end can be found without
   reference to the byte count.  This is for historical reasons, as the
   original, now-obsolete protocol version 2 did not have an explicit length
   field.  It also aids validity checking though.
  </para>

  <variablelist>
   <varlistentry id="protocol-message-formats-AuthenticationOk">
    <term>AuthenticationOk (B)</term>
    <listitem>
     <variablelist>
      <varlistentry>
       <term>Byte1('R')</term>
       <listitem>
        <para>
         Identifies the message as an authentication request.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>Int32(8)</term>
       <listitem>
        <para>
         Length of message contents in bytes, including self.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>Int32(0)</term>
       <listitem>
        <para>
         Specifies that the authentication was successful.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
    </listitem>
   </varlistentry>

   <varlistentry id="protocol-message-formats-AuthenticationKerberosV5">
    <term>AuthenticationKerberosV5 (B)</term>
    <listitem>

     <variablelist>
      <varlistentry>
       <term>Byte1('R')</term>
       <listitem>
        <para>
         Identifies the message as an authentication request.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>Int32(8)</term>
       <listitem>
        <para>
         Length of message contents in bytes, including self.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>Int32(2)</term>
       <listitem>
        <para>
         Specifies that Kerberos V5 authentication is required.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
    </listitem>
   </varlistentry>

   <varlistentry id="protocol-message-formats-AuthenticationCleartextPassword">
    <term>AuthenticationCleartextPassword (B)</term>
    <listitem>

     <variablelist>
      <varlistentry>
       <term>Byte1('R')</term>
       <listitem>
        <para>
         Identifies the message as an authentication request.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>Int32(8)</term>
       <listitem>
        <para>
         Length