<p>A synchronization request between a client and server consists of
one or more HTTP requests as described in the previous section.  This
section details the "x-fossil" content type.</p>

<h3>3.1 Line-oriented Format</h3>

<p>The x-fossil content type consists of zero or more "cards".  Cards
are separated by the newline character ("\n").  Leading and trailing
whitespace on a card is ignored.  Blank cards are ignored.</p>

<p>Each card is divided into zero or more space separated tokens.
The first token on each card is the operator.  Subsequent tokens
are arguments.  The set of operators understood by servers is slightly
different from the operators understood by clients, though the two
are very similar.</p>

<p>File cards are sent in both directions: client to server and
server to client.  A delta might be sent before the source of
the delta, so both client and server should remember deltas
and be able to apply them when their source arrives.</p>

<h3>3.4 Push and Pull Cards</h3>

<p>Among the first cards in a client-to-server message are
the push and pull cards.  The push card tells the server that
the client is pushing content.  The pull card tells the server
that the client wants to pull content.  In the event of a sync,
both cards are sent.  The format is as follows:</p>

<blockquote>
<b>push</b> <i>servercode projectcode</i><br>
<b>pull</b> <i>servercode projectcode</i>
</blockquote>

<h4>3.5.1 Protocol 2</h4>

<p>The latest clients send a two-argument clone message with a
protocol version of "2".  (Future versions of Fossil might use larger
protocol version numbers.)  The sequence-number sent is the number
of artifacts received so far.  For the first clone message, the
sequence number is 0.  The server will respond by sending file
cards for some number of artifacts up to the maximum message size.

<p>The server will also send a single "clone_seqno" card to the client
so that the client can know where the server left off.

<blockquote>
<b>clone_seqno</b>  <i>sequence-number</i>
</blockquote>

<p>The clone message in subsequent HTTP requests for the same clone
operation will use the sequence-number from the
clone_seqno of the previous reply.</p>

<p>In response to an initial clone message, the server also sends the client
a push message so that the client can discover the projectcode for
this project.</p>