Ticket #153: remote-protocol-minor-version.patch

docs/remote_protocol.html

@@ -7 +7 @@
 <h1>Remote Backend Protocol</h1>
 
 <p>
-This document describes <em>version 29</em> of the protocol used by Xapian's
+This document describes <em>version 30</em> of the protocol used by Xapian's
 remote backend.  The protocol assumes a reliable two-way connection across which
 arbitrary data can be sent - this could be provided by a TCP socket for example
 (as it is with xapian-tcpsrv), but any such connection could be used.  For
@@ -58 +58 @@
 <h2>Server greeting and statistics</h2>
 
 <ul>
-<li> <code>REPLY_GREETING &lt;protocol version&gt; I&lt;db doc count&gt; I&lt;last docid&gt; B&lt;has positions?&gt; F&lt;db average length&gt;</code>
+<li> <code>REPLY_GREETING &lt;protocol major version&gt; &lt;protocol minor version&gt; I&lt;db doc count&gt; I&lt;last docid&gt; B&lt;has positions?&gt; F&lt;db average length&gt;</code>
 </ul>
 
 <p>
-The protocol version is simply passed as a single byte (<code>'\x09'</code>
-for version 9).
+The protocol major and minor versions are passed as a single byte each (e.g.
+<code>'\x1e\x01'</code> for version 30.1).  The server and client must
+understand the same protocol major version, and the server protocol minor
+version must be greater than or equal to that of the client (this means that
+the server understands newer MSG_<i>XXX</i>, but will only send newer
+REPLY_<i>YYY</i> in response to an appropriate client message.
 </p>
 
 <h2>Exception</h2>

net/remoteserver.cc

@@ -90 +90 @@
 
     // Send greeting message.
     string message;
-    message += char(XAPIAN_REMOTE_PROTOCOL_VERSION);
+    message += char(XAPIAN_REMOTE_PROTOCOL_MAJOR_VERSION);
+    message += char(XAPIAN_REMOTE_PROTOCOL_MINOR_VERSION);
     message += encode_length(db->get_doccount());
     message += encode_length(db->get_lastdocid());
     message += (db->has_positions() ? '1' : '0');

common/remoteprotocol.h

@@ -32 +32 @@
 // 27: Support for postlists (always passes the whole list across)
 // 28: Pass document length in reply to MSG_TERMLIST
 // 29: Serialisation of Xapian::Error includes error_string.
-#define XAPIAN_REMOTE_PROTOCOL_VERSION 29
+#define XAPIAN_REMOTE_PROTOCOL_MAJOR_VERSION 30
+#define XAPIAN_REMOTE_PROTOCOL_MINOR_VERSION 0
 
 /// Message types (client -> server).
 enum message_type {

backends/remote/remote-database.cc

@@ -74 +74 @@
     const char *p = message.c_str();
     const char *p_end = p + message.size();
 
-    if (*p != XAPIAN_REMOTE_PROTOCOL_VERSION) {
+    // The protocol major versions must match.  The protocol minor version of
+    // the server must be >= that of the client.
+    int protocol_major = static_cast<unsigned char>(*p++);
+    int protocol_minor = static_cast<unsigned char>(*p++);
+    if (protocol_major != XAPIAN_REMOTE_PROTOCOL_MAJOR_VERSION ||
+        protocol_minor < XAPIAN_REMOTE_PROTOCOL_MINOR_VERSION) {
         string errmsg("Unknown protocol version ");
+        errmsg += om_tostring(protocol_major);
+        errmsg += '.';
         errmsg += om_tostring(int(*p));
-        errmsg += " ("STRINGIZE(XAPIAN_REMOTE_PROTOCOL_VERSION)" supported)";
+        errmsg += " ("STRINGIZE(XAPIAN_REMOTE_PROTOCOL_MAJOR_VERSION)"."STRINGIZE(XAPIAN_REMOTE_PROTOCOL_MINOR_VERSION)" supported)";
         throw Xapian::NetworkError(errmsg, context);
     }
-    ++p;
 
     doccount = decode_length(&p, p_end, false);
     lastdocid = decode_length(&p, p_end, false);