Changed most instances of "remote_version" to "protocol_version", and

others to "remote_protocol".  Downgrade the protocol_version if the
remote_protocol" is lower.  Output the protocol values if the verbose
level is large enough.  Exit if the user tried to force a protocol
value that is not within the range that we can handle.  Fixed the
output of the "very old version of rsync" message to output the right
Client/Server string.

compat.c

@@ -25,6 +25,8 @@
 
 #include "rsync.h"
 
+int remote_protocol = 0;
+
 extern int am_server;
 
 extern int preserve_links;
@@ -37,7 +39,7 @@ extern int always_checksum;
 extern int checksum_seed;
 
 
-extern int remote_version;
+extern int protocol_version;
 extern int verbose;
 
 extern int read_batch;  /* dw */
@@ -45,25 +47,42 @@ extern int write_batch;  /* dw */
 
 void setup_protocol(int f_out,int f_in)
 {
-	if (remote_version == 0) {
+	if (remote_protocol == 0) {
 		if (am_server) {
-			remote_version = read_int(f_in);
-			write_int(f_out,PROTOCOL_VERSION);
+			remote_protocol = read_int(f_in);
+			write_int(f_out, protocol_version);
 		} else {
-			write_int(f_out,PROTOCOL_VERSION);
-			remote_version = read_int(f_in);
+			write_int(f_out, protocol_version);
+			remote_protocol = read_int(f_in);
 		}
+		if (protocol_version > remote_protocol)
+			protocol_version = remote_protocol;
 	}
 
-	if (remote_version < MIN_PROTOCOL_VERSION ||
-	    remote_version > MAX_PROTOCOL_VERSION) {
+	if (verbose > 3) {
+		rprintf(FINFO, "(%s) Protocol versions: remote=%d, negotiated=%d\n",
+			am_server? "Server" : "Client", remote_protocol, protocol_version);
+	}
+	if (remote_protocol < MIN_PROTOCOL_VERSION
+	 || remote_protocol > MAX_PROTOCOL_VERSION) {
 		rprintf(FERROR,"protocol version mismatch - is your shell clean?\n");
 		rprintf(FERROR,"(see the rsync man page for an explanation)\n");
 		exit_cleanup(RERR_PROTOCOL);
-	}	
-	if (remote_version < OLD_PROTOCOL_VERSION)
+	}
+	if (remote_protocol < OLD_PROTOCOL_VERSION) {
 		rprintf(FINFO,"%s is very old version of rsync, upgrade recommended.\n",
-			am_server ? "Server" : "Client");
+			am_server? "Client" : "Server");
+	}
+	if (protocol_version < MIN_PROTOCOL_VERSION) {
+		rprintf(FERROR, "--protocol must be at least %d on the %s.\n",
+			MIN_PROTOCOL_VERSION, am_server? "Server" : "Client");
+		exit_cleanup(RERR_PROTOCOL);
+	}
+	if (protocol_version > PROTOCOL_VERSION) {
+		rprintf(FERROR, "--protocol must be no more than %d on the %s.\n",
+			PROTOCOL_VERSION, am_server? "Server" : "Client");
+		exit_cleanup(RERR_PROTOCOL);
+	}
 
 	if (am_server) {
 		if (read_batch || write_batch) /* dw */
@@ -75,4 +94,3 @@ void setup_protocol(int f_out,int f_in)
 		checksum_seed = read_int(f_in);
 	}
 }
-