Limit uploaded file sizes, accounting for free disk space

The lower of the configured maximum file size (for the FTP server) and
the available disk space minus the configured minimum free disk space
is used as the maximum file size to allow upload. Appended files
are accounted for too.

src/sbbs3/ftpsrvr.c

@@ -909,6 +909,24 @@ static void receive_thread(void* arg)
 			,xfer.ctrl_sock,xfer.user->alias, *xfer.data_sock,xfer.filename,xfer.filepos);
 
 	fseeko(fp,xfer.filepos,SEEK_SET);
+
+	// Determine the maximum file size to allow, accounting for minimum free space
+	char path[MAX_PATH + 1];
+	SAFECOPY(path, xfer.filename);
+	*getfname(path) = '\0';
+	uint64_t avail = getfreediskspace(path, 1);
+	if(avail <= scfg.min_dspace)
+		avail = 0;
+	else
+		avail -= scfg.min_dspace;
+	uint64_t max_fsize = xfer.filepos + avail;
+	if(startup->max_fsize > 0 && startup->max_fsize < max_fsize)
+		max_fsize = startup->max_fsize;
+	if(startup->options & FTP_OPT_DEBUG_DATA)
+		lprintf(LOG_DEBUG, "%04d <%s> DATA Limiting uploaded file size to %" PRIu64 " (%s) bytes"
+			,xfer.ctrl_sock, xfer.user->alias, max_fsize
+			,byte_estimate_to_str(max_fsize, tmp, sizeof(tmp), 1, 1));
+
 	last_report=start=time(NULL);
 	while(1) {
 
@@ -929,7 +947,7 @@ static void receive_thread(void* arg)
 			last_total=total;
 			last_report=now;
 		}
-		if(startup->max_fsize && (xfer.filepos+total) > startup->max_fsize) {
+		if(xfer.filepos + total > max_fsize) {
 			lprintf(LOG_WARNING,"%04d <%s> !DATA received %"PRIdOFF" bytes of %s exceeds maximum allowed (%"PRIu64" bytes)"
 				,xfer.ctrl_sock, xfer.user->alias, xfer.filepos+total, xfer.filename, startup->max_fsize);
 			sockprintf(xfer.ctrl_sock,sess,"552 File size exceeds maximum allowed (%"PRIu64" bytes)", startup->max_fsize);
@@ -4625,9 +4643,9 @@ static void ctrl_thread(void* arg)
 				freespace = getfreediskspace(scfg.dir[dir]->path, 1);
 			}
 			if(freespace < scfg.min_dspace) {
-				lprintf(LOG_ERR, "%04d <%s> !insufficient disk free space (%" PRIu64 " bytes) to allow upload"
-					,sock, user.alias, freespace);
-				sockprintf(sock, sess, "452 insufficient free disk space, try again later");
+				lprintf(LOG_ERR, "%04d <%s> !Insufficient free disk space (%s bytes) to allow upload"
+					,sock, user.alias, byte_estimate_to_str(freespace, str, sizeof(str), 1,1));
+				sockprintf(sock, sess, "452 Insufficient free disk space, try again later");
 				continue;
 			}
 			sockprintf(sock,sess,"150 Opening BINARY mode data connection for file transfer.");