DFReader: added support for adding new messages to bin logs

DFReader.py

@@ -1032,6 +1032,38 @@ def _parse_next(self):
 
         return m
 
+    def find_unused_format(self):
+        '''find an unused format code'''
+        for i in range(254, 1, -1):
+            if not i in self.formats:
+                return i
+        return None
+
+    def add_format(self, fmt):
+        '''add a new format'''
+        new_type = self.find_unused_format()
+        if new_type is None:
+            return None
+        fmt.type = new_type
+        self.formats[new_type] = fmt
+        return fmt
+
+    def make_msgbuf(self, fmt, values):
+        '''make a message buffer from a list of values'''
+        ret = struct.pack("BBB", 0xA3, 0x95, fmt.type)
+        ret += struct.pack(fmt.msg_struct, *values)
+        return ret
+
+    def make_format_msgbuf(self, fmt):
+        '''make a message buffer for a FMT message'''
+        fmt_fmt = self.formats[0x80]
+        ret = struct.pack("BBB", 0xA3, 0x95, 0x80)
+        ret += struct.pack(fmt_fmt.msg_struct, *[fmt.type,struct.calcsize(fmt.msg_struct)+3,
+                                                 fmt.name.encode('ascii'),
+                                                 fmt.format.encode('ascii'),
+                                                 ','.join(fmt.columns).encode('ascii')])
+        return ret
+
 
 def DFReader_is_text_log(filename):
     '''return True if a file appears to be a valid text log'''

examples/add_msg_to_bin.py

@@ -0,0 +1,36 @@
+#!/usr/bin/env python3
+'''
+this shows how to add a new message to a bin log
+'''
+
+from pymavlink import DFReader
+
+import argparse
+parser = argparse.ArgumentParser("add msg example")
+parser.add_argument("login")
+parser.add_argument("logout")
+
+args = parser.parse_args()
+
+inf = DFReader.DFReader_binary(args.login)
+outf = open(args.logout, 'wb')
+
+# make a GPSX message which will mirror GPS message
+GPSX = inf.add_format(DFReader.DFFormat(0, "GPSX", 0, "QLLf", "TimeUS,Lat,Lng,Alt"))
+outf.write(inf.make_format_msgbuf(GPSX))
+
+count = 0
+
+while True:
+    m = inf.recv_msg()
+    if m is None:
+        break
+    outf.write(m.get_msgbuf())
+    if m.get_type() == 'GPS':
+        # mirror GPS message as GPSX
+        values = [m.TimeUS, int(m.Lat*1.0e7), int(m.Lng*1.0e7), m.Alt]
+        outf.write(inf.make_msgbuf(GPSX, values))
+        count += 1
+
+print("Added %u GPSX messages to %s from %s" % (count, args.logout, args.login))
+