From: Eugene Crosser <crosser@average.org>
Date: Mon, 9 May 2022 20:28:06 +0000 (+0200)
Subject: A hack in packet framing to false stop bytes match
X-Git-Tag: 0.90~5
X-Git-Url: http://www.average.org/gitweb/?p=loctrkd.git;a=commitdiff_plain;h=69d3f8b9d8a3cd603dcb07065115eb7426ca9a34

A hack in packet framing to false stop bytes match
---

diff --git a/gps303/collector.py b/gps303/collector.py
index de65394..7326e1f 100644
--- a/gps303/collector.py
+++ b/gps303/collector.py
@@ -69,7 +69,20 @@ class Client:
                 )
                 self.buffer = self.buffer[framestart:]
             # At this point, buffer starts with a packet
-            frameend = self.buffer.find(b"\r\n", 4)
+            if len(self.buffer) < 6:  # no len and proto - cannot proceed
+                break
+            exp_end = self.buffer[2] + 3  # Expect '\r\n' here
+            frameend = 0
+            # Length field can legitimeely be much less than the
+            # length of the packet (e.g. WiFi positioning), but
+            # it _should not_ be greater. Still sometimes it is.
+            # Luckily, not by too much: by maybe two or three bytes?
+            # Do this embarrassing hack to avoid accidental match
+            # of some binary data in the packet against '\r\n'.
+            while True:
+                frameend = self.buffer.find(b"\r\n", frameend)
+                if frameend >= (exp_end - 3):  # Found realistic match
+                    break
             if frameend == -1:  # Incomplete frame, return what we have
                 break
             packet = self.buffer[2:frameend]