net: add a test to ensure that our TLS handshake doesn't get too large.

third_party/tlslite/tlslite/messages.py

Index: third_party/tlslite/tlslite/messages.py
diff --git a/third_party/tlslite/tlslite/messages.py b/third_party/tlslite/tlslite/messages.py
index fa4d8174c1aeb81f0ddd00af614e568dde22b450..fc23f4cdf74582a9be0d07bbb5db9c3fffff6d98 100644
--- a/third_party/tlslite/tlslite/messages.py
+++ b/third_party/tlslite/tlslite/messages.py
@@ -131,6 +131,9 @@ class ClientHello(HandshakeMsg):
         self.compression_methods = []   # a list of 8-bit values
         self.srp_username = None        # a string
         self.channel_id = False
+        # client_hello_length is the length of the ClientHello record - i.e.
+        # including the handshake type byte and 3 byte handshake length.
+        self.client_hello_length = 0
 
     def create(self, version, random, session_id, cipher_suites,
                certificate_types=None, srp_username=None):
@@ -159,6 +162,11 @@ class ClientHello(HandshakeMsg):
 
             #We're not doing a stopLengthCheck() for SSLv2, oh well..
         else:
+            self.client_hello_length = len(p.bytes) - p.index
+            # Account for the handshake type byte which has already been
+            # removed.
+            self.client_hello_length += 1
+
             p.startLengthCheck(3)
             self.client_version = (p.get(1), p.get(1))
             self.random = p.getFixBytes(32)