ClientHello and ServerHello are not allowed to include duplicate extensions.
Add a new helper function to check this and call as appropriate. Remove ad-hoc
per-extension duplicate checks which are no unnecessary.
Add runner.go tests to verify such message correctly rejected.
Change-Id: I7babd5b642dfec941459512869e2dd6de26a831c
Reviewed-on: https://boringssl-review.googlesource.com/1100
Reviewed-by: Adam Langley <agl@google.com>
With this change, calling SSL_enable_fallback_scsv on a client SSL* will
cause the fallback SCSV to be sent.
This is intended to be set when the client is performing TLS fallback
after a failed connection. (This only happens if the application itself
implements this behaviour: OpenSSL does not do fallback automatically.)
The fallback SCSV indicates to the server that it should reject the
connection if the version indicated by the client is less than the
version supported by the server.
See http://tools.ietf.org/html/draft-bmoeller-tls-downgrade-scsv-02.
Change-Id: I478d6d5135016f1b7c4aaa6c306a1a64b1d215a6
Initial fork from f2d678e6e89b6508147086610e985d4e8416e867 (1.0.2 beta).
(This change contains substantial changes from the original and
effectively starts a new history.)
