This extends the packet adaptor protocol to send three commands:
  type command =
    | Packet of []byte
    | Timeout of time.Duration
    | TimeoutAck

When the shim processes a Timeout in BIO_read, it sends TimeoutAck, fails the
BIO_read, returns out of the SSL stack, advances the clock, calls
DTLSv1_handle_timeout, and continues.

If the Go side sends Timeout right between sending handshake flight N and
reading flight N+1, the shim won't read the Timeout until it has sent flight
N+1 (it only processes packet commands in BIO_read), so the TimeoutAck comes
after N+1. Go then drops all packets before the TimeoutAck, thus dropping one
transmit of flight N+1 without having to actually process the packets to
determine the end of the flight. The shim then sees the updated clock, calls
DTLSv1_handle_timeout, and re-sends flight N+1 for Go to process for real.

When dropping packets, Go checks the epoch and increments sequence numbers so
that we can continue to be strict here. This requires tracking the initial
sequence number of the next epoch.

The final Finished message takes an additional special-case to test. DTLS
triggers retransmits on either a timeout or seeing a stale flight. OpenSSL only
implements the former which should be sufficient (and is necessary) EXCEPT for
the final Finished message. If the peer's final Finished message is lost, it
won't be waiting for a message from us, so it won't time out anything. That
retransmit must be triggered on stale message, so we retransmit the Finished
message in Go.

Change-Id: I3ffbdb1de525beb2ee831b304670a3387877634c
Reviewed-on: https://boringssl-review.googlesource.com/3212
Reviewed-by: Adam Langley <agl@google.com>

Including string.h in base.h causes any file that includes a BoringSSL
header to include string.h. Generally this wouldn't be a problem,
although string.h might slow down the compile if it wasn't otherwise
needed. However, it also causes problems for ipsec-tools in Android
because OpenSSL didn't have this behaviour.

This change removes string.h from base.h and, instead, adds it to each
.c file that requires it.

Change-Id: I5968e50b0e230fd3adf9b72dd2836e6f52d6fb37
Reviewed-on: https://boringssl-review.googlesource.com/3200
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

This commit fixes a number of crashes caused by malloc failures. They
were found using the -malloc-test=0 option to runner.go which runs tests
many times, causing a different allocation call to fail in each case.

(This test only works on Linux and only looks for crashes caused by
allocation failures, not memory leaks or other errors.)

This is not the complete set of crashes! More can be found by collecting
core dumps from running with -malloc-test=0.

Change-Id: Ia61d19f51e373bccb7bc604642c51e043a74bd83
Reviewed-on: https://boringssl-review.googlesource.com/2320
Reviewed-by: Adam Langley <agl@google.com>

Change-Id: I7407261bdb2d788c879f2e67e617a615d9ff8f8b
Reviewed-on: https://boringssl-review.googlesource.com/1505
Reviewed-by: Adam Langley <agl@google.com>