Clear the error queue on entry to core SSL operations.

OpenSSL historically made some poor API decisions. Rather than returning a
status enum in SSL_read, etc., these functions must be paired with
SSL_get_error which determines the cause of the last error's failure. This
requires SSL_read communicate with SSL_get_error with some stateful flag,

Further, probably as workarounds for bugs elsewhere, SSL_get_error does not
trust rwstate. Among other quirks, if the error queue is non-empty,
SSL_get_error overrides rwstate and returns a value based on that. This
requires that SSL_read, etc., be called with an empty error queue. (Or we hit
one of the spurious ERR_clear_error calls in the handshake state machine,
likely added as further self-workarounds.)

Since requiring callers consistently clear the error queue everywhere is
unreasonable (, clear ERR_clear_error *once* at the entry
point. Until/unless[*] we make SSL_get_error sane, this is the most reasonable
way to get to the point that clearing the error queue on error is optional.

With those in place, the calls in the handshake state machine are no longer
needed. (I suspect all the ERR_clear_system_error calls can also go, but I'll
investigate and think about that separately.)

[*] I'm not even sure it's possible anymore, thanks to the possibility of
BIO_write pushing to the error queue.


Change-Id: I564ace199e5a4a74b2554ad3335e99cd17120741
Reviewed-by: Steven Valdez <>
Reviewed-by: David Benjamin <>
6 files changed
tree: 061387453b292031244b5b1a77b03e2bb546bd16
  1. .clang-format
  2. .github/
  3. .gitignore
  5. CMakeLists.txt
  12. codereview.settings
  13. crypto/
  14. decrepit/
  15. fuzz/
  16. include/
  17. ssl/
  18. tool/
  19. util/


BoringSSL is a fork of OpenSSL that is designed to meet Google's needs.

Although BoringSSL is an open source project, it is not intended for general use, as OpenSSL is. We don't recommend that third parties depend upon it. Doing so is likely to be frustrating because there are no guarantees of API or ABI stability.

Programs ship their own copies of BoringSSL when they use it and we update everything as needed when deciding to make API changes. This allows us to mostly avoid compromises in the name of compatibility. It works for us, but it may not work for you.

BoringSSL arose because Google used OpenSSL for many years in various ways and, over time, built up a large number of patches that were maintained while tracking upstream OpenSSL. As Google's product portfolio became more complex, more copies of OpenSSL sprung up and the effort involved in maintaining all these patches in multiple places was growing steadily.

Currently BoringSSL is the SSL library in Chrome/Chromium, Android (but it's not part of the NDK) and a number of other apps/programs.

There are other files in this directory which might be helpful: