portability/OpenSSL: Don't assume 1.1.1 implies blake2 availability

Reviewed By: yfeldblum

Differential Revision: D31414552

fbshipit-source-id: 0a814de998d88950f5e6e61c23b20f40c2eb0a37

folly/portability/OpenSSL.h

@@ -25,6 +25,10 @@
 
 #include <openssl/opensslv.h>
 
+// The OpenSSL public header that describes build time configuration and
+// availability (or lack of availability) of certain optional ciphers.
+#include <openssl/opensslconf.h>
+
 #include <openssl/asn1.h>
 #include <openssl/bio.h>
 #include <openssl/bn.h>
@@ -91,10 +95,22 @@
 #define FOLLY_OPENSSL_HAS_ALPN 0
 #endif
 
-// OpenSSL 1.1.1 and above have TLS 1.3 and BLAKE2B support
+/**
+ * OpenSSL 1.1.1 specific checks.
+ */
 #if OPENSSL_VERSION_NUMBER >= 0x1010100fL
+
+// TLS 1.3 was introduced in OpenSSL 1.1.1
 #define FOLLY_OPENSSL_HAS_TLS13 1
+
+// OpenSSL 1.1.1 introduced several new ciphers and digests. Unless they are
+// explicitly compiled out, they are assumed to be present
+#if !defined(OPENSSL_NO_BLAKE2)
 #define FOLLY_OPENSSL_HAS_BLAKE2B 1
+#else
+#define FOLLY_OPENSSL_HAS_BLAKE2B 0
+#endif
+
 #else
 #define FOLLY_OPENSSL_HAS_TLS13 0
 #define FOLLY_OPENSSL_HAS_BLAKE2B 0