Add SSLKEYLOGFILE support to S2N

s2n_keylog.patch

diff --git a/tls/s2n_handshake_io.c b/tls/s2n_handshake_io.c
index 40a8fb0..0c7c2b4 100644
--- a/third-party-src/tls/s2n_handshake_io.c
+++ b/third-party-src/tls/s2n_handshake_io.c
@@ -16,6 +16,7 @@
 #include <sys/param.h>
 
 #include <errno.h>
+#include <stdio.h>
 #include <s2n.h>
 
 #include "error/s2n_errno.h"
@@ -635,6 +636,42 @@ static int handshake_read_io(struct s2n_connection *conn)
     return 0;
 }
 
+static void s2n_write_keylog(struct s2n_connection *conn)
+{
+       char *keylog_fn;
+       FILE *keylog_fp;
+
+       keylog_fn = getenv("SSLKEYLOGFILE");
+       if (!keylog_fn) {
+               return;
+       }
+
+       keylog_fp = fopen(keylog_fn, "a");
+       if (!keylog_fp) {
+               return;
+       }
+
+       fprintf(keylog_fp, "CLIENT_RANDOM ");
+       for(size_t i=0; i<sizeof(conn->secure.client_random); i++) {
+               uint8_t unibble = conn->secure.client_random[i] >> 4;
+               uint8_t lnibble = conn->secure.client_random[i] & 15;
+               unibble += (unibble < 10) ? '0' : ('a' - 10);
+               lnibble += (lnibble < 10) ? '0' : ('a' - 10);
+               fprintf(keylog_fp, "%c%c", unibble, lnibble);
+       }
+       fprintf(keylog_fp, " ");
+       for(size_t i=0; i<sizeof(conn->secure.master_secret); i++) {
+               uint8_t unibble = conn->secure.master_secret[i] >> 4;
+               uint8_t lnibble = conn->secure.master_secret[i] & 15;
+               unibble += (unibble < 10) ? '0' : ('a' - 10);
+               lnibble += (lnibble < 10) ? '0' : ('a' - 10);
+               fprintf(keylog_fp, "%c%c", unibble, lnibble);
+       }
+       fprintf(keylog_fp, "\n");
+
+       fclose(keylog_fp);
+}
+
 int s2n_negotiate(struct s2n_connection *conn, s2n_blocked_status * blocked)
 {
     char this = 'S';
@@ -677,6 +714,8 @@ int s2n_negotiate(struct s2n_connection *conn, s2n_blocked_status * blocked)
         }
     }
 
+    s2n_write_keylog(conn);
+
     *blocked = S2N_NOT_BLOCKED;
 
     return 0;