Minor tweaks and improvements to the tunala demo.

- Add "-cipher" and "-out_state" command line arguments to control SSL
  cipher-suites and handshake debug output respectively.

- Implemented error handling for SSL handshakes that break down. This uses
  a cheat - storing a non-NULL pointer as "app_data" in the SSL structure
  when the SSL should be killed.

demos/tunala/cb.c

@@ -0,0 +1,39 @@
+#include "tunala.h"
+
+#ifndef NO_OPENSSL
+
+/* For callbacks generating output, here are their file-descriptors. */
+static FILE *fp_cb_ssl_info = NULL;
+
+/* This function is largely borrowed from the one used in OpenSSL's "s_client"
+ * and "s_server" utilities. */
+void cb_ssl_info(SSL *s, int where, int ret)
+{
+	char *str1, *str2;
+	int w;
+
+	if(!fp_cb_ssl_info)
+		return;
+
+	w = where & ~SSL_ST_MASK;
+	str1 = (w & SSL_ST_CONNECT ? "SSL_connect" : (w & SSL_ST_ACCEPT ?
+				"SSL_accept" : "undefined")),
+	str2 = SSL_state_string_long(s);
+
+	if (where & SSL_CB_LOOP)
+		fprintf(stderr, "%s:%s\n", str1, str2);
+	else if (where & SSL_CB_EXIT) {
+		if (ret == 0)
+			fprintf(stderr, "%s:failed in %s\n", str1, str2);
+		else if (ret < 0)
+			fprintf(stderr, "%s:error in %s\n", str1, str2);
+	}
+}
+
+void cb_ssl_info_set_output(FILE *fp)
+{
+	fp_cb_ssl_info = fp;
+}
+
+#endif /* !defined(NO_OPENSSL) */
+