tls-aux.c: add helper to obtain default cert paths

...and compile it as standalone test program. After "make check",
you can check t.tls-aux.log in the build area for the defaults.

Note that environment overrides can be made, see
SSL_CTX_set_default_verify_paths(3) or, for instance,
https://www.openssl.org/docs/man1.1.1/man3/SSL_CTX_set_default_verify_paths.html

OpenSSL 3.x may ship an openssl-env(7) manual page.

4 files changed, 68 insertions, 2 deletions

diff --git a/Makefile.am b/Makefile.am
index 083c5340..d7d0320c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -47,7 +47,7 @@ DEPENDENCIES=		libfm.a $(LIBOBJS)
 
 check_PROGRAMS=
 
-TESTS=			t.smoke t.validate-xhtml10 t.validate-xhtml t.x509_name_match t.realpath
+TESTS=			t.smoke t.validate-xhtml10 t.validate-xhtml t.x509_name_match t.realpath t.tls-aux
 LOG_COMPILER=		env LC_ALL=C TZ=UTC $(SHELL)
 
 if NEED_TRIO
@@ -102,8 +102,10 @@ if NEED_GETADDRINFO
 fetchmail_SOURCES += libesmtp/getaddrinfo.h libesmtp/getaddrinfo.c
 endif
 
+tls_aux_SOURCES = 	tls-aux.c
+
 check_PROGRAMS +=	rfc822 unmime netrc rfc2047e mxget rfc822valid \
-			x509_name_match fm_realpath
+			x509_name_match fm_realpath tls-aux
 
 fm_realpath_CFLAGS=	-DTEST
 
@@ -113,6 +115,8 @@ rfc822valid_CFLAGS=	-DTEST
 
 rfc822_CFLAGS=		-DMAIN
 
+tls_aux_CFLAGS=		-DTEST
+
 x509_name_match_CFLAGS=	-DTEST
 
 unmime_SOURCES=	unmime.c
diff --git a/fetchmail.h b/fetchmail.h
index 902aae18..a5f15e8d 100644
--- a/fetchmail.h
+++ b/fetchmail.h
@@ -796,4 +796,8 @@ int ntlm_helper(int sock, struct query *ctl, const char *protocol);
 /* fm_realpath.c */
 char *fm_realpath(const char *restrict file_name);
 
+/* tls-aux.c */
+const char *get_default_cert_path(void);
+const char *get_default_cert_file(void);
+
 /* fetchmail.h ends here */
diff --git a/t.tls-aux b/t.tls-aux
new file mode 100644
index 00000000..29f0ca12
--- /dev/null
+++ b/t.tls-aux
@@ -0,0 +1,2 @@
+#!/bin/sh
+exec ./tls-aux
diff --git a/tls-aux.c b/tls-aux.c
new file mode 100644
index 00000000..a3fc7908
--- /dev/null
+++ b/tls-aux.c
@@ -0,0 +1,56 @@
+#include "config.h"
+#include "fetchmail.h"
+
+#ifdef SSL_ENABLE
+#include <stdlib.h>
+#include <string.h>
+#include <openssl/x509.h>
+
+/** return a constant copy of the default SSL certificate path
+ * the directory with hashed certificates, see
+ * SSL_CTX_load_verify_locations(3),
+ * not to be modified by caller. */
+const char *get_default_cert_path(void) {
+	const char *rb = (char *)0, *tmp;
+
+	tmp = X509_get_default_cert_dir_env();
+	if (tmp) rb = getenv(tmp);
+	if (!rb) rb = X509_get_default_cert_dir();
+
+	return rb;
+}
+
+/** return a constant copy of the default SSL certificate file
+ * the directory with hashed certificates, see
+ * SSL_CTX_load_verify_locations(3),
+ * not to be modified by caller. */
+const char *get_default_cert_file(void) {
+	const char *rb = (char *)0, *tmp;
+
+	tmp = X509_get_default_cert_file_env();
+	if (tmp) rb = getenv(tmp);
+	if (!rb) rb = X509_get_default_cert_file();
+
+	return rb;
+}
+
+#endif /* SSL_ENABLE */
+
+#ifdef TEST
+#include <stdio.h>
+
+int main(void) {
+#ifdef SSL_ENABLE
+	const char *tmp;
+
+	tmp = get_default_cert_file();
+	printf("X509 default cert file: %s\n", tmp ? tmp : "(null)");
+
+	tmp = get_default_cert_path();
+	printf("X509 default cert path: %s\n", tmp ? tmp : "(null)");
+#else
+	puts("SSL support not compiled in.");
+#endif /* SSL_ENABLE */
+	exit(EXIT_SUCCESS);
+}
+#endif /* TEST */