SSL server certificate verification fails in code but not with openssl - https

Question

I am trying to code a web service client in a RHEL 4 system (openssl 0.9.8b) (upgrade is not an option). I got the CA cert file to use, with two certificates, one is a self-signed root certificate. It works with "openssl s_client", but not from code. There I get error 7 (SSL certificate validation failed) from SSL_get_verify_result.
I made a test program, here are the basic parts:
SSL_library_init();
SSL_load_error_strings();
ctx = SSL_CTX_new(SSLv23_method());
SSL_CTX_load_verify_locations(ctx, "/etc/pki/mycert/cacert.pem", 0);
ssl = SSL_new(ctx);
sbio = BIO_new_socket(sock, BIO_NOCLOSE); /* The socket is already connected */
SSL_set_bio(ssl, sbio, sbio);
SSL_connect(ssl);
err = SSL_get_verify_result(ssl);
The connection works and the server sends its certificate; I have dumped it out with PEM_write_X509 and verified that it is accepted by "openssl verify".
I have used
SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER, verify_callback);
to write out the steps of the verification in a callback function:
static int verify_callback(int preverify_ok, X509_STORE_CTX *ctx)
{
char buf[256];
X509 *err_cert;
int err, depth;
err_cert = X509_STORE_CTX_get_current_cert(ctx);
err = X509_STORE_CTX_get_error(ctx);
depth = X509_STORE_CTX_get_error_depth(ctx);
X509_NAME_oneline(X509_get_subject_name(err_cert), buf, 256);
if (!preverify_ok)
printf("verify error:num=%d:%s:depth=%d:%s\n", err,
X509_verify_cert_error_string(err), depth, buf);
else
printf("Preverify OK, depth=%d:%s, err=%d\n", depth, buf, err);
...
The output of this is (some certificate data replaced with "..."):
Preverify OK, depth=2:/ST=GP/L=JHB/C ... QA Root CA 01, err=0
Preverify OK, depth=1:/C=ZA/DC=za/DC ... QA Issue CA 01, err=0
verify error:num=7:certificate signature failure:depth=0:/C=ZA ...
When running "openssl s_client" with this CA cert file as "-CAfile", the output starts with:
depth=2 /ST=GP/L=JHB/C ... QA Root CA 01
verify return:1
depth=1 /C=ZA/DC=za/DC ... QA Issue CA 01
verify return:1
depth=0 /C=ZA/ST ...
verify return:1
So what is the difference between what "openssl s_client" is doing, and what the code is doing?

Answer 1

I got it to work by adding "OpenSSL_add_all_algorithms()" to the code. It turned out that the algorithm used by the server cert was not found. The difference between the code and the openssl s_client command is obviously this call.
The code in the test program was taken from the Axis2/C source code, since my client is based on Axis2/C. So this call is missing there too.