YAZ only offers HTTP as transport carrier for SOAP, but it is relatively easy to change that.

The following definition of Z_GDU (Generic Data Unit) allows for both HTTP and Z39.50 in one packet.

#include <yaz/zgdu.h>

#define Z_GDU_Z3950         1
#define Z_GDU_HTTP_Request  2
#define Z_GDU_HTTP_Response 3
typedef struct {
  int which;
  union {
    Z_APDU *z3950;
    Z_HTTP_Request *HTTP_Request;
    Z_HTTP_Response *HTTP_Response;
  } u;
} Z_GDU ;
    

The corresponding Z_GDU encoder/decoder is z_GDU. The z3950 is any of the known BER encoded Z39.50 APDUs. HTTP_Request and HTTP_Response is the HTTP Request and Response respectively.