3. SOAP Packages
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## 3. SOAP Packages

Every SOAP package in YAZ is represented as follows:

    #include <yaz/soap.h>

    typedef struct {
        char *fault_code;
        char *fault_string;
        char *details;
    } Z_SOAP_Fault;

    typedef struct {
        int no;
        char *ns;
        void *p;
    } Z_SOAP_Generic;

    #define Z_SOAP_fault 1
    #define Z_SOAP_generic 2
    #define Z_SOAP_error 3
    typedef struct {
        int which;
        union {
            Z_SOAP_Fault   *fault;
            Z_SOAP_Generic *generic;
            Z_SOAP_Fault   *soap_error;
        } u;
        const char *ns;
    } Z_SOAP;

The `fault` and `soap_error` arms represent both a SOAP fault - struct `Z_SOAP_Fault`. Any other generic (valid) package is represented by `Z_SOAP_Generic`.

The `ns` as part of `Z_SOAP` is the namespace for SOAP itself and reflects the SOAP version. For version 1.1 it is `http://schemas.xmlsoap.org/soap/envelope/`, for version 1.2 it is `http://www.w3.org/2001/06/soap-envelope`.

    int z_soap_codec(ODR o, Z_SOAP **pp,
                     char **content_buf, int *content_len,
                     Z_SOAP_Handler *handlers);

The `content_buf` and `content_len` is XML buffer and length of buffer respectively.

The `handlers` is a list of SOAP codec handlers - one handler for each service namespace. For SRU SOAP, the namespace would be `http://www.loc.gov/zing/srw/v1.0/`.

When decoding, the `z_soap_codec` inspects the XML content and tries to match one of the services namespaces of the supplied handlers. If there is a match a handler function is invoked which decodes that particular SOAP package. If successful, the returned `Z_SOAP` package will be of type `Z_SOAP_Generic`. Member `no` is set the offset of handler that matched; `ns` is set to namespace of matching handler; the void pointer `p` is set to the C data structure assocatiated with the handler.

When a NULL namespace is met (member `ns` bwlow), that specifies end-of-list.

Each handler is defined as follows:

    typedef struct {
        char *ns;
        void *client_data;
        Z_SOAP_fun f;
    } Z_SOAP_Handler;

The `ns` is namespace of service associated with handler `f`. `client_data` is user-defined data which is passed to handler.

The prototype for a SOAP service handler is:

    int handler(ODR o, void * ptr, void **handler_data,
                void *client_data, const char *ns);

The `o` specifies the mode (decode/encode) as usual. The second argument, `ptr`, is a libxml2 tree node pointer (`xmlNodePtr`) and is a pointer to the `Body` element of the SOAP package. The `handler_data` is an opaque pointer to a C definitions associated with the SOAP service. `client_data` is the pointer which was set as part of the `Z_SOAP_handler`. Finally, `ns` the service namespace.

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