snl(3) manual page

To receive a message, use snl_read_message(). Currently, this call is blocking.

The library provides an easy way to convert the message to the pre-defined C structure. For each message type, one needs to define rules, converting the protocol header fields and the desired attributes to the specified structure. It can be accomplished by using message parsers. Each message parser consists of an array of attribute getters and an array of header field getters. The former array needs to be sorted by the attribute type. There is a SNL_VERIFY_PARSERS() macro to check if the order is correct. SNL_DECLARE_PARSER(parser_name, family header type, struct snl_field_parser[], struct snl_attr_parser[]) can be used to create a new parser. SNL_DECLARE_ATTR_PARSER(parser_name, struct snl_field_parser[]) can be used to create an attribute-only message parser.

Each attribute getter needs to be embedded in the following structure:

typedef bool snl_parse_attr_f(struct snl_state *ss, struct nlattr *attr, const void *arg, void *target);
struct snl_attr_parser {
        uint16_t                type;   /* Attribute type */
        uint16_t                off;    /* field offset in the target structure */
        snl_parse_attr_f        *cb;    /* getter function to call */
        const void              *arg;   /* getter function custom argument */
};

The generic attribute getter has the following signature: bool snl_attr_get_<type>(struct snl_state *ss, struct nlattr *nla, const void *arg, void *target). nla contains the pointer of the attribute to use as the datasource. The target field is the pointer to the field in the target structure. It is up to the getter to know the type of the target field. The getter must check the input attribute and return false if the attribute is not formed correctly. Otherwise, the getter fetches the attribute value and stores it in the target, then returns true. It is possible to use snl_allocz() to create the desired data structure . A number of predefined getters for the common data types exist. snl_attr_get_flag() converts a flag-type attribute to an uint8_t value of 1 or 0, depending on the attribute presence. snl_attr_get_uint8() stores a uint8_t type attribute into the uint8_t target field. snl_attr_get_uint16() stores a uint16_t type attribute into the uint16_t target field. snl_attr_get_uint32() stores a uint32_t type attribute into the uint32_t target field. snl_attr_get_uint64() stores a uint64_t type attribute into the uint64_t target field. snl_attr_get_ip() and snl_attr_get_ipvia() stores a pointer to the sockaddr structure with the IPv4/IPv6 address contained in the attribute. Sockaddr is allocated using snl_allocz(). snl_attr_get_string() stores a pointer to the NULL-terminated string. The string itself is allocated using snl_allocz(). snl_attr_get_nla() stores a pointer to the specified attribute. snl_attr_get_stringn() stores a pointer to the non-NULL-terminated string.

Similarly, each family header getter needs to be embedded in the following structure:

typedef void snl_parse_field_f(struct snl_state *ss, void *hdr, void *target);
struct snl_field_parser {
        uint16_t                off_in; /* field offset in the input structure */
        uint16_t                off_out;/* field offset in the target structure */
        snl_parse_field_f       *cb;    /* getter function to call */
};

The generic field getter has the following signature: void snl_field_get_<type> "struct snl_state *ss" "void *src" "void *target" . A number of pre-defined getters for the common data types exist. snl_field_get_uint8() fetches an uint8_t value and stores it in the target. snl_field_get_uint16() fetches an uint8_t value and stores it in the target. snl_field_get_uint32() fetches an uint32_t value and stores it in the target.

Manual Pages — SNL

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CONTENTS

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INITIALISATION

MEMORY ALLOCATION

COMPOSING AND SENDING MESSAGES

RECEIVING AND PARSING MESSAGES

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