# lwres_resutil

## Name

lwres_string_parse, lwres_addr_parse, lwres_getaddrsbyname, lwres_getnamebyaddr -- lightweight resolver utility functions

## Synopsis

    #include <lwres/lwres.h>

``lwres_result_t lwres_string_parse`(lwres_buffer_t *b, char **c, lwres_uint16_t *len);`

``lwres_result_t lwres_addr_parse`(lwres_buffer_t *b, lwres_addr_t *addr);`

``lwres_result_t lwres_getaddrsbyname`(lwres_context_t *ctx, const char *name, lwres_uint32_t addrtypes, lwres_gabnresponse_t **structp);`

``lwres_result_t lwres_getnamebyaddr`(lwres_context_t *ctx, lwres_uint32_t addrtype, lwres_uint16_t addrlen, const unsigned char *addr, lwres_gnbaresponse_t **structp);`

## DESCRIPTION

`lwres_string_parse()` retrieves a DNS-encoded string starting the current pointer of lightweight resolver buffer `b`: i.e. `b->current`. When the function returns, the address of the first byte of the encoded string is returned via `*c` and the length of that string is given by `*len`. The buffer's current pointer is advanced to point at the character following the string length, the encoded string, and the trailing NULL character.

`lwres_addr_parse()` extracts an address from the buffer `b`. The buffer's current pointer `b->current` is presumed to point at an encoded address: the address preceded by a 32-bit protocol family identifier and a 16-bit length field. The encoded address is copied to `addr->address` and `addr->length` indicates the size in bytes of the address that was copied. `b->current` is advanced to point at the next byte of available data in the buffer following the encoded address.

`lwres_getaddrsbyname()` and `lwres_getnamebyaddr()` use the lwres_gnbaresponse_t structure defined below:

    typedef struct {
            lwres_uint32_t          flags;
            lwres_uint16_t          naliases;
            lwres_uint16_t          naddrs;
            char                   *realname;
            char                  **aliases;
            lwres_uint16_t          realnamelen;
            lwres_uint16_t         *aliaslen;
            lwres_addrlist_t        addrs;
            void                   *base;
            size_t                  baselen;
    } lwres_gabnresponse_t;

The contents of this structure are not manipulated directly but they are controlled through the lwres_gabn(3) functions.

The lightweight resolver uses `lwres_getaddrsbyname()` to perform foward lookups. Hostname `name` is looked up using the resolver context `ctx` for memory allocation. `addrtypes` is a bitmask indicating which type of addresses are to be looked up. Current values for this bitmask are LWRES_ADDRTYPE_V4 for IPv4 addresses and LWRES_ADDRTYPE_V6 for IPv6 addresses. Results of the lookup are returned in `*structp`.

`lwres_getnamebyaddr()` performs reverse lookups. Resolver context `ctx` is used for memory allocation. The address type is indicated by `addrtype`: LWRES_ADDRTYPE_V4 or LWRES_ADDRTYPE_V6. The address to be looked up is given by `addr` and its length is `addrlen` bytes. The result of the function call is made available through `*structp`.

## RETURN VALUES

Successful calls to `lwres_string_parse()` and `lwres_addr_parse()` return LWRES_R_SUCCESS. Both functions return LWRES_R_FAILURE if the buffer is corrupt or LWRES_R_UNEXPECTEDEND if the buffer has less space than expected for the components of the encoded string or address.

`lwres_getaddrsbyname()` returns LWRES_R_SUCCESS on success and it returns LWRES_R_NOTFOUND if the hostname `name` could not be found.

LWRES_R_SUCCESS is returned by a successful call to `lwres_getnamebyaddr()`.

Both `lwres_getaddrsbyname()` and `lwres_getnamebyaddr()` return LWRES_R_NOMEMORY when memory allocation requests fail and LWRES_R_UNEXPECTEDEND if the buffers used for sending queries and receiving replies are too small.

## SEE ALSO

lwres_buffer(3), lwres_gabn(3).