These functions are used to manipulate a previously allocated and initialized context, see getdns_context (3) for more details on the functions used to allocate, initialized and destroy contexts and for a more detailed discussion of the getdns_context in general.
a previously allocated and initialized getdns_context
.HP3
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a callback function that will be called when changes are made to the system files (/etc/resolv.conf and /etc/hosts) for contexts created with set_from_os = 1. When this function is called the changed_item parameter indicates which item in the context has changed.
may be one of GETDNS_CONTEXT_UDP_FIRST_AND_FALL_BACK_TO_TCP, GETDNS_CONTEXT_UDP_ONLY, GETDNS_CONTEXT_TCP_ONLY, GETDNS_CONTEXT_TCP_ONLY_KEEP_CONNECTIONS_OPEN. If you need more information on what each of these means reread the mnemonic and take a guess ;)
If set to GETDNS_REDIRECTS_FOLLOW (the default) then the eventual target of the redirect is returned. If set to GETDNS_REDIRECTS_DO_NOT_FOLLOW then the CNAME or DNAME is returned and NOT the eventual target.
the maximum number of concurrent outstanding (unanswered) DNS queries, if exceeded the API will queue queries and issue them as the number of outstanding queries drops. A value of 0 indicates that there is no limit.
The namespaces array contains an ordered list of namespaces that will be queried. Important: this context setting is ignored for the getdns_general and getdns_general_sync functions; it is used for the other functions. The values are GETDNS_CONTEXT_NAMESPACE_DNS, GETDNS_CONTEXT_NAMESPACE_LOCALNAMES, GETDNS_CONTEXT_NAMESPACE_NETBIOS, GETDNS_CONTEXT_NAMESPACE_MDNS, and GETDNS_CONTEXT_NAMESPACE_NIS. When a normal lookup is done, the API does the lookups in the order given and stops when it gets the first result; a different method with the same result would be to run the queries in parallel and return when it gets the first result. Because lookups might be done over different mechanisms because of the different namespaces, there can be information leakage that is similar to that seen with getaddrinfo(). The default is determined by the OS.
the number of milliseconds the API will wait for a response, after which the callback will be invoked (or the synchronous function will return) with a timeout error.
