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| author | Laurent Bercot <ska-skaware@skarnet.org> | 2014-12-10 03:05:47 +0000 |
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| committer | Laurent Bercot <ska-skaware@skarnet.org> | 2014-12-10 03:05:47 +0000 |
| commit | 416ef5e2bf59bb2e45066a1d5d91ac677c0f48e5 (patch) | |
| tree | 1c746d673dcec7a8488c6ac51db8245411034376 /doc/libs6dns/s6dns-resolve.html | |
| download | s6-dns-416ef5e2bf59bb2e45066a1d5d91ac677c0f48e5.tar.xz | |
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diff --git a/doc/libs6dns/s6dns-resolve.html b/doc/libs6dns/s6dns-resolve.html new file mode 100644 index 0000000..bbb3f57 --- /dev/null +++ b/doc/libs6dns/s6dns-resolve.html @@ -0,0 +1,387 @@ +<html> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <meta http-equiv="Content-Language" content="en" /> + <title>s6-dns: the s6dns_resolve library interface</title> + <meta name="Description" content="s6-dns: the s6dns_resolve library interface" /> + <meta name="Keywords" content="s6-dns dns s6dns_resolve library libs6dns" /> + <!-- <link rel="stylesheet" type="text/css" href="http://skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">libs6dns</a><br /> +<a href="../">s6-dns</a><br /> +<a href="http://skarnet.org/software/">Software</a><br /> +<a href="http://skarnet.org/">skarnet.org</a> +</p> + +<h1> The <tt>s6dns_resolve</tt> library interface </h1> + +<p> + The following functions are declared in the <tt>s6-dns/s6dns-resolve.h</tt> header, +and implemented in the <tt>libs6dns.a</tt> or <tt>libs6dns.so</tt> library. +</p> + +<h2> General information </h2> + +<p> + <tt>s6dns_resolve</tt> provides functions and macros - mostly macros - +to perform high level synchronous DNS resolution. +</p> + +<p> + All the functions declared here make synchronous calls to the network, so +they can block for a non-negligible amount of time. To avoid unbounded +waiting times, they always take 2 arguments at the end, <em>deadline</em> +and <em>stamp</em>. <em>deadline</em> is the read-only address of a +<a href="http://skarnet.org/software/skalibs/libstddjb/tai.h">struct taia</a> +containing an absolute time which is the deadline for the function, and +<em>stamp</em> is the read-write address of a <tt>struct taia</tt> being +an accurate enough representation of the current absolute time. If +the function has not returned by *<em>deadline</em>, then it immediately +returns with a failure code and errno set to ETIMEDOUT. In every case, +*<em>stamp</em> is automatically updated so it always represents the +absolute time accurately enough. +</p> + +<p> + In a single-threaded program, the STAMP global variable can be used to +store the current time. Macros ending with <tt>_g</tt> use this variable +automatically so you don't have to provide the <em>stamp</em> argument +everytime. Additionally, several resolution functions make implicit use +of global variables such as: +</p> + +<ul> + <li> <tt>s6dns_engine_here</tt>: a global +<a href="s6dns-engine.html">s6dns_engine_t</a> storing the current +query, for sequential queries. </li> + <li> <tt>s6dns_debughook_zero</tt>: a global <tt>s6dns_debughook_t</tt> +meaning no debugging is needed. </li> + <li> <tt>s6dns_rci_here</tt>: a global +<a href="s6dns-rci.html">s6dns_rci_t</a> containing the current +resolv.conf information. </li> +</ul> + +<p> + Reentrant, non-global-using functions are also provided, with the <tt>_r</tt> +suffix. In other words, if <em>foobarfunc</em> is a resolution function, +the following prototypes are generally provided, from the simplest to the +most complex: +</p> + +<ul> + <li> <em>foobarfunc_g</em>: only the relevant parameters and a deadline +must be given, the function uses the STAMP global and maybe DNS-specific +globals </li> + <li> <em>foobarfunc</em>: a deadline and stamp must be given, the function +uses all the DNS-specific globals </li> + <li> <em>foobarfunc_r_g</em>: No DNS-specific globals are used, the +information must be given via parameters, but the STAMP global is used </li> + <li> <em>foobarfunc_r</em>: fully reentrant function using no globals +at all </li> +</ul> + +<p> + For each set of four functions, only one is documented here. +The other prototypes can be found in the <tt>s6-dns/s6dns-resolve.h</tt> file. +</p> + +<p> + Some <tt>errno</tt> codes reported by these functions do not have +exactly the system meaning given by +<a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/strerror.html">strerror()</a>. +To get a user-friendly error message, use +<tt>s6dns_constants_error_str(errno)</tt> instead. The <tt>s6dns_constants_error_str</tt> +function is declared in the <tt>s6dns-constants.h</tt> header. +</p> + +<h2> Functions </h2> + +<h3> Single query resolution </h3> + +<p> + These functions are ordered from the lowest level to the highest level. +</p> + +<h4> Basic wrapper around s6dns_engine </h4> + +<p> +<code> int s6dns_resolve_loop_r_g (s6dns_engine_t *dt, struct taia const *deadline) </code> <br /> +Resolves the query stored in <tt>dt</tt>. +Returns 1 on success or 0 on failure. +</p> + +<h4> Generic resolution functions </h4> + +<p> +<code> int s6dns_resolve_core_g (s6dns_domain_t const *d, uint16 qtype, struct taia const *deadline) </code> <br /> +Resolves the query on domain *<em>d</em> (in packet form), of type <em>qtype</em>. +Returns 0 on failure, or 1 on success, in which case +<tt>s6dns_engine_here</tt> contains the answer. +</p> + +<p> +<code> int s6dns_resolve_parse_g (s6dns_domain_t const *d, uint16 qtype, s6dns_message_rr_func_t *f, void *data, struct taia const *deadline) </code> <br /> +Resolves the query on domain *<em>d</em> (in packet form), of type <em>qtype</em>, +then parses the answer with function <em>f</em> and stores the result into <em>data</em>. +Returns 1 if it succeeds, 0 if no data can be extracted from the answer, or -1 if an +error occurs. Sets errno in the last two cases. +</p> + +<p> + Note that the function can return 1 without appending anything to <em>data</em>. +This means that the servers confirmed that the domain exists, but <em>f</em> +has not been able to find any data relevant to the query in the answer. +This is very different from NXDOMAIN, which means that +the servers deny the actual existence of the domain, and which is reported +here as a return code of 0 with errno set to ENOENT. +</p> + +<p> +<code> int s6dns_resolvenoq_g (char const *name, unsigned int len, uint16 qtype, s6dns_message_rr_func_t *f, void *data, struct taia const *deadline) </code> <br /> +Performs a query of type <em>qtype</em> on name <em>name</em> of length <em>len</em>, +without qualifying it. Parses the answer with function <em>f</em> and stores the +result into <em>data</em>. Returns 1 if it succeeds, 0 if no data can be extracted, +or -1 if an error occurs. Sets errno in the last two cases. +</p> + +<p> +<code> int s6dns_resolveq_g (char const *name, unsigned int len, uint16 qtype, s6dns_message_rr_func_t *f, void *data, struct taia const *deadline) </code> <br /> +Performs a query of type <em>qtype</em> on name <em>name</em> of length <em>len</em>, +qualifying it first. Parses the answer with function <em>f</em> and stores the +result into <em>data</em>. Returns 1 if it succeeds, 0 if none of the FQDNs can +get a positive answer, or -1 if an error occurs. Sets errno in the last two cases. +</p> + +<p> +<code> int s6dns_resolve_g (char const *name, unsigned int len, uint16 qtype, s6dns_message_rr_func_t *f, void *data, int qualif, struct taia const *deadline) </code> <br /> +Performs a query of type <em>qtype</em> on name <em>name</em> of length <em>len</em>. +Qualifies <em>name</em> first if <em>qualif</em> is nonzero; else, does not +qualify it. Parses the answer with function <em>f</em> and stores the +result into <em>data</em>. Returns 1 if it succeeds, 0 if none of the FQDNs can +get a positive answer, or -1 if an error occurs. Sets errno in the last two cases. +</p> + +<h4> High-level type-specific functions </h4> + +<p> +<code> int s6dns_resolve_a_g (stralloc *ips, char const *name, unsigned int len, int qualif, struct taia const *deadline) </code> <br /> +Performs an A query on name <em>name</em> of length <em>len</em>, qualifying it +iff <em>qualif</em> is nonzero. Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or 1 if it succeeds, in which case the IPs are +appended to the stralloc *<em>ips</em>, using 4 bytes per answer. +</p> + +<p> +<code> int s6dns_resolve_aaaa_g (stralloc *ips, char const *name, unsigned int len, int qualif, struct taia const *deadline) </code> <br /> +Performs an AAAA query on name <em>name</em> of length <em>len</em>, qualifying it +iff <em>qualif</em> is nonzero. Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or 1 if it succeeds, in which case the IPs are +appended to the stralloc *<em>ips</em>, using 16 bytes per answer. +</p> + +<p> +<code> int s6dns_resolve_aaaaa_g (genalloc *ips, char const *name, unsigned int len, int qualif, struct taia const *deadline) </code> <br /> +Performs an AAAA query and an A query at the same time on name <em>name</em> +of length <em>len</em>, qualifying it first iff <em>qualif</em> is nonzero. +Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or a positive number if it succeeds: 1 if IPv4 addresses +were found, 2 if IPv6 addresses were found, and 3 if both were found. +The IPs are appended to the genalloc *<em>ips</em>, which contains an array of +<tt>ip46_t</tt>, the skalibs structure used to store IPv4 and IPv6 addresses +indiscriminately. +</p> + +<p> +<code> int s6dns_resolve_ptr_g (genalloc *ds, char const *name, unsigned int len, int qualif, struct taia const *deadline) </code> <br /> +Performs a PTR query on name <em>name</em> of length <em>len</em>, qualifying it +iff <em>qualif</em> is nonzero. Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or 1 if it succeeds, in which case the domains are +appended to the genalloc *<em>ds</em>, which contains an array of <tt>s6dns_domain_t</tt>. +</p> + +<p> +<code> int s6dns_resolve_name4_g (genalloc *ds, char const *ip, struct taia const *deadline) </code> <br /> +Performs a PTR query on the <tt>in-addr.arpa.</tt> name representing the IPv4 +address <em>ip</em> (4 network-order bytes). +Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or 1 if it succeeds, in which case the domains are +appended to the genalloc *<em>ds</em>, which contains an array of <tt>s6dns_domain_t</tt>. +</p> + +<p> +<code> int s6dns_resolve_name6_g (genalloc *ds, char const *ip, struct taia const *deadline) </code> <br /> +Performs a PTR query on the <tt>ip6.arpa.</tt> name representing the IPv6 +address <em>ip</em> (16 network-order bytes). +Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or 1 if it succeeds, in which case the domains are +appended to the genalloc *<em>ds</em>, which contains an array of <tt>s6dns_domain_t</tt>. +</p> + +<p> +<code> int s6dns_resolve_name46_g (genalloc *ds, ip46_t const *ip, struct taia const *deadline) </code> <br /> +Calls <tt>s6dns_resolve_name6_g()</tt> or <tt>s6dns_resolve_name4_g()</tt> +depending on which <em>ip</em> is an IPv6 or IPv4 address. +</p> + +<p> +<code> int s6dns_resolve_ns_g (genalloc *ds, char const *name, unsigned int len, int qualif, struct taia const *deadline) </code> <br /> +Performs a NS query on name <em>name</em> of length <em>len</em>, qualifying it +iff <em>qualif</em> is nonzero. Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or 1 if it succeeds, in which case the domains are +appended to the genalloc *<em>ds</em>, which contains an array of <tt>s6dns_domain_t</tt>. +</p> + +<p> +<code> int s6dns_resolve_cname_g (genalloc *ds, char const *name, unsigned int len, int qualif, struct taia const *deadline) </code> <br /> +Performs a CNAME query on name <em>name</em> of length <em>len</em>, qualifying it +iff <em>qualif</em> is nonzero. Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or 1 if it succeeds, in which case the domains are +appended to the genalloc *<em>ds</em>, which contains an array of <tt>s6dns_domain_t</tt>. +</p> + +<p> +<code> int s6dns_resolve_hinfo_g (genalloc *hinfos, char const *name, +unsigned int len, int qualif, struct taia const *deadline) </code> <br /> + Performs an HINFO query on name <em>name</em> of length <em>len</em>, qualifying it +iff <em>qualif</em> is nonzero. Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or 1 if it succeeds, in which case the domains are +appended to the genalloc *<em>hinfos</em>, which contains an array of +<tt>s6dns_message_rr_hinfo_t</tt>. +</p> + +<p> +<code> int s6dns_resolve_mx_g (genalloc *mxs, char const *name, +unsigned int len, int qualif, struct taia const *deadline) </code> <br /> + Performs an MX query on name <em>name</em> of length <em>len</em>, qualifying it +iff <em>qualif</em> is nonzero. Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or 1 if it succeeds, in which case the domains are +appended to the genalloc *<em>mxs</em>, which contains an array of +<tt>s6dns_message_rr_mx_t</tt>. +</p> + +<p> +<code> int s6dns_resolve_soa_g (genalloc *soas, char const *name, +unsigned int len, int qualif, struct taia const *deadline) </code> <br /> + Performs an SOA query on name <em>name</em> of length <em>len</em>, qualifying it +iff <em>qualif</em> is nonzero. Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or 1 if it succeeds, in which case the domains are +appended to the genalloc *<em>soas</em>, which contains an array of +<tt>s6dns_message_rr_soa_t</tt>. +</p> + +<p> +<code> int s6dns_resolve_srv_g (genalloc *srvs, char const *name, +unsigned int len, int qualif, struct taia const *deadline) </code> <br /> + Performs an SRV query on name <em>name</em> of length <em>len</em>, qualifying it +iff <em>qualif</em> is nonzero. Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or 1 if it succeeds, in which case the domains are +appended to the genalloc *<em>srvs</em>, which contains an array of +<tt>s6dns_message_rr_srv_t</tt>. +</p> + +<p> +<code> int s6dns_resolve_txt_g (stralloc *sa, genalloc *offsets, char const *name, +unsigned int len, int qualif, struct taia const *deadline) </code> <br /> + Performs an TXT query on name <em>name</em> of length <em>len</em>, qualifying it +iff <em>qualif</em> is nonzero. Returns -1 if an error occurs, or 0 if no answer +can be obtained from servers, or 1 if it succeeds, in which case: +</p> + +<ul> + <li> The resulting strings are all stored into stralloc *<em>sa</em>. +Every string is terminated by a null character. </li> + <li> A series of unsigned ints is appended to genalloc *<em>offsets</em>. +Every integer represents the offset in *<em>sa</em> at which a string is stored. +The number of appended integers is the total number of answers. </li> +</ul> + +<h4> Parallel resolution </h4> + +<p> +<code> int s6dns_resolven_loop_g (s6dns_engine_t *dtl, unsigned int n, +unsigned int or, struct taia const *deadline) </code> <br /> + Resolves the <em>n</em> queries stored in the array pointed to by <em>dtl</em>, +in parallel. If <em>or</em> is zero, it does not return before all answers +have arrived. If <em>or</em> is 1, it returns when an answer arrives, but does +not return if a query generates an error (unless all queries do so). If +<em>or</em> is 2, it returns when an answer arrives or an error occurs. +Other values of <em>or</em> are unspecified yet. + +<p> + The return code is as follows: +</p> + +<ul> + <li> If <em>or</em> is 0: -1 on a global error (i.e. not specific to +a query), or a non-negative number which is the total of successful +queries. </li> + <li> If <em>or</em> is 1 or 2: -1 on a global error, or a non-negative +number which is the index of the query that triggered the event. </li> +</ul> + +<p> + If <em>or</em> is 1, a return code of -1 with errno set to ENOENT +means that all the queries failed. +</p> + +<p> + After the function returns, the <tt>status</tt> field of each +<tt>s6dns_engine_t</tt> contains the error code relative to the query. +A status of 0 means that an answer has properly arrived; EAGAIN means +that the query is still pending (and the s6dns_engine_t has not been +recycled); ECONNABORTED means that the query has not been properly +initialized. Other codes report various network problems. +</p> + +<p> +<code> int s6dns_resolven_parse_g (s6dns_resolve_t const *list, unsigned int n, +struct taia const *deadline) </code> <br /> +Performs <em>n</em> complete resolutions in parallel, parsing the results. +Returns 1 in case of success or 0 if a global error occurred. +</p> + +<p> +<em>list</em> is a pointer to an array of <em>n</em> <tt>s6dns_resolve_t</tt>, +which is a structure containing at least the following fields: +</p> + +<ul> + <li> <tt>q</tt> : a <tt>s6dns_domain_t</tt> containing the query. +It must be in encoded form. </li> + <li> <tt>qtype</tt> : a <tt>uint16</tt> containing the query type. +A list of valid query types can be found in the <tt>s6dns-constants.h</tt> +header. </li> + <li> <tt>options</tt> : a <tt>uint32</tt> containing options passed +to <a href="s6dns_engine.html">s6dns_engine_init()</a>. </li> + <li> <tt>deadline</tt> : a <tt>struct taia</tt> containing the +deadline for this query, i.e. the query will fail with an ETIMEDOUT code +if no answer has arrived by then. Note that the <em>deadline</em> +argument given to s6dns_resolven_parse() is a global deadline that +can make the function return with 0 ETIMEDOUT, but is independent from +this field, which is local to every query. </li> + <li> <tt>parsefunc</tt> : a <tt>s6dns_message_rr_func_t</tt> +function that will be used to parse the answer. </li> + <li> <tt>data</tt> : a <tt>void *</tt> that will be passed as an +additional pointer to the <tt>parsefunc</tt> function; it is generally +used to store the parsing result. </li> + <li> <tt>status</tt> : an <tt>int</tt>. It does not need to be +initialized. It will contain the error code for the query after the +function returns. ECONNABORTED means that the query could not be +started at all; EAGAIN means that the query was still pending when +an error happened; other codes report various network problems. </li> +</ul> + +<p> + The s6dns_resolven_parse() function is a simple, convenient way to +perform several resolutions in parallel to avoid the waiting time +incurred by serial resolutions. However, it is still a synchronous +function, and cannot replace a real asynchronous DNS library: for +more complex parallel resolution needs, use the +<a href="../skadns/">skadns</a> library. +</p> + +</body> +</html> |