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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-message.html | |
| download | s6-dns-416ef5e2bf59bb2e45066a1d5d91ac677c0f48e5.tar.xz | |
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diff --git a/doc/libs6dns/s6dns-message.html b/doc/libs6dns/s6dns-message.html new file mode 100644 index 0000000..e06aa91 --- /dev/null +++ b/doc/libs6dns/s6dns-message.html @@ -0,0 +1,261 @@ +<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_message library interface</title> + <meta name="Description" content="s6-dns: the s6dns_message library interface" /> + <meta name="Keywords" content="s6-dns dns s6dns_message 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_message</tt> library interface </h1> + +<p> + The following functions are declared in the <tt>s6-dns/s6dns-message.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_message</tt> provides functions to read and parse DNS messages +sent by servers and caches and containing answers to queries. +</p> + +<h2> Data structures </h2> + +<p> + A <tt>s6dns_message_header_t</tt> is a structure containing the header +of a received DNS packet, broken down for easy access to the bits. +</p> + +<p> + A <tt>s6dns_message_rr_t</tt> is a structure containing the information +about a resource record given by an answer packet - all of it, except the +value of the answer itself, which is rtype-specific and has to be decoded +by rtype-specific functions. +</p> + +<p> + A <tt>s6dns_message_rr_func_t</tt> is the type of such a function. The +prototype is <br /> +<code> int f (s6dns_message_rr_t const *rr, char const *packet, unsigned int packetlen, unsigned int pos, unsigned int section, void *data) </code> <br /> +</p> + +<ul> + <li> *<em>rr</em> contains the header information of the resource record, +including the domain to which it applies, the rtype, and the ttl. </li> + <li> <em>packet</em> points to the <strong>whole DNS packet</strong> the RR +is a part of. </li> + <li> <em>packetlen</em> is the total length of said packet. </li> + <li> <em>pos</em> is the offset of the RR in the DNS packet, i.e. <em>f</em> +should start parsing at <em>packet + pos</em>. </li> + <li> <em>section</em> is the section the RR belongs to: 2 for answer, 3 for +authority, 4 for additional. </li> + <li> <em>data</em> is a user-specified pointer; it is typically used to +write the decoded output, in a rtype-specific way. </li> + <li> <em>f</em> must return 1 or more if it succeeds in decoding the packet. +Else it must set errno appropriately, and return -1 if the error is local, +unrelated to the packet - for instance, it has run out of memory - or 0 if it +cannot decode the RR because of the packet contents. </li> +</ul> + +<p> + Various structures designed to store specific resource record types are +also provided. The list includes: +</p> + +<ul> + <li> <tt>s6dns_message_rr_hinfo</tt> for HINFO RRs </li> + <li> <tt>s6dns_message_rr_mx</tt> for MX RRs </li> + <li> <tt>s6dns_message_rr_soa</tt> for SOA RRs </li> + <li> <tt>s6dns_message_rr_srv</tt> for SRV RRs </li> +</ul> + +<h2> Functions </h2> + +<h3> Header management </h3> + +<p> +<code> void s6dns_message_header_pack (char *s, s6dns_message_header_t const *h) </code> <br /> +Packs the header *<em>h</em> into the 12 bytes pointed to by <em>s</em>. +</p> + +<p> +<code> void s6dns_message_header_unpack (char const *s, s6dns_message_header_t *h) </code> <br /> +Unpacks the 12 bytes pointed to by <em>s</em> into the structure *<em>h</em>. +</p> + +<h3> Low-level RR decoding </h3> + +<p> + The following primitives are used in the implementation of +<tt>s6dns_message_rr_func_t</tt>-typed functions, to read and decode information +stored in a DNS packet. Their arguments are: +</p> + +<ol> + <li> A pointer to the structure where the information is going to be stored </li> + <li> A read-only pointer to the beginning of the DNS packet </li> + <li> The length of the DNS packet </li> + <li> A pointer to an integer containing the current position in the +DNS packet, i.e. where the information is going to be read. If the functions +succeed, they automatically update the position so information can be read +sequentially. </li> +</ol> + +<p> +<code> int s6dns_message_get_string (s6dns_domain_t *d, char const *packet, unsigned int packetlen, unsigned int *pos) </code> <br /> +Reads a character-string and stores it into *<em>d</em>. Returns 1 on success +and 0 on failure. Note that *<em>d</em> does not contain a domain, but the +<tt>s6dns_domain_t</tt> structure is adapted to store strings that do not +exceed 255 characters. <em>d</em>→s can be used to access the string, +and <em>d</em>→len its length. +</p> + +<p> +<code> int s6dns_message_get_strings (char *s, unsigned int rdlength, char const *packet, unsigned int packetlen, unsigned int *pos </code> <br /> +This function takes an additional parameter <em>rdlength</em>. It reads a series of +character-strings and stores their concatenation into the string <em>s</em>, which +must be preallocated; it can never store more than <em>rdlength</em> bytes. It returns +-1 if it fails; on success, it returns the number of bytes written. The +<em>rdlength</em> parameter must be the length of the resource record containing +the series of character-strings. +</p> + +<p> +<code> unsigned int s6dns_message_get_domain (s6dns_domain_t *d, char const *packet, unsigned int packetlen, unsigned int *pos) </code> <br /> +Reads a domain and stores it, in string form, into *<em>d</em>. +Returns 1 on success and 0 on failure, and sets errno: +</p> + +<ul> + <li> EPROTO: there is no proper domain to be read in position *<em>pos</em> of +<em>packet</em>. Either the packet is malformed or the function is being +misused. </li> + <li> EPROTONOSUPPORT: the domain encoding uses an extension that the function +does not recognize. </li> +</ul> + +<p> +<code> int s6dns_message_get_hinfo (s6dns_message_rr_hinfo_t *p, char const *packet, unsigned int packetlen, unsigned int *pos) </code> <br /> +Reads a HINFO RR and stores it into *<em>p</em>. Returns 1 on success or 0 +on failure. +</p> + +<p> +<code> int s6dns_message_get_mx (s6dns_message_rr_mx_t *p, char const *packet, unsigned int packetlen, unsigned int *pos) </code> <br /> +Reads a MX RR and stores it into *<em>p</em>. Returns 1 on success or 0 on failure. +</p> + +<p> +<code> int s6dns_message_get_soa (s6dns_message_rr_soa_t *p, char const *packet, unsigned int packetlen, unsigned int *pos) </code> <br /> +Reads a SOA RR and stores it into *<em>p</em>. Returns 1 on success or 0 on failure. +</p> + +<p> +<code> int s6dns_message_get_srv (s6dns_message_rr_srv_t *p, char const *packet, unsigned int packetlen, unsigned int *pos) </code> <br /> +Reads a SRV RR and stores it into *<em>p</em>. Returns 1 on success or 0 on failure. +</p> + +<h3> High-level RR-specific parsing functions </h3> + +<p> +<code> s6dns_message_func_t s6dns_message_parse_answer_strings </code> <br /> +Parses character-strings located in the answer section of the packet. The +<em>data</em> argument is interpreted as a pointer to a <tt>s6dns_mpag_t</tt>, +which is a structure defined in the <tt>s6-dns/s6dns-message.h</tt> header +and used to store multiple character-strings. +</p> + +<p> +<code> s6dns_message_func_t s6dns_message_parse_answer_domain </code> <br /> +Parses domains located in the answer section of the packet. The +<em>data</em> argument is interpreted as a pointer to a <tt>s6dns_dpag_t</tt>, +which is a structure defined in the <tt>s6-dns/s6dns-message.h</tt> header +and used to store multiple domains. +</p> + +<p> +<code> s6dns_message_func_t s6dns_message_parse_answer_a </code> <br /> +Parses A RRs located in the answer section of the packet. The +<em>data</em> argument is interpreted as a pointer to a +<a href="http://skarnet.org/software/skalibs/libstddjb/stralloc.html">stralloc</a>, +and 4 bytes are appended to this stralloc for every IPv4 address found. +</p> + + +<code> s6dns_message_func_t s6dns_message_parse_answer_aaaa </code> <br /> +Parses AAAA RRs located in the answer section of the packet. The +<em>data</em> argument is interpreted as a pointer to a +<a href="http://skarnet.org/software/skalibs/libstddjb/stralloc.html">stralloc</a>, +and 16 bytes are appended to this stralloc for every IPv6 address found. +</p> + +<p> +<code> s6dns_message_func_t s6dns_message_parse_answer_hinfo </code> <br /> +Parses HINFO RRs located in the answer section of the packet. The +<em>data</em> argument is interpreted as a pointer to a +<a href="http://skarnet.org/software/skalibs/libstddjb/genalloc.html">genalloc</a> +containing <tt>s6dns_message_rr_hinfo_t</tt> structures. +</p> + +<p> +<code> s6dns_message_func_t s6dns_message_parse_answer_mx </code> <br /> +Parses MX RRs located in the answer section of the packet. The +<em>data</em> argument is interpreted as a pointer to a +<a href="http://skarnet.org/software/skalibs/libstddjb/genalloc.html">genalloc</a> +containing <tt>s6dns_message_rr_mx_t</tt> structures. +</p> + +<p> +<code> s6dns_message_func_t s6dns_message_parse_answer_soa </code> <br /> +Parses SOA RRs located in the answer section of the packet. The +<em>data</em> argument is interpreted as a pointer to a +<a href="http://skarnet.org/software/skalibs/libstddjb/genalloc.html">genalloc</a> +containing <tt>s6dns_message_rr_soa_t</tt> structures. +</p> + +<p> +<code> s6dns_message_func_t s6dns_message_parse_answer_srv </code> <br /> +Parses SRV RRs located in the answer section of the packet. The +<em>data</em> argument is interpreted as a pointer to a +<a href="http://skarnet.org/software/skalibs/libstddjb/genalloc.html">genalloc</a> +containing <tt>s6dns_message_rr_srv_t</tt> structures. +</p> + +<h3> High-level packet parsing </h3> + +<p> +<code> int s6dns_message_parse (s6dns_message_header_t *h, char const *packet, unsigned int packetlen, s6dns_message_rr_func_t *f, void *data) </code> <br /> + This function parses the DNS packet <em>packet</em> of length <em>packetlen</em>. +It stores the packet header into *<em>h</em>. Then, for every RR in the answer, +authority or additional section of the packet, it calls <em>f</em> with the +relevant parameters. <em>data</em> is the extra pointer given to <em>f</em> to +store information. The function returns 1 if the parsing succeeds. Otherwise it +returns -1 if there is a local error unrelated to the packet, or 0 if no +appropriate answer can be decoded from the packet. errno then contains one +of the following values: +</p> + +<ul> + <li> EPROTO: the packet is malformed, syntax error </li> + <li> EBADMSG: rcode 1, query format error </li> + <li> EBUSY: rcode 2, server failure </li> + <li> ENOENT: rcode 3, nxdomain </li> + <li> ENOTSUP: rcode 4, query type not implemented </li> + <li> ECONNREFUSED: rcode 5, operation refused by server </li> + <li> EIO: unknown rcode </li> + <li> any other value being set by <em>f</em> if it returns a failure code. </li> +</ul> + +</body> +</html> |