Initial implementation of dnslink
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3 changed files with 332 additions and 5 deletions
295
dnslink/dnslink.c
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295
dnslink/dnslink.c
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/*
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Package dnslink implements a dns link resolver. dnslink is a basic
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standard for placing traversable links in dns itself. See dnslink.info
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A dnslink is a path link in a dns TXT record, like this:
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dnslink=/ipfs/QmR7tiySn6vFHcEjBeZNtYGAFh735PJHfEMdVEycj9jAPy
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For example:
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> dig TXT ipfs.io
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ipfs.io. 120 IN TXT dnslink=/ipfs/QmR7tiySn6vFHcEjBeZNtYGAFh735PJHfEMdVEycj9jAPy
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This package eases resolving and working with thse dns links. For example:
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import (
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dnslink "github.com/jbenet/go-dnslink"
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)
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link, err := dnslink.Resolve("ipfs.io")
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// link = "/ipfs/QmR7tiySn6vFHcEjBeZNtYGAFh735PJHfEMdVEycj9jAPy"
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It even supports recursive resolution. Suppose you have three domains with
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dnslink records like these:
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> dig TXT foo.com
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foo.com. 120 IN TXT dnslink=/dns/bar.com/f/o/o
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> dig TXT bar.com
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bar.com. 120 IN TXT dnslink=/dns/long.test.baz.it/b/a/r
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> dig TXT long.test.baz.it
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long.test.baz.it. 120 IN TXT dnslink=/b/a/z
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Expect these resolutions:
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dnslink.ResolveN("long.test.baz.it", 0) // "/dns/long.test.baz.it"
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dnslink.Resolve("long.test.baz.it") // "/b/a/z"
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dnslink.ResolveN("bar.com", 1) // "/dns/long.test.baz.it/b/a/r"
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dnslink.Resolve("bar.com") // "/b/a/z/b/a/r"
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dnslink.ResolveN("foo.com", 1) // "/dns/bar.com/f/o/o/"
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dnslink.ResolveN("foo.com", 2) // "/dns/long.test.baz.it/b/a/r/f/o/o/"
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dnslink.Resolve("foo.com") // "/b/a/z/b/a/r/f/o/o"
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*/
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#include <stdlib.h>
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#include <string.h>
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#include <netinet/in.h>
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#include <arpa/nameser.h>
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#include <resolv.h>
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#include "ipfs/namesys/namesys.h"
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#define IPFS_DNSLINK_C
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#include "ipfs/dnslink/dnslink.h"
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#include "ipfs/cid/cid.h"
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#include "ipfs/path/path.h"
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// ipfs_dnslink_resolve resolves the dnslink at a particular domain. It will
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// recursively keep resolving until reaching the defaultDepth of Resolver. If
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// the depth is reached, ipfs_dnslink_resolve will return the last value
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// retrieved, and ErrResolveLimit. If TXT records are found but are not valid
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// dnslink records, ipfs_dnslink_resolve will return ErrInvalidDNSLink.
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// ipfs_dnslink_resolve will check every TXT record returned. If resolution
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// fails otherwise, ipfs_dnslink_resolve will return ErrResolveFailed
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int ipfs_dnslink_resolve (char **p, char *domain)
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{
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return ipfs_dnslink_resolve_n (p, domain, DefaultDepthLimit);
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}
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// ipfs_dnslink_lookup_txt is a function that looks up a TXT record in some dns resolver.
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// This is useful for testing or passing your own dns resolution process, which
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// could take into account non-standard TLDs like .bit, .onion, .ipfs, etc.
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int (*ipfs_dnslink_lookup_txt)(char ***txt, char *name) = NULL;
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// ipfs_dnslink_resolve_n is just like Resolve, with the option to specify a
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// maximum resolution depth.
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int ipfs_dnslink_resolve_n (char **p, char *d, int depth)
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{
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int err, i, l;
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char *rest, **link, tail[500], buf[500], domain[500];
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char dns_prefix[] = "/dns/";
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domain[sizeof(domain)-1] = '\0';
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strncpy (domain, d, sizeof(domain) - 1);
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for (i=0 ; i < depth ; i++) {
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err = ipfs_dnslink_resolve_once (&link, domain);
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if (err) {
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return err;
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}
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// if does not have /dns/ as a prefix, done.
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if (memcmp (*link, dns_prefix, sizeof(dns_prefix) - 1)!=0) {
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l = strlen(*link) + strlen(tail);
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*p = malloc(l + 1);
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if (!*p) {
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free(*link);
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free(link);
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return ErrAllocFailed;
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}
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*p[l] = '\0';
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strncpy(*p, *link, l);
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free(*link);
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free(link);
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strncat(*p, tail, l - strlen(*p));
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return 0; // done
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}
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// keep resolving
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err = ipfs_dnslink_parse_link_domain (&d, &rest, *link);
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free (*link);
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free (link);
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if (err) {
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*p = NULL;
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return err;
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}
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strncpy (domain, d, sizeof(domain) - 1);
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free (d);
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strncpy (buf, tail, sizeof(buf) - 1);
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strncpy (tail, rest, sizeof(tail) - 1);
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strncat (tail, buf, sizeof(tail) - 1 - strlen(tail));
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}
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strncpy (buf, tail, sizeof(buf) - 1);
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strncpy (tail, dns_prefix, sizeof(tail) - 1);
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strncat (tail, domain, sizeof(tail) - 1 - strlen(tail));
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strncat (tail, buf, sizeof(tail) - 1 - strlen(tail));
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return ErrResolveLimit;
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}
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// lookup using libresolv -lresolv
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int ipfs_dnslink_resolv_lookupTXT(char ***txt, char *domain)
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{
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char buf[4096], *p;
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int responseLength;
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int i, l, n = 0;
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ns_msg query_parse_msg;
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ns_rr query_parse_rr;
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u_char responseByte[4096];
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// Use res_query from libresolv to retrieve TXT record from DNS server.
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if ((responseLength = res_query(domain,C_IN,T_TXT,responseByte,sizeof(responseByte))) < 0 ||
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ns_initparse(responseByte,responseLength,&query_parse_msg) < 0) {
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return ErrResolveFailed;
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} else {
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l = sizeof (buf);
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buf[--l] = '\0';
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p = buf;
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// save every TXT record to buffer separating with a \0
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for (i=0 ; i < ns_msg_count(query_parse_msg,ns_s_an) ; i++) {
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if (ns_parserr(&query_parse_msg,ns_s_an,i,&query_parse_rr)) {
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return ErrResolveFailed;
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} else {
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char *rdata = ns_rr_rdata(query_parse_rr);
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memcpy(p, rdata+1, *rdata); // first byte is record length
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p += *rdata; // update pointer
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*p++ = '\0'; // mark end-of-record and update pointer to next record.
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n++; // update record count
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}
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}
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// allocate array for all records + NULL pointer terminator.
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*txt = calloc(n+1, sizeof(void*));
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if (!*txt) {
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return ErrAllocFailed;
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}
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l = p - buf; // length of all records in buffer.
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p = malloc(l); // allocate memory that will be used as string data at *txt array.
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if (!p) {
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free(*txt);
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*txt = NULL;
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return ErrAllocFailed;
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}
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memcpy(p, buf, l); // transfer from buffer to allocated memory.
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for (i = 0 ; i < n ; i++) {
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*txt[i] = p; // save position of current record at *txt array.
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p = memchr(p, '\0', l - (p - *txt[0])) + 1; // find next record position after next \0
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}
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}
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return 0;
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}
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// ipfs_dnslink_resolve_once implements resolver.
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int ipfs_dnslink_resolve_once (char ***p, char *domain)
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{
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int err, i;
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char **txt;
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if (!p || !domain) {
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return ErrInvalidParam;
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}
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*p = NULL;
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if (!ipfs_isdomain_is_domain (domain)) {
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return ErrInvalidDomain;
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}
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if (!ipfs_dnslink_lookup_txt) { // if not set
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ipfs_dnslink_lookup_txt = ipfs_dnslink_resolv_lookupTXT; // use default libresolv
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}
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err = ipfs_dnslink_lookup_txt (&txt, domain);
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if (err) {
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return err;
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}
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err = ErrResolveFailed;
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for (i=0 ; txt[i] ; i++) {
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err = ipfs_dnslink_parse_txt(*p, txt[i]);
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if (!err) {
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break;
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}
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}
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free(*txt);
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free(txt);
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return err;
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}
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// ipfs_dnslink_parse_txt parses a TXT record value for a dnslink value.
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// The TXT record must follow the dnslink format:
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// TXT dnslink=<path>
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// TXT dnslink=/foo/bar/baz
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// ipfs_dnslink_parse_txt will return ErrInvalidDNSLink if parsing fails.
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int ipfs_dnslink_parse_txt (char **path, char *txt)
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{
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char **parts;
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if (!path || !txt) {
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return ErrInvalidParam;
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}
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parts = ipfs_path_split_n (txt, "=", 2);
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if (!parts) {
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return ErrAllocFailed;
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}
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if (ipfs_path_segments_length (parts) == 2 && strcmp(parts[0], "dnslink")==0 && memcmp(parts[1], "/", 1)==0) {
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*path = ipfs_path_clean_path(parts[1]);
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if (path) {
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ipfs_path_free_segments (&parts);
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return 0;
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}
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}
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ipfs_path_free_segments (&parts);
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*path = NULL;
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return ErrInvalidDNSLink;
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}
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// ipfs_dnslink_parse_link_domain parses a domain from a dnslink path.
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// The link path must follow the dnslink format:
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// /dns/<domain>/<path>
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// /dns/ipfs.io
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// /dns/ipfs.io/blog/0-hello-worlds
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// ipfs_dnslink_parse_link_domain will return ErrInvalidDNSLink if parsing
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// fails, and ErrInvalidDomain if the domain is not valid.
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int ipfs_dnslink_parse_link_domain (char **domain, char**rest, char *txt)
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{
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char **parts;
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int parts_len;
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if (!domain || !rest || !txt) {
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return ErrInvalidParam;
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}
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*domain = *rest = NULL;
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parts = ipfs_path_split_n (txt, "/", 4);
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parts_len = ipfs_path_segments_length(parts);
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if (!parts || parts_len < 3 || parts[0][0]!='\0' || strcmp(parts[1], "dns") != 0) {
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return ErrInvalidDNSLink;
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}
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if (! ipfs_isdomain_is_domain (parts[2])) {
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ipfs_path_free_segments (&parts);
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return ErrInvalidDomain;
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}
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*domain = malloc(strlen (parts[2]) + 1);
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if (!*domain) {
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ipfs_path_free_segments (&parts);
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return ErrAllocFailed;
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}
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strcpy(*domain, parts[2]);
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if (parts_len > 3) {
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*rest = malloc(strlen (parts[3]) + 1);
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if (!*rest) {
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ipfs_path_free_segments (&parts);
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free (*domain);
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*domain = NULL;
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return ErrAllocFailed;
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}
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strcpy(*rest, parts[3]);
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}
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return 0;
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}
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26
include/ipfs/dnslink/dnslink.h
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26
include/ipfs/dnslink/dnslink.h
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#ifndef DNSLINK_H
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#define DNSLINK_H
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#include "ipfs/errs.h"
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// DefaultDepthLimit controls how many dns links to resolve through before
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// returning. Users can override this default.
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#ifndef DefaultDepthLimit
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#define DefaultDepthLimit 16
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#endif
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// MaximumDepthLimit governs the max number of recursive resolutions.
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#ifndef MaximumDepthLimit
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#define MaximumDepthLimit 256
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#endif
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#ifndef IPFS_DNSLINK_C
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extern int (*ipfs_dnslink_lookup_txt)(char ***, char *);
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#endif // IPFS_DNSLINK_C
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int ipfs_dnslink_resolve (char **p, char *domain);
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int ipfs_dnslink_resolve_n (char **p, char *d, int depth);
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int ipfs_dnslink_resolv_lookupTXT(char ***txt, char *domain);
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int ipfs_dnslink_resolve_once (char ***p, char *domain);
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int ipfs_dnslink_parse_txt (char **path, char *txt);
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int ipfs_dnslink_parse_link_domain (char **domain, char**rest, char *txt);
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#endif // DNSLINK_H
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@ -1,5 +1,5 @@
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#ifndef IPFS_ERRS_H
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#define IPFS_ERRS_H
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#define IPFS_ERRS_H
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char *Err[] = {
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NULL,
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"unrecognized validity type",
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"not a valid proquint string",
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"not a valid domain name",
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"not a valid dnslink entry"
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"not a valid dnslink entry",
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// ErrBadPath is returned when a given path is incorrectly formatted
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"invalid 'ipfs ref' path",
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// Paths after a protocol must contain at least one component
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"path must contain at least one component",
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"TODO: ErrCidDecode",
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NULL,
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"no link named %s under %s"
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"no link named %s under %s",
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"ErrInvalidParam",
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// ErrResolveLimit is returned when a recursive resolution goes over
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// the limit.
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"resolve depth exceeded"
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};
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enum {
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@ -36,11 +40,13 @@
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ErrUnrecognizedValidity,
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ErrInvalidProquint,
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ErrInvalidDomain,
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ErrInvalidDNSLink
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ErrInvalidDNSLink,
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ErrBadPath,
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ErrNoComponents,
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ErrCidDecode,
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ErrNoLink,
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ErrNoLinkFmt
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ErrNoLinkFmt,
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ErrInvalidParam,
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ErrResolveLimit
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} ErrsIdx;
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#endif // IPFS_ERRS_H
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