From: Miek Gieben <miekg@NLnetLabs.nl>
Date: Tue, 15 Mar 2005 12:34:24 +0000 (+0000)
Subject: added the whole mx program
X-Git-Tag: release-0.50~246
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f003ca1f2bc65fbfbf43b8d327b7d3b907171f63;p=thirdparty%2Fldns.git

added the whole mx program
---

diff --git a/doc/tutorial b/doc/tutorial
index a0d71a09..1abb6094 100644
--- a/doc/tutorial
+++ b/doc/tutorial
@@ -77,5 +77,106 @@ In this tutorial we will make a small application which takes a domain name
 and looks up the MX records for this domain. We will call this program:
 'mx'.
 
-todo
+The general flow of the program is as follows:
+1. make a resolver structure 
+2. use the resolver to generate an mx query
+3. print the result.
+
+First we begin with some boiler plating:
+<code>
+      1 /*
+      2  * mx is a small programs that prints out the mx records
+      3  * for a particulary domain
+      4  */
+      5 
+      6 #include <stdio.h>
+      7 #include <config.h>
+      8 #include <ldns/dns.h>
+      9 
+     10 int
+     11 usage(FILE *fp, char *prog) {
+     12         fprintf(fp, "%s zone\n", prog);
+     13         fprintf(fp, "  print out the mx for the domain\n");
+     14         return 0;
+     15 }
+     16 
+</code>
+
+Line 9 is the important one here, this includes all the stuff we need
+from ldns. 
+
+<code>
+     17 int
+     18 main(int argc, char *argv[])
+     19 {
+     20         ldns_resolver *res;
+     21         ldns_rdf *domain;
+     22         ldns_pkt *p;
+     23         ldns_rr_list *mx;
+     24         char *domstr;
+     25 
+     26         if (argc != 2) {
+     27                 usage(stdout, argv[0]);
+     28                 exit(1);
+     29         } else {
+     30                 /* create a rdf from the command line arg */
+     31                 domain = ldns_dname_new_frm_str(argv[1]);
+     32                 if (!domain) {
+     33                         usage(stdout, argv[0]);
+     34                         exit(1);
+     35                 }
+     36                 /* transform it in a string for the error msg (if needed) */
+     37                 domstr = ldns_rdf2str(domain);
+     38         }
+     39 
+     40         /* create a new resolver from /etc/resolv.conf */
+     41         res = ldns_resolver_new_frm_file(NULL);
+     42         if (!res) {
+     43                 free(domstr);
+     44                 exit(1);
+     45         }
+     46 
+     47         /* use the resolver to send it a query for the mx 
+     48          * records of the domain given on the command line
+     49          */
+     50         p = ldns_resolver_query(res, domain, LDNS_RR_TYPE_MX, LDNS_RR_CLASS_IN, LDNS_RD);
+     51         if (!p)  {
+     52                 free(domstr);
+     53                 exit(1);
+     54         } else {
+     55                 /* retrieve the MX records from the answer section of that
+     56                  * packet
+     57                  */
+     58                 mx = ldns_pkt_rr_list_by_type(p, LDNS_RR_TYPE_MX, LDNS_SECTION_ANSWER);
+     59                 if (!mx) {
+     60                         fprintf(stderr,
+     61                                         " *** invalid answer name %s after MX query for %s\n        ",
+     62                                         domstr, domstr);
+     63                         free(domstr);
+     64                         exit(1);
+     65                 } else {
+     66                         /* sort the list nicely */
+     67                         ldns_rr_list_sort(mx);
+     68                         /* print the rrlist to stdout */
+     69                         ldns_rr_list_print(stdout, mx);
+     70                 }
+     71         }
+     72         return 0;
+     73 }
+</code>
+
+</code>
+
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