1package dns
2
3import (
4	"bufio"
5	"io"
6	"os"
7	"strconv"
8	"strings"
9)
10
11// ClientConfig wraps the contents of the /etc/resolv.conf file.
12type ClientConfig struct {
13	Servers  []string // servers to use
14	Search   []string // suffixes to append to local name
15	Port     string   // what port to use
16	Ndots    int      // number of dots in name to trigger absolute lookup
17	Timeout  int      // seconds before giving up on packet
18	Attempts int      // lost packets before giving up on server, not used in the package dns
19}
20
21// ClientConfigFromFile parses a resolv.conf(5) like file and returns
22// a *ClientConfig.
23func ClientConfigFromFile(resolvconf string) (*ClientConfig, error) {
24	file, err := os.Open(resolvconf)
25	if err != nil {
26		return nil, err
27	}
28	defer file.Close()
29	return ClientConfigFromReader(file)
30}
31
32// ClientConfigFromReader works like ClientConfigFromFile but takes an io.Reader as argument
33func ClientConfigFromReader(resolvconf io.Reader) (*ClientConfig, error) {
34	c := new(ClientConfig)
35	scanner := bufio.NewScanner(resolvconf)
36	c.Servers = make([]string, 0)
37	c.Search = make([]string, 0)
38	c.Port = "53"
39	c.Ndots = 1
40	c.Timeout = 5
41	c.Attempts = 2
42
43	for scanner.Scan() {
44		if err := scanner.Err(); err != nil {
45			return nil, err
46		}
47		line := scanner.Text()
48		f := strings.Fields(line)
49		if len(f) < 1 {
50			continue
51		}
52		switch f[0] {
53		case "nameserver": // add one name server
54			if len(f) > 1 {
55				// One more check: make sure server name is
56				// just an IP address.  Otherwise we need DNS
57				// to look it up.
58				name := f[1]
59				c.Servers = append(c.Servers, name)
60			}
61
62		case "domain": // set search path to just this domain
63			if len(f) > 1 {
64				c.Search = make([]string, 1)
65				c.Search[0] = f[1]
66			} else {
67				c.Search = make([]string, 0)
68			}
69
70		case "search": // set search path to given servers
71			c.Search = make([]string, len(f)-1)
72			for i := 0; i < len(c.Search); i++ {
73				c.Search[i] = f[i+1]
74			}
75
76		case "options": // magic options
77			for i := 1; i < len(f); i++ {
78				s := f[i]
79				switch {
80				case len(s) >= 6 && s[:6] == "ndots:":
81					n, _ := strconv.Atoi(s[6:])
82					if n < 0 {
83						n = 0
84					} else if n > 15 {
85						n = 15
86					}
87					c.Ndots = n
88				case len(s) >= 8 && s[:8] == "timeout:":
89					n, _ := strconv.Atoi(s[8:])
90					if n < 1 {
91						n = 1
92					}
93					c.Timeout = n
94				case len(s) >= 9 && s[:9] == "attempts:":
95					n, _ := strconv.Atoi(s[9:])
96					if n < 1 {
97						n = 1
98					}
99					c.Attempts = n
100				case s == "rotate":
101					/* not imp */
102				}
103			}
104		}
105	}
106	return c, nil
107}
108
109// NameList returns all of the names that should be queried based on the
110// config. It is based off of go's net/dns name building, but it does not
111// check the length of the resulting names.
112func (c *ClientConfig) NameList(name string) []string {
113	// if this domain is already fully qualified, no append needed.
114	if IsFqdn(name) {
115		return []string{name}
116	}
117
118	// Check to see if the name has more labels than Ndots. Do this before making
119	// the domain fully qualified.
120	hasNdots := CountLabel(name) > c.Ndots
121	// Make the domain fully qualified.
122	name = Fqdn(name)
123
124	// Make a list of names based off search.
125	names := []string{}
126
127	// If name has enough dots, try that first.
128	if hasNdots {
129		names = append(names, name)
130	}
131	for _, s := range c.Search {
132		names = append(names, Fqdn(name+s))
133	}
134	// If we didn't have enough dots, try after suffixes.
135	if !hasNdots {
136		names = append(names, name)
137	}
138	return names
139}
140