doggo/internal/app/nameservers.go

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package app
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import (
"fmt"
"net"
"net/url"
"github.com/mr-karan/doggo/pkg/config"
"github.com/mr-karan/doggo/pkg/models"
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)
// LoadNameservers reads all the user given
// nameservers and loads to App.
func (app *App) LoadNameservers() error {
for _, srv := range app.QueryFlags.Nameservers {
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ns, err := initNameserver(srv)
if err != nil {
return fmt.Errorf("error parsing nameserver: %s", srv)
}
// check if properly initialised.
if ns.Address != "" && ns.Type != "" {
app.Nameservers = append(app.Nameservers, ns)
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}
}
// Set `ndots` to the user specified value.
app.ResolverOpts.Ndots = app.QueryFlags.Ndots
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// fallback to system nameserver
// in case no nameserver is specified by user.
if len(app.Nameservers) == 0 {
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ns, ndots, search, err := getDefaultServers()
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if err != nil {
return fmt.Errorf("error fetching system default nameserver")
}
// `-1` indicates the flag is not set.
// use from config if user hasn't specified any value.
if app.ResolverOpts.Ndots == -1 {
app.ResolverOpts.Ndots = ndots
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}
if len(search) > 0 && app.QueryFlags.UseSearchList {
app.ResolverOpts.SearchList = search
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}
app.Nameservers = append(app.Nameservers, ns...)
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}
// if the user hasn't given any override of `ndots` AND has
// given a custom nameserver. Set `ndots` to 1 as the fallback value
if app.ResolverOpts.Ndots == -1 {
app.ResolverOpts.Ndots = 0
}
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return nil
}
func initNameserver(n string) (models.Nameserver, error) {
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// Instantiate a UDP resolver with default port as a fallback.
ns := models.Nameserver{
Type: models.UDPResolver,
Address: net.JoinHostPort(n, models.DefaultUDPPort),
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}
u, err := url.Parse(n)
if err != nil {
return ns, err
}
if u.Scheme == "https" {
ns.Type = models.DOHResolver
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ns.Address = u.String()
}
if u.Scheme == "tls" {
ns.Type = models.DOTResolver
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if u.Port() == "" {
ns.Address = net.JoinHostPort(u.Hostname(), models.DefaultTLSPort)
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} else {
ns.Address = net.JoinHostPort(u.Hostname(), u.Port())
}
}
if u.Scheme == "tcp" {
ns.Type = models.TCPResolver
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if u.Port() == "" {
ns.Address = net.JoinHostPort(u.Hostname(), models.DefaultTCPPort)
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} else {
ns.Address = net.JoinHostPort(u.Hostname(), u.Port())
}
}
if u.Scheme == "udp" {
ns.Type = models.UDPResolver
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if u.Port() == "" {
ns.Address = net.JoinHostPort(u.Hostname(), models.DefaultUDPPort)
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} else {
ns.Address = net.JoinHostPort(u.Hostname(), u.Port())
}
}
return ns, nil
}
func getDefaultServers() ([]models.Nameserver, int, []string, error) {
dnsServers, ndots, search, err := config.GetDefaultServers()
if err != nil {
return nil, 0, nil, err
}
servers := make([]models.Nameserver, 0, len(dnsServers))
for _, s := range dnsServers {
ns := models.Nameserver{
Type: models.UDPResolver,
Address: net.JoinHostPort(s, models.DefaultUDPPort),
}
servers = append(servers, ns)
}
return servers, ndots, search, nil
}