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fix: fallback to tcp if response is truncated 

Based on a report `doggo txt google.com  @udp://1.1.1.1` failed.
This record had 704 bytes as the message length however the response
gets truncated if it exceeds 512 bytes with UDP.

`dig` transparently fallbacks to `tcp`, so this commit adds the same
mechanism.
pull/41/head v0.5.3
Karan Sharma 2022-06-02 14:59:27 +05:30
parent 53f7b70af4
commit ea7cb3c6cd
1 changed files with 18 additions and 0 deletions
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18
pkg/resolvers/classic.go
View File

@ -79,6 +79,24 @@ func (r *ClassicResolver) Lookup(question dns.Question) (Response, error) {
if err != nil { if err != nil {
return rsp, err return rsp, err
} }
// In case the response size exceeds 512 bytes (can happen with lot of TXT records),
// fallback to TCP as with UDP the response is truncated. Fallback mechanism is in-line with `dig`.
if in.Truncated {
switch r.client.Net {
case "udp":
r.client.Net = "tcp"
case "udp4":
r.client.Net = "tcp4"
case "udp6":
r.client.Net = "tcp6"
default:
r.client.Net = "tcp"
}
r.resolverOptions.Logger.WithField("protocol", r.client.Net).Debug("Response truncated; retrying now")
return r.Lookup(question)
}
// Pack questions in output. // Pack questions in output.
for _, q := range msg.Question { for _, q := range msg.Question {
ques := Question{ ques := Question{