Regression when using Resolver::txt_lookup

[glts]

I have been using trust_dns_resolver::Resolver::txt_lookup successfully with version 0.20.4.

The same lookup now fails with version 0.21.0-alpha.4.

To reproduce:

use trust_dns_resolver::Resolver;

fn main() {
    let resolver = Resolver::default().unwrap();

    let name = "bmc.org";
    match resolver.txt_lookup(name) {
        Ok(lookup) => {
            for txt in lookup {
                eprintln!(
                    "<{:?}>",
                    txt.iter()
                        .map(|data| String::from_utf8_lossy(data))
                        .collect::<String>()
                );
            }
        }
        Err(e) => {
            eprintln!("error: {}", e);
        }
    }
}

Output with trust-dns-resolver 0.20.4:

<"docusign=5140f07f-9f9c-4561-8a94-e69761a38442">
<"OVrFqSjwZz9OshiM1LGcVWYjzhtYrg930HlRDNn43M3PFP0Vx3XSv2w0rNxzACUUtgmhp0iXx15yK18nnl0svg==">
<"ZOOM_verify_xJpoFs3nSDywDsvmMWygGg">
<"">
<"4FVu/Fi5/VTEsxj+08airJyjv1oKUMC6yFTlOfWCg3ol7HwVAu3lmZre+8UOrQXKpzgJ1vbe/zRUepCN7cnFJg==">
<"v*spf1 include:servers.mcsv.net ?all">
<"v=spf1 a mx include:us._netblocks.mimecast.com include:spf1.service.formassembly.com -all">
<"apple-domain-verification=UnyCDv1Ozqb0yjW7">
<"docusign=2d29c1de-6a95-474d-ada4-3b7c3ee40fa8">

Output with trust-dns-resolver 0.21.0-alpha.4:

error: no record found for name: bmc.org. type: TXT class: IN

I can reproduce this on two separate hosts (home and VPS).

[bluejekyll]

Thanks the for the report. I think there are two potential changes related to this: #1556 and #1562

I was able to reproduce this with the resolve command and when enabling debug, you can see that the difference between the two requests is that in the 0.20 version it fails the intial request, then reattempts with TCP. In the 0.21 (main) branch, it appears that the promotion to TCP resolution isn't attempted.

My guess is that this is due to the larger record response on all the TXT records, and it requires TCP (> 512 byte reponse).

@peterthejohnston, I think we're going to need to revisit some of those changes. @glts, thank you for finding this before we pushed the next release for 0.21.

[bluejekyll]

#1629 appears to resolve this. I want to make sure that we have a test case to reproduce this before merging.

[bluejekyll]

The patch for this was released today in v0.21.0-alpha.5.