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Properly report DNSLink errors #12

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merged 2 commits into from
Apr 21, 2021
Merged

Properly report DNSLink errors #12

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4dedb19
Properly report DNSLink errors
gammazero Apr 20, 2021
5657d7b
Keep original behavior for TXT record lookup precedence
gammazero Apr 21, 2021
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9 changes: 0 additions & 9 deletions base.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,6 @@ package namesys

import (
"context"
"fmt"
"strings"
"time"

Expand Down Expand Up @@ -37,14 +36,6 @@ func resolve(ctx context.Context, r resolver, name string, options opts.ResolveO
}
}

if err == ErrResolveFailed {
i := len(name) - 1
for i >= 0 && name[i] != '/' {
i--
}
// Wrap error so that it can be tested if it is a ErrResolveFailed
err = fmt.Errorf("%w: %q is missing a DNSLink record (https://docs.ipfs.io/concepts/dnslink/)", ErrResolveFailed, name[i+1:])
}
return p, err
}

Expand Down
28 changes: 27 additions & 1 deletion dns.go
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Original file line number Diff line number Diff line change
Expand Up @@ -88,6 +88,7 @@ func (r *DNSResolver) resolveOnceAsync(ctx context.Context, name string, options

go func() {
defer close(out)
var rootResErr, subResErr error
for {
select {
case subRes, ok := <-subChan:
Expand All @@ -100,6 +101,7 @@ func (r *DNSResolver) resolveOnceAsync(ctx context.Context, name string, options
emitOnceResult(ctx, out, onceResult{value: p, err: err})
return
}
subResErr = subRes.error
case rootRes, ok := <-rootChan:
if !ok {
rootChan = nil
Expand All @@ -108,11 +110,26 @@ func (r *DNSResolver) resolveOnceAsync(ctx context.Context, name string, options
if rootRes.error == nil {
p, err := appendPath(rootRes.path)
emitOnceResult(ctx, out, onceResult{value: p, err: err})
return
}
rootResErr = rootRes.error
case <-ctx.Done():
return
}
if subChan == nil && rootChan == nil {
// If here, then both lookups failed
//
// If both lookup errors were due to no TXT records with a
// dnslink, then output a more specific error message
if rootResErr == ErrResolveFailed && subResErr == ErrResolveFailed {
i := len(name) - 1
for i >= 0 && name[i] != '/' {
i--
}
// Wrap error so that it can be tested if it is a ErrResolveFailed
err := fmt.Errorf("%w: %q is missing a DNSLink record (https://docs.ipfs.io/concepts/dnslink/)", ErrResolveFailed, name[i+1:])
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@aschmahmann aschmahmann Apr 21, 2021 •
edited
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Does this mean "is missing a DNSLink record, or the host could not be found" (or some phrasing like that)?

It looks like we're also covering dnsErr.IsNotFound which is "host could not be found" https://golang.org/pkg/net/#DNSError

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This error covers both. So, r.lookupTXT(name) returns a host not found error when DNS does not return a TXT record, but in either case (1. Has TXT records, but none contain DNSLink. 2. No TXT records returned) it is correct that name is missing a DNSLink record.

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If your machine is offline to you also get a host not found?

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No. You do not. I determine that by checking the dnsErr.IsNotFound flag here. If you are offline, then IsNotFound is false.

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If you are offline, then IsNotFound is false.

The DNSError struct documentation is kind of sparse ("host not found" seems like it could mean a bunch of things). If you've tested that IsNotFound doesn't apply when you cannot reach DNS then 👍

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Yes tested

emitOnceResult(ctx, out, onceResult{err: err})
}
return
}
}
Expand All @@ -126,7 +143,14 @@ func workDomain(r *DNSResolver, name string, res chan lookupRes) {

txt, err := r.lookupTXT(name)
if err != nil {
// Error is != nil
if dnsErr, ok := err.(*net.DNSError); ok {
// If no TXT records found, return same error as when no text
// records contain dnslink. Otherwise, return the actual error.
if dnsErr.IsNotFound {
err = ErrResolveFailed
}
}
// Could not look up any text records for name
res <- lookupRes{"", err}
return
}
Expand All @@ -138,6 +162,8 @@ func workDomain(r *DNSResolver, name string, res chan lookupRes) {
return
}
}

// There were no TXT records with a dnslink
res <- lookupRes{"", ErrResolveFailed}
}

Expand Down