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copy rrs (#4416) 

* Revert "make copies of RRs before returning them (#4409)"

This reverts commit 8b2ff6c388.

* Document copying responses

See #4409 and the comments. This documents that issue, but doesn't
change the in-tree plugins just yet.

Signed-off-by: Miek Gieben <miek@miek.nl>

* Update plugin.md

Co-authored-by: Chris O'Haver <cohaver@infoblox.com>

Co-authored-by: Chris O'Haver <cohaver@infoblox.com>
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Miek Gieben 2021-01-28 16:50:35 +01:00 committed by GitHub
parent d8d2c16905
commit 60e1490ed6
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2 changed files with 10 additions and 6 deletions
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9
plugin.md
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@ -131,6 +131,15 @@ The `fallthrough` directive should optionally accept a list of zones. Only queri
in one of those zones should be allowed to fallthrough. See `plugin/pkg/fallthrough` for the
implementation.
## Mutating a Response
Using a custom `ResponseWriter`, a plugin can mutate a response when another plugin further down the chain writes the response to the client.
If a plugin mutates a response it MUST make a copy of the entire response before doing so. A
response is a pointer to a `dns.Msg` and as such you will be manipulating the original response,
which could have been generated from a data store. E.g. the *file* plugin creates a response that
the *rewrite* plugin then rewrites; not copying the data, means it's **also** mutating the data of
the *file*'s data store. A response can be copied by using the `Copy()` method.
## General Guidelines
Some general guidelines:

7
plugin/file/lookup.go
View File

@ -171,12 +171,7 @@ func (z *Zone) Lookup(ctx context.Context, state request.Request, qname string)
return z.externalLookup(ctx, state, elem, rrs)
}
treeRRs := elem.Type(qtype)
// make a copy of the element RRs to prevent response writers from mutating the tree
rrs := make([]dns.RR, len(treeRRs))
for i, rr := range treeRRs {
rrs[i] = dns.Copy(rr)
}
rrs := elem.Type(qtype)
// NODATA
if len(rrs) == 0 {