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fix truncation bug (#2261)

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* fix truncation bug

* Generate records with generic RRs

* Remove SoundCloud from test name

* Comment for binary-search -1 adjustment

Explain why the binary search may have exited with
a reply size that is too large by one record.

* Refactor to remove sub variable

patch suggested by miek removes unnecessary sub
variable for removing a single line from the
reply.Extra length.
This commit is contained in:
stuart nelson
2018-11-03 11:01:56 +01:00
committed by Miek Gieben
parent 1ad002c9f3
commit cac6fe1d07
2 changed files with 49 additions and 11 deletions
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30
request/request.go
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@@ -250,18 +250,16 @@ func (r *Request) Scrub(reply *dns.Msg) *dns.Msg {
}
// Account for the OPT record that gets added in SizeAndDo(), subtract that length.
sub := 0
re := len(reply.Extra)
if r.Req.IsEdns0() != nil {
sub = optLen
size -= optLen
// re can never be 0 because we have an OPT RR.
re--
}
// subtract to make spaces for re-added EDNS0 OPT RR.
re := len(reply.Extra) - sub
size -= sub
l, m := 0, 0
origExtra := reply.Extra
for l < re {
for l <= re {
m = (l + re) / 2
reply.Extra = origExtra[:m]
rl = reply.Len()
@@ -278,13 +276,18 @@ func (r *Request) Scrub(reply *dns.Msg) *dns.Msg {
}
}
// We may come out of this loop with one rotation too many, m makes it too large, but m-1 works.
// The binary search only breaks on an exact match, which will be
// pretty rare. Normally, the loop will exit when l > re, meaning that
// in the previous iteration either:
// rl < size: no need to do anything.
// rl > size: the final size is too large, and if m > 0, the preceeding
// iteration the size was too small. Select that preceeding size.
if rl > size && m > 0 {
reply.Extra = origExtra[:m-1]
rl = reply.Len()
}
if rl < size {
if rl <= size {
r.SizeAndDo(reply)
return reply
}
@@ -292,7 +295,7 @@ func (r *Request) Scrub(reply *dns.Msg) *dns.Msg {
ra := len(reply.Answer)
l, m = 0, 0
origAnswer := reply.Answer
for l < ra {
for l <= ra {
m = (l + ra) / 2
reply.Answer = origAnswer[:m]
rl = reply.Len()
@@ -309,7 +312,12 @@ func (r *Request) Scrub(reply *dns.Msg) *dns.Msg {
}
}
// We may come out of this loop with one rotation too many, m makes it too large, but m-1 works.
// The binary search only breaks on an exact match, which will be
// pretty rare. Normally, the loop will exit when l > ra, meaning that
// in the previous iteration either:
// rl < size: no need to do anything.
// rl > size: the final size is too large, and if m > 0, the preceeding
// iteration the size was too small. Select that preceeding size.
if rl > size && m > 0 {
reply.Answer = origAnswer[:m-1]
// No need to recalc length, as we don't use it. We set truncated anyway. Doing