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net/netip: Prefix.Bits and Prefix.IsValid are inconsistent #54525

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dsnet opened this issue Aug 18, 2022 · 2 comments
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net/netip: Prefix.Bits and Prefix.IsValid are inconsistent #54525

dsnet opened this issue Aug 18, 2022 · 2 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@dsnet
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dsnet commented Aug 18, 2022

The documentation for Prefix.Bits says:

Bits returns p's prefix length.
It reports -1 if invalid.

The documentation for Prefix.IsValid says:

IsValid reports whether p.Bits() has a valid range for p.IP().
If p.Addr() is the zero Addr, IsValid returns false.
Note that if p is the zero Prefix, then p.IsValid() == false.

Thus, we expect the zero Prefix to be invalid, but also report -1 bits.
Instead, we get 0 bits.

https://go.dev/play/p/rsc2Uy_jMX1

Either the behavior or the documentation should be adjusted.

\cc @bradfitz @josharian
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Change https://go.dev/cl/424816 mentions this issue: net/netip: report -1 from Prefix.Bits() when Prefix is invalid

@joedian joedian added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Aug 19, 2022
@seankhliao seankhliao added this to the Unplanned milestone Aug 20, 2022
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Change https://go.dev/cl/425035 mentions this issue: net/netip: fix invalid representation of Prefix

johanbrandhorst pushed a commit to Pryz/go that referenced this issue Feb 12, 2023
@dsnet @johanbrandhorst
net/netip: fix invalid representation of Prefix
6dd422e 
For a given Addr, ensure there is exactly one invalid representation.
This allows invalid representations to be safely comparable.
To ensure that the zero value of Prefix is invalid,
we modify the encoding of bits to simply be the bit count plus one.

Since Addr is immutable, we check in the PrefixFrom constructor that
the provided Addr is valid and only store a non-zero bits length if so.
IsValid is simplified to just checking whether bitsPlusOne is non-zero.

Fixes golang#54525

Change-Id: I9244cae2fd160cc9c81d007866992df2e422d3b9
Reviewed-on: https://go-review.googlesource.com/c/go/+/425035
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Joseph Tsai <joetsai@digital-static.net>
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