nuget install / nuget restore extracts .signature.p7s to disk; collides when multiple signed packages share an install root

NuGet Product Used

NuGet.exe

Product Version

nuget 7.3.0

Worked before?

No

Impact

It's more difficult to complete my work

Repro Steps & Context

Minimal repro

1. Author-sign two .nupkg files using dotnet sign code azure-key-vault (or any tool that wraps NuGet.Packaging.Signing.SigningUtility). Call them pkg-a.1.0.0.nupkg and pkg-b.1.0.0.nupkg. Each will contain .signature.p7s at the ZIP root.
2. Push both to any NuGet feed.
3. On a consumer, run:

   nuget.exe install pkg-a -Source <feed> -OutputDirectory C:\extracted -PackageSaveMode nupkg -ExcludeVersion
   nuget.exe install pkg-b -Source <feed> -OutputDirectory C:\extracted -PackageSaveMode nupkg -ExcludeVersion
   

4. Inspect C:\extracted\pkg-a\ and C:\extracted\pkg-b\. Both contain .signature.p7s at the directory root, despite NuGet correctly stripping every other piece of NuGet metadata (_rels/, package/, [Content_Types].xml, *.sha512, *.nupkg.metadata).

What I expected

.signature.p7s is part of the NuGet package signature spec (NuGet/NuGet.Client/src/NuGet.Core/NuGet.Packaging/Signing/Specifications/SigningSpecificationsV1.cs, hardcoded as private const string _signaturePath = ".signature.p7s"). It is metadata, not content. It belongs in the same exclude list as the other signing/structural metadata files.

The expected behavior: NuGet client verifies the signature during restore, then strips .signature.p7s from the extracted output, just as it strips _rels/, package/, [Content_Types].xml, *.sha512, and *.nupkg.metadata.

What I got

.signature.p7s extracted to disk alongside the package payload. For consumers that do not merge multiple packages into one directory, this is harmless cruft. For consumers that do merge (e.g. vcpkg's --x-install-root model), any second package collides on the path:

error: The following files are already installed in
       <install-root>/x64-windows
       and are in conflict with vcpkg-cmake:x64-windows
       Installed by vcpkg-cmake-config:x64-windows: .signature.p7s

Where the omission lives (NuGet source)

NuGet.Packaging.PackageExtraction.PackageHelper.ExcludePaths (https://github.com/NuGet/NuGet.Client/blob/dev/src/NuGet.Core/NuGet.Packaging/PackageExtraction/PackageHelper.cs) currently filters:

_rels/
package/
[Content_Types].xml
*.sha512
*.nupkg.metadata

It does NOT filter .signature.p7s. Adding it is a one-line change. The signature blob has already served its verification purpose by the time extraction runs; there is no consumer use case for reading it from disk after restore.

Why this matters beyond vcpkg

Anyone whose consumer-side workflow assumes "extracted contents == package payload" hits this. vcpkg is the public example we tripped on. Internal build systems that consume NuGet feeds as opaque archive storage (and there are several — anything that uses NuGet as transport for non-.NET artifacts) would hit it the same way. The fix shifts the responsibility of stripping .signature.p7s from "every consumer that cares" to "the NuGet client, once, where it belongs."

Suggested fix (one-line change)

In NuGet.Packaging.PackageExtraction.PackageHelper.ExcludePaths, append .signature.p7s to the static array of excluded paths. (.signature.p7s is the sole signature-file path constant in the spec, defined as _signaturePath in SigningSpecificationsV1.cs.) Signature verification still runs against the in-memory ZIP entry before extraction; nothing else needs to change.

Verbose Logs

PS> & vcpkg.exe install --triplet x64-windows-v143-hybrid --binarysource="clear;nuget,vcpkg-deps,read" ...
Detecting compiler hash for triplet x64-windows-v143-hybrid...
Restored 0 package(s) from C:\Users\runneradmin\AppData\Local\vcpkg\archives in 67.2 us. Use --debug to see more details.
Installing 1/3 vcpkg-cmake-config:x64-windows@2024-05-23#0...
Restored 0 package(s) from NuGet feed: vcpkg-deps in 245.7 ms. Use --debug to see more details.
Installing 2/3 vcpkg-cmake:x64-windows@2024-04-23#0...
error: The following files are already installed in
       <redacted>/packages/vcpkg/x64-windows-v143-hybrid/x64-windows
       and are in conflict with vcpkg-cmake:x64-windows
       Installed by vcpkg-cmake-config:x64-windows: .signature.p7s

Start in NuGet.Packaging/PackageExtraction/PackageHelper.cs at PackageHelper.ExcludePaths, then read the .signature.p7s definition in SigningSpecificationsV1.cs. Confirm extraction of signed packages omits the signature entry while signature verification still occurs before extraction.