git: Add strict checks for supported extensions by pjbgf · Pull Request #1850 · go-git/go-git

pjbgf · 2026-02-16T16:56:06Z

The upstream Git enforces fail-safe heuristics to ensure that older git versions
will avoid handling repositories using extensions they are unaware of.

The logic is largely based on the value of core.repositoryformatversion. As per
official Git docs:

This version specifies the rules for operating on the on-disk repository data.
An implementation of git which does not understand a particular version
advertised by an on-disk repository MUST NOT operate on that repository;
doing so risks not only producing wrong results, but actually losing data.

Now go-git will ensure that:

The git.Open logic will verify and enforces the extension support rules.
go-git will keep track of built-in extensions that it supports.
Any extension that is Storer-specific (e.g. objectformat, reftables),
will be confirmed by the specific Storer via new x/storage.ExtensionChecker
interface. Failing to do so, it will be assumed that the extension is
unsupported and the git.Open operation will return an error.

This is a breaking change and it will force go-git to not be able to open
repositories that it in fact doesn't really support. Conversaly, the error
messages will be more useful (e.g. unknown extension vs object not found).

Upstream refs:

pjbgf · 2026-02-16T17:04:01Z

repository.go

+	err = verifyExtensions(s, cfg)
+	if err != nil {
+		return nil, err


@aymanbagabas following-up from the previous discussion on ObjectFormatGetter, this PR removes the need for that interface from a data corruption perspective.

As a separate change, I'll look into dropping the Getter/Setter.

Amazing! This looks much better!

Copilot

Pull request overview

This PR adds strict repository extension validation during git.Open, aligning go-git behavior with upstream Git’s fail-safe rules to avoid operating on repositories that declare unsupported/unknown extensions.

Changes:

Introduces x/storage.ExtensionChecker so storers can explicitly confirm support for storage-specific Git extensions.
Adds extension verification logic (verifyExtensions) and integrates it into Open.
Implements and tests SupportsExtension for memory and filesystem storers; adds repo-level tests for extension verification.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
`x/storage/storer.go`	Adds the `ExtensionChecker` interface for storage-specific extension support checks.
`repository_extensions.go`	Implements extension discovery + strict validation logic used during `Open`.
`repository_extensions_test.go`	Adds tests covering extension validation behavior across repo format versions.
`repository.go`	Calls `verifyExtensions` during `Open` (replacing prior objectformat-only heuristic).
`storage/memory/storage.go`	Implements `SupportsExtension` for in-memory storage (objectformat).
`storage/memory/storage_test.go`	Adds tests ensuring memory storage implements/behaves per `ExtensionChecker`.
`storage/filesystem/storage.go`	Implements `SupportsExtension` for filesystem storage (objectformat).
`storage/filesystem/storage_test.go`	Adds tests ensuring filesystem storage implements/behaves per `ExtensionChecker`.
`repository_test.go`	Adjusts server cleanup to ignore `srv.Close()` errors in one test.

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repository_extensions.go

repository_test.go

Git extensions may be Storer-specific, like reftables or objectformat. By implementing this interface, the Storers will be able to tell the core go-git precisely what extensions they support. Signed-off-by: Paulo Gomes <[email protected]>

Signed-off-by: Paulo Gomes <[email protected]>

The SHA256 implementation introduced a temporary ObjectFormatGetter interface that had two key goals: - Provide a way to access the ObjectFormat from a storer.Storer, without changing the existing API. - Be able to distinguish between storer.Storer implementations that support the objectformat extension. The PR go-git#1850 ensures that the storer.Storer being used supports the required objectformat. With that, this interface can be replaced by config.ConfigStorer, making the config the single source of truth for the objectformat. Signed-off-by: Paulo Gomes <[email protected]>

The upstream Git enforces fail-safe heuristics to ensure that older git versions will avoid handling repositories using extensions they are unaware of. The logic is largely based on the value of core.repositoryformatversion. As per official Git docs: > This version specifies the rules for operating on the on-disk repository data. > An implementation of git which does not understand a particular version > advertised by an on-disk repository MUST NOT operate on that repository; > doing so risks not only producing wrong results, but actually losing data. Now go-git will ensure that: - The git.Open logic will verify and enforces the extension support rules. - go-git will keep track of built-in extensions that it supports. - Any extension that is Storer-specific (e.g. objectformat, reftables), will be confirmed by the specific Storer via new x/storage.ExtensionChecker interface. Failing to do so, it will be assumed that the extension is unsupported and the Open operation will return an error. This is a breaking change and it will force go-git to not be able to open repositories that it in fact doesn't really support. Conversaly, the error messages will be more useful (e.g. unknown extension vs object not found). Upstream refs: - https://git-scm.com/docs/git-config#Documentation/git-config.txt-extensions - https://git-scm.com/docs/gitrepository-layout#_git_repository_format_versions Signed-off-by: Paulo Gomes <[email protected]>

The SHA256 implementation introduced a temporary ObjectFormatGetter interface that had two key goals: - Provide a way to access the ObjectFormat from a storer.Storer, without changing the existing API. - Be able to distinguish between storer.Storer implementations that support the objectformat extension. The PR go-git#1850 ensures that the storer.Storer being used supports the required objectformat. With that, this interface can be replaced by config.ConfigStorer, making the config the single source of truth for the objectformat. Signed-off-by: Paulo Gomes <[email protected]>

Copilot AI review requested due to automatic review settings February 16, 2026 16:56

Copilot started reviewing on behalf of pjbgf February 16, 2026 16:56 View session

pjbgf requested a review from aymanbagabas February 16, 2026 16:56

pjbgf commented Feb 16, 2026

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pjbgf added 3 commits February 16, 2026 17:06

storage: memory, Implement ExtensionChecker

cc74280

Signed-off-by: Paulo Gomes <[email protected]>

storage: filesystem, Implement ExtensionChecker

f1d3870

Signed-off-by: Paulo Gomes <[email protected]>

pjbgf force-pushed the fail-safe branch 2 times, most recently from 2769d8f to 8b473d6 Compare February 16, 2026 22:28

pjbgf mentioned this pull request Feb 16, 2026

x: storage, Drop ObjectFormatGetter interface #1851

Open

pjbgf force-pushed the fail-safe branch from 8b473d6 to 829f321 Compare February 16, 2026 23:00

pjbgf force-pushed the fail-safe branch from 829f321 to 9a71010 Compare February 16, 2026 23:05

aymanbagabas approved these changes Feb 17, 2026

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pjbgf merged commit 39044ba into main Feb 17, 2026
24 of 26 checks passed

pjbgf deleted the fail-safe branch February 17, 2026 21:55

pjbgf mentioned this pull request Feb 23, 2026

[v5] git: Add strict checks for supported extensions #1861

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pjbgf merged 4 commits intomainfrom
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pjbgf commented Feb 16, 2026 •

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Pull request overview

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pjbgf commented Feb 16, 2026 •

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