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git-annex: create modules/annex (#21)
This moves the `annexObjectPath()` helper out of the tests and into a dedicated sub-package as `annex.ContentLocation()`, and expands it with `.Pointer()` (which validates using `git annex examinekey`), `.IsAnnexed()` and `.Content()` to make it a more useful module. The tests retain their own wrapper version of `ContentLocation()` because I tried to follow close to the API modules/lfs uses, which in terms of abstract `git.Blob` and `git.TreeEntry` objects, not in terms of `repoPath string`s which are more convenient for the tests.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,154 @@ | ||
| // Copyright 2022 The Gitea Authors. All rights reserved. | ||
| // SPDX-License-Identifier: MIT | ||
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| // Unlike modules/lfs, which operates mainly on git.Blobs, this operates on git.TreeEntrys. | ||
| // The motivation for this is that TreeEntrys have an easy pointer to the on-disk repo path, | ||
| // while blobs do not (in fact, if building with TAGS=gogit, blobs might exist only in a mock | ||
| // filesystem, living only in process RAM). We must have the on-disk path to do anything | ||
| // useful with git-annex because all of its interesting data is on-disk under .git/annex/. | ||
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| package annex | ||
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| import ( | ||
| "errors" | ||
| "fmt" | ||
| "os" | ||
| "path" | ||
| "strings" | ||
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| "code.gitea.io/gitea/modules/git" | ||
| "code.gitea.io/gitea/modules/setting" | ||
| "code.gitea.io/gitea/modules/util" | ||
| ) | ||
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| const ( | ||
| // > The maximum size of a pointer file is 32 kb. | ||
| // - https://git-annex.branchable.com/internals/pointer_file/ | ||
| // It's unclear if that's kilobytes or kibibytes; assuming kibibytes: | ||
| blobSizeCutoff = 32 * 1024 | ||
| ) | ||
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| // ErrInvalidPointer occurs if the pointer's value doesn't parse | ||
| var ErrInvalidPointer = errors.New("Not a git-annex pointer") | ||
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| // Gets the content of the blob as raw text, up to n bytes. | ||
| // (the pre-existing blob.GetBlobContent() has a hardcoded 1024-byte limit) | ||
| func getBlobContent(b *git.Blob, n int) (string, error) { | ||
| dataRc, err := b.DataAsync() | ||
| if err != nil { | ||
| return "", err | ||
| } | ||
| defer dataRc.Close() | ||
| buf := make([]byte, n) | ||
| n, _ = util.ReadAtMost(dataRc, buf) | ||
| buf = buf[:n] | ||
| return string(buf), nil | ||
| } | ||
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| func Pointer(blob *git.Blob) (string, error) { | ||
| // git-annex doesn't seem fully spec what its pointer are, but | ||
| // the fullest description is here: | ||
| // https://git-annex.branchable.com/internals/pointer_file/ | ||
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| // a pointer can be: | ||
| // the original format, generated by `git annex add`: a symlink to '.git/annex/objects/$HASHDIR/$HASHDIR2/$KEY/$KEY' | ||
| // the newer, git-lfs influenced, format, generated by `git annex smudge`: a text file containing '/annex/objects/$KEY' | ||
| // | ||
| // in either case we can extract the $KEY the same way, and we need not actually know if it's a symlink or not because | ||
| // git.Blob.DataAsync() works like open() + readlink(), handling both cases in one. | ||
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| if blob.Size() > blobSizeCutoff { | ||
| // > The maximum size of a pointer file is 32 kb. If it is any longer, it is not considered to be a valid pointer file. | ||
| // https://git-annex.branchable.com/internals/pointer_file/ | ||
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| // It's unclear to me whether the same size limit applies to symlink-pointers, but it seems sensible to limit them too. | ||
| return "", ErrInvalidPointer | ||
| } | ||
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| pointer, err := getBlobContent(blob, blobSizeCutoff) | ||
| if err != nil { | ||
| return "", fmt.Errorf("error reading %s: %w", blob.Name(), err) | ||
| } | ||
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| // the spec says a pointer file can contain multiple lines each with a pointer in them | ||
| // but that makes no sense to me, so I'm just ignoring all but the first | ||
| lines := strings.Split(pointer, "\n") | ||
| if len(lines) < 1 { | ||
| return "", ErrInvalidPointer | ||
| } | ||
| pointer = lines[0] | ||
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| // in both the symlink and pointer-file formats, the pointer must have "/annex/" somewhere in it | ||
| if !strings.Contains(pointer, "/annex/") { | ||
| return "", ErrInvalidPointer | ||
| } | ||
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| // extract $KEY | ||
| pointer = path.Base(strings.TrimSpace(pointer)) | ||
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| // ask git-annex's opinion on $KEY | ||
| // XXX: this is probably a bit slow, especially if this operation gets run often | ||
| // and examinekey is not that strict: | ||
| // - it doesn't enforce that the "BACKEND" tag is one it knows, | ||
| // - it doesn't enforce that the fields and their format fit the "BACKEND" tag | ||
| // so maybe this is a wasteful step | ||
| _, examineStderr, err := git.NewCommandContextNoGlobals(git.DefaultContext, "annex", "examinekey").AddDynamicArguments(pointer).RunStdString(&git.RunOpts{Dir: blob.Repo().Path}) | ||
| if err != nil { | ||
| // TODO: make ErrInvalidPointer into a type capable of wrapping err | ||
| if strings.TrimSpace(examineStderr) == "git-annex: bad key" { | ||
| return "", ErrInvalidPointer | ||
| } | ||
| return "", err | ||
| } | ||
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| return pointer, nil | ||
| } | ||
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| // return the absolute path of the content pointed to by the annex pointer stored in the git object | ||
| // errors if the content is not found in this repo | ||
| func ContentLocation(blob *git.Blob) (string, error) { | ||
| pointer, err := Pointer(blob) | ||
| if err != nil { | ||
| return "", err | ||
| } | ||
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| contentLocation, _, err := git.NewCommandContextNoGlobals(git.DefaultContext, "annex", "contentlocation").AddDynamicArguments(pointer).RunStdString(&git.RunOpts{Dir: blob.Repo().Path}) | ||
| if err != nil { | ||
| return "", fmt.Errorf("in %s: %s does not seem to be a valid annexed file: %w", blob.Repo().Path, pointer, err) | ||
| } | ||
| contentLocation = strings.TrimSpace(contentLocation) | ||
| contentLocation = path.Clean("/" + contentLocation)[1:] // prevent directory traversals | ||
| contentLocation = path.Join(blob.Repo().Path, contentLocation) | ||
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| return contentLocation, nil | ||
| } | ||
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| // returns a stream open to the annex content | ||
| func Content(blob *git.Blob) (*os.File, error) { | ||
| contentLocation, err := ContentLocation(blob) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
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| return os.Open(contentLocation) | ||
| } | ||
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| // whether the object appears to be a valid annex pointer | ||
| // does *not* verify if the content is actually in this repo; | ||
| // for that, use ContentLocation() | ||
| func IsAnnexed(blob *git.Blob) (bool, error) { | ||
| if !setting.Annex.Enabled { | ||
| return false, nil | ||
| } | ||
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| // Pointer() is written to only return well-formed pointers | ||
| // so the test is just to see if it errors | ||
| _, err := Pointer(blob) | ||
| if err != nil { | ||
| if errors.Is(err, ErrInvalidPointer) { | ||
| return false, nil | ||
| } | ||
| return false, err | ||
| } | ||
| return true, nil | ||
| } |
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