index

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Published: Sep 6, 2018 License: Apache-2.0 Imports: 16 Imported by: 0

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Overview

Package index implements encoding and decoding of index format files.

Git index format
================

== The Git index file has the following format

  All binary numbers are in network byte order. Version 2 is described
  here unless stated otherwise.

  - A 12-byte header consisting of

    4-byte signature:
      The signature is { 'D', 'I', 'R', 'C' } (stands for "dircache")

    4-byte version number:
      The current supported versions are 2, 3 and 4.

    32-bit number of index entries.

  - A number of sorted index entries (see below).

  - Extensions

    Extensions are identified by signature. Optional extensions can
    be ignored if Git does not understand them.

    Git currently supports cached tree and resolve undo extensions.

    4-byte extension signature. If the first byte is 'A'..'Z' the
    extension is optional and can be ignored.

    32-bit size of the extension

    Extension data

  - 160-bit SHA-1 over the content of the index file before this
    checksum.

== Index entry

  Index entries are sorted in ascending order on the name field,
  interpreted as a string of unsigned bytes (i.e. memcmp() order, no
  localization, no special casing of directory separator '/'). Entries
  with the same name are sorted by their stage field.

  32-bit ctime seconds, the last time a file's metadata changed
    this is stat(2) data

  32-bit ctime nanosecond fractions
    this is stat(2) data

  32-bit mtime seconds, the last time a file's data changed
    this is stat(2) data

  32-bit mtime nanosecond fractions
    this is stat(2) data

  32-bit dev
    this is stat(2) data

  32-bit ino
    this is stat(2) data

  32-bit mode, split into (high to low bits)

    4-bit object type
      valid values in binary are 1000 (regular file), 1010 (symbolic link)
      and 1110 (gitlink)

    3-bit unused

    9-bit unix permission. Only 0755 and 0644 are valid for regular files.
    Symbolic links and gitlinks have value 0 in this field.

  32-bit uid
    this is stat(2) data

  32-bit gid
    this is stat(2) data

  32-bit file size
    This is the on-disk size from stat(2), truncated to 32-bit.

  160-bit SHA-1 for the represented object

  A 16-bit 'flags' field split into (high to low bits)

    1-bit assume-valid flag

    1-bit extended flag (must be zero in version 2)

    2-bit stage (during merge)

    12-bit name length if the length is less than 0xFFF; otherwise 0xFFF
    is stored in this field.

  (Version 3 or later) A 16-bit field, only applicable if the
  "extended flag" above is 1, split into (high to low bits).

    1-bit reserved for future

    1-bit skip-worktree flag (used by sparse checkout)

    1-bit intent-to-add flag (used by "git add -N")

    13-bit unused, must be zero

  Entry path name (variable length) relative to top level directory
    (without leading slash). '/' is used as path separator. The special
    path components ".", ".." and ".git" (without quotes) are disallowed.
    Trailing slash is also disallowed.

    The exact encoding is undefined, but the '.' and '/' characters
    are encoded in 7-bit ASCII and the encoding cannot contain a NUL
    byte (iow, this is a UNIX pathname).

  (Version 4) In version 4, the entry path name is prefix-compressed
    relative to the path name for the previous entry (the very first
    entry is encoded as if the path name for the previous entry is an
    empty string).  At the beginning of an entry, an integer N in the
    variable width encoding (the same encoding as the offset is encoded
    for OFS_DELTA pack entries; see pack-format.txt) is stored, followed
    by a NUL-terminated string S.  Removing N bytes from the end of the
    path name for the previous entry, and replacing it with the string S
    yields the path name for this entry.

  1-8 nul bytes as necessary to pad the entry to a multiple of eight bytes
  while keeping the name NUL-terminated.

  (Version 4) In version 4, the padding after the pathname does not
  exist.

  Interpretation of index entries in split index mode is completely
  different. See below for details.

== Extensions

=== Cached tree

  Cached tree extension contains pre-computed hashes for trees that can
  be derived from the index. It helps speed up tree object generation
  from index for a new commit.

  When a path is updated in index, the path must be invalidated and
  removed from tree cache.

  The signature for this extension is { 'T', 'R', 'E', 'E' }.

  A series of entries fill the entire extension; each of which
  consists of:

  - NUL-terminated path component (relative to its parent directory);

  - ASCII decimal number of entries in the index that is covered by the
    tree this entry represents (entry_count);

  - A space (ASCII 32);

  - ASCII decimal number that represents the number of subtrees this
    tree has;

  - A newline (ASCII 10); and

  - 160-bit object name for the object that would result from writing
    this span of index as a tree.

  An entry can be in an invalidated state and is represented by having
  a negative number in the entry_count field. In this case, there is no
  object name and the next entry starts immediately after the newline.
  When writing an invalid entry, -1 should always be used as entry_count.

  The entries are written out in the top-down, depth-first order.  The
  first entry represents the root level of the repository, followed by the
  first subtree--let's call this A--of the root level (with its name
  relative to the root level), followed by the first subtree of A (with
  its name relative to A), ...

=== Resolve undo

  A conflict is represented in the index as a set of higher stage entries.
  When a conflict is resolved (e.g. with "git add path"), these higher
  stage entries will be removed and a stage-0 entry with proper resolution
  is added.

  When these higher stage entries are removed, they are saved in the
  resolve undo extension, so that conflicts can be recreated (e.g. with
  "git checkout -m"), in case users want to redo a conflict resolution
  from scratch.

  The signature for this extension is { 'R', 'E', 'U', 'C' }.

  A series of entries fill the entire extension; each of which
  consists of:

  - NUL-terminated pathname the entry describes (relative to the root of
    the repository, i.e. full pathname);

  - Three NUL-terminated ASCII octal numbers, entry mode of entries in
    stage 1 to 3 (a missing stage is represented by "0" in this field);
    and

  - At most three 160-bit object names of the entry in stages from 1 to 3
    (nothing is written for a missing stage).

=== Split index

  In split index mode, the majority of index entries could be stored
  in a separate file. This extension records the changes to be made on
  top of that to produce the final index.

  The signature for this extension is { 'l', 'i', 'n', 'k' }.

  The extension consists of:

  - 160-bit SHA-1 of the shared index file. The shared index file path
    is $GIT_DIR/sharedindex.<SHA-1>. If all 160 bits are zero, the
    index does not require a shared index file.

  - An ewah-encoded delete bitmap, each bit represents an entry in the
    shared index. If a bit is set, its corresponding entry in the
    shared index will be removed from the final index.  Note, because
    a delete operation changes index entry positions, but we do need
    original positions in replace phase, it's best to just mark
    entries for removal, then do a mass deletion after replacement.

  - An ewah-encoded replace bitmap, each bit represents an entry in
    the shared index. If a bit is set, its corresponding entry in the
    shared index will be replaced with an entry in this index
    file. All replaced entries are stored in sorted order in this
    index. The first "1" bit in the replace bitmap corresponds to the
    first index entry, the second "1" bit to the second entry and so
    on. Replaced entries may have empty path names to save space.

  The remaining index entries after replaced ones will be added to the
  final index. These added entries are also sorted by entry name then
  stage.

== Untracked cache

  Untracked cache saves the untracked file list and necessary data to
  verify the cache. The signature for this extension is { 'U', 'N',
  'T', 'R' }.

  The extension starts with

  - A sequence of NUL-terminated strings, preceded by the size of the
    sequence in variable width encoding. Each string describes the
    environment where the cache can be used.

  - Stat data of $GIT_DIR/info/exclude. See "Index entry" section from
    ctime field until "file size".

  - Stat data of plumbing.excludesfile

  - 32-bit dir_flags (see struct dir_struct)

  - 160-bit SHA-1 of $GIT_DIR/info/exclude. Null SHA-1 means the file
    does not exist.

  - 160-bit SHA-1 of plumbing.excludesfile. Null SHA-1 means the file does
    not exist.

  - NUL-terminated string of per-dir exclude file name. This usually
    is ".gitignore".

  - The number of following directory blocks, variable width
    encoding. If this number is zero, the extension ends here with a
    following NUL.

  - A number of directory blocks in depth-first-search order, each
    consists of

    - The number of untracked entries, variable width encoding.

    - The number of sub-directory blocks, variable width encoding.

    - The directory name terminated by NUL.

    - A number of untracked file/dir names terminated by NUL.

The remaining data of each directory block is grouped by type:

  - An ewah bitmap, the n-th bit marks whether the n-th directory has
    valid untracked cache entries.

  - An ewah bitmap, the n-th bit records "check-only" bit of
    read_directory_recursive() for the n-th directory.

  - An ewah bitmap, the n-th bit indicates whether SHA-1 and stat data
    is valid for the n-th directory and exists in the next data.

  - An array of stat data. The n-th data corresponds with the n-th
    "one" bit in the previous ewah bitmap.

  - An array of SHA-1. The n-th SHA-1 corresponds with the n-th "one" bit
    in the previous ewah bitmap.

  - One NUL.

Source https://www.kernel.org/pub/software/scm/git/docs/technical/index-format.txt

Index

Constants

This section is empty.

Variables

View Source
var (
	// DecodeVersionSupported is the range of supported index versions
	DecodeVersionSupported = struct{ Min, Max uint32 }{Min: 2, Max: 4}

	// ErrMalformedSignature is returned by Decode when the index header file is
	// malformed
	ErrMalformedSignature = errors.New("malformed index signature file")
	// ErrInvalidChecksum is returned by Decode if the SHA1 hash missmatch with
	// the read content
	ErrInvalidChecksum = errors.New("invalid checksum")
)
View Source
var (
	// EncodeVersionSupported is the range of supported index versions
	EncodeVersionSupported uint32 = 2

	// ErrInvalidTimestamp is returned by Encode if a Index with a Entry with
	// negative timestamp values
	ErrInvalidTimestamp = errors.New("negative timestamps are not allowed")
)
View Source
var (
	// ErrUnsupportedVersion is returned by Decode when the index file version
	// is not supported.
	ErrUnsupportedVersion = errors.New("unsupported version")
	// ErrEntryNotFound is returned by Index.Entry, if an entry is not found.
	ErrEntryNotFound = errors.New("entry not found")
)

Functions

This section is empty.

Types

type Decoder

type Decoder struct {
	// contains filtered or unexported fields
}

A Decoder reads and decodes index files from an input stream.

func NewDecoder

func NewDecoder(r io.Reader) *Decoder

NewDecoder returns a new decoder that reads from r.

func (*Decoder) Decode

func (d *Decoder) Decode(idx *Index) error

Decode reads the whole index object from its input and stores it in the value pointed to by idx.

type Encoder

type Encoder struct {
	// contains filtered or unexported fields
}

An Encoder writes an Index to an output stream.

func NewEncoder

func NewEncoder(w io.Writer) *Encoder

NewEncoder returns a new encoder that writes to w.

func (*Encoder) Encode

func (e *Encoder) Encode(idx *Index) error

Encode writes the Index to the stream of the encoder.

type Entry

type Entry struct {
	// Hash is the SHA1 of the represented file
	Hash plumbing.Hash
	// Name is the  Entry path name relative to top level directory
	Name string
	// CreatedAt time when the tracked path was created
	CreatedAt time.Time
	// ModifiedAt time when the tracked path was changed
	ModifiedAt time.Time
	// Dev and Inode of the tracked path
	Dev, Inode uint32
	// Mode of the path
	Mode filemode.FileMode
	// UID and GID, userid and group id of the owner
	UID, GID uint32
	// Size is the length in bytes for regular files
	Size uint32
	// Stage on a merge is defines what stage is representing this entry
	// https://git-scm.com/book/en/v2/Git-Tools-Advanced-Merging
	Stage Stage
	// SkipWorktree used in sparse checkouts
	// https://git-scm.com/docs/git-read-tree#_sparse_checkout
	SkipWorktree bool
	// IntentToAdd record only the fact that the path will be added later
	// https://git-scm.com/docs/git-add ("git add -N")
	IntentToAdd bool
}

Entry represents a single file (or stage of a file) in the cache. An entry represents exactly one stage of a file. If a file path is unmerged then multiple Entry instances may appear for the same path name.

func (Entry) String

func (e Entry) String() string

type Index

type Index struct {
	// Version is index version
	Version uint32
	// Entries collection of entries represented by this Index. The order of
	// this collection is not guaranteed
	Entries []*Entry
	// Cache represents the 'Cached tree' extension
	Cache *Tree
	// ResolveUndo represents the 'Resolve undo' extension
	ResolveUndo *ResolveUndo
}

Index contains the information about which objects are currently checked out in the worktree, having information about the working files. Changes in worktree are detected using this Index. The Index is also used during merges

func (*Index) Add

func (i *Index) Add(path string) *Entry

Add creates a new Entry and returns it. The caller should first check that another entry with the same path does not exist.

func (*Index) Entry

func (i *Index) Entry(path string) (*Entry, error)

Entry returns the entry that match the given path, if any.

func (*Index) Glob

func (i *Index) Glob(pattern string) (matches []*Entry, err error)

Glob returns the all entries matching pattern or nil if there is no matching entry. The syntax of patterns is the same as in filepath.Glob.

func (*Index) Remove

func (i *Index) Remove(path string) (*Entry, error)

Remove remove the entry that match the give path and returns deleted entry.

func (*Index) String

func (i *Index) String() string

String is equivalent to `git ls-files --stage --debug`

type ResolveUndo

type ResolveUndo struct {
	Entries []ResolveUndoEntry
}

ResolveUndo is used when a conflict is resolved (e.g. with "git add path"), these higher stage entries are removed and a stage-0 entry with proper resolution is added. When these higher stage entries are removed, they are saved in the resolve undo extension.

type ResolveUndoEntry

type ResolveUndoEntry struct {
	Path   string
	Stages map[Stage]plumbing.Hash
}

ResolveUndoEntry contains the information about a conflict when is resolved

type Stage

type Stage int

Stage during merge

const (
	// Merged is the default stage, fully merged
	Merged Stage = 1
	// AncestorMode is the base revision
	AncestorMode Stage = 1
	// OurMode is the first tree revision, ours
	OurMode Stage = 2
	// TheirMode is the second tree revision, theirs
	TheirMode Stage = 3
)

type Tree

type Tree struct {
	Entries []TreeEntry
}

Tree contains pre-computed hashes for trees that can be derived from the index. It helps speed up tree object generation from index for a new commit.

type TreeEntry

type TreeEntry struct {
	// Path component (relative to its parent directory)
	Path string
	// Entries is the number of entries in the index that is covered by the tree
	// this entry represents.
	Entries int
	// Trees is the number that represents the number of subtrees this tree has
	Trees int
	// Hash object name for the object that would result from writing this span
	// of index as a tree.
	Hash plumbing.Hash
}

TreeEntry entry of a cached Tree

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