Documentation

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.
    
     == File System Monitor cache
    
       The file system monitor cache tracks files for which the core.fsmonitor
       hook has told us about changes.  The signature for this extension is
       { 'F', 'S', 'M', 'N' }.
    
       The extension starts with
    
       - 32-bit version number: the current supported version is 1.
    
       - 64-bit time: the extension data reflects all changes through the given
         time which is stored as the nanoseconds elapsed since midnight,
         January 1, 1970.
    
      - 32-bit bitmap size: the size of the CE_FSMONITOR_VALID bitmap.
    
      - An ewah bitmap, the n-th bit indicates whether the n-th index entry
        is not CE_FSMONITOR_VALID.
    
    == End of Index Entry
    
      The End of Index Entry (EOIE) is used to locate the end of the variable
      length index entries and the beginning of the extensions. Code can take
      advantage of this to quickly locate the index extensions without having
      to parse through all of the index entries.
    
      Because it must be able to be loaded before the variable length cache
      entries and other index extensions, this extension must be written last.
      The signature for this extension is { 'E', 'O', 'I', 'E' }.
    
      The extension consists of:
    
      - 32-bit offset to the end of the index entries
    
      - 160-bit SHA-1 over the extension types and their sizes (but not
        their contents).  E.g. if we have "TREE" extension that is N-bytes
        long, "REUC" extension that is M-bytes long, followed by "EOIE",
        then the hash would be:
    
        SHA-1("TREE" + <binary representation of N> +
          "REUC" + <binary representation of M>)
    
    == Index Entry Offset Table
    
      The Index Entry Offset Table (IEOT) is used to help address the CPU
      cost of loading the index by enabling multi-threading the process of
      converting cache entries from the on-disk format to the in-memory format.
      The signature for this extension is { 'I', 'E', 'O', 'T' }.
    
      The extension consists of:
    
      - 32-bit version (currently 1)
    
      - A number of index offset entries each consisting of:
    
      - 32-bit offset from the beginning of the file to the first cache entry
        in this block of entries.
    
      - 32-bit count of cache entries in this blockpackage index
    

    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 mismatch 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 EndOfIndexEntry

                type EndOfIndexEntry struct {
                	// Offset to the end of the index entries
                	Offset uint32
                	// Hash is a SHA-1 over the extension types and their sizes (but not
                	//	their contents).
                	Hash plumbing.Hash
                }

                  EndOfIndexEntry is the End of Index Entry (EOIE) is used to locate the end of the variable length index entries and the beginning of the extensions. Code can take advantage of this to quickly locate the index extensions without having to parse through all of the index entries.

                  Because it must be able to be loaded before the variable length cache
                  entries and other index extensions, this extension must be written last.
                  

                  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
                    	// EndOfIndexEntry represents the 'End of Index Entry' extension
                    	EndOfIndexEntry *EndOfIndexEntry
                    }

                      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