packfile

package
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 Go to latest Published: Jun 21, 2017 License: MIT Imports: 15 Imported by: 1,372

Documentation

Overview

Package packfile implements encoding and decoding of packfile format. 

== pack-*.pack files have the following format:

  - A header appears at the beginning and consists of the following:

    4-byte signature:
        The signature is: {'P', 'A', 'C', 'K'}

    4-byte version number (network byte order):
        GIT currently accepts version number 2 or 3 but
        generates version 2 only.

    4-byte number of objects contained in the pack (network byte order)

    Observation: we cannot have more than 4G versions ;-) and
    more than 4G objects in a pack.

  - The header is followed by number of object entries, each of
    which looks like this:

    (undeltified representation)
    n-byte type and length (3-bit type, (n-1)*7+4-bit length)
    compressed data

    (deltified representation)
    n-byte type and length (3-bit type, (n-1)*7+4-bit length)
    20-byte base object name
    compressed delta data

    Observation: length of each object is encoded in a variable
    length format and is not constrained to 32-bit or anything.

 - The trailer records 20-byte SHA1 checksum of all of the above.

Source: https://www.kernel.org/pub/software/scm/git/docs/v1.7.5/technical/pack-protocol.txt

Index

Constants

View Source 
const (
	// VersionSupported is the packfile version supported by this package
	VersionSupported uint32 = 2
)

Variables

View Source 
var (
	// ErrMaxObjectsLimitReached is returned by Decode when the number
	// of objects in the packfile is higher than
	// Decoder.MaxObjectsLimit.
	ErrMaxObjectsLimitReached = NewError("max. objects limit reached")
	// ErrInvalidObject is returned by Decode when an invalid object is
	// found in the packfile.
	ErrInvalidObject = NewError("invalid git object")
	// ErrPackEntryNotFound is returned by Decode when a reference in
	// the packfile references and unknown object.
	ErrPackEntryNotFound = NewError("can't find a pack entry")
	// ErrZLib is returned by Decode when there was an error unzipping
	// the packfile contents.
	ErrZLib = NewError("zlib reading error")
	// ErrCannotRecall is returned by RecallByOffset or RecallByHash if the object
	// to recall cannot be returned.
	ErrCannotRecall = NewError("cannot recall object")
	// ErrResolveDeltasNotSupported is returned if a NewDecoder is used with a
	// non-seekable scanner and without a plumbing.ObjectStorage
	ErrResolveDeltasNotSupported = NewError("resolve delta is not supported")
	// ErrNonSeekable is returned if a ReadObjectAt method is called without a
	// seekable scanner
	ErrNonSeekable = NewError("non-seekable scanner")
	// ErrRollback error making Rollback over a transaction after an error
	ErrRollback = NewError("rollback error, during set error")
	// ErrAlreadyDecoded is returned if NewDecoder is called for a second time
	ErrAlreadyDecoded = NewError("packfile was already decoded")
)
View Source 
var (
	// ErrEmptyPackfile is returned by ReadHeader when no data is found in the packfile
	ErrEmptyPackfile = NewError("empty packfile")
	// ErrBadSignature is returned by ReadHeader when the signature in the packfile is incorrect.
	ErrBadSignature = NewError("malformed pack file signature")
	// ErrUnsupportedVersion is returned by ReadHeader when the packfile version is
	// different than VersionSupported.
	ErrUnsupportedVersion = NewError("unsupported packfile version")
	// ErrSeekNotSupported returned if seek is not support
	ErrSeekNotSupported = NewError("not seek support")
)

Functions

func ApplyDelta 

func ApplyDelta(target, base plumbing.EncodedObject, delta []byte) error

ApplyDelta writes to target the result of applying the modification deltas in delta to base.

func DiffDelta 

func DiffDelta(src []byte, tgt []byte) []byte

DiffDelta returns the delta that transforms src into tgt.

func GetDelta 

func GetDelta(base, target plumbing.EncodedObject) (plumbing.EncodedObject, error)

GetDelta returns an EncodedObject of type OFSDeltaObject. Base and Target object, will be loaded into memory to be able to create the delta object. To generate target again, you will need the obtained object and "base" one. Error will be returned if base or target object cannot be read.

func PatchDelta 

func PatchDelta(src, delta []byte) []byte

PatchDelta returns the result of applying the modification deltas in delta to src.

func UpdateObjectStorage 

func UpdateObjectStorage(s storer.EncodedObjectStorer, packfile io.Reader) error

UpdateObjectStorage updates the given storer.EncodedObjectStorer with the contents of the packfile.

Types

type Decoder 

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

Decoder reads and decodes packfiles from an input Scanner, if an ObjectStorer was provided the decoded objects are store there. If not the decode object is destroyed. The Offsets and CRCs are calculated whether an ObjectStorer was provided or not.

func NewDecoder 

func NewDecoder(s *Scanner, o storer.EncodedObjectStorer) (*Decoder, error)

NewDecoder returns a new Decoder that decodes a Packfile using the given Scanner and stores the objects in the provided EncodedObjectStorer. ObjectStorer can be nil, in this If the passed EncodedObjectStorer is nil, objects are not stored, but offsets on the Packfile and CRCs are calculated.

If EncodedObjectStorer is nil and the Scanner is not Seekable, ErrNonSeekable is returned.

If the ObjectStorer implements storer.Transactioner, a transaction is created during the Decode execution. If anything fails, Rollback is called

func NewDecoderForType 

func NewDecoderForType(s *Scanner, o storer.EncodedObjectStorer,
	t plumbing.ObjectType) (*Decoder, error)

NewDecoderForType returns a new Decoder but in this case for a specific object type. When an object is read using this Decoder instance and it is not of the same type of the specified one, nil will be returned. This is intended to avoid the content deserialization of all the objects

func (*Decoder) CRCs 

func (d *Decoder) CRCs() map[plumbing.Hash]uint32

CRCs returns the CRC-32 for each read object. Decode method should be called before to calculate the CRCs

func (*Decoder) Close 

func (d *Decoder) Close() error

Close closes the Scanner. usually this mean that the whole reader is read and discarded

func (*Decoder) Decode 

func (d *Decoder) Decode() (checksum plumbing.Hash, err error)

Decode reads a packfile and stores it in the value pointed to by s. The offsets and the CRCs are calculated by this method

func (*Decoder) DecodeObject 

func (d *Decoder) DecodeObject() (plumbing.EncodedObject, error)

DecodeObject reads the next object from the scanner and returns it. This method can be used in replacement of the Decode method, to work in a interactive way. If you created a new decoder instance using NewDecoderForType constructor, if the object decoded is not equals to the specified one, nil will be returned

func (*Decoder) DecodeObjectAt 

func (d *Decoder) DecodeObjectAt(offset int64) (plumbing.EncodedObject, error)

DecodeObjectAt reads an object at the given location. Every EncodedObject returned is added into a internal index. This is intended to be able to regenerate objects from deltas (offset deltas or reference deltas) without an package index (.idx file). If Decode wasn't called previously objects offset should provided using the SetOffsets method.

func (*Decoder) Offsets 

func (d *Decoder) Offsets() map[plumbing.Hash]int64

Offsets returns the objects read offset, Decode method should be called before to calculate the Offsets

func (*Decoder) SetOffsets 

func (d *Decoder) SetOffsets(offsets map[plumbing.Hash]int64)

SetOffsets sets the offsets, required when using the method DecodeObjectAt, without decoding the full packfile

type Encoder 

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

Encoder gets the data from the storage and write it into the writer in PACK format

func NewEncoder 

func NewEncoder(w io.Writer, s storer.EncodedObjectStorer, useRefDeltas bool) *Encoder

NewEncoder creates a new packfile encoder using a specific Writer and EncodedObjectStorer. By default deltas used to generate the packfile will be OFSDeltaObject. To use Reference deltas, set useRefDeltas to true.

func (*Encoder) Encode 

func (e *Encoder) Encode(hashes []plumbing.Hash) (plumbing.Hash, error)

Encode creates a packfile containing all the objects referenced in hashes and writes it to the writer in the Encoder.

type Error 

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

Error specifies errors returned during packfile parsing.

func NewError 

func NewError(reason string) *Error

NewError returns a new error.

func (*Error) AddDetails 

func (e *Error) AddDetails(format string, args ...interface{}) *Error

AddDetails adds details to an error, with additional text.

func (*Error) Error 

func (e *Error) Error() string

Error returns a text representation of the error.

type Format 

type Format int

Format specifies if the packfile uses ref-deltas or ofs-deltas. 

const (
	UnknownFormat Format = iota
	OFSDeltaFormat
	REFDeltaFormat
)

Possible values of the Format type.

type ObjectHeader 

type ObjectHeader struct {
	Type            plumbing.ObjectType
	Offset          int64
	Length          int64
	Reference       plumbing.Hash
	OffsetReference int64
}

ObjectHeader contains the information related to the object, this information is collected from the previous bytes to the content of the object.

type ObjectToPack 

type ObjectToPack struct {
	// The main object to pack, it could be any object, including deltas
	Object plumbing.EncodedObject
	// Base is the object that a delta is based on (it could be also another delta).
	// If the main object is not a delta, Base will be null
	Base *ObjectToPack
	// Original is the object that we can generate applying the delta to
	// Base, or the same object as EncodedObject in the case of a non-delta
	// object.
	Original plumbing.EncodedObject
	// Depth is the amount of deltas needed to resolve to obtain Original
	// (delta based on delta based on ...)
	Depth int
}

ObjectToPack is a representation of an object that is going to be into a pack file.

func (*ObjectToPack) IsDelta 

func (o *ObjectToPack) IsDelta() bool

func (*ObjectToPack) SetDelta 

func (o *ObjectToPack) SetDelta(base *ObjectToPack, delta plumbing.EncodedObject)

type Scanner 

type Scanner struct {

	// lsSeekable says if this scanner can do Seek or not, to have a Scanner
	// seekable a r implementing io.Seeker is required
	IsSeekable bool
	// contains filtered or unexported fields
}

func NewScanner 

func NewScanner(r io.Reader) *Scanner

NewScanner returns a new Scanner based on a reader, if the given reader implements io.ReadSeeker the Scanner will be also Seekable

func (*Scanner) Checksum 

func (s *Scanner) Checksum() (plumbing.Hash, error)

Checksum returns the checksum of the packfile

func (*Scanner) Close 

func (s *Scanner) Close() error

Close reads the reader until io.EOF

func (*Scanner) Header 

func (s *Scanner) Header() (version, objects uint32, err error)

Header reads the whole packfile header (signature, version and object count). It returns the version and the object count and performs checks on the validity of the signature and the version fields.

func (*Scanner) NextObject 

func (s *Scanner) NextObject(w io.Writer) (written int64, crc32 uint32, err error)

NextObject writes the content of the next object into the reader, returns the number of bytes written, the CRC32 of the content and an error, if any

func (*Scanner) NextObjectHeader 

func (s *Scanner) NextObjectHeader() (*ObjectHeader, error)

NextObjectHeader returns the ObjectHeader for the next object in the reader

func (*Scanner) SeekFromStart 

func (s *Scanner) SeekFromStart(offset int64) (previous int64, err error)

SeekFromStart sets a new offset from start, returns the old position before the change.

Source Files

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