etag

Documentation

Index

• func Equal(a, b ETag) bool
• func Wrap(wrapped, content io.Reader) io.Reader
• type ETag
  • func FromContentMD5(h http.Header) (ETag, error)
  • func Multipart(etags ...ETag) ETag
  • func Parse(s string) (ETag, error)
  • func (e ETag) ETag() ETag
  • func (e ETag) IsEncrypted() bool
  • func (e ETag) IsMultipart() bool
  • func (e ETag) Parts() int
  • func (e ETag) String() string
• type Reader
  • func NewReader(r io.Reader, etag ETag) *Reader
  • func (r *Reader) ETag() ETag
  • func (r *Reader) Read(p []byte) (int, error)
• type Tagger
• type VerifyError
  • func (v VerifyError) Error() string

Functions

func Equal

func Equal(a, b ETag) bool

Equal returns true if and only if the two ETags are identical.

func Wrap

func Wrap(wrapped, content io.Reader) io.Reader

Wrap returns an io.Reader that reads from the wrapped io.Reader and implements the Tagger interaface.

If content implements Tagger then the returned Reader returns ETag of the content. Otherwise, it returns nil as ETag.

Wrap provides an adapter for io.Reader implemetations that don't implement the Tagger interface. It is mainly used to provide a high-level io.Reader access to the ETag computed by a low-level io.Reader:

content := etag.NewReader(r.Body, nil)

compressedContent := Compress(content)
encryptedContent := Encrypt(compressedContent)

// Now, we need an io.Reader that can access
// the ETag computed over the content.
reader := etag.Wrap(encryptedContent, content)

Types

type ETag

type ETag []byte

ETag is a single S3 ETag.

An S3 ETag sometimes corresponds to the MD5 of the S3 object content. However, when an object is encrypted, compressed or uploaded using the S3 multipart API then its ETag is not necessarily the MD5 of the object content.

For a more detailed description of S3 ETags take a look at the package documentation.

func FromContentMD5

func FromContentMD5(h http.Header) (ETag, error)

FromContentMD5 decodes and returns the Content-MD5 as ETag, if set. If no Content-MD5 header is set it returns an empty ETag and no error.

func Multipart

func Multipart(etags ...ETag) ETag

Multipart computes an S3 multipart ETag given a list of S3 singlepart ETags. It returns nil if the list of ETags is empty.

Any encrypted or multipart ETag will be ignored and not used to compute the returned ETag.

func Parse

func Parse(s string) (ETag, error)

Parse parses s as an S3 ETag, returning the result. The string can be an encrypted, singlepart or multipart S3 ETag. It returns an error if s is not a valid textual representation of an ETag.

func (ETag) ETag

func (e ETag) ETag() ETag

ETag returns the ETag itself.

By providing this method ETag implements the Tagger interface.

func (ETag) IsEncrypted

func (e ETag) IsEncrypted() bool

IsEncrypted reports whether the ETag is encrypted.

func (ETag) IsMultipart

func (e ETag) IsMultipart() bool

IsMultipart reports whether the ETag belongs to an object that has been uploaded using the S3 multipart API. An S3 multipart ETag has a -<part-number> suffix.

func (ETag) Parts

func (e ETag) Parts() int

Parts returns the number of object parts that are referenced by this ETag. It returns 1 if the object has been uploaded using the S3 singlepart API.

Parts may panic if the ETag is an invalid multipart ETag.

func (ETag) String

func (e ETag) String() string

String returns the string representation of the ETag.

The returned string is a hex representation of the binary ETag with an optional '-<part-number>' suffix.

type Reader

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

A Reader wraps an io.Reader and computes the MD5 checksum of the read content as ETag.

Optionally, a Reader can also verify that the computed ETag matches an expected value. Therefore, it compares both ETags once the underlying io.Reader returns io.EOF. If the computed ETag does not match the expected ETag then Read returns a VerifyError.

Reader implements the Tagger interface.

func NewReader

func NewReader(r io.Reader, etag ETag) *Reader

NewReader returns a new Reader that computes the MD5 checksum of the content read from r as ETag.

If the provided etag is not nil the returned Reader compares the etag with the computed MD5 sum once the r returns io.EOF.

func (*Reader) ETag

func (r *Reader) ETag() ETag

ETag returns the ETag of all the content read so far. Reading more content changes the MD5 checksum. Therefore, calling ETag multiple times may return different results.

func (*Reader) Read

func (r *Reader) Read(p []byte) (int, error)

Read reads up to len(p) bytes from the underlying io.Reader as specified by the io.Reader interface.

type Tagger

type Tagger interface {
	ETag() ETag
}

Tagger is the interface that wraps the basic ETag method.

type VerifyError

type VerifyError struct {
	Expected ETag
	Computed ETag
}

VerifyError is an error signaling that a computed ETag does not match an expected ETag.

func (VerifyError) Error

func (v VerifyError) Error() string