# abstract class Digest

- Digest
- Reference
- Object

##
Overview

`Digest` is the base type of hashing algorithms like `Digest::MD5`, `Digest::SHA1`, `Digest::SHA256`, or `Digest::SHA512`.

A `Digest` instance holds the state of an ongoing hash calculation. It can receive new data to include in the hash via `#update`, `#<<`, or `#file`. Once all data is included, use `#final` or `#hexfinal` to get the hash. This will mark the ongoing calculation as finished. A finished calculation can't receive new data.

A `digest.dup.final` call may be used to get an intermediate hash value.

Use `#reset` to reuse the `Digest` instance for a new calculation.

##
Direct Known Subclasses

- Digest::Adler32
- Digest::CRC32
- OpenSSL::Digest

##
Defined in:

digest/digest.cr

##
Instance Method Summary

- #<<(data) : self

  Reads the io's data and updates the digest with it.

- #digest_size : Int32

  Returns the digest output size in bytes.

- #file(file_name : Path | String) : self

  Reads the file's content and updates the digest with it.

- #final(dst : Bytes) : Bytes

  Puts the final digest output into `dst`.

- #final : Bytes

  Returns the final digest output.

- #final_impl(dst : Bytes) : Nil

  Stores the output digest of #digest_size bytes in dst.

- #hexfinal(dst : Bytes) : Nil

  Writes a hexadecimal-encoded digest to `dst`.

- #hexfinal(io : IO) : Nil

  Writes a hexadecimal-encoded digest to `IO`.

- #hexfinal : String

  Returns a hexadecimal-encoded digest in a new `String`.

- #reset : self

  Resets the state of this object.

- #reset_impl : Nil

  Resets the object to it's initial state.

- #update(data : Bytes) : self
- #update(io : IO) : self

  Reads the io's data and updates the digest with it.

- #update(data) : self
- #update_impl(data : Bytes) : Nil

  Hashes data incrementally.

### Instance methods inherited from class `Reference`

==(other : self)
==(other : JSON::Any)
==(other : YAML::Any)
==(other) ==, dup dup, hash(hasher) hash, initialize initialize, inspect(io : IO) : Nil inspect, object_id : UInt64 object_id, pretty_print(pp) : Nil pretty_print, same?(other : Reference) : Bool
same?(other : Nil) same?, to_s(io : IO) : Nil to_s

### Constructor methods inherited from class `Reference`

new new, unsafe_construct(address : Pointer, *args, **opts) : self unsafe_construct

### Class methods inherited from class `Reference`

pre_initialize(address : Pointer) pre_initialize

### Instance methods inherited from class `Object`

! : Bool !, !=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other) ===, =~(other) =~, as(type : Class) as, as?(type : Class) as?, class class, dup dup, hash(hasher)
hash hash, in?(collection : Object) : Bool
in?(*values : Object) : Bool in?, inspect(io : IO) : Nil
inspect : String inspect, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil!(message)
not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, responds_to?(name : Symbol) : Bool responds_to?, tap(&) tap, to_json(io : IO) : Nil
to_json : String to_json, to_pretty_json(indent : String = " ") : String
to_pretty_json(io : IO, indent : String = " ") : Nil to_pretty_json, to_s(io : IO) : Nil
to_s : String to_s, to_yaml(io : IO) : Nil
to_yaml : String to_yaml, try(&) try, unsafe_as(type : T.class) forall T unsafe_as

### Class methods inherited from class `Object`

from_json(string_or_io : String | IO, root : String)
from_json(string_or_io : String | IO) from_json, from_yaml(string_or_io : String | IO) from_yaml

### Macros inherited from class `Object`

class_getter(*names, &block) class_getter, class_getter!(*names) class_getter!, class_getter?(*names, &block) class_getter?, class_property(*names, &block) class_property, class_property!(*names) class_property!, class_property?(*names, &block) class_property?, class_setter(*names) class_setter, def_clone def_clone, def_equals(*fields) def_equals, def_equals_and_hash(*fields) def_equals_and_hash, def_hash(*fields) def_hash, delegate(*methods, to object) delegate, forward_missing_to(delegate) forward_missing_to, getter(*names, &block) getter, getter!(*names) getter!, getter?(*names, &block) getter?, property(*names, &block) property, property!(*names) property!, property?(*names, &block) property?, setter(*names) setter

##
Instance Method Detail

def <<(data) : self #

Reads the io's data and updates the digest with it.

abstract def digest_size : Int32 #

Returns the digest output size in bytes.

def file(file_name : Path | String) : self #

Reads the file's content and updates the digest with it.

def final(dst : Bytes) : Bytes #

Puts the final digest output into `dst`.

Faster than the `Bytes` allocating version. Use when hashing in loops.

`#final` or `#hexfinal` can only be called once and raises `FinalizedError` on subsequent calls.

NOTE `.dup.final(dst)` call may be used to get an intermediate hash value.

def final : Bytes #

Returns the final digest output.

`#final` or `#hexfinal` can only be called once and raises `FinalizedError` on subsequent calls.

NOTE `.dup.final` call may be used to get an intermediate hash value.

abstract def final_impl(dst : Bytes) : Nil #

Stores the output digest of #digest_size bytes in dst.

def hexfinal(dst : Bytes) : Nil #

Writes a hexadecimal-encoded digest to `dst`.

Faster than the `String` allocating version. Use when hashing in loops.

`#final` or `#hexfinal` can only be called once and raises `FinalizedError` on subsequent calls.

NOTE `.dup.final` call may be used to get an intermediate hash value.

def hexfinal(io : IO) : Nil #

Writes a hexadecimal-encoded digest to `IO`.

Faster than the `String` allocating version.

`#final` or `#hexfinal` can only be called once and raises `FinalizedError` on subsequent calls.

NOTE `.dup.final` call may be used to get an intermediate hash value.

This method is restricted to a maximum digest size of 64 bits. Implementations that allow a larger digest size should override this method to use a larger buffer.

def hexfinal : String #

Returns a hexadecimal-encoded digest in a new `String`.

`#final` or `#hexfinal` can only be called once and raises `FinalizedError` on subsequent calls.

NOTE `.dup.hexfinal` call may be used to get an intermediate hash value.

def reset : self #

Resets the state of this object. Use to get another hash value without creating a new object.

abstract def reset_impl : Nil #

Resets the object to it's initial state.

def update(data : Bytes) : self #
def update(io : IO) : self #

Reads the io's data and updates the digest with it.

def update(data) : self #
abstract def update_impl(data : Bytes) : Nil #

Hashes data incrementally.