Module std.digest.digest

APIs

There are two APIs for digests: The template API and the OOP API. The template API uses structs and template helpers like isDigest. The OOP API implements digests as classes inheriting the Digest interface. All digests are named so that the template API struct is called "x" and the OOP API class is called "xDigest". For example we have MD5 <--> MD5Digest, CRC32 <--> CRC32Digest, etc.

The template API is slightly more efficient. It does not have to allocate memory dynamically, all memory is allocated on the stack. The OOP API has to allocate in the finish method if no buffer was provided. If you provide a buffer to the OOP APIs finish function, it doesn't allocate, but the Digest classes still have to be created using new which allocates them using the GC.

The OOP API is useful to change the digest function and/or digest backend at 'runtime'. The benefit here is that switching e.g. Phobos MD5Digest and an OpenSSLMD5Digest implementation is ABI compatible.

If just one specific digest type and backend is needed, the template API is usually a good fit. In this simplest case, the template API can even be used without templates: Just use the "x" structs directly.

CTFE

Digests do not work in CTFE

TODO

Digesting single bits (as opposed to bytes) is not implemented. This will be done as another template constraint helper (hasBitDigesting!T) and an additional interface (BitDigest)

Example

import std.digest.crc;

//Simple example
char[8] hexHash = hexDigest!CRC32("The quick brown fox jumps over the lazy dog");
assert(hexHash == "39A34F41");

//Simple example, using the API manually
CRC32 context = makeDigest!CRC32();
context.put(cast(ubyte[])"The quick brown fox jumps over the lazy dog");
ubyte[4] hash = context.finish();
assert(toHexString(hash) == "39A34F41");

Example

//Generating the hashes of a file, idiomatic D way
import std.digest.crc, std.digest.sha, std.digest.md;
import std.stdio;

// Digests a file and prints the result.
void digestFile(Hash)(string filename) if(isDigest!Hash)
{
    auto file = File(filename);
    auto result = digest!Hash(file.byChunk(4096 * 1024));
    writefln("%s (%s) = %s", Hash.stringof, filename, toHexString(result));
}

void main(string[] args)
{
    foreach (name; args[1 .. $])
    {
        digestFile!MD5(name);
        digestFile!SHA1(name);
        digestFile!CRC32(name);
    }
}

Example

//Generating the hashes of a file using the template API
import std.digest.crc, std.digest.sha, std.digest.md;
import std.stdio;
// Digests a file and prints the result.
void digestFile(Hash)(ref Hash hash, string filename) if(isDigest!Hash)
{
    File file = File(filename);

    //As digests imlement OutputRange, we could use std.algorithm.copy
    //Let's do it manually for now
    foreach (buffer; file.byChunk(4096 * 1024))
        hash.put(buffer);

    auto result = hash.finish();
    writefln("%s (%s) = %s", Hash.stringof, filename, toHexString(result));
}

void uMain(string[] args)
{
    MD5 md5;
    SHA1 sha1;
    CRC32 crc32;

    md5.start();
    sha1.start();
    crc32.start();

    foreach (arg; args[1 .. $])
    {
        digestFile(md5, arg);
        digestFile(sha1, arg);
        digestFile(crc32, arg);
    }
}

Example

import std.digest.crc, std.digest.sha, std.digest.md;
import std.stdio;

// Digests a file and prints the result.
void digestFile(Digest hash, string filename)
{
    File file = File(filename);

    //As digests implement OutputRange, we could use std.algorithm.copy
    //Let's do it manually for now
    foreach (buffer; file.byChunk(4096 * 1024))
      hash.put(buffer);

    ubyte[] result = hash.finish();
    writefln("%s (%s) = %s", typeid(hash).toString(), filename, toHexString(result));
}

void umain(string[] args)
{
    auto md5 = new MD5Digest();
    auto sha1 = new SHA1Digest();
    auto crc32 = new CRC32Digest();

    foreach (arg; args[1 .. $])
    {
      digestFile(md5, arg);
      digestFile(sha1, arg);
      digestFile(crc32, arg);
    }
}