Nix/src/libutil/hash.hh

#pragma once

#include "types.hh"
#include "serialise.hh"


namespace nix {


MakeError(BadHash, Error);


enum HashType : char { htMD5 = 42, htSHA1, htSHA256, htSHA512 };


const int md5HashSize = 16;
const int sha1HashSize = 20;
const int sha256HashSize = 32;
const int sha512HashSize = 64;

extern std::set<std::string> hashTypes;

extern const string base32Chars;

enum Base : int { Base64, Base32, Base16, SRI };


struct Hash
{
    constexpr static size_t maxHashSize = 64;
    size_t hashSize = 0;
    uint8_t hash[maxHashSize] = {};

    HashType type;

    /* Create a zero-filled hash object. */
    Hash(HashType type);

    /* Parse the hash from a string representation in the format
       "[<type>:]<base16|base32|base64>" or "<type>-<base64>" (a
       Subresource Integrity hash expression). If the 'type' argument
       is not present, then the hash type must be specified in the
       string. */
    static Hash parseAny(std::string_view s, std::optional<HashType> type);

    /* Parse a hash from a string representation like the above, except the
       type prefix is mandatory is there is no separate arguement. */
    static Hash parseAnyPrefixed(std::string_view s);

    /* Parse a plain hash that musst not have any prefix indicating the type.
       The type is passed in to disambiguate. */
    static Hash parseNonSRIUnprefixed(std::string_view s, HashType type);

    static Hash parseSRI(std::string_view original);

private:
    /* The type must be provided, the string view must not include <type>
       prefix. `isSRI` helps disambigate the various base-* encodings. */
    Hash(std::string_view s, HashType type, bool isSRI);

public:
    /* Check whether two hash are equal. */
    bool operator == (const Hash & h2) const;

    /* Check whether two hash are not equal. */
    bool operator != (const Hash & h2) const;

    /* For sorting. */
    bool operator < (const Hash & h) const;

    /* Returns the length of a base-16 representation of this hash. */
    size_t base16Len() const
    {
        return hashSize * 2;
    }

    /* Returns the length of a base-32 representation of this hash. */
    size_t base32Len() const
    {
        return (hashSize * 8 - 1) / 5 + 1;
    }

    /* Returns the length of a base-64 representation of this hash. */
    size_t base64Len() const
    {
        return ((4 * hashSize / 3) + 3) & ~3;
    }

    /* Return a string representation of the hash, in base-16, base-32
       or base-64. By default, this is prefixed by the hash type
       (e.g. "sha256:"). */
    std::string to_string(Base base, bool includeType) const;

    std::string gitRev() const
    {
        assert(type == htSHA1);
        return to_string(Base16, false);
    }

    std::string gitShortRev() const
    {
        assert(type == htSHA1);
        return std::string(to_string(Base16, false), 0, 7);
    }

    static Hash dummy;
};

/* Helper that defaults empty hashes to the 0 hash. */
Hash newHashAllowEmpty(std::string hashStr, std::optional<HashType> ht);

/* Print a hash in base-16 if it's MD5, or base-32 otherwise. */
string printHash16or32(const Hash & hash);

/* Compute the hash of the given string. */
Hash hashString(HashType ht, std::string_view s);

/* Compute the hash of the given file. */
Hash hashFile(HashType ht, const Path & path);

/* Compute the hash of the given path.  The hash is defined as
   (essentially) hashString(ht, dumpPath(path)). */
typedef std::pair<Hash, uint64_t> HashResult;
HashResult hashPath(HashType ht, const Path & path,
    PathFilter & filter = defaultPathFilter);

/* Compress a hash to the specified number of bytes by cyclically
   XORing bytes together. */
Hash compressHash(const Hash & hash, unsigned int newSize);

/* Parse a string representing a hash type. */
HashType parseHashType(std::string_view s);

/* Will return nothing on parse error */
std::optional<HashType> parseHashTypeOpt(std::string_view s);

/* And the reverse. */
string printHashType(HashType ht);


union Ctx;

struct AbstractHashSink : virtual Sink
{
    virtual HashResult finish() = 0;
};

class HashSink : public BufferedSink, public AbstractHashSink
{
private:
    HashType ht;
    Ctx * ctx;
    uint64_t bytes;

public:
    HashSink(HashType ht);
    HashSink(const HashSink & h);
    ~HashSink();
    void write(const unsigned char * data, size_t len) override;
    HashResult finish() override;
    HashResult currentHash();
};


}