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hash.hh
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hash.hh
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#pragma once
///@file
#include "types.hh"
#include "serialise.hh"
#include "file-system.hh"
namespace nix {
MakeError(BadHash, Error);
enum struct HashAlgorithm : char { MD5 = 42, SHA1, SHA256, SHA512 };
const int md5HashSize = 16;
const int sha1HashSize = 20;
const int sha256HashSize = 32;
const int sha512HashSize = 64;
extern const std::set<std::string> hashAlgorithms;
extern const std::string nix32Chars;
/**
* @brief Enumeration representing the hash formats.
*/
enum struct HashFormat : int {
/// @brief Base 64 encoding.
/// @see [IETF RFC 4648, section 4](https://datatracker.ietf.org/doc/html/rfc4648#section-4).
Base64,
/// @brief Nix-specific base-32 encoding. @see nix32Chars
Nix32,
/// @brief Lowercase hexadecimal encoding. @see base16Chars
Base16,
/// @brief "<hash algo>:<Base 64 hash>", format of the SRI integrity attribute.
/// @see W3C recommendation [Subresource Intergrity](https://www.w3.org/TR/SRI/).
SRI
};
extern const std::set<std::string> hashFormats;
struct Hash
{
constexpr static size_t maxHashSize = 64;
size_t hashSize = 0;
uint8_t hash[maxHashSize] = {};
HashAlgorithm algo;
/**
* Create a zero-filled hash object.
*/
explicit Hash(HashAlgorithm algo);
/**
* 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 algorithm must be specified in the
* string.
*/
static Hash parseAny(std::string_view s, std::optional<HashAlgorithm> optAlgo);
/**
* 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, HashAlgorithm algo);
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, HashAlgorithm algo, bool isSRI);
public:
/**
* Check whether two hashes are equal.
*/
bool operator == (const Hash & h2) const noexcept;
/**
* Compare how two hashes are ordered.
*/
std::strong_ordering operator <=> (const Hash & h2) const noexcept;
/**
* Returns the length of a base-16 representation of this hash.
*/
[[nodiscard]] size_t base16Len() const
{
return hashSize * 2;
}
/**
* Returns the length of a base-32 representation of this hash.
*/
[[nodiscard]] size_t base32Len() const
{
return (hashSize * 8 - 1) / 5 + 1;
}
/**
* Returns the length of a base-64 representation of this hash.
*/
[[nodiscard]] 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 algo
* (e.g. "sha256:").
*/
[[nodiscard]] std::string to_string(HashFormat hashFormat, bool includeAlgo) const;
[[nodiscard]] std::string gitRev() const
{
return to_string(HashFormat::Base16, false);
}
[[nodiscard]] std::string gitShortRev() const
{
return std::string(to_string(HashFormat::Base16, false), 0, 7);
}
static Hash dummy;
/**
* @return a random hash with hash algorithm `algo`
*/
static Hash random(HashAlgorithm algo);
};
/**
* Helper that defaults empty hashes to the 0 hash.
*/
Hash newHashAllowEmpty(std::string_view hashStr, std::optional<HashAlgorithm> ha);
/**
* Print a hash in base-16 if it's MD5, or base-32 otherwise.
*/
std::string printHash16or32(const Hash & hash);
/**
* Compute the hash of the given string.
*/
Hash hashString(HashAlgorithm ha, std::string_view s);
/**
* Compute the hash of the given file, hashing its contents directly.
*
* (Metadata, such as the executable permission bit, is ignored.)
*/
Hash hashFile(HashAlgorithm ha, const Path & path);
/**
* The final hash and the number of bytes digested.
*
* @todo Convert to proper struct
*/
typedef std::pair<Hash, uint64_t> HashResult;
/**
* 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 format.
*/
HashFormat parseHashFormat(std::string_view hashFormatName);
/**
* std::optional version of parseHashFormat that doesn't throw error.
*/
std::optional<HashFormat> parseHashFormatOpt(std::string_view hashFormatName);
/**
* The reverse of parseHashFormat.
*/
std::string_view printHashFormat(HashFormat hashFormat);
/**
* Parse a string representing a hash algorithm.
*/
HashAlgorithm parseHashAlgo(std::string_view s);
/**
* Will return nothing on parse error
*/
std::optional<HashAlgorithm> parseHashAlgoOpt(std::string_view s);
/**
* And the reverse.
*/
std::string_view printHashAlgo(HashAlgorithm ha);
union Ctx;
struct AbstractHashSink : virtual Sink
{
virtual HashResult finish() = 0;
};
class HashSink : public BufferedSink, public AbstractHashSink
{
private:
HashAlgorithm ha;
Ctx * ctx;
uint64_t bytes;
public:
HashSink(HashAlgorithm ha);
HashSink(const HashSink & h);
~HashSink();
void writeUnbuffered(std::string_view data) override;
HashResult finish() override;
HashResult currentHash();
};
}