lix/src/libstore/content-address.hh
jade 1fa6a3e335 Fix various clang-tidy lints
* some things that can throw are marked noexcept
  yet the linter seems to think not. Maybe they can't throw in practice.
  I would rather not have the UB possibility in pretty obvious cold
  paths.
* various default-case-missing complaints
* a fair pile of casts from integer to character, which are in fact
  deliberate.
* an instance of <https://clang.llvm.org/extra/clang-tidy/checks/bugprone/move-forwarding-reference.html>
* bugprone-not-null-terminated-result on handing a string to curl in
  chunks of bytes. our usage is fine.
* reassigning a unique_ptr by CRIMES instead of using release(), then
  using release() and ignoring the result. wild. let's use release() for
  its intended purpose.

Change-Id: Ic3e7affef12383576213a8a7c8145c27e662513d
2024-03-29 20:26:38 -07:00

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#pragma once
///@file
#include <variant>
#include "hash.hh"
#include "path.hh"
#include "comparator.hh"
#include "variant-wrapper.hh"
namespace nix {
/*
* Content addressing method
*/
/* We only have one way to hash text with references, so this is a single-value
type, mainly useful with std::variant.
*/
/**
* The single way we can serialize "text" file system objects.
*
* Somewhat obscure, used by \ref Derivation derivations and
* `builtins.toFile` currently.
*
* TextIngestionMethod is identical to FileIngestionMethod::Fixed except that
* the former may not have self-references and is tagged `text:${algo}:${hash}`
* rather than `fixed:${algo}:${hash}`. The contents of the store path are
* ingested and hashed identically, aside from the slightly different tag and
* restriction on self-references.
*/
struct TextIngestionMethod : std::monostate { };
/**
* An enumeration of the main ways we can serialize file system
* objects.
*/
enum struct FileIngestionMethod : uint8_t {
/**
* Flat-file hashing. Directly ingest the contents of a single file
*/
Flat = false,
/**
* Recursive (or NAR) hashing. Serializes the file-system object in Nix
* Archive format and ingest that
*/
Recursive = true
};
/**
* Compute the prefix to the hash algorithm which indicates how the
* files were ingested.
*/
std::string makeFileIngestionPrefix(FileIngestionMethod m);
/**
* An enumeration of all the ways we can serialize file system objects.
*
* Just the type of a content address. Combine with the hash itself, and
* we have a `ContentAddress` as defined below. Combine that, in turn,
* with info on references, and we have `ContentAddressWithReferences`,
* as defined further below.
*/
struct ContentAddressMethod
{
typedef std::variant<
TextIngestionMethod,
FileIngestionMethod
> Raw;
Raw raw;
GENERATE_CMP(ContentAddressMethod, me->raw);
MAKE_WRAPPER_CONSTRUCTOR(ContentAddressMethod);
/**
* Parse the prefix tag which indicates how the files
* were ingested, with the fixed output case not prefixed for back
* compat.
*
* @param [in] m A string that should begin with the prefix.
* @param [out] m The remainder of the string after the prefix.
*/
static ContentAddressMethod parsePrefix(std::string_view & m);
/**
* Render the prefix tag which indicates how the files wre ingested.
*
* The rough inverse of `parsePrefix()`.
*/
std::string renderPrefix() const;
/**
* Parse a content addressing method and hash type.
*/
static std::pair<ContentAddressMethod, HashType> parse(std::string_view rawCaMethod);
/**
* Render a content addressing method and hash type in a
* nicer way, prefixing both cases.
*
* The rough inverse of `parse()`.
*/
std::string render(HashType ht) const;
};
/*
* Mini content address
*/
/**
* We've accumulated several types of content-addressed paths over the
* years; fixed-output derivations support multiple hash algorithms and
* serialisation methods (flat file vs NAR). Thus, ca has one of the
* following forms:
*
* - text:sha256:<sha256 hash of file contents>: For paths
* computed by Store::makeTextPath() / Store::addTextToStore().
*
* - fixed:<r?>:<ht>:<h>: For paths computed by
* Store::makeFixedOutputPath() / Store::addToStore().
*/
struct ContentAddress
{
/**
* How the file system objects are serialized
*/
ContentAddressMethod method;
/**
* Hash of that serialization
*/
Hash hash;
GENERATE_CMP(ContentAddress, me->method, me->hash);
/**
* Compute the content-addressability assertion
* (`ValidPathInfo::ca`) for paths created by
* `Store::makeFixedOutputPath()` / `Store::addToStore()`.
*/
std::string render() const;
static ContentAddress parse(std::string_view rawCa);
static std::optional<ContentAddress> parseOpt(std::string_view rawCaOpt);
std::string printMethodAlgo() const;
};
/**
* Render the `ContentAddress` if it exists to a string, return empty
* string otherwise.
*/
std::string renderContentAddress(std::optional<ContentAddress> ca);
/*
* Full content address
*
* See the schema for store paths in store-api.cc
*/
/**
* A set of references to other store objects.
*
* References to other store objects are tracked with store paths, self
* references however are tracked with a boolean.
*/
struct StoreReferences
{
/**
* References to other store objects
*/
StorePathSet others;
/**
* Reference to this store object
*/
bool self = false;
/**
* @return true iff no references, i.e. others is empty and self is
* false.
*/
bool empty() const;
/**
* Returns the numbers of references, i.e. the size of others + 1
* iff self is true.
*/
size_t size() const;
GENERATE_CMP(StoreReferences, me->self, me->others);
};
// This matches the additional info that we need for makeTextPath
struct TextInfo
{
/**
* Hash of the contents of the text/file.
*/
Hash hash;
/**
* References to other store objects only; self references
* disallowed
*/
StorePathSet references;
GENERATE_CMP(TextInfo, me->hash, me->references);
};
struct FixedOutputInfo
{
/**
* How the file system objects are serialized
*/
FileIngestionMethod method;
/**
* Hash of that serialization
*/
Hash hash;
/**
* References to other store objects or this one.
*/
StoreReferences references;
GENERATE_CMP(FixedOutputInfo, me->hash, me->references);
};
/**
* Ways of content addressing but not a complete ContentAddress.
*
* A ContentAddress without a Hash.
*/
struct ContentAddressWithReferences
{
typedef std::variant<
TextInfo,
FixedOutputInfo
> Raw;
Raw raw;
GENERATE_CMP(ContentAddressWithReferences, me->raw);
MAKE_WRAPPER_CONSTRUCTOR(ContentAddressWithReferences);
/**
* Create a `ContentAddressWithReferences` from a mere
* `ContentAddress`, by claiming no references.
*/
static ContentAddressWithReferences withoutRefs(const ContentAddress &);
/**
* Create a `ContentAddressWithReferences` from 3 parts:
*
* @param method Way ingesting the file system data.
*
* @param hash Hash of ingested file system data.
*
* @param refs References to other store objects or oneself.
*
* Do note that not all combinations are supported; `nullopt` is
* returns for invalid combinations.
*/
static std::optional<ContentAddressWithReferences> fromPartsOpt(
ContentAddressMethod method, Hash hash, StoreReferences refs);
ContentAddressMethod getMethod() const;
Hash getHash() const;
};
}