rippled/include/xrpl/conditions/detail/PreimageSha256.h

#pragma once

#include <xrpl/basics/Buffer.h>
#include <xrpl/basics/Slice.h>
#include <xrpl/conditions/Condition.h>
#include <xrpl/conditions/Fulfillment.h>
#include <xrpl/conditions/detail/error.h>
#include <xrpl/protocol/digest.h>

#include <memory>

namespace xrpl {
namespace cryptoconditions {

class PreimageSha256 final : public Fulfillment
{
public:
    /** The maximum allowed length of a preimage.

        The specification does not specify a minimum supported
        length, nor does it require all conditions to support
        the same minimum length.

        While future versions of this code will never lower
        this limit, they may opt to raise it.
    */
    static constexpr std::size_t maxPreimageLength = 128;

    /** Parse the payload for a PreimageSha256 condition

        @param s A slice containing the DER encoded payload
        @param ec indicates success or failure of the operation
        @return the preimage, if successful; empty pointer otherwise.
    */
    static std::unique_ptr<Fulfillment>
    deserialize(Slice s, std::error_code& ec)
    {
        // Per the RFC, a preimage fulfillment is defined as
        // follows:
        //
        // PreimageFulfillment ::= SEQUENCE {
        //     preimage             OCTET STRING
        // }

        using namespace der;

        auto p = parsePreamble(s, ec);
        if (ec)
            return nullptr;

        if (!isPrimitive(p) || !isContextSpecific(p))
        {
            ec = error::incorrect_encoding;
            return {};
        }

        if (p.tag != 0)
        {
            ec = error::unexpected_tag;
            return {};
        }

        if (s.size() != p.length)
        {
            ec = error::trailing_garbage;
            return {};
        }

        if (s.size() > maxPreimageLength)
        {
            ec = error::preimage_too_long;
            return {};
        }

        auto b = parseOctetString(s, p.length, ec);
        if (ec)
            return {};

        return std::make_unique<PreimageSha256>(std::move(b));
    }

private:
    Buffer payload_;

public:
    PreimageSha256(Buffer&& b) noexcept : payload_(std::move(b))
    {
    }

    PreimageSha256(Slice s) noexcept : payload_(s)
    {
    }

    Type
    type() const override
    {
        return Type::preimageSha256;
    }

    Buffer
    fingerprint() const override
    {
        sha256_hasher h;
        h(payload_.data(), payload_.size());
        auto const d = static_cast<sha256_hasher::result_type>(h);
        return {d.data(), d.size()};
    }

    std::uint32_t
    cost() const override
    {
        return static_cast<std::uint32_t>(payload_.size());
    }

    Condition
    condition() const override
    {
        return {type(), cost(), fingerprint()};
    }

    bool
    validate(Slice) const override
    {
        // Perhaps counterintuitively, the message isn't
        // relevant.
        return true;
    }
};

}  // namespace cryptoconditions
}  // namespace xrpl