nix-super/src/libutil/memory-source-accessor.cc

#include "memory-source-accessor.hh"

namespace nix {

MemorySourceAccessor::File *
MemorySourceAccessor::open(const CanonPath & path, std::optional<File> create)
{
    File * cur = &root;

    bool newF = false;

    for (std::string_view name : path)
    {
        auto * curDirP = std::get_if<File::Directory>(&cur->raw);
        if (!curDirP)
            return nullptr;
        auto & curDir = *curDirP;

        auto i = curDir.contents.find(name);
        if (i == curDir.contents.end()) {
            if (!create)
                return nullptr;
            else {
                newF = true;
                i = curDir.contents.insert(i, {
                    std::string { name },
                    File::Directory {},
                });
            }
        }
        cur = &i->second;
    }

    if (newF && create) *cur = std::move(*create);

    return cur;
}

std::string MemorySourceAccessor::readFile(const CanonPath & path)
{
    auto * f = open(path, std::nullopt);
    if (!f)
        throw Error("file '%s' does not exist", path);
    if (auto * r = std::get_if<File::Regular>(&f->raw))
        return r->contents;
    else
        throw Error("file '%s' is not a regular file", path);
}

bool MemorySourceAccessor::pathExists(const CanonPath & path)
{
    return open(path, std::nullopt);
}

MemorySourceAccessor::Stat MemorySourceAccessor::File::lstat() const
{
    return std::visit(overloaded {
        [](const Regular & r) {
            return Stat {
                .type = tRegular,
                .fileSize = r.contents.size(),
                .isExecutable = r.executable,
            };
        },
        [](const Directory &) {
            return Stat {
                .type = tDirectory,
            };
        },
        [](const Symlink &) {
            return Stat {
                .type = tSymlink,
            };
        },
    }, this->raw);
}

std::optional<MemorySourceAccessor::Stat>
MemorySourceAccessor::maybeLstat(const CanonPath & path)
{
    const auto * f = open(path, std::nullopt);
    return f ? std::optional { f->lstat() } : std::nullopt;
}

MemorySourceAccessor::DirEntries MemorySourceAccessor::readDirectory(const CanonPath & path)
{
    auto * f = open(path, std::nullopt);
    if (!f)
        throw Error("file '%s' does not exist", path);
    if (auto * d = std::get_if<File::Directory>(&f->raw)) {
        DirEntries res;
        for (auto & [name, file] : d->contents)
            res.insert_or_assign(name, file.lstat().type);
        return res;
    } else
        throw Error("file '%s' is not a directory", path);
    return {};
}

std::string MemorySourceAccessor::readLink(const CanonPath & path)
{
    auto * f = open(path, std::nullopt);
    if (!f)
        throw Error("file '%s' does not exist", path);
    if (auto * s = std::get_if<File::Symlink>(&f->raw))
        return s->target;
    else
        throw Error("file '%s' is not a symbolic link", path);
}

SourcePath MemorySourceAccessor::addFile(CanonPath path, std::string && contents)
{
    auto * f = open(path, File { File::Regular {} });
    if (!f)
        throw Error("file '%s' cannot be made because some parent file is not a directory", path);
    if (auto * r = std::get_if<File::Regular>(&f->raw))
        r->contents = std::move(contents);
    else
        throw Error("file '%s' is not a regular file", path);

    return SourcePath{ref(shared_from_this()), path};
}


using File = MemorySourceAccessor::File;

void MemorySink::createDirectory(const Path & path)
{
    auto * f = dst.open(CanonPath{path}, File { File::Directory { } });
    if (!f)
        throw Error("file '%s' cannot be made because some parent file is not a directory", path);

    if (!std::holds_alternative<File::Directory>(f->raw))
        throw Error("file '%s' is not a directory", path);
};

struct CreateMemoryRegularFile : CreateRegularFileSink {
    File::Regular & regularFile;

    CreateMemoryRegularFile(File::Regular & r)
        : regularFile(r)
    { }

    void operator () (std::string_view data) override;
    void isExecutable() override;
    void preallocateContents(uint64_t size) override;
};

void MemorySink::createRegularFile(const Path & path, std::function<void(CreateRegularFileSink &)> func)
{
    auto * f = dst.open(CanonPath{path}, File { File::Regular {} });
    if (!f)
        throw Error("file '%s' cannot be made because some parent file is not a directory", path);
    if (auto * rp = std::get_if<File::Regular>(&f->raw)) {
        CreateMemoryRegularFile crf { *rp };
        func(crf);
    } else
        throw Error("file '%s' is not a regular file", path);
}

void CreateMemoryRegularFile::isExecutable()
{
    regularFile.executable = true;
}

void CreateMemoryRegularFile::preallocateContents(uint64_t len)
{
    regularFile.contents.reserve(len);
}

void CreateMemoryRegularFile::operator () (std::string_view data)
{
    regularFile.contents += data;
}

void MemorySink::createSymlink(const Path & path, const std::string & target)
{
    auto * f = dst.open(CanonPath{path}, File { File::Symlink { } });
    if (!f)
        throw Error("file '%s' cannot be made because some parent file is not a directory", path);
    if (auto * s = std::get_if<File::Symlink>(&f->raw))
        s->target = target;
    else
        throw Error("file '%s' is not a symbolic link", path);
}

ref<SourceAccessor> makeEmptySourceAccessor()
{
    static auto empty = make_ref<MemorySourceAccessor>().cast<SourceAccessor>();
    return empty;
}

}