lix/src/libutil/serialise.hh

#pragma once

#include <memory>

#include "types.hh"
#include "util.hh"

namespace boost::context { struct stack_context; }

namespace nix {


/* Abstract destination of binary data. */
struct Sink
{
    virtual ~Sink() { }
    virtual void operator () (std::string_view data) = 0;
    virtual bool good() { return true; }
};

/* Just throws away data. */
struct NullSink : Sink
{
    void operator () (std::string_view data) override
    { }
};


struct FinishSink : virtual Sink
{
    virtual void finish() = 0;
};


/* A buffered abstract sink. Warning: a BufferedSink should not be
   used from multiple threads concurrently. */
struct BufferedSink : virtual Sink
{
    size_t bufSize, bufPos;
    std::unique_ptr<char[]> buffer;

    BufferedSink(size_t bufSize = 32 * 1024)
        : bufSize(bufSize), bufPos(0), buffer(nullptr) { }

    void operator () (std::string_view data) override;

    void flush();

    virtual void write(std::string_view data) = 0;
};


/* Abstract source of binary data. */
struct Source
{
    virtual ~Source() { }

    /* Store exactly ‘len’ bytes in the buffer pointed to by ‘data’.
       It blocks until all the requested data is available, or throws
       an error if it is not going to be available.   */
    void operator () (char * data, size_t len);

    /* Store up to ‘len’ in the buffer pointed to by ‘data’, and
       return the number of bytes stored.  It blocks until at least
       one byte is available. */
    virtual size_t read(char * data, size_t len) = 0;

    virtual bool good() { return true; }

    void drainInto(Sink & sink);

    std::string drain();
};


/* A buffered abstract source. Warning: a BufferedSource should not be
   used from multiple threads concurrently. */
struct BufferedSource : Source
{
    size_t bufSize, bufPosIn, bufPosOut;
    std::unique_ptr<char[]> buffer;

    BufferedSource(size_t bufSize = 32 * 1024)
        : bufSize(bufSize), bufPosIn(0), bufPosOut(0), buffer(nullptr) { }

    size_t read(char * data, size_t len) override;

    bool hasData();

protected:
    /* Underlying read call, to be overridden. */
    virtual size_t readUnbuffered(char * data, size_t len) = 0;
};


/* A sink that writes data to a file descriptor. */
struct FdSink : BufferedSink
{
    int fd;
    size_t written = 0;

    FdSink() : fd(-1) { }
    FdSink(int fd) : fd(fd) { }
    FdSink(FdSink&&) = default;

    FdSink & operator=(FdSink && s)
    {
        flush();
        fd = s.fd;
        s.fd = -1;
        written = s.written;
        return *this;
    }

    ~FdSink();

    void write(std::string_view data) override;

    bool good() override;

private:
    bool _good = true;
};


/* A source that reads data from a file descriptor. */
struct FdSource : BufferedSource
{
    int fd;
    size_t read = 0;

    FdSource() : fd(-1) { }
    FdSource(int fd) : fd(fd) { }
    FdSource(FdSource&&) = default;

    FdSource& operator=(FdSource && s)
    {
        fd = s.fd;
        s.fd = -1;
        read = s.read;
        return *this;
    }

    bool good() override;
protected:
    size_t readUnbuffered(char * data, size_t len) override;
private:
    bool _good = true;
};


/* A sink that writes data to a string. */
struct StringSink : Sink
{
    std::string s;
    StringSink() { }
    explicit StringSink(const size_t reservedSize)
    {
      s.reserve(reservedSize);
    };
    StringSink(std::string && s) : s(std::move(s)) { };
    void operator () (std::string_view data) override;
};


/* A source that reads data from a string. */
struct StringSource : Source
{
    std::string_view s;
    size_t pos;
    StringSource(std::string_view s) : s(s), pos(0) { }
    size_t read(char * data, size_t len) override;
};


/* A sink that writes all incoming data to two other sinks. */
struct TeeSink : Sink
{
    Sink & sink1, & sink2;
    TeeSink(Sink & sink1, Sink & sink2) : sink1(sink1), sink2(sink2) { }
    virtual void operator () (std::string_view data)
    {
        sink1(data);
        sink2(data);
    }
};


/* Adapter class of a Source that saves all data read to a sink. */
struct TeeSource : Source
{
    Source & orig;
    Sink & sink;
    TeeSource(Source & orig, Sink & sink)
        : orig(orig), sink(sink) { }
    size_t read(char * data, size_t len)
    {
        size_t n = orig.read(data, len);
        sink({data, n});
        return n;
    }
};

/* A reader that consumes the original Source until 'size'. */
struct SizedSource : Source
{
    Source & orig;
    size_t remain;
    SizedSource(Source & orig, size_t size)
        : orig(orig), remain(size) { }
    size_t read(char * data, size_t len)
    {
        if (this->remain <= 0) {
            throw EndOfFile("sized: unexpected end-of-file");
        }
        len = std::min(len, this->remain);
        size_t n = this->orig.read(data, len);
        this->remain -= n;
        return n;
    }

    /* Consume the original source until no remain data is left to consume. */
    size_t drainAll()
    {
        std::vector<char> buf(8192);
        size_t sum = 0;
        while (this->remain > 0) {
            size_t n = read(buf.data(), buf.size());
            sum += n;
        }
        return sum;
    }
};

/* A sink that that just counts the number of bytes given to it */
struct LengthSink : Sink
{
    uint64_t length = 0;

    void operator () (std::string_view data) override
    {
        length += data.size();
    }
};

/* Convert a function into a sink. */
struct LambdaSink : Sink
{
    typedef std::function<void(std::string_view data)> lambda_t;

    lambda_t lambda;

    LambdaSink(const lambda_t & lambda) : lambda(lambda) { }

    void operator () (std::string_view data) override
    {
        lambda(data);
    }
};


/* Convert a function into a source. */
struct LambdaSource : Source
{
    typedef std::function<size_t(char *, size_t)> lambda_t;

    lambda_t lambda;

    LambdaSource(const lambda_t & lambda) : lambda(lambda) { }

    size_t read(char * data, size_t len) override
    {
        return lambda(data, len);
    }
};

/* Chain two sources together so after the first is exhausted, the second is
   used */
struct ChainSource : Source
{
    Source & source1, & source2;
    bool useSecond = false;
    ChainSource(Source & s1, Source & s2)
        : source1(s1), source2(s2)
    { }

    size_t read(char * data, size_t len) override;
};

std::unique_ptr<FinishSink> sourceToSink(std::function<void(Source &)> fun);

/* Convert a function that feeds data into a Sink into a Source. The
   Source executes the function as a coroutine. */
std::unique_ptr<Source> sinkToSource(
    std::function<void(Sink &)> fun,
    std::function<void()> eof = []() {
        throw EndOfFile("coroutine has finished");
    });


void writePadding(size_t len, Sink & sink);
void writeString(std::string_view s, Sink & sink);

inline Sink & operator << (Sink & sink, uint64_t n)
{
    unsigned char buf[8];
    buf[0] = n & 0xff;
    buf[1] = (n >> 8) & 0xff;
    buf[2] = (n >> 16) & 0xff;
    buf[3] = (n >> 24) & 0xff;
    buf[4] = (n >> 32) & 0xff;
    buf[5] = (n >> 40) & 0xff;
    buf[6] = (n >> 48) & 0xff;
    buf[7] = (unsigned char) (n >> 56) & 0xff;
    sink({(char *) buf, sizeof(buf)});
    return sink;
}

Sink & operator << (Sink & in, const Error & ex);
Sink & operator << (Sink & sink, std::string_view s);
Sink & operator << (Sink & sink, const Strings & s);
Sink & operator << (Sink & sink, const StringSet & s);


MakeError(SerialisationError, Error);


template<typename T>
T readNum(Source & source)
{
    unsigned char buf[8];
    source((char *) buf, sizeof(buf));

    uint64_t n =
        ((uint64_t) buf[0]) |
        ((uint64_t) buf[1] << 8) |
        ((uint64_t) buf[2] << 16) |
        ((uint64_t) buf[3] << 24) |
        ((uint64_t) buf[4] << 32) |
        ((uint64_t) buf[5] << 40) |
        ((uint64_t) buf[6] << 48) |
        ((uint64_t) buf[7] << 56);

    if (n > (uint64_t)std::numeric_limits<T>::max())
        throw SerialisationError("serialised integer %d is too large for type '%s'", n, typeid(T).name());

    return (T) n;
}


inline unsigned int readInt(Source & source)
{
    return readNum<unsigned int>(source);
}


inline uint64_t readLongLong(Source & source)
{
    return readNum<uint64_t>(source);
}


void readPadding(size_t len, Source & source);
size_t readString(char * buf, size_t max, Source & source);
std::string readString(Source & source, size_t max = std::numeric_limits<size_t>::max());
template<class T> T readStrings(Source & source);

Source & operator >> (Source & in, std::string & s);

template<typename T>
Source & operator >> (Source & in, T & n)
{
    n = readNum<T>(in);
    return in;
}

template<typename T>
Source & operator >> (Source & in, bool & b)
{
    b = readNum<uint64_t>(in);
    return in;
}

Error readError(Source & source);


/* An adapter that converts a std::basic_istream into a source. */
struct StreamToSourceAdapter : Source
{
    std::shared_ptr<std::basic_istream<char>> istream;

    StreamToSourceAdapter(std::shared_ptr<std::basic_istream<char>> istream)
        : istream(istream)
    { }

    size_t read(char * data, size_t len) override
    {
        if (!istream->read(data, len)) {
            if (istream->eof()) {
                if (istream->gcount() == 0)
                    throw EndOfFile("end of file");
            } else
                throw Error("I/O error in StreamToSourceAdapter");
        }
        return istream->gcount();
    }
};


/* A source that reads a distinct format of concatenated chunks back into its
   logical form, in order to guarantee a known state to the original stream,
   even in the event of errors.

   Use with FramedSink, which also allows the logical stream to be terminated
   in the event of an exception.
*/
struct FramedSource : Source
{
    Source & from;
    bool eof = false;
    std::vector<char> pending;
    size_t pos = 0;

    FramedSource(Source & from) : from(from)
    { }

    ~FramedSource()
    {
        if (!eof) {
            while (true) {
                auto n = readInt(from);
                if (!n) break;
                std::vector<char> data(n);
                from(data.data(), n);
            }
        }
    }

    size_t read(char * data, size_t len) override
    {
        if (eof) throw EndOfFile("reached end of FramedSource");

        if (pos >= pending.size()) {
            size_t len = readInt(from);
            if (!len) {
                eof = true;
                return 0;
            }
            pending = std::vector<char>(len);
            pos = 0;
            from(pending.data(), len);
        }

        auto n = std::min(len, pending.size() - pos);
        memcpy(data, pending.data() + pos, n);
        pos += n;
        return n;
    }
};

/* Write as chunks in the format expected by FramedSource.

   The exception_ptr reference can be used to terminate the stream when you
   detect that an error has occurred on the remote end.
*/
struct FramedSink : nix::BufferedSink
{
    BufferedSink & to;
    std::exception_ptr & ex;

    FramedSink(BufferedSink & to, std::exception_ptr & ex) : to(to), ex(ex)
    { }

    ~FramedSink()
    {
        try {
            to << 0;
            to.flush();
        } catch (...) {
            ignoreException();
        }
    }

    void write(std::string_view data) override
    {
        /* Don't send more data if the remote has
            encountered an error. */
        if (ex) {
            auto ex2 = ex;
            ex = nullptr;
            std::rethrow_exception(ex2);
        }
        to << data.size();
        to(data);
    };
};

/* Stack allocation strategy for sinkToSource.
   Mutable to avoid a boehm gc dependency in libutil.

   boost::context doesn't provide a virtual class, so we define our own.
 */
struct StackAllocator {
    virtual boost::context::stack_context allocate() = 0;
    virtual void deallocate(boost::context::stack_context sctx) = 0;

    /* The stack allocator to use in sinkToSource and potentially elsewhere.
       It is reassigned by the initGC() method in libexpr. */
    static StackAllocator *defaultAllocator;
};

}