ruby--ruby/io_buffer.c

/**********************************************************************

  io_buffer.c

  Copyright (C) 2021 Samuel Grant Dawson Williams

**********************************************************************/

#include "ruby/io.h"
#include "ruby/io/buffer.h"

#include "internal/string.h"
#include "internal/bits.h"
#include "internal/error.h"

VALUE rb_cIOBuffer;
VALUE rb_eIOBufferLockedError;
VALUE rb_eIOBufferAllocationError;
VALUE rb_eIOBufferMutationError;
VALUE rb_eIOBufferInvalidatedError;

size_t RUBY_IO_BUFFER_PAGE_SIZE;
size_t RUBY_IO_BUFFER_DEFAULT_SIZE;

#ifdef _WIN32
#else
#include <unistd.h>
#include <sys/mman.h>
#endif

struct rb_io_buffer {
    void *base;
    size_t size;
    enum rb_io_buffer_flags flags;

#if defined(_WIN32)
    HANDLE mapping;
#endif

    VALUE source;
};

static inline void *
io_buffer_map_memory(size_t size)
{
#if defined(_WIN32)
    void * base = VirtualAlloc(0, size, MEM_COMMIT, PAGE_READWRITE);

    if (!base) {
        rb_sys_fail("io_buffer_map_memory:VirtualAlloc");
    }
#else
    void * base = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);

    if (base == MAP_FAILED) {
        rb_sys_fail("io_buffer_map_memory:mmap");
    }
#endif

    return base;
}

static void
io_buffer_map_file(struct rb_io_buffer *data, int descriptor, size_t size, off_t offset, enum rb_io_buffer_flags flags)
{
#if defined(_WIN32)
    HANDLE file = (HANDLE)_get_osfhandle(descriptor);
    if (!file) rb_sys_fail("io_buffer_map_descriptor:_get_osfhandle");

    DWORD protect = PAGE_READONLY, access = FILE_MAP_READ;

    if (flags & RB_IO_BUFFER_READONLY) {
        data->flags |= RB_IO_BUFFER_READONLY;
    }
    else {
        protect = PAGE_READWRITE;
        access = FILE_MAP_WRITE;
    }

    HANDLE mapping = CreateFileMapping(file, NULL, protect, 0, 0, NULL);
    if (!mapping) rb_sys_fail("io_buffer_map_descriptor:CreateFileMapping");

    if (flags & RB_IO_BUFFER_PRIVATE) {
        access |= FILE_MAP_COPY;
        data->flags |= RB_IO_BUFFER_PRIVATE;
    } else {
        // This buffer refers to external data.
        data->flags |= RB_IO_BUFFER_EXTERNAL;
    }

    void *base = MapViewOfFile(mapping, access, (DWORD)(offset >> 32), (DWORD)(offset & 0xFFFFFFFF), size);

    if (!base) {
        CloseHandle(mapping);
        rb_sys_fail("io_buffer_map_file:MapViewOfFile");
    }

    data->mapping = mapping;
#else
    int protect = PROT_READ, access = 0;

    if (flags & RB_IO_BUFFER_READONLY) {
        data->flags |= RB_IO_BUFFER_READONLY;
    }
    else {
        protect |= PROT_WRITE;
    }

    if (flags & RB_IO_BUFFER_PRIVATE) {
        data->flags |= RB_IO_BUFFER_PRIVATE;
    }
    else {
        // This buffer refers to external data.
        data->flags |= RB_IO_BUFFER_EXTERNAL;
        access |= MAP_SHARED;
    }

    void *base = mmap(NULL, size, protect, access, descriptor, offset);

    if (base == MAP_FAILED) {
        rb_sys_fail("io_buffer_map_file:mmap");
    }
#endif

    data->base = base;
    data->size = size;

    data->flags |= RB_IO_BUFFER_MAPPED;
}

static inline void
io_buffer_unmap(void* base, size_t size)
{
#ifdef _WIN32
    VirtualFree(base, 0, MEM_RELEASE);
#else
    munmap(base, size);
#endif
}

static void
io_buffer_experimental(void)
{
    static int warned = 0;

    if (warned) return;

    warned = 1;

    if (rb_warning_category_enabled_p(RB_WARN_CATEGORY_EXPERIMENTAL)) {
        rb_category_warn(RB_WARN_CATEGORY_EXPERIMENTAL,
          "IO::Buffer is experimental and both the Ruby and C interface may change in the future!"
        );
    }
}

static void
io_buffer_initialize(struct rb_io_buffer *data, void *base, size_t size, enum rb_io_buffer_flags flags, VALUE source)
{
    data->flags = flags;
    data->size = size;

    if (base) {
        data->base = base;
    }
    else {
        if (data->flags & RB_IO_BUFFER_INTERNAL) {
            data->base = calloc(data->size, 1);
        }
        else if (data->flags & RB_IO_BUFFER_MAPPED) {
            data->base = io_buffer_map_memory(data->size);
        }
    }

    if (!data->base) {
        rb_raise(rb_eIOBufferAllocationError, "Could not allocate buffer!");
    }

    data->source = source;
}

static void
io_buffer_zero(struct rb_io_buffer *data)
{
    data->base = NULL;
    data->size = 0;
#if defined(_WIN32)
    data->mapping = NULL;
#endif
    data->source = Qnil;
}

static int
io_buffer_free(struct rb_io_buffer *data)
{
    if (data->base) {
        if (data->flags & RB_IO_BUFFER_INTERNAL) {
            free(data->base);
        }

        if (data->flags & RB_IO_BUFFER_MAPPED) {
            io_buffer_unmap(data->base, data->size);
        }

        if (RB_TYPE_P(data->source, T_STRING)) {
            rb_str_unlocktmp(data->source);
        }

        data->base = NULL;

#if defined(_WIN32)
        if (data->mapping) {
            CloseHandle(data->mapping);
            data->mapping = NULL;
        }
#endif

        data->size = 0;

        return 1;
    }

    return 0;
}

void
rb_io_buffer_type_mark(void *_data)
{
    struct rb_io_buffer *data = _data;
    rb_gc_mark(data->source);
}

void
rb_io_buffer_type_free(void *_data)
{
    struct rb_io_buffer *data = _data;

    io_buffer_free(data);

    free(data);
}

size_t
rb_io_buffer_type_size(const void *_data)
{
    const struct rb_io_buffer *data = _data;
    size_t total = sizeof(struct rb_io_buffer);

    if (data->flags) {
        total += data->size;
    }

    return total;
}

static const rb_data_type_t rb_io_buffer_type = {
    .wrap_struct_name = "IO::Buffer",
    .function = {
        .dmark = rb_io_buffer_type_mark,
        .dfree = rb_io_buffer_type_free,
        .dsize = rb_io_buffer_type_size,
    },
    .data = NULL,
    .flags = RUBY_TYPED_FREE_IMMEDIATELY,
};

VALUE
rb_io_buffer_type_allocate(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    VALUE instance = TypedData_Make_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    io_buffer_zero(data);

    return instance;
}

VALUE
rb_io_buffer_type_for(VALUE klass, VALUE string)
{
    io_buffer_experimental();

    StringValue(string);

    VALUE instance = rb_io_buffer_type_allocate(klass);

    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(instance, struct rb_io_buffer, &rb_io_buffer_type, data);

    rb_str_locktmp(string);

    enum rb_io_buffer_flags flags = RB_IO_BUFFER_EXTERNAL;

    if (RB_OBJ_FROZEN(string))
        flags |= RB_IO_BUFFER_READONLY;

    io_buffer_initialize(data, RSTRING_PTR(string), RSTRING_LEN(string), flags, string);

    return instance;
}

VALUE
rb_io_buffer_new(void *base, size_t size, enum rb_io_buffer_flags flags)
{
    VALUE instance = rb_io_buffer_type_allocate(rb_cIOBuffer);

    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(instance, struct rb_io_buffer, &rb_io_buffer_type, data);

    io_buffer_initialize(data, base, size, flags, Qnil);

    return instance;
}

VALUE
rb_io_buffer_map(VALUE io, size_t size, off_t offset, enum rb_io_buffer_flags flags)
{
    io_buffer_experimental();

    VALUE instance = rb_io_buffer_type_allocate(rb_cIOBuffer);

    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(instance, struct rb_io_buffer, &rb_io_buffer_type, data);

    int descriptor = rb_io_descriptor(io);

    io_buffer_map_file(data, descriptor, size, offset, flags);

    return instance;
}

static VALUE
io_buffer_map(int argc, VALUE *argv, VALUE klass)
{
    if (argc < 1 || argc > 4) {
        rb_error_arity(argc, 2, 4);
    }

    VALUE io = argv[0];

    size_t size;
    if (argc >= 2) {
        size = RB_NUM2SIZE(argv[1]);
    }
    else {
        off_t file_size = rb_file_size(io);

        // Compiler can confirm that we handled file_size < 0 case:
        if (file_size < 0) {
            rb_raise(rb_eArgError, "Invalid negative file size!");
        }
        // Here, we assume that file_size is positive:
        else if ((uintmax_t)file_size > SIZE_MAX) {
            rb_raise(rb_eArgError, "File larger than address space!");
        }
        else {
            // This conversion shoud be safe:
            size = (size_t)file_size;
        }
    }

    off_t offset = 0;
    if (argc >= 3) {
        offset = NUM2OFFT(argv[2]);
    }

    enum rb_io_buffer_flags flags = RB_IO_BUFFER_READONLY;
    if (argc >= 4) {
        flags = RB_NUM2UINT(argv[3]);
    }

    return rb_io_buffer_map(io, size, offset, flags);
}

// Compute the optimal allocation flags for a buffer of the given size.
static inline enum rb_io_buffer_flags
io_flags_for_size(size_t size)
{
    if (size > RUBY_IO_BUFFER_PAGE_SIZE) {
        return RB_IO_BUFFER_MAPPED;
    }

    return RB_IO_BUFFER_INTERNAL;
}

VALUE
rb_io_buffer_initialize(int argc, VALUE *argv, VALUE self)
{
    io_buffer_experimental();

    if (argc < 0 || argc > 2) {
        rb_error_arity(argc, 0, 2);
    }

    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    size_t size;

    if (argc > 0) {
        size = RB_NUM2SIZE(argv[0]);
    } else {
        size = RUBY_IO_BUFFER_DEFAULT_SIZE;
    }

    enum rb_io_buffer_flags flags = 0;
    if (argc >= 2) {
        flags = RB_NUM2UINT(argv[1]);
    }
    else {
        flags |= io_flags_for_size(size);
    }

    io_buffer_initialize(data, NULL, size, flags, Qnil);

    return self;
}

static int
io_buffer_validate_slice(VALUE source, void *base, size_t size)
{
    const void *source_base = NULL;
    size_t source_size = 0;

    if (RB_TYPE_P(source, T_STRING)) {
        RSTRING_GETMEM(source, source_base, source_size);
    }
    else {
        rb_io_buffer_get_readonly(source, &source_base, &source_size);
    }

    // Source is invalid:
    if (source_base == NULL) return 0;

    // Base is out of range:
    if (base < source_base) return 0;

    const void *source_end = (char*)source_base + source_size;
    const void *end = (char*)base + size;

    // End is out of range:
    if (end > source_end) return 0;

    // It seems okay:
    return 1;
}

static int
io_buffer_validate(struct rb_io_buffer *data)
{
    if (data->source != Qnil) {
        // Only slices incur this overhead, unfortunately... better safe than sorry!
        return io_buffer_validate_slice(data->source, data->base, data->size);
    }
    else {
        return 1;
    }
}

VALUE
rb_io_buffer_to_s(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    VALUE result = rb_str_new_cstr("#<");

    rb_str_append(result, rb_class_name(CLASS_OF(self)));
    rb_str_catf(result, " %p+%"PRIdSIZE, data->base, data->size);

    if (data->base == NULL) {
        rb_str_cat2(result, " NULL");
    }

    if (data->flags & RB_IO_BUFFER_INTERNAL) {
        rb_str_cat2(result, " INTERNAL");
    }

    if (data->flags & RB_IO_BUFFER_MAPPED) {
        rb_str_cat2(result, " MAPPED");
    }

    if (data->flags & RB_IO_BUFFER_LOCKED) {
        rb_str_cat2(result, " LOCKED");
    }

    if (data->flags & RB_IO_BUFFER_READONLY) {
        rb_str_cat2(result, " READONLY");
    }

    if (data->source != Qnil) {
        rb_str_cat2(result, " SLICE");
    }

    if (!io_buffer_validate(data)) {
        rb_str_cat2(result, " INVALID");
    }

    return rb_str_cat2(result, ">");
}

static VALUE
io_buffer_hexdump(VALUE string, size_t width, char *base, size_t size)
{
    char *text = alloca(width+1);
    text[width] = '\0';

    for (size_t offset = 0; offset < size; offset += width) {
        memset(text, '\0', width);
        rb_str_catf(string, "\n0x%08zx ", offset);

        for (size_t i = 0; i < width; i += 1) {
            if (offset+i < size) {
                unsigned char value = ((unsigned char*)base)[offset+i];

                if (value < 127 && isprint(value)) {
                    text[i] = (char)value;
                }
                else {
                    text[i] = '.';
                }

                rb_str_catf(string, " %02x", value);
            }
            else {
                rb_str_cat2(string, "   ");
            }
        }

        rb_str_catf(string, " %s", text);
    }

    rb_str_cat2(string, "\n");

    return string;
}

VALUE
rb_io_buffer_inspect(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    VALUE result = rb_io_buffer_to_s(self);

    if (io_buffer_validate(data)) {
        // Limit the maximum size genearted by inspect.
        if (data->size <= 256) {
            io_buffer_hexdump(result, 16, data->base, data->size);
        }
    }

    return result;
}

VALUE
rb_io_buffer_size(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    return SIZET2NUM(data->size);
}

static VALUE
rb_io_buffer_null_p(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    return data->base ? Qfalse : Qtrue;
}

static VALUE
rb_io_buffer_empty_p(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    return data->size ? Qtrue : Qfalse;
}

static VALUE
rb_io_buffer_external_p(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    return data->flags & RB_IO_BUFFER_EXTERNAL ? Qtrue : Qfalse;
}

static VALUE
rb_io_buffer_internal_p(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    return data->flags & RB_IO_BUFFER_INTERNAL ? Qtrue : Qfalse;
}

static VALUE
rb_io_buffer_mapped_p(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    return data->flags & RB_IO_BUFFER_MAPPED ? Qtrue : Qfalse;
}

static VALUE
rb_io_buffer_locked_p(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    return data->flags & RB_IO_BUFFER_LOCKED ? Qtrue : Qfalse;
}

int
rb_io_buffer_readonly_p(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    return data->flags & RB_IO_BUFFER_READONLY;
}

static VALUE
io_buffer_readonly_p(VALUE self)
{
    return rb_io_buffer_readonly_p(self) ? Qtrue : Qfalse;
}

VALUE
rb_io_buffer_lock(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    if (data->flags & RB_IO_BUFFER_LOCKED) {
        rb_raise(rb_eIOBufferLockedError, "Buffer already locked!");
    }

    data->flags |= RB_IO_BUFFER_LOCKED;

    return self;
}

VALUE
rb_io_buffer_unlock(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    if (!(data->flags & RB_IO_BUFFER_LOCKED)) {
        rb_raise(rb_eIOBufferLockedError, "Buffer not locked!");
    }

    data->flags &= ~RB_IO_BUFFER_LOCKED;

    return self;
}

VALUE
rb_io_buffer_locked(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    if (data->flags & RB_IO_BUFFER_LOCKED) {
        rb_raise(rb_eIOBufferLockedError, "Buffer already locked!");
    }

    data->flags |= RB_IO_BUFFER_LOCKED;

    VALUE result = rb_yield(self);

    data->flags &= ~RB_IO_BUFFER_LOCKED;

    return result;
}

VALUE
rb_io_buffer_free(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    if (data->flags & RB_IO_BUFFER_LOCKED) {
        rb_raise(rb_eIOBufferLockedError, "Buffer is locked!");
    }

    io_buffer_free(data);

    return self;
}

static inline void
rb_io_buffer_validate(struct rb_io_buffer *data, size_t offset, size_t length)
{
    if (offset + length > data->size) {
        rb_raise(rb_eArgError, "Specified offset + length exceeds source size!");
    }
}

VALUE
rb_io_buffer_slice(VALUE self, VALUE _offset, VALUE _length)
{
    // TODO fail on negative offets/lengths.
    size_t offset = NUM2SIZET(_offset);
    size_t length = NUM2SIZET(_length);

    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    rb_io_buffer_validate(data, offset, length);

    VALUE instance = rb_io_buffer_type_allocate(rb_class_of(self));
    struct rb_io_buffer *slice = NULL;
    TypedData_Get_Struct(instance, struct rb_io_buffer, &rb_io_buffer_type, slice);

    slice->base = (char*)data->base + offset;
    slice->size = length;

    // The source should be the root buffer:
    if (data->source != Qnil)
        slice->source = data->source;
    else
        slice->source = self;

    return instance;
}

static void
io_buffer_get(struct rb_io_buffer *data, void **base, size_t *size)
{
    if (data->flags & RB_IO_BUFFER_READONLY) {
        rb_raise(rb_eIOBufferMutationError, "Buffer is not writable!");
    }

    if (!io_buffer_validate(data)) {
        rb_raise(rb_eIOBufferInvalidatedError, "Buffer has been invalidated!");
    }

    if (data && data->base) {
        *base = data->base;
        *size = data->size;

        return;
    }

    rb_raise(rb_eIOBufferAllocationError, "Buffer is not allocated!");
}

void
rb_io_buffer_get(VALUE self, void **base, size_t *size)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    io_buffer_get(data, base, size);
}

void
rb_io_buffer_get_readonly(VALUE self, const void **base, size_t *size)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    if (!io_buffer_validate(data)) {
        rb_raise(rb_eIOBufferInvalidatedError, "Buffer has been invalidated!");
    }

    if (data && data->base) {
        *base = data->base;
        *size = data->size;

        return;
    }

    rb_raise(rb_eIOBufferAllocationError, "Buffer is not allocated!");
}

VALUE
rb_io_buffer_transfer(VALUE self)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    if (data->flags & RB_IO_BUFFER_LOCKED) {
        rb_raise(rb_eIOBufferLockedError, "Cannot transfer ownership of locked buffer!");
    }

    VALUE instance = rb_io_buffer_type_allocate(rb_class_of(self));
    struct rb_io_buffer *transferred;
    TypedData_Get_Struct(instance, struct rb_io_buffer, &rb_io_buffer_type, transferred);

    *transferred = *data;
    io_buffer_zero(data);

    return instance;
}

static void
io_buffer_resize_clear(struct rb_io_buffer *data, void* base, size_t size)
{
    if (size > data->size) {
        memset((unsigned char*)base+data->size, 0, size - data->size);
    }
}

static void
io_buffer_resize_copy(struct rb_io_buffer *data, size_t size)
{
    // Slow path:
    struct rb_io_buffer resized;
    io_buffer_initialize(&resized, NULL, size, io_flags_for_size(size), Qnil);

    if (data->base) {
        size_t preserve = data->size;
        if (preserve > size) preserve = size;
        memcpy(resized.base, data->base, preserve);

        io_buffer_resize_clear(data, resized.base, size);
    }

    io_buffer_free(data);
    *data = resized;
}

void
rb_io_buffer_resize(VALUE self, size_t size)
{
    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    if (data->flags & RB_IO_BUFFER_LOCKED) {
        rb_raise(rb_eIOBufferLockedError, "Cannot resize locked buffer!");
    }

    if (data->base == NULL) {
        io_buffer_initialize(data, NULL, size, io_flags_for_size(size), Qnil);
        return;
    }

    if (data->flags & RB_IO_BUFFER_EXTERNAL) {
        rb_raise(rb_eIOBufferMutationError, "Cannot resize external buffer!");
    }

#ifdef MREMAP_MAYMOVE
    if (data->flags & RB_IO_BUFFER_MAPPED) {
        void *base = mremap(data->base, data->size, size, MREMAP_MAYMOVE);

        if (base == MAP_FAILED) {
            rb_sys_fail("rb_io_buffer_resize:mremap");
        }

        io_buffer_resize_clear(data, base, size);

        data->base = base;
        data->size = size;

        return;
    }
#endif

    if (data->flags & RB_IO_BUFFER_INTERNAL) {
        void *base = realloc(data->base, size);

        if (!base) {
            rb_sys_fail("rb_io_buffer_resize:realloc");
        }

        io_buffer_resize_clear(data, base, size);

        data->base = base;
        data->size = size;

        return;
    }

    io_buffer_resize_copy(data, size);
}

static VALUE
io_buffer_resize(VALUE self, VALUE size)
{
    rb_io_buffer_resize(self, NUM2SIZET(size));

    return self;
}

static VALUE
rb_io_buffer_compare(VALUE self, VALUE other)
{
    const void *ptr1, *ptr2;
    size_t size1, size2;

    rb_io_buffer_get_readonly(self, &ptr1, &size1);
    rb_io_buffer_get_readonly(other, &ptr2, &size2);

    if (size1 < size2) {
        return RB_INT2NUM(-1);
    }

    if (size1 > size2) {
        return RB_INT2NUM(1);
    }

    return RB_INT2NUM(memcmp(ptr1, ptr2, size1));
}

static void
io_buffer_validate_type(size_t size, size_t offset)
{
    if (offset > size) {
        rb_raise(rb_eArgError, "Type extends beyond end of buffer!");
    }
}

// Lower case: little endian.
// Upper case: big endian (network endian).
//
// :U8        | unsigned 8-bit integer.
// :S8        | signed 8-bit integer.
//
// :u16, :U16 | unsigned 16-bit integer.
// :s16, :S16 | signed 16-bit integer.
//
// :u32, :U32 | unsigned 32-bit integer.
// :s32, :S32 | signed 32-bit integer.
//
// :u64, :U64 | unsigned 64-bit integer.
// :s64, :S64 | signed 64-bit integer.
//
// :f32, :F32 | 32-bit floating point number.
// :f64, :F64 | 64-bit floating point number.

#define ruby_swap8(value) value

union swapf32 {
    uint32_t integral;
    float value;
};

static float
ruby_swapf32(float value)
{
    union swapf32 swap = {.value = value};
    swap.integral = ruby_swap32(swap.integral);
    return swap.value;
}

union swapf64 {
    uint64_t integral;
    double value;
};

static double
ruby_swapf64(double value)
{
    union swapf64 swap = {.value = value};
    swap.integral = ruby_swap64(swap.integral);
    return swap.value;
}

#define DECLARE_TYPE(name, type, endian, wrap, unwrap, swap) \
static ID RB_IO_BUFFER_TYPE_##name; \
\
static VALUE \
io_buffer_read_##name(const void* base, size_t size, size_t *offset) \
{ \
    io_buffer_validate_type(size, *offset + sizeof(type)); \
    type value; \
    memcpy(&value, (char*)base + *offset, sizeof(type)); \
    if (endian != RB_IO_BUFFER_HOST_ENDIAN) value = swap(value); \
    *offset += sizeof(type); \
    return wrap(value); \
} \
\
static void \
io_buffer_write_##name(const void* base, size_t size, size_t *offset, VALUE _value) \
{ \
    io_buffer_validate_type(size, *offset + sizeof(type)); \
    type value = unwrap(_value); \
    if (endian != RB_IO_BUFFER_HOST_ENDIAN) value = swap(value); \
    memcpy((char*)base + *offset, &value, sizeof(type)); \
    *offset += sizeof(type); \
}

DECLARE_TYPE(U8, uint8_t, RB_IO_BUFFER_BIG_ENDIAN, RB_UINT2NUM, RB_NUM2UINT, ruby_swap8)
DECLARE_TYPE(S8, int8_t, RB_IO_BUFFER_BIG_ENDIAN, RB_INT2NUM, RB_NUM2INT, ruby_swap8)

DECLARE_TYPE(u16, uint16_t, RB_IO_BUFFER_LITTLE_ENDIAN, RB_UINT2NUM, RB_NUM2UINT, ruby_swap16)
DECLARE_TYPE(U16, uint16_t, RB_IO_BUFFER_BIG_ENDIAN, RB_UINT2NUM, RB_NUM2UINT, ruby_swap16)
DECLARE_TYPE(s16, int16_t, RB_IO_BUFFER_LITTLE_ENDIAN, RB_INT2NUM, RB_NUM2INT, ruby_swap16)
DECLARE_TYPE(S16, int16_t, RB_IO_BUFFER_BIG_ENDIAN, RB_INT2NUM, RB_NUM2INT, ruby_swap16)

DECLARE_TYPE(u32, uint32_t, RB_IO_BUFFER_LITTLE_ENDIAN, RB_UINT2NUM, RB_NUM2UINT, ruby_swap32)
DECLARE_TYPE(U32, uint32_t, RB_IO_BUFFER_BIG_ENDIAN, RB_UINT2NUM, RB_NUM2UINT, ruby_swap32)
DECLARE_TYPE(s32, int32_t, RB_IO_BUFFER_LITTLE_ENDIAN, RB_INT2NUM, RB_NUM2INT, ruby_swap32)
DECLARE_TYPE(S32, int32_t, RB_IO_BUFFER_BIG_ENDIAN, RB_INT2NUM, RB_NUM2INT, ruby_swap32)

DECLARE_TYPE(u64, uint64_t, RB_IO_BUFFER_LITTLE_ENDIAN, RB_ULL2NUM, RB_NUM2ULL, ruby_swap64)
DECLARE_TYPE(U64, uint64_t, RB_IO_BUFFER_BIG_ENDIAN, RB_ULL2NUM, RB_NUM2ULL, ruby_swap64)
DECLARE_TYPE(s64, int64_t, RB_IO_BUFFER_LITTLE_ENDIAN, RB_LL2NUM, RB_NUM2LL, ruby_swap64)
DECLARE_TYPE(S64, int64_t, RB_IO_BUFFER_BIG_ENDIAN, RB_LL2NUM, RB_NUM2LL, ruby_swap64)

DECLARE_TYPE(f32, float, RB_IO_BUFFER_LITTLE_ENDIAN, DBL2NUM, NUM2DBL, ruby_swapf32)
DECLARE_TYPE(F32, float, RB_IO_BUFFER_BIG_ENDIAN, DBL2NUM, NUM2DBL, ruby_swapf32)
DECLARE_TYPE(f64, double, RB_IO_BUFFER_LITTLE_ENDIAN, DBL2NUM, NUM2DBL, ruby_swapf64)
DECLARE_TYPE(F64, double, RB_IO_BUFFER_BIG_ENDIAN, DBL2NUM, NUM2DBL, ruby_swapf64)
#undef DECLARE_TYPE

VALUE
rb_io_buffer_get_value(const void* base, size_t size, ID type, size_t offset)
{
#define READ_TYPE(name) if (type == RB_IO_BUFFER_TYPE_##name) return io_buffer_read_##name(base, size, &offset);
    READ_TYPE(U8)
    READ_TYPE(S8)

    READ_TYPE(u16)
    READ_TYPE(U16)
    READ_TYPE(s16)
    READ_TYPE(S16)

    READ_TYPE(u32)
    READ_TYPE(U32)
    READ_TYPE(s32)
    READ_TYPE(S32)

    READ_TYPE(u64)
    READ_TYPE(U64)
    READ_TYPE(s64)
    READ_TYPE(S64)

    READ_TYPE(f32)
    READ_TYPE(F32)
    READ_TYPE(f64)
    READ_TYPE(F64)
#undef READ_TYPE

    rb_raise(rb_eArgError, "Invalid type name!");
}

static VALUE
io_buffer_get_value(VALUE self, VALUE type, VALUE _offset)
{
    const void *base;
    size_t size;
    size_t offset = NUM2SIZET(_offset);

    rb_io_buffer_get_readonly(self, &base, &size);

    return rb_io_buffer_get_value(base, size, RB_SYM2ID(type), offset);
}

void
rb_io_buffer_set_value(const void* base, size_t size, ID type, size_t offset, VALUE value)
{
#define WRITE_TYPE(name) if (type == RB_IO_BUFFER_TYPE_##name) {io_buffer_write_##name(base, size, &offset, value); return;}
    WRITE_TYPE(U8)
    WRITE_TYPE(S8)

    WRITE_TYPE(u16)
    WRITE_TYPE(U16)
    WRITE_TYPE(s16)
    WRITE_TYPE(S16)

    WRITE_TYPE(u32)
    WRITE_TYPE(U32)
    WRITE_TYPE(s32)
    WRITE_TYPE(S32)

    WRITE_TYPE(u64)
    WRITE_TYPE(U64)
    WRITE_TYPE(s64)
    WRITE_TYPE(S64)

    WRITE_TYPE(f32)
    WRITE_TYPE(F32)
    WRITE_TYPE(f64)
    WRITE_TYPE(F64)
#undef WRITE_TYPE

    rb_raise(rb_eArgError, "Invalid type name!");
}

static VALUE
io_buffer_set_value(VALUE self, VALUE type, VALUE _offset, VALUE value)
{
    void *base;
    size_t size;
    size_t offset = NUM2SIZET(_offset);

    rb_io_buffer_get(self, &base, &size);

    rb_io_buffer_set_value(base, size, RB_SYM2ID(type), offset, value);

    return SIZET2NUM(offset);
}

static void
io_buffer_memcpy(struct rb_io_buffer *data, size_t offset, const void *source_base, size_t source_offset, size_t source_size, size_t length)
{
    void *base;
    size_t size;
    io_buffer_get(data, &base, &size);

    rb_io_buffer_validate(data, offset, length);

    if (source_offset + length > source_size) {
        rb_raise(rb_eArgError, "The computed source range exceeds the size of the source!");
    }

    memcpy((unsigned char*)base+offset, (unsigned char*)source_base+source_offset, length);
}

// (offset, length, source_offset) -> length
static VALUE
io_buffer_copy_from(struct rb_io_buffer *data, const void *source_base, size_t source_size, int argc, VALUE *argv)
{
    size_t offset;
    size_t length;
    size_t source_offset;

    // The offset we copy into the buffer:
    if (argc >= 1) {
        offset = NUM2SIZET(argv[0]);
    } else {
        offset = 0;
    }

    // The offset we start from within the string:
    if (argc >= 3) {
        source_offset = NUM2SIZET(argv[2]);

        if (source_offset > source_size) {
            rb_raise(rb_eArgError, "The given source offset is bigger than the source itself!");
        }
    } else {
        source_offset = 0;
    }

    // The length we are going to copy:
    if (argc >= 2 && !RB_NIL_P(argv[1])) {
        length = NUM2SIZET(argv[1]);
    } else {
        // Default to the source offset -> source size:
        length = source_size - source_offset;
    }

    io_buffer_memcpy(data, offset, source_base, source_offset, source_size, length);

    return SIZET2NUM(length);
}

// (string_or_buffer, offset, length, source_offset)
static VALUE
io_buffer_copy(int argc, VALUE *argv, VALUE self)
{
    if (argc < 1 || argc > 4) rb_error_arity(argc, 1, 4);

    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    VALUE source = argv[0];
    const void *source_base;
    size_t source_size;

    rb_io_buffer_get_readonly(source, &source_base, &source_size);

    return io_buffer_copy_from(data, source_base, source_size, argc-1, argv+1);
}

// buffer.get_string(offset, length, encoding)
static VALUE
io_buffer_get_string(int argc, VALUE *argv, VALUE self)
{
    if (argc > 3) rb_error_arity(argc, 0, 3);

    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    size_t offset = 0;
    size_t length = data->size;
    rb_encoding *encoding = rb_ascii8bit_encoding();

    if (argc >= 1) {
        offset = NUM2SIZET(argv[0]);
    }

    if (argc >= 2 && !RB_NIL_P(argv[1])) {
        length = NUM2SIZET(argv[1]);
    } else {
        length = data->size - offset;
    }

    if (argc >= 3) {
        encoding = rb_find_encoding(argv[2]);
    }

    rb_io_buffer_validate(data, offset, length);

    return rb_enc_str_new((char*)data->base + offset, length, encoding);
}

// (string_or_to_str, offset, length, source_offset)
static VALUE
io_buffer_set_string(int argc, VALUE *argv, VALUE self)
{
    if (argc < 1 || argc > 4) rb_error_arity(argc, 1, 4);

    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    VALUE string = rb_str_to_str(argv[0]);

    const void *source_base = RSTRING_PTR(string);
    size_t source_size = RSTRING_LEN(string);

    return io_buffer_copy_from(data, source_base, source_size, argc-1, argv+1);
}

void
rb_io_buffer_clear(VALUE self, uint8_t value, size_t offset, size_t length)
{
    void *base;
    size_t size;

    rb_io_buffer_get(self, &base, &size);

    if (offset + length > size) {
        rb_raise(rb_eArgError, "The given offset + length out of bounds!");
    }

    memset((char*)base + offset, value, length);
}

static VALUE
io_buffer_clear(int argc, VALUE *argv, VALUE self)
{
    if (argc > 3) rb_error_arity(argc, 0, 3);

    struct rb_io_buffer *data = NULL;
    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

    uint8_t value = 0;
    if (argc >= 1) {
        value = NUM2UINT(argv[0]);
    }

    size_t offset = 0;
    if (argc >= 2) {
        offset = NUM2SIZET(argv[1]);
    }

    size_t length;
    if (argc >= 3) {
        length = NUM2SIZET(argv[2]);
    } else {
        length = data->size - offset;
    }

    rb_io_buffer_clear(self, value, offset, length);

    return self;
}

static
size_t io_buffer_default_size(size_t page_size) {
    // Platform agnostic default size, based on emperical performance observation:
    const size_t platform_agnostic_default_size = 64*1024;

    // Allow user to specify custom default buffer size:
    const char *default_size = getenv("RUBY_IO_BUFFER_DEFAULT_SIZE");
    if (default_size) {
        // For the purpose of setting a default size, 2^31 is an acceptable maximum:
        int value = atoi(default_size);

        // assuming sizeof(int) <= sizeof(size_t)
        if (value > 0) {
            return value;
        }
    }

    if (platform_agnostic_default_size < page_size) {
        return page_size;
    }

    return platform_agnostic_default_size;
}

void
Init_IO_Buffer(void)
{
    rb_cIOBuffer = rb_define_class_under(rb_cIO, "Buffer", rb_cObject);
    rb_eIOBufferLockedError = rb_define_class_under(rb_cIOBuffer, "LockedError", rb_eRuntimeError);
    rb_eIOBufferAllocationError = rb_define_class_under(rb_cIOBuffer, "AllocationError", rb_eRuntimeError);
    rb_eIOBufferMutationError = rb_define_class_under(rb_cIOBuffer, "MutationError", rb_eRuntimeError);
    rb_eIOBufferInvalidatedError = rb_define_class_under(rb_cIOBuffer, "InvalidatedError", rb_eRuntimeError);

    rb_define_alloc_func(rb_cIOBuffer, rb_io_buffer_type_allocate);
    rb_define_singleton_method(rb_cIOBuffer, "for", rb_io_buffer_type_for, 1);

#ifdef _WIN32
    SYSTEM_INFO info;
    GetSystemInfo(&info);
    RUBY_IO_BUFFER_PAGE_SIZE = info.dwPageSize;
#else /* not WIN32 */
    RUBY_IO_BUFFER_PAGE_SIZE = sysconf(_SC_PAGESIZE);
#endif

    RUBY_IO_BUFFER_DEFAULT_SIZE = io_buffer_default_size(RUBY_IO_BUFFER_PAGE_SIZE);

    // Efficient sizing of mapped buffers:
    rb_define_const(rb_cIOBuffer, "PAGE_SIZE", SIZET2NUM(RUBY_IO_BUFFER_PAGE_SIZE));
    rb_define_const(rb_cIOBuffer, "DEFAULT_SIZE", SIZET2NUM(RUBY_IO_BUFFER_DEFAULT_SIZE));

    rb_define_singleton_method(rb_cIOBuffer, "map", io_buffer_map, -1);

    // General use:
    rb_define_method(rb_cIOBuffer, "initialize", rb_io_buffer_initialize, -1);
    rb_define_method(rb_cIOBuffer, "inspect", rb_io_buffer_inspect, 0);
    rb_define_method(rb_cIOBuffer, "to_s", rb_io_buffer_to_s, 0);
    rb_define_method(rb_cIOBuffer, "size", rb_io_buffer_size, 0);

    // Ownership:
    rb_define_method(rb_cIOBuffer, "transfer", rb_io_buffer_transfer, 0);

    // Flags:
    rb_define_const(rb_cIOBuffer, "EXTERNAL", RB_INT2NUM(RB_IO_BUFFER_EXTERNAL));
    rb_define_const(rb_cIOBuffer, "INTERNAL", RB_INT2NUM(RB_IO_BUFFER_INTERNAL));
    rb_define_const(rb_cIOBuffer, "MAPPED", RB_INT2NUM(RB_IO_BUFFER_MAPPED));
    rb_define_const(rb_cIOBuffer, "LOCKED", RB_INT2NUM(RB_IO_BUFFER_LOCKED));
    rb_define_const(rb_cIOBuffer, "PRIVATE", RB_INT2NUM(RB_IO_BUFFER_PRIVATE));
    rb_define_const(rb_cIOBuffer, "READONLY", RB_INT2NUM(RB_IO_BUFFER_READONLY));

    // Endian:
    rb_define_const(rb_cIOBuffer, "LITTLE_ENDIAN", RB_INT2NUM(RB_IO_BUFFER_LITTLE_ENDIAN));
    rb_define_const(rb_cIOBuffer, "BIG_ENDIAN", RB_INT2NUM(RB_IO_BUFFER_BIG_ENDIAN));
    rb_define_const(rb_cIOBuffer, "HOST_ENDIAN", RB_INT2NUM(RB_IO_BUFFER_HOST_ENDIAN));
    rb_define_const(rb_cIOBuffer, "NETWORK_ENDIAN", RB_INT2NUM(RB_IO_BUFFER_NETWORK_ENDIAN));

    rb_define_method(rb_cIOBuffer, "null?", rb_io_buffer_null_p, 0);
    rb_define_method(rb_cIOBuffer, "empty?", rb_io_buffer_empty_p, 0);
    rb_define_method(rb_cIOBuffer, "external?", rb_io_buffer_external_p, 0);
    rb_define_method(rb_cIOBuffer, "internal?", rb_io_buffer_internal_p, 0);
    rb_define_method(rb_cIOBuffer, "mapped?", rb_io_buffer_mapped_p, 0);
    rb_define_method(rb_cIOBuffer, "locked?", rb_io_buffer_locked_p, 0);
    rb_define_method(rb_cIOBuffer, "readonly?", io_buffer_readonly_p, 0);

    // Locking to prevent changes while using pointer:
    // rb_define_method(rb_cIOBuffer, "lock", rb_io_buffer_lock, 0);
    // rb_define_method(rb_cIOBuffer, "unlock", rb_io_buffer_unlock, 0);
    rb_define_method(rb_cIOBuffer, "locked", rb_io_buffer_locked, 0);

    // Manipulation:
    rb_define_method(rb_cIOBuffer, "slice", rb_io_buffer_slice, 2);
    rb_define_method(rb_cIOBuffer, "<=>", rb_io_buffer_compare, 1);
    rb_define_method(rb_cIOBuffer, "resize", io_buffer_resize, 1);
    rb_define_method(rb_cIOBuffer, "clear", io_buffer_clear, -1);
    rb_define_method(rb_cIOBuffer, "free", rb_io_buffer_free, 0);

    rb_include_module(rb_cIOBuffer, rb_mComparable);

#define DEFINE_TYPE(name) RB_IO_BUFFER_TYPE_##name = rb_intern_const(#name)
    DEFINE_TYPE(U8); DEFINE_TYPE(S8);
    DEFINE_TYPE(u16); DEFINE_TYPE(U16); DEFINE_TYPE(s16); DEFINE_TYPE(S16);
    DEFINE_TYPE(u32); DEFINE_TYPE(U32); DEFINE_TYPE(s32); DEFINE_TYPE(S32);
    DEFINE_TYPE(u64); DEFINE_TYPE(U64); DEFINE_TYPE(s64); DEFINE_TYPE(S64);
    DEFINE_TYPE(f32); DEFINE_TYPE(F32); DEFINE_TYPE(f64); DEFINE_TYPE(F64);
#undef DEFINE_TYPE

    // Data access:
    rb_define_method(rb_cIOBuffer, "get_value", io_buffer_get_value, 2);
    rb_define_method(rb_cIOBuffer, "set_value", io_buffer_set_value, 3);

    rb_define_method(rb_cIOBuffer, "copy", io_buffer_copy, -1);

    rb_define_method(rb_cIOBuffer, "get_string", io_buffer_get_string, -1);
    rb_define_method(rb_cIOBuffer, "set_string", io_buffer_set_string, -1);
}