class IO::Buffer

IO::Buffer is a low-level efficient buffer for input/output. There are three ways of using buffer:

Create an empty buffer with ::new, fill it with data using copy or set_value, set_string, get data with get_string;
Create a buffer mapped to some string with ::for, then it could be used both for reading with get_string or get_value, and writing (writing will change the source string, too);
Create a buffer mapped to some file with ::map, then it could be used for reading and writing the underlying file.

Interaction with string and file memory is performed by efficient low-level C mechanisms like ‘memcpy`.

The class is meant to be an utility for implementing more high-level mechanisms like Fiber::SchedulerInterface#io_read and Fiber::SchedulerInterface#io_write.

Examples of usage:

Empty buffer:

buffer = IO::Buffer.new(8)  # create empty 8-byte buffer
#  =>
# #<IO::Buffer 0x0000555f5d1a5c50+8 INTERNAL>
# ...
buffer
#  =>
# <IO::Buffer 0x0000555f5d156ab0+8 INTERNAL>
# 0x00000000  00 00 00 00 00 00 00 00
buffer.set_string('test', 2) # put there bytes of the "test" string, starting from offset 2
# => 4
buffer.get_string  # get the result
# => "\x00\x00test\x00\x00"

Buffer from string:

string = 'data'
buffer = IO::Buffer.for(str)
#  =>
# #<IO::Buffer 0x00007f3f02be9b18+4 SLICE>
# ...
buffer
#  =>
# #<IO::Buffer 0x00007f3f02be9b18+4 SLICE>
# 0x00000000  64 61 74 61                                     data

buffer.get_string(2)  # read content starting from offset 2
# => "ta"
buffer.set_string('---', 1) # write content, starting from offset 1
# => 3
buffer
#  =>
# #<IO::Buffer 0x00007f3f02be9b18+4 SLICE>
# 0x00000000  64 2d 2d 2d                                     d---
string  # original string changed, too
# => "d---"

Buffer from file:

File.write('test.txt', 'test data')
# => 9
buffer = IO::Buffer.map(File.open('test.txt'))
#  =>
# #<IO::Buffer 0x00007f3f0768c000+9 MAPPED IMMUTABLE>
# ...
buffer.get_string(5, 2) # read 2 bytes, starting from offset 5
# => "da"
buffer.set_string('---', 1) # attempt to write
# in `set_string': Buffer is not writable! (IO::Buffer::AccessError)

# To create writable file-mapped buffer
# Open file for read-write, pass size, offset, and flags=0
buffer = IO::Buffer.map(File.open('test.txt', 'r+'), 9, 0, 0)
buffer.set_string('---', 1)
# => 3 -- bytes written
File.read('test.txt')
# => "t--- data"

The class is experimental and the interface is subject to change.

Constants

BIG_ENDIAN
DEFAULT_SIZE
EXTERNAL
HOST_ENDIAN
INTERNAL
LITTLE_ENDIAN
LOCKED
MAPPED
NETWORK_ENDIAN
PAGE_SIZE
PRIVATE
READONLY

Public Class Methods

IO::Buffer.for(string) → io_buffer click to toggle source

Creates a IO::Buffer from the given string’s memory. The buffer remains associated with the string, and writing to a buffer will update the string’s contents.

Until free is invoked on the buffer, either explicitly or via the garbage collector, the source string will be locked and cannot be modified.

If the string is frozen, it will create a read-only buffer which cannot be modified.

string = 'test'
buffer = IO::Buffer.for(str)
buffer.external? #=> true

buffer.get_string(0, 1)
# => "t"
string
# => "best"

buffer.resize(100)
# in `resize': Cannot resize external buffer! (IO::Buffer::AccessError)

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;
}

IO::Buffer.map(file, [size, [offset, [flags]]]) → io_buffer click to toggle source

Create an IO::Buffer for reading from file by memory-mapping the file. file_io should be a File instance, opened for reading.

Optional size and offset of mapping can be specified.

By default, the buffer would be immutable (read only); to create a writable mapping, you need to open a file in read-write mode, and explicitly pass flags argument without IO::Buffer::IMMUTABLE.

File.write('test.txt', 'test')

buffer = IO::Buffer.map(File.open('test.txt'), nil, 0, IO::Buffer::READONLY)
# => #<IO::Buffer 0x00000001014a0000+4 MAPPED READONLY>

buffer.readonly?   # => true

buffer.get_string
# => "test"

buffer.set_string('b', 0)
# `set_string': Buffer is not writable! (IO::Buffer::AccessError)

# create read/write mapping: length 4 bytes, offset 0, flags 0
buffer = IO::Buffer.map(File.open('test.txt', 'r+'), 4, 0)
buffer.set_string('b', 0)
# => 1

# Check it
File.read('test.txt')
# => "best"

Note that some operating systems may not have cache coherency between mapped buffers and file reads.

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

    // We might like to handle a string path?
    VALUE io = argv[0];

    size_t size;
    if (argc >= 2 && !RB_NIL_P(argv[1])) {
        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 should be safe:
            size = (size_t)file_size;
        }
    }

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

    enum rb_io_buffer_flags flags = 0;
    if (argc >= 4) {
        flags = RB_NUM2UINT(argv[3]);
    }

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

IO::Buffer.new([size = DEFAULT_SIZE, [flags = 0]]) → io_buffer click to toggle source

Create a new zero-filled IO::Buffer of size bytes. By default, the buffer will be internal: directly allocated chunk of the memory. But if the requested size is more than OS-specific IO::Bufer::PAGE_SIZE, the buffer would be allocated using the virtual memory mechanism (anonymous mmap on Unix, VirtualAlloc on Windows). The behavior can be forced by passing IO::Buffer::MAPPED as a second parameter.

Examples

buffer = IO::Buffer.new(4)
# =>
#  #<IO::Buffer 0x000055b34497ea10+4 INTERNAL>
#  0x00000000  00 00 00 00                                     ....

buffer.get_string(0, 1) # => "\x00"

buffer.set_string("test")
buffer
#  =>
# #<IO::Buffer 0x000055b34497ea10+4 INTERNAL>
# 0x00000000  74 65 73 74                                     test

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;
}

Public Instance Methods

<=>(other) → true or false click to toggle source

Buffers are compared by size and exact contents of the memory they are referencing using memcmp.

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

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

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

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

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

clear(value = 0, [offset, [length]]) → self click to toggle source

Fill buffer with value, starting with offset and going for length bytes.

buffer = IO::Buffer.for('test')
# =>
#   <IO::Buffer 0x00007fca40087c38+4 SLICE>
#   0x00000000  74 65 73 74         test

buffer.clear
# =>
#   <IO::Buffer 0x00007fca40087c38+4 SLICE>
#   0x00000000  00 00 00 00         ....

buf.clear(1) # fill with 1
# =>
#   <IO::Buffer 0x00007fca40087c38+4 SLICE>
#   0x00000000  01 01 01 01         ....

buffer.clear(2, 1, 2) # fill with 2, starting from offset 1, for 2 bytes
# =>
#   <IO::Buffer 0x00007fca40087c38+4 SLICE>
#   0x00000000  01 02 02 01         ....

buffer.clear(2, 1) # fill with 2, starting from offset 1
# =>
#   <IO::Buffer 0x00007fca40087c38+4 SLICE>
#   0x00000000  01 02 02 02         ....

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;
}

copy(source, [offset, [length, [source_offset]]]) → size click to toggle source

Efficiently copy data from a source IO::Buffer into the buffer, at offset using memcpy. For copying String instances, see set_string.

buffer = IO::Buffer.new(32)
#  =>
# #<IO::Buffer 0x0000555f5ca22520+32 INTERNAL>
# 0x00000000  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
# 0x00000010  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................  *

buffer.copy(IO::Buffer.for("test"), 8)
# => 4 -- size of data copied
buffer
#  =>
# #<IO::Buffer 0x0000555f5cf8fe40+32 INTERNAL>
# 0x00000000  00 00 00 00 00 00 00 00 74 65 73 74 00 00 00 00 ........test....
# 0x00000010  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ *

copy can be used to put data into strings associated with buffer:

string= "data:    "
# => "data:    "
buffer = IO::Buffer.for(str)
buffer.copy(IO::Buffer.for("test"), 5)
# => 4
string
# => "data:test"

Attempt to copy into a read-only buffer will fail:

File.write('test.txt', 'test')
buffer = IO::Buffer.map(File.open('test.txt'), nil, 0, IO::Buffer::READONLY)
buffer.copy(IO::Buffer.for("test"), 8)
# in `copy': Buffer is not writable! (IO::Buffer::AccessError)

See ::map for details of creation of mutable file mappings, this will work:

buffer = IO::Buffer.map(File.open('test.txt', 'r+'))
buffer.copy("boom", 0)
# => 4
File.read('test.txt')
# => "boom"

Attempt to copy the data which will need place outside of buffer’s bounds will fail:

buffer = IO::Buffer.new(2)
buffer.copy('test', 0)
# in `copy': Specified offset+length exceeds source size! (ArgumentError)

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_bytes_for_reading(source, &source_base, &source_size);

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

external? → true or false click to toggle source

If the buffer is _external_, meaning it references from memory which is not
allocated or mapped by the buffer itself.

A buffer created using ::for has an external reference to the string's
memory.

External buffer can’t be resized.

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 RBOOL(data->size == 0);
}

external?() click to toggle source

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 RBOOL(data->flags & RB_IO_BUFFER_EXTERNAL);
}

free → self click to toggle source

If the buffer references memory, release it back to the operating system.

for a mapped buffer (e.g. from file): unmap.
for a buffer created from scratch: free memory.
for a buffer created from string: undo the association.

After the buffer is freed, no further operations can’t be performed on it.

buffer = IO::Buffer.for('test')
buffer.free
# => #<IO::Buffer 0x0000000000000000+0 NULL>

buffer.get_value(:U8, 0)
# in `get_value': The buffer is not allocated! (IO::Buffer::AllocationError)

buffer.get_string
# in `get_string': The buffer is not allocated! (IO::Buffer::AllocationError)

buffer.null?
# => true

You can resize a freed buffer to re-allocate it.

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;
}

get_string([offset, [length, [encoding]]]) → string click to toggle source

Read a chunk or all of the buffer into a string, in the specified encoding. If no encoding is provided Encoding::BINARY is used.

buffer = IO::Buffer.for('test')
buffer.get_string
# => "test"
buffer.get_string(2)
# => "st"
buffer.get_string(2, 1)
# => "s"

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);

    const void *base;
    size_t size;
    io_buffer_get_bytes_for_reading(data, &base, &size);

    size_t offset = 0;
    size_t length = 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 = size - offset;
    }

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

    io_buffer_validate_range(data, offset, length);

    return rb_enc_str_new((const char*)base + offset, length, encoding);
}

get_value(type, offset) → numeric click to toggle source

Read from buffer a value of type at offset. type should be one of symbols:

:U8: unsigned integer, 1 byte
:S8: signed integer, 1 byte
:u16: unsigned integer, 2 bytes, little-endian
:U16: unsigned integer, 2 bytes, big-endian
:s16: signed integer, 2 bytes, little-endian
:S16: signed integer, 2 bytes, big-endian
:u32: unsigned integer, 4 bytes, little-endian
:U32: unsigned integer, 4 bytes, big-endian
:s32: signed integer, 4 bytes, little-endian
:S32: signed integer, 4 bytes, big-endian
:u64: unsigned integer, 8 bytes, little-endian
:U64: unsigned integer, 8 bytes, big-endian
:s64: signed integer, 8 bytes, little-endian
:S64: signed integer, 8 bytes, big-endian
:f32: float, 4 bytes, little-endian
:F32: float, 4 bytes, big-endian
:f64: double, 8 bytes, little-endian
:F64: double, 8 bytes, big-endian

Example:

string = [1.5].pack('f')
# => "\x00\x00\xC0?"
IO::Buffer.for(string).get_value(:f32, 0)
# => 1.5

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_bytes_for_reading(self, &base, &size);

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

hexdump() click to toggle source

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

    VALUE result = Qnil;

    if (io_buffer_validate(data) && data->base) {
        result = rb_str_buf_new(data->size*3 + (data->size/16)*12 + 1);

        io_buffer_hexdump(result, 16, data->base, data->size, 1);
    }

    return result;
}

inspect() click to toggle source

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, 0);
        }
    }

    return result;
}

internal? → true or false click to toggle source

If the buffer is internal, meaning it references memory allocated by the buffer itself.

An internal buffer is not associated with any external memory (e.g. string) or file mapping.

Internal buffers are created using ::new and is the default when the requested size is less than the IO::Buffer::PAGE_SIZE and it was not requested to be mapped on creation.

Internal buffers can be resized, and such an operation will typically invalidate all slices, but not always.

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 RBOOL(data->flags & RB_IO_BUFFER_INTERNAL);
}

locked { ... } click to toggle source

Allows to process a buffer in exclusive way, for concurrency-safety. While the block is performed, the buffer is considered locked, and no other code can enter the lock. Also, locked buffer can’t be changed with resize or free.

buffer = IO::Buffer.new(4)
buffer.locked? #=> false

Fiber.schedule do
  buffer.locked do
    buffer.write(io) # theoretical system call interface
  end
end

Fiber.schedule do
  # in `locked': Buffer already locked! (IO::Buffer::LockedError)
  buffer.locked do
    buffer.set_string(...)
  end
end

The following operations acquire a lock: resize, free.

Locking is not thread safe. It is designed as a safety net around non-blocking system calls. You can only share a buffer between threads with appropriate synchronisation techniques.

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;
}

locked? → true or false click to toggle source

If the buffer is locked, meaning it is inside locked block execution. Locked buffer can’t be resized or freed, and another lock can’t be acquired on it.

Locking is not thread safe, but is a semantic used to ensure buffers don’t move while being used by a system call.

buffer.locked do
  buffer.write(io) # theoretical system call interface
end

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 RBOOL(data->flags & RB_IO_BUFFER_LOCKED);
}

mapped? → true or false click to toggle source

If the buffer is mapped, meaning it references memory mapped by the buffer.

Mapped buffers are either anonymous, if created by ::new with the IO::Buffer::MAPPED flag or if the size was at least IO::Buffer::PAGE_SIZE, or backed by a file if created with ::map.

Mapped buffers can usually be resized, and such an operation will typically invalidate all slices, but not always.

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 RBOOL(data->flags & RB_IO_BUFFER_MAPPED);
}

null? → true or false click to toggle source

If the buffer was freed with free or was never allocated in the first place.

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 RBOOL(data->base == NULL);
}

pread(p1, p2, p3) click to toggle source

static VALUE
io_buffer_pread(VALUE self, VALUE io, VALUE length, VALUE offset)
{
    return rb_io_buffer_pread(self, io, RB_NUM2SIZE(length), NUM2OFFT(offset));
}

pwrite(p1, p2, p3) click to toggle source

static VALUE
io_buffer_pwrite(VALUE self, VALUE io, VALUE length, VALUE offset)
{
    return rb_io_buffer_pwrite(self, io, RB_NUM2SIZE(length), NUM2OFFT(offset));
}

read(p1, p2) click to toggle source

static VALUE
io_buffer_read(VALUE self, VALUE io, VALUE length)
{
    return rb_io_buffer_read(self, io, RB_NUM2SIZE(length));
}

readonly?() click to toggle source

static VALUE
io_buffer_readonly_p(VALUE self)
{
    return RBOOL(rb_io_buffer_readonly_p(self));
}

resize(new_size) → self click to toggle source

Resizes a buffer to a new_size bytes, preserving its content. Depending on the old and new size, the memory area associated with the buffer might be either extended, or rellocated at different address with content being copied.

buffer = IO::Buffer.new(4)
buffer.set_string("test", 0)
buffer.resize(8) # resize to 8 bytes
#  =>
# #<IO::Buffer 0x0000555f5d1a1630+8 INTERNAL>
# 0x00000000  74 65 73 74 00 00 00 00                         test....

External buffer (created with ::for), and locked buffer can not be resized.

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

    return self;
}

set_string(*args) click to toggle source

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);
}

set_value(type, offset, value) → offset click to toggle source

Write to a buffer a value of type at offset. type should be one of symbols described in get_value.

buffer = IO::Buffer.new(8)
#  =>
# #<IO::Buffer 0x0000555f5c9a2d50+8 INTERNAL>
# 0x00000000  00 00 00 00 00 00 00 00
buffer.set_value(:U8, 1, 111)
# => 1
buffer
#  =>
# #<IO::Buffer 0x0000555f5c9a2d50+8 INTERNAL>
# 0x00000000  00 6f 00 00 00 00 00 00                         .o......

Note that if the type is integer and value is Float, the implicit truncation is performed:

buffer = IO::Buffer.new(8)
buffer.set_value(:U32, 0, 2.5)
buffer
#   =>
#  #<IO::Buffer 0x0000555f5c9a2d50+8 INTERNAL>
#  0x00000000  00 00 00 02 00 00 00 00
#                       ^^ the same as if we'd pass just integer 2

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_bytes_for_writing(self, &base, &size);

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

    return SIZET2NUM(offset);
}

size → integer click to toggle source

Returns the size of the buffer that was explicitly set (on creation with ::new or on resize), or deduced on buffer’s creation from string or file.

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);
}

slice(offset, length) → io_buffer click to toggle source

Produce another IO::Buffer which is a slice (or view into) the current one starting at offset bytes and going for length bytes.

The slicing happens without copying of memory, and the slice keeps being associated with the original buffer’s source (string, or file), if any.

Raises RuntimeError if the <tt>offset+length<tt> is out of the current buffer’s bounds.

string = 'test'
buffer = IO::Buffer.for(string)

slice = buffer.slice(1, 2)
# =>
#  #<IO::Buffer 0x00007fc3d34ebc49+2 SLICE>
#  0x00000000  65 73                                           es

# Put "o" into 0s position of the slice
slice.set_string('o', 0)
slice
# =>
#  #<IO::Buffer 0x00007fc3d34ebc49+2 SLICE>
#  0x00000000  6f 73                                           os

# it is also visible at position 1 of the original buffer
buffer
# =>
#  #<IO::Buffer 0x00007fc3d31e2d80+4 SLICE>
#  0x00000000  74 6f 73 74                                     tost

# ...and original string
string
# => tost

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);

    io_buffer_validate_range(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;
}

to_s → string click to toggle source

Short representation of the buffer. It includes the address, size and symbolic flags. This format is subject to change.

puts IO::Buffer.new(4) # uses to_s internally
# #<IO::Buffer 0x000055769f41b1a0+4 INTERNAL>

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_EXTERNAL) {
        rb_str_cat2(result, " EXTERNAL");
    }

    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, ">");
}

transfer → new_io_buffer click to toggle source

Transfers ownership to a new buffer, deallocating the current one.

buffer = IO::Buffer.new('test')
other = buffer.transfer
other
#  =>
# #<IO::Buffer 0x00007f136a15f7b0+4 SLICE>
# 0x00000000  74 65 73 74                                     test
buffer
#  =>
# #<IO::Buffer 0x0000000000000000+0 NULL>
buffer.null?
# => true

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;
}

valid? → true or false click to toggle source

Returns whether the buffer data is accessible.

A buffer becomes invalid if it is a slice of another buffer which has been freed.

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

    return RBOOL(io_buffer_validate(data));
}

write(p1, p2) click to toggle source

static VALUE
io_buffer_write(VALUE self, VALUE io, VALUE length)
{
    return rb_io_buffer_write(self, io, RB_NUM2SIZE(length));
}