# Buffer and Codec

# Objective

In this section, you'll learn about using the Buffer object and the Codec module to interact with binary data streams.

# Definitions

The Titanium.Buffer is a container for bytes. It differs from Titanium.Blob in that a `Buffer` is mutable and resizable.

The Titanium.Codec provides utility methods to convert to and from binary data.

Buffer and Codec are primarily used in conjunction with Titanium.IOStream objects, including Titanium.Network.Socket.TCP and Titanium.Filesystem.FileStream.

The Titanium.Stream module provides additional utility methods for working with streams.

# Titanium.Buffer

Buffers are created from the Titanium module using Titanium.createBuffer(). Buffers are similar to byte arrays in other programming languages but have the ability to be resized. Buffers may be grown by setting the length property to a larger value, or when using the insert() or append() methods. Their length may also be reduced by setting the length property to a smaller value or using the release() method.

You can create an empty buffer with a specified initial size, or use a string or numeric value as the initial value of a buffer. The following code excerpt show several ways to initialize a buffer.

// Create a Buffer with initial length of 0
var buffer1 = Ti.createBuffer();

// Create a buffer with initial size of 512 bytes
var buffer2 = Ti.createBuffer({ length: 512 });

// Create a buffer, initialized with a string value.
var buffer3 = Ti.createBuffer({ value: "This is a string, which will form the contents of a new buffer."});

The following code excerpt shows some other manipulations on a buffer, including appending one buffer to another and truncating buffers.

var buffer1 = Ti.createBuffer({ value: "One buffer full of data. " });
var buffer2 = Ti.createBuffer({ value: "Another buffer full of data." });

// Append the contents of one buffer to another

// Truncate the buffer to 32 bytes
buffer1.length = 32;

// Set buffers to zero length and release underlying storage.

Buffers can also be addressed directly as if they were arrays of byte values, as shown in the following code excerpt.

var buffer = Ti.createBuffer({ length: 2 });
buffer[0] = 1;
buffer[1] = 3;

var buffer2 = Ti.createBuffer({ length: 1 });
buffer2[0] = 2;
buffer.insert(buffer2, 1);

// writes 123
Ti.API.info(String(buffer[0]) + String(buffer[1]) + String(buffer[2]));

The Buffer object's append, copy, and insert methods resize the buffer as needed. However, when you access a buffer as an array, the buffer is not automatically extended like a JavaScript array. For example, the following code throws an exception, because the value is being assigned to a position past the end of the buffer.

var buffer = Ti.createBuffer({ length: 2 });
buffer[100] = 1;

Also note that when assigning values to the buffer this way, the values must be byte values.

// Assigning a string value -- throws an exception
buffer[0] = "a";
// Assigning a byte value works
buffer[0] = "a".charCodeAt(0);

# Titanium.Codec

The Titanium.Codec module provides methods for encoding and decoding binary data from buffers into JavaScript primitives. The Codec module supports conversion of two basic primitive types: Numbers and Strings. Codec also handles byte order conversion.

The Codec module methods do not resize the target buffer.

# Numeric conversions

Numeric conversion is provided for the following types: byte, short, int, long, float, and double.

The following code excerpt encodes a 4-byte integer into the buffer, starting at index 10 (the 11th byte of the integer).

// Encode a 4 byte integer into position 10 using BIG_ENDIAN encoding
var buffer = Ti.createBuffer({ length: 100 });
    source: 0x3456789a,
    dest: buffer,
    position: 10,
    type: Ti.Codec.TYPE_INT,
    byteOrder: Ti.Codec.BIG_ENDIAN

The following code excerpt decodes the 4-byte integer written to the buffer in the previous example.

//Decode a 4 byte integer from position 10 using BIG_ENDIAN encoding
var value = Ti.Codec.decodeNumber({
    source: buffer,
    position: 10,
    type: Ti.Codec.TYPE_INT,
    byteOrder: Ti.Codec.BIG_ENDIAN

# String conversions

String conversion is provided using the following character sets: ISO_LATIN1, UTF8, UTF16, UTF16BE, and UTF16LE. The default is UTF-8. Titanium.Codec also suports both Big Endian and Little Endian byte ordering.

The following excerpt encodes a string into a buffer, then trims the buffer to the length of the encoded string.

var buffer = Ti.createBuffer({ length: 1024 });
var encodedLength = Ti.Codec.encodeString({
    source: "hello world",
    dest: buffer
buffer.length = encodedLength;

The following excerpt decodes a UTF-8 string from a buffer.

var string = Ti.Codec.decodeString({ source: buffer });

# Buffer creation with encode

Titanium.createBuffer() has convenience options for creating a buffer from existing data. These options are just a convenient alternative to calling `createBuffer` and `encodeString` or `encodeNumber` separately, as shown in the following excerpt.

// Create a buffer and encode a string at the same time.
// Using default encoding of Ti.Codec.CHARSET_UTF8
var buffer_utf8 = Ti.createBuffer({ value: "Hello World" });

// Create a buffer and encode a string to UTF16
var buffer_utf16 = Ti.createBuffer({
    value: "Hello World",
    type: Ti.Codec.CHARSET_UTF16