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js-struct.js
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js-struct.js
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/*
* js-struct.js - Utility to assist in parsing c-style structs from an ArrayBuffer
*/
/*
* Copyright (c) 2011 Brandon Jones
*
* This software is provided 'as-is', without any express or implied
* warranty. In no event will the authors be held liable for any damages
* arising from the use of this software.
*
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
*
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
*
* 2. Altered source versions must be plainly marked as such, and must not
* be misrepresented as being the original software.
*
* 3. This notice may not be removed or altered from any source
* distribution.
*/
"use strict";
// TODO: Ugh, this is messy. Do it differentely soon, please!
var nextStructId = 0;
var Struct = Object.create(Object, {
/**
* Defines a single byte integer value (byte/char).
* @param name Property name
*/
int8: {
value: function(name) {
return { name: name, readCode: "v.getInt8(o, true);", byteLength: 1, defaultValue: 0, structProperty: true };
}
},
/**
* Defines an unsigned single byte integer value (ubyte/uchar).
* @param name Property name
*/
uint8: {
value: function(name) {
return { name: name, readCode: "v.getUint8(o, true);", byteLength: 1, defaultValue: 0, structProperty: true };
}
},
/**
* Defines a two byte integer value (short).
* @param name Property name
*/
int16: {
value: function(name) {
return { name: name, readCode: "v.getInt16(o, true);", byteLength: 2, defaultValue: 0, structProperty: true };
}
},
/**
* Defines an unsigned two byte integer value (ushort).
* @param name Property name
*/
uint16: {
value: function(name) {
return { name: name, readCode: "v.getUint16(o, true);", byteLength: 2, defaultValue: 0, structProperty: true };
}
},
/**
* Defines a four byte integer value (int/long).
* @param name Property name
*/
int32: {
value: function(name) {
return { name: name, readCode: "v.getInt32(o, true);", byteLength: 4, defaultValue: 0, structProperty: true };
}
},
/**
* Defines an unsigned four byte integer value (uint/ulong).
* @param name Property name
*/
uint32: {
value: function(name) {
return { name: name, readCode: "v.getUint32(o, true);", byteLength: 4, defaultValue: 0, structProperty: true };
}
},
/**
* Defines a four byte floating point value (float).
* @param name Property name
*/
float32: {
value: function(name) {
return { name: name, readCode: "v.getFloat32(o, true);", byteLength: 4, defaultValue: 0, structProperty: true };
}
},
/**
* Defines an eight byte floating point value (double).
* @param name Property name
*/
float64: {
value: function(name) {
return { name: name, readCode: "v.getFloat64(o, true);", byteLength: 8, defaultValue: 0, structProperty: true };
}
},
/**
* Defines a fixed-length ASCII string.
* Will always read the number of characters specified, but the returned string will truncate at the first null char.
* @param name Property name
* @param length Number of characters to read
*/
string: {
value: function(name, length) {
var code = "(function(o) {\n";
code += " var str = \"\";\n";
code += " for(var j = 0; j < " + length + "; ++j) {\n";
code += " var char = v.getUint8(o+j, true);\n";
code += " if(char === 0) { break; }\n";
code += " str += String.fromCharCode(char);\n";
code += " }\n";
code += " return str;\n";
code += "})(o);\n";
return {
name: name,
readCode: code,
byteLength: length,
defaultValue: "",
structProperty: true
};
}
},
/**
* Defines a fixed-length array of structs or primitives
* @param name Property name
* @param type struct or primitive type to read
* @param length Number of elements to read. Total bytes read will be type.byteLength * length
*/
array: {
value: function(name, type, length) {
var code = "(function(o) {\n";
code += " var aa = new Array(" + length + "), av;\n";
code += " for(var j = 0; j < " + length + "; ++j) {\n";
code += " av = " + type.readCode + "\n";
code += " o += " + type.byteLength + ";\n";
code += " aa[j] = av;\n";
code += " }\n";
code += " return aa;\n"
code += "})(o);\n";
return {
name: name,
readCode: code,
byteLength: type.byteLength * length,
defaultValue: null,
array: true,
structProperty: true
};
}
},
/**
* Defines a nested struct
* @param name Property name
* @param struct Struct to read
*/
struct: {
value: function(name, struct) {
return {
name: name,
readCode: struct.readCode,
byteLength: struct.byteLength,
defaultValue: null,
struct: true,
structProperty: true
};
}
},
/**
* Defines a number of the bytes to be skipped over.
* @param length Number of bytes to be skipped
*/
skip: {
value: function(length) {
return {
name: null,
readCode: "null;\n",
byteLength: length,
structProperty: true
};
}
},
/**
* Compiles the code to read a struct from the struct's definition
* @param structDef Object sequentially defining the binary types to read
* @param prototype Optional, additional prototypes to apply to the returned struct object
* @returns An object containing a "readStructs" function that can read an array of the defined type from an ArrayBuffer
*/
create: {
value: function(/* collected via arguments */) {
var type;
var properties = arguments[arguments.length-1].structProperty ? {} : arguments[arguments.length-1];
var byteLength = 0;
var struct = Object.create(Object.prototype, properties);
// This new struct will be assigned a unique name so that instances can be easily constructed later.
// It is not recommended that you use these names for anything outside this class, as they are not
// intended to be stable from run to run.
Object.defineProperty(struct, "struct_type_id", { value: "struct_id_" + nextStructId, enumerable: false, configurable: false, writable: false });
Object.defineProperty(this, struct.struct_type_id, { value: struct, enumerable: false, configurable: false, writable: false });
nextStructId += 1;
// Build the code to read a single struct, calculate byte lengths, and define struct properties
var readCode = "(function(o) { var st = Object.create(Struct." + struct.struct_type_id + ");\n";
for(var i = 0; i < arguments.length; ++i) {
type = arguments[i];
if(!type.structProperty) { continue; }
if(type.name) {
Object.defineProperty(struct, type.name, { value: type.defaultValue, enumerable: true, configurable: true, writable: true });
readCode += "st." + type.name + " = " + type.readCode + "\n";
}
readCode += "o += " + type.byteLength + ";\n";
byteLength += type.byteLength;
}
readCode += "return st; })(o);";
// Build the code to read an array of this struct type
var parseScript = "var a = new Array(count);\n var s;\n";
parseScript += "var v = new DataView(arrayBuffer, offset);\n"; // TODO: I should be able to specify a length here (count * this.byteLength), but it consistently gives me an INDEX_SIZE_ERR. Wonder why?
parseScript += "var o = 0, so = 0;\n";
parseScript += "for(var i = 0; i < count; ++i) {\n";
parseScript += " so = o;\n";
parseScript += " s = " + readCode + "\n";
parseScript += " o += this.byteLength;\n";
parseScript += " if(callback) { callback(s, offset+so); }\n";
parseScript += " a[i] = s;\n";
parseScript += "}\n";
parseScript += "return a;\n";
Object.defineProperty(struct, "byteLength", { value: byteLength, enumerable: true, configurable: true, writable: true });
Object.defineProperty(struct, "readCode", { value: readCode, enumerable: true, configurable: true, writable: true });
var parseFunc = new Function("arrayBuffer", "offset", "count", "callback", parseScript);
Object.defineProperty(struct, "readStructs", { value: parseFunc, configurable: true, writable: true });
return struct;
}
},
//
// Utility functions to read simple arrays of data from a buffer
//
/**
* Read an ASCII string from an ArrayBuffer
* @param buffer Buffer to read from
* @param offset Offset in bytes to start reading at
* @param length Optional, number of characters to read. If not given will read until a NULL char is reached
*/
readString: {
value: function(buffer, offset, length) {
var str = "", charBuffer;
// Hm... any way I can do this?
//var str = String.fromCharCode.apply(charBuffer);
if(length) {
charBuffer = new Uint8Array(buffer, offset, length);
for(var i = 0; i < length; ++i) {
var char = charBuffer[i];
if(char === 0) { break; }
str += String.fromCharCode(char);
}
} else {
charBuffer = new Uint8Array(buffer, offset);
var i = 0;
while(true) {
var char = charBuffer[i++];
if(char === 0) { break; }
str += String.fromCharCode(char);
}
}
return str;
}
},
// I wonder if there's a more efficent way to do these that doesn't run afoul the offset restrictions of TypedArrays
/**
* Read an array of 8 bit integers
* @param buffer Buffer to read from
* @param offset Offset in bytes to start reading at
* @param elements Number of integers to read
*/
readInt8Array: {
value: function(buffer, offset, elements) {
var array = new Int8Array(elements);
var v = new DataView(buffer, offset);
for(var i = 0; i < elements; ++i) {
array[i] = v.getInt8(i, true);
}
return array;
}
},
/**
* Read an array of 8 bit unsigned integers
* @param buffer Buffer to read from
* @param offset Offset in bytes to start reading at
* @param elements Number of integers to read
*/
readUint8Array: {
value: function(buffer, offset, elements) {
var array = new Uint8Array(elements);
var v = new DataView(buffer, offset);
for(var i = 0; i < elements; ++i) {
array[i] = v.getUint8(i, true);
}
return array;
}
},
/**
* Read an array of 16 bit integers
* @param buffer Buffer to read from
* @param offset Offset in bytes to start reading at
* @param elements Number of integers to read
*/
readInt16Array: {
value: function(buffer, offset, elements) {
var array = new Int16Array(elements);
var v = new DataView(buffer, offset);
for(var i = 0; i < elements; ++i) {
array[i] = v.getInt16(i*2, true);
}
return array;
}
},
/**
* Read an array of 16 bit unsigned integers
* @param buffer Buffer to read from
* @param offset Offset in bytes to start reading at
* @param elements Number of integers to read
*/
readUint16Array: {
value: function(buffer, offset, elements) {
var array = new Uint16Array(elements);
var v = new DataView(buffer, offset);
for(var i = 0; i < elements; ++i) {
array[i] = v.getUint16(i*2, true);
}
return array;
}
},
/**
* Read an array of 32 bit integers
* @param buffer Buffer to read from
* @param offset Offset in bytes to start reading at
* @param elements Number of integers to read
*/
readInt32Array: {
value: function(buffer, offset, elements) {
var array = new Int32Array(elements);
var v = new DataView(buffer, offset);
for(var i = 0; i < elements; ++i) {
array[i] = v.getInt32(i*4, true);
}
return array;
}
},
/**
* Read an array of 32 bit unsigned integers
* @param buffer Buffer to read from
* @param offset Offset in bytes to start reading at
* @param elements Number of integers to read
*/
readUint32Array: {
value: function(buffer, offset, elements) {
var array = new Uint32Array(elements);
var v = new DataView(buffer, offset);
for(var i = 0; i < elements; ++i) {
array[i] = v.getUint32(i*4, true);
}
return array;
}
},
/**
* Read an array of 32 bit floats
* @param buffer Buffer to read from
* @param offset Offset in bytes to start reading at
* @param elements Number of floats to read
*/
readFloat32Array: {
value: function(buffer, offset, elements) {
var array = new Float32Array(elements);
var v = new DataView(buffer, offset);
for(var i = 0; i < elements; ++i) {
array[i] = v.getFloat32(i*4, true);
}
return array;
}
},
/**
* Read an array of 64 bit floats
* @param buffer Buffer to read from
* @param offset Offset in bytes to start reading at
* @param elements Number of floats to read
*/
readFloat64Array: {
value: function(buffer, offset, elements) {
var array = new Float64Array(elements);
var v = new DataView(buffer, offset);
for(var i = 0; i < elements; ++i) {
array[i] = v.getFloat64(i*8, true);
}
return array;
}
},
});