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More Buffer descriptions and examples. 

Updated Script examples for New Script methods.
v0.7.4-release
Matt Ranney 15 years ago
committed by Ryan Dahl
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@ -25,123 +25,185 @@ it with the node program
All of the examples in the documentation can be run similarly.
## Modules
Node uses the CommonJS module system.
## Standard Modules
Node has a simple module loading system. In Node, files and modules are in
one-to-one correspondence. As an example, `foo.js` loads the module
`circle.js` in the same directory.
Node comes with a number of modules that are compiled in to the process,
most of which are documented below. The most common way to use these modules
is with `require('name')` and then assigning the return value to a local
variable with the same name as the module.
The contents of `foo.js`:
Example:
var circle = require('./circle');
var sys = require('sys');
sys.puts( 'The area of a circle of radius 4 is '
+ circle.area(4));
It is possible to extend node with other modules. See `'Modules'`
The contents of `circle.js`:
var PI = 3.14;
## Buffers
exports.area = function (r) {
return PI * r * r;
};
Pure Javascript is Unicode friendly but not nice to binary data. When
dealing with TCP streams or the file system, it's necessary to handle octet
streams. Node has several strategies for manipulating, creating, and
consuming octet streams.
exports.circumference = function (r) {
return 2 * PI * r;
};
Raw data is stored in instances of the `Buffer` class. A `Buffer` is similar
to an array of integers but corresponds to a raw memory allocation outside
the V8 heap. A `Buffer` cannot be resized.
Access the class with `require('buffer').Buffer`.
The module `circle.js` has exported the functions `area()` and
`circumference()`. To export an object, add to the special `exports`
object. (Alternatively, one can use `this` instead of `exports`.) Variables
local to the module will be private. In this example the variable `PI` is
private to `circle.js`. The function `puts()` comes from the module `'sys'`,
which is a built-in module. Modules which are not prefixed by `'./'` are
built-in module--more about this later.
Converting between Buffers and JavaScript string objects requires an explicit encoding
method. Node supports 3 string encodings: UTF-8 (`'utf8'`), ASCII (`'ascii'`), and
Binary (`'binary'`).
A module prefixed with `'./'` is relative to the file calling `require()`.
That is, `circle.js` must be in the same directory as `foo.js` for
`require('./circle')` to find it.
* `'ascii'` - for 7 bit ASCII data only. This encoding method is very fast, and will
strip the high bit if set.
* `'binary'` - for 8 bit binary data such as images.
Without the leading `'./'`, like `require('assert')` the module is searched
for in the `require.paths` array. `require.paths` on my system looks like
this:
* `'utf8'` - Unicode characters. Many web pages and other document formats use UTF-8.
`[ '/home/ryan/.node_libraries' ]`
That is, when `require('assert')` is called Node looks for:
### new Buffer(size)
* 1: `/home/ryan/.node_libraries/assert.js`
* 2: `/home/ryan/.node_libraries/assert.node`
* 3: `/home/ryan/.node_libraries/assert/index.js`
* 4: `/home/ryan/.node_libraries/assert/index.node`
Allocates a new buffer of `size` octets.
interrupting once a file is found. Files ending in `'.node'` are binary Addon
Modules; see the section below about addons. `'index.js'` allows one to
package a module as a directory.
### buffer.write(string, encoding, offset)
`require.paths` can be modified at runtime by simply unshifting new
paths onto it, or at startup with the `NODE_PATH` environmental
variable (which should be a list of paths, colon separated).
Writes `string` to the buffer at `offset` using the given encoding. Returns
number of octets written. If `buffer` did not contain enough space to fit
the entire string it will write a partial amount of the string. In the case
of `'utf8'` encoding, the method will not write partial characters.
Example: write a utf8 string into a buffer, then print it
## Buffers
var sys = require('sys'),
Buffer = require('buffer').Buffer,
buf = new Buffer(256),
len;
Pure Javascript is Unicode friendly but not nice to pure binary data. When
dealing with TCP streams or the file system, it's necessary to handle octet
streams. Node has several strategies for manipulating, creating, and
consuming octet streams.
len = buf.write('\u00bd + \u00bc = \u00be', 'utf8', 0);
sys.puts(len + " bytes: " + buf.toString('utf8', 0, len));
Raw data is stored in instances of the `Buffer` class. A `Buffer` is similar
to an array of integers but correspond to a raw memory allocation outside
the V8 heap. A `Buffer` cannot be resized.
Access the class at `require('buffer').Buffer`.
// 12 bytes: ½ + ¼ = ¾
### buffer.toString(encoding, start, end)
Decodes and returns a string from buffer data encoded with `encoding`
beginning at `start` and ending at `end`.
See `buffer.write()` example, above.
### buffer[index]
Get and set the octet at `index`. The values refer to individual bytes,
so the legal range is between `0x00` and `0xFF` hex or `0` and `255`.
Example: copy an ASCII string into a buffer, one byte at a time:
var sys = require('sys'),
Buffer = require('buffer').Buffer,
str = "node.js",
buf = new Buffer(str.length),
i;
for (i = 0; i < str.length ; i += 1) {
buf[i] = str.charCodeAt(i);
}
sys.puts(buf);
// node.js
Node supports 3 string encodings. UTF-8 (`'utf8'`), ASCII (`'ascii'`), and
Binary (`'binary'`). `'ascii'` and `'binary'` only look at the first 8 bits
of the 16bit JavaScript string characters.
### Buffer.byteLength(string, encoding)
Gives the actual byte length of a string. This is not the same as
Gives the actual byte length of a string. This is not the same as
`String.prototype.length` since that returns the number of *characters* in a
string.
// Takes in a UTF8 string, gives back a buffer
function stringToBuffer(string) {
var buffer = new Buffer(Buffer.byteLength(string));
buffer.utf8Write(string);
return buffer;
};
Example:
### new Buffer(size)
Allocates a new buffer of `size` octets.
var sys = require('sys'),
Buffer = require('buffer').Buffer,
str = '\u00bd + \u00bc = \u00be';
sys.puts(str + ": " + str.length + " characters, " +
Buffer.byteLength(str, 'utf8') + " bytes");
// ½ + ¼ = ¾: 9 characters, 12 bytes
### buffer[index]
Get and set the octet at `index`. The value can be between `0x00` and `0xFF`.
### buffer.length
length in octets.
### buffer.copy(targetBuffer, targetStart, start, end)
The size of the buffer in bytes. Note that this is not necessarily the size
of the contents. `length` refers to the amount of memory allocated for the
buffer object. It does not change when the contents of the buffer are changed.
var sys = require('sys'),
Buffer = require('buffer').Buffer,
buf = new Buffer(1234);
sys.puts(buf.length);
buf.write("some string", "ascii", 0);
sys.puts(buf.length);
// 1234
// 1234
### buffer.copy(targetBuffer, targetStart, sourceStart, sourceEnd)
Does a memcpy() between buffers.
Example: build two Buffers, then copy `buf1` from byte 16 through byte 20
into `buf2`, starting at the 8th byte in `buf2`.
var sys = require('sys'),
Buffer = require('buffer').Buffer,
buf1 = new Buffer(26),
buf2 = new Buffer(26),
i;
for (i = 0 ; i < 26 ; i += 1) {
buf1[i] = i + 97; // 97 is ASCII a
buf2[i] = 33; // ASCII !
}
buf1.copy(buf2, 8, 16, 20);
sys.puts(buf2.toString('ascii', 0, 25));
// !!!!!!!!qrst!!!!!!!!!!!!!
### buffer.slice(start, end)
Returns a new buffer which references the
same memory as the old, but offset and cropped by the `start` and `end`
indexes. **Modifying the new buffer slice will modify memory in the original
buffer!**
indexes.
### buffer.write(string, encoding, offset)
Writes `string` to the buffer at `offset` using the given encoding. Returns
number of octets written. If `buffer` did not contain enough space to fit
the entire string it will write a partial amount of the string. In the case
of `encoding=='utf8'`, the method will not write partial characters.
**Modifying the new buffer slice will modify memory in the original buffer!**
### buffer.toString(encoding, start, end)
Decodes and returns a string assuming in the given encoding beginning at
`start` and ending at `end`.
Example: build a Buffer with the ASCII alphabet, take a slice, then modify one byte
from the original Buffer.
var sys = require('sys'),
Buffer = require('buffer').Buffer,
buf1 = new Buffer(26), buf2,
i;
for (i = 0 ; i < 26 ; i += 1) {
buf1[i] = i + 97; // 97 is ASCII a
}
buf2 = buf1.slice(0, 3);
sys.puts(buf2.toString('ascii', 0, buf2.length));
buf1[0] = 33;
sys.puts(buf2.toString('ascii', 0, buf2.length));
// abc
// !bc
## EventEmitter
@ -244,12 +306,15 @@ Makes the data event emit a string instead of a `Buffer`. `encoding` can be
`'utf8'`, `'ascii'`, or `'binary'`.
### stream.pause()
Pauses the incoming `'data'` events.
### stream.resume()
Resumes the incoming `'data'` events after a `pause()`.
### stream.destroy()
Closes the underlying file descriptor. Stream will not emit any more events.
@ -278,6 +343,7 @@ Emitted on error with the exception `e`.
Emitted when the underlying file descriptor has been closed.
### stream.write(string, encoding)
Writes `string` with the given `encoding` to the stream. Returns `true` if
the string has been flushed to the kernel buffer. Returns `false` to
indicate that the kernel buffer is full, and the data will be sent out in
@ -286,19 +352,24 @@ empty again. The `encoding` defaults to `'utf8'`.
### stream.write(buffer)
Same as the above except with a raw buffer.
### stream.end()
Terminates the stream with EOF or FIN.
### stream.end(string, encoding)
Sends `string` with the given `encoding` and terminates the stream with EOF
or FIN. This is useful to reduce the number of packets sent.
### stream.end(buffer)
Same as above but with a `buffer`.
### stream.destroy()
Closes the underlying file descriptor. Stream will not emit any more events.
@ -307,25 +378,51 @@ Closes the underlying file descriptor. Stream will not emit any more events.
These object are available in the global scope and can be accessed from anywhere.
### global
The global namespace object.
### process
The process object. Most stuff lives in here. See the 'process object'
The process object. Most stuff lives in here. See the `'process object'`
section.
### require()
To require modules. See the modules section.
To require modules. See the `'Modules'` section.
### require.paths
The search path for absolute path arguments to `require()`.
An array of search paths for `require()`. This array can be modified to add custom paths.
Example: add a new path to the beginning of the search list
var sys = require('sys');
require.paths.unshift('/usr/local/node');
sys.puts(require.paths);
// /usr/local/node,/Users/mjr/.node_libraries
### __filename
The filename of the script being executed.
The filename of the script being executed. This is the absolute path, and not necessarily
the same filename passed in as a command line argument.
### __dirname
The dirname of the script being executed.
Example: running `node example.js` from `/Users/mjr`
var sys = require('sys');
sys.puts(__filename);
sys.puts(__dirname);
// /Users/mjr/example.js
// /Users/mjr
### module
A reference to the current module (of type `process.Module`). In particular
`module.exports` is the same as the `exports` object. See `src/process.js`
for more information.
@ -361,7 +458,6 @@ Example of listening for `exit`:
`function (err) { } `
Emitted when an exception bubbles all the way back to the event loop. If a
listener is added for this exception, the default action (which is to print
a stack trace and exit) will not occur.
@ -419,7 +515,6 @@ Example: the definition of `sys.puts`
};
### process.openStdin()
Opens the standard input stream, returns a readable stream.
@ -462,7 +557,6 @@ This will generate:
4: four
### process.chdir(directory)
Changes the current working directory of the process or throws an exception if that fails.
@ -519,7 +613,6 @@ Returns the current working directory of the process.
An object containing the user environment. See environ(7).
### process.exit(code)
Ends the process with the specified `code`. If omitted, exit uses the
@ -568,7 +661,7 @@ Gets/sets the user identity of the process. (See setuid(2).) This is the numeri
A compiled-in property that exposes `NODE_PREFIX`.
require('sys').puts('Install prefix: ' + process.installPrefix);
require('sys').puts('Prefix: ' + process.installPrefix);
### process.kill(pid, signal)
@ -909,13 +1002,14 @@ output, and return it all in a callback.
exec = require('child_process').exec,
child;
child = exec('cat *.js bad_file | wc -l', function (error, stdout, stderr) {
sys.print('stdout: ' + stdout);
sys.print('stderr: ' + stderr);
if (error !== null) {
sys.puts('exec error: ' + error);
}
});
child = exec('cat *.js bad_file | wc -l',
function (error, stdout, stderr) {
sys.print('stdout: ' + stdout);
sys.print('stderr: ' + stderr);
if (error !== null) {
sys.puts('exec error: ' + error);
}
});
The callback gets the arguments `(error, stdout, stderr)`. On success, `error`
will be `null`. On error, `error` will be an instance of `Error` and `err.code`
@ -939,13 +1033,14 @@ the child process is killed.
## Script
`Script` class provides with compiling, remembering and running pieces of Javascript code. You can get `Script` class by issuing
`Script` class compiles and runs JavaScript code. You can access this class with:
var Script = process.binding('evals').Script;
New JavaScript code can be compiled and run immediately or compiled, saved, and run later.
### Script.runInThisContext(code, filename='evalmachine.< anonymous >')
### Script.runInThisContext(code, filename)
Similar to `process.compile`. `Script.runInThisContext` compiles `code` as if it were loaded from `filename`,
runs it and returns the result. Running code does not have access to local scope. `filename` is optional.
@ -954,12 +1049,16 @@ Example of using `Script.runInThisContext` and `eval` to run the same code:
var sys = require('sys'),
localVar = 123,
usingscript, evaled;
usingscript, evaled,
Script = process.binding('evals').Script;
usingscript = Script.runInThisContext('localVar = 1;', 'myfile.js');
sys.puts('localVar: ' + localVar + ', usingscript: ' + usingscript);
usingscript = Script.runInThisContext('localVar = 1;',
'myfile.js');
sys.puts('localVar: ' + localVar + ', usingscript: ' +
usingscript);
evaled = eval('localVar = 1;');
sys.puts('localVar: ' + localVar + ', evaled: ' + evaled);
sys.puts('localVar: ' + localVar + ', evaled: ' +
evaled);
// localVar: 123, usingscript: 1
// localVar: 1, evaled: 1
@ -971,92 +1070,106 @@ In case of syntax error in `code`, `Script.runInThisContext` emits the syntax er
and throws.an exception.
### Script.runInNewContext(code, sandbox={}, filename='evalmachine.< anonymous >')
### Script.runInNewContext(code, sandbox, filename)
`Script.runInNewContext` compiles `code` to run in `sandbox` as if it were loaded from `filename`,
then runs it and returns the result. Running code does not have access to local scope and
the object `sandbox` will be used as the global object for `code`.
`sandbox` and `filename` are optional.
Example: compile and execute code that increments a global variable and sets a new one.
These globals are contained in the sandbox.
var sys = require('sys'),
Script = process.binding('evals').Script,
sandbox = {
animal: 'cat',
count: 2
};
Script.runInNewContext('count += 1; name = 'kitty'', sandbox, 'myfile.js');
Script.runInNewContext(
'count += 1; name = "kitty"', sandbox, 'myfile.js');
sys.puts(sys.inspect(sandbox));
// { animal: 'cat', count: 3, name: 'kitty' }
Note that running untrusted code is a tricky business requiring great care. To prevent accidental
global variable leakage, `Script.runInNewContext` is quite useful, but to safely run untrusted code, many more steps
must be taken.
global variable leakage, `Script.runInNewContext` is quite useful, but safely running untrusted code
requires a separate process.
In case of syntax error in `code`, `Script.runInThisContext` emits the syntax error to stderr
and throws.an exception.
and throws an exception.
### new Script(code, filename='evalmachine.< anonymous >')
### new Script(code, filename)
`new Script` compiles `code` as if it were loaded from `filename`,
but does not run it. Instead, it returns Script object representing this compiled code.
but does not run it. Instead, it returns a `Script` object representing this compiled code.
This script can be run later many times using methods below.
The returned script is not bound to any global object,
it is bound before each run, just for that run. `filename` is optional.
The returned script is not bound to any global object.
It is bound before each run, just for that run. `filename` is optional.
In case of syntax error in `code`, `new Script` emits the syntax error to stderr
and throws.an exception.
and throws an exception.
### script.runInThisContext()
Similar to "static" version in `Script.runInThisContext`, but now being a method of precompiled Script object.
`script.runInThisContext` runs the code of `script` and returns the result. Running code does not have access to local scope
and is run for actual `global` object (v8: in actual context).
Similar to `Script.runInThisContext` (note capital 'S'), but now being a method of a precompiled Script object.
`script.runInThisContext` runs the code of `script` and returns the result.
Running code does not have access to local scope, but does have access to the `global` object
(v8: in actual context).
Example of using `script.runInThisContext` and `eval` to run the same code:
Example of using `script.runInThisContext` to compile code once and run it multiple times:
var sys = require('sys'),
localVar = 123,
script, usingscript, evaled;
Script = process.binding('evals').Script,
scriptObj, i;
globalVar = 0;
script = new Script('localVar = 1', 'myfile.js');
usingscript = script.runInThisContext();
sys.puts('localVar: ' + localVar + ', usingscript: ' + usingscript);
evaled = eval('localVar = 1;');
sys.puts('localVar: ' + localVar + ', evaled: ' + evaled);
scriptObj = new Script('globalVar += 1', 'myfile.js');
// localVar: 123, usingscript: 1
// localVar: 1, evaled: 1
for (i = 0; i < 1000 ; i += 1) {
scriptObj.runInThisContext();
}
`script.runInThisContext` does not have access to the local scope, so `localVar` is unchanged.
`eval` does have access to the local scope, so `localVar` is changed.
sys.puts(globalVar);
// 1000
### script.runInNewContext(sandbox={})
### script.runInNewContext(sandbox)
Similar to "static" version in `Script.runInNewContext`, but now being a method of precompiled Script object.
`script.runInNewContext` runs the code of `script` in a `sandbox` and returns the result.
Running code does not have access to local scope and the object `sandbox` will be used as the global object for the code.
`sandbox`is optional.
Similar to `Script.runInNewContext` (note capital 'S'), but now being a method of a precompiled Script object.
`script.runInNewContext` runs the code of `script` with `sandbox` as the global object and returns the result.
Running code does not have access to local scope. `sandbox` is optional.
Example: compile code that increments a global variable and sets one, then execute this code multiple times.
These globals are contained in the sandbox.
var sys = require('sys'),
script = new Script('count += 1; name = 'kitty'', 'myfile.js'),
Script = process.binding('evals').Script,
scriptObj, i,
sandbox = {
animal: 'cat',
count: 2
};
script.runInNewContext(sandbox);
scriptObj = new Script(
'count += 1; name = "kitty"', 'myfile.js');
for (i = 0; i < 10 ; i += 1) {
scriptObj.runInNewContext(sandbox);
}
sys.puts(sys.inspect(sandbox));
Note that running untrusted code is a tricky business requiring great care. To prevent accidental
global variable leakage, `Script.runInNewContext` is quite useful, but to safely run untrusted code, many more steps
must be taken.
// { animal: 'cat', count: 12, name: 'kitty' }
Note that running untrusted code is a tricky business requiring great care. To prevent accidental
global variable leakage, `script.runInNewContext` is quite useful, but safely running untrusted code
requires a separate process.
## File System
@ -2489,6 +2602,66 @@ There are a few special REPL commands:
- `.help` - Show this list of special commands.
## Modules
Node uses the CommonJS module system.
Node has a simple module loading system. In Node, files and modules are in
one-to-one correspondence. As an example, `foo.js` loads the module
`circle.js` in the same directory.
The contents of `foo.js`:
var circle = require('./circle'),
sys = require('sys');
sys.puts( 'The area of a circle of radius 4 is '
+ circle.area(4));
The contents of `circle.js`:
var PI = 3.14;
exports.area = function (r) {
return PI * r * r;
};
exports.circumference = function (r) {
return 2 * PI * r;
};
The module `circle.js` has exported the functions `area()` and
`circumference()`. To export an object, add to the special `exports`
object. (Alternatively, one can use `this` instead of `exports`.) Variables
local to the module will be private. In this example the variable `PI` is
private to `circle.js`. The function `puts()` comes from the module `'sys'`,
which is a built-in module. Modules which are not prefixed by `'./'` are
built-in module--more about this later.
A module prefixed with `'./'` is relative to the file calling `require()`.
That is, `circle.js` must be in the same directory as `foo.js` for
`require('./circle')` to find it.
Without the leading `'./'`, like `require('assert')` the module is searched
for in the `require.paths` array. `require.paths` on my system looks like
this:
`[ '/home/ryan/.node_libraries' ]`
That is, when `require('assert')` is called Node looks for:
* 1: `/home/ryan/.node_libraries/assert.js`
* 2: `/home/ryan/.node_libraries/assert.node`
* 3: `/home/ryan/.node_libraries/assert/index.js`
* 4: `/home/ryan/.node_libraries/assert/index.node`
interrupting once a file is found. Files ending in `'.node'` are binary Addon
Modules; see 'Addons' below. `'index.js'` allows one to package a module as
a directory.
`require.paths` can be modified at runtime by simply unshifting new
paths onto it, or at startup with the `NODE_PATH` environmental
variable (which should be a list of paths, colon separated).
## Addons

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