Reference

• nginx objects
• HTTP Request
• Stream Session
• Response
• ngx
• built-in objects
• njs
• process
• String
• web API
• Text Decoder
• Text Encoder
• timers
• built-in modules
• Buffer
• Crypto
• File System
• Query String

njs provides objects, methods and properties for extending nginx functionality.

This reference contains only njs specific properties, methods and modules not compliant with ECMAScript. Definitions of njs properties and methods compliant with ECMAScript can be found in ECMAScript specification. List of all njs properties and methods can be found in Compatibility.

nginx objects

HTTP Request

The HTTP request object is available only in the ngx_http_js_module module. All string properties of the object are byte strings.

r.args{}

request arguments object, read-only

r.done()

after calling this function, next data chunks will be passed to client without calling js_body_filter (0.5.2). May be called only from the js_body_filter function

r.error(string)

writes a string to the error log on the error level of logging

r.finish()

finishes sending a response to the client

r.headersIn{}

incoming headers object, read-only.

The Foo request header can be accessed with the syntax: headersIn.foo or headersIn['Foo'].

The “Authorization”, “Content-Length”, “Content-Range”, “Content-Type”, “ETag”, “Expect”, “From”, “Host”, “If-Match”, “If-Modified-Since”, “If-None-Match”, “If-Range”, “If-Unmodified-Since”, “Max-Forwards”, “Proxy-Authorization”, “Referer”, “Transfer-Encoding”, and “User-Agent” request headers can have only one field value (0.4.1). Duplicate field values in “Cookie” headers are separated by semicolon (;). Duplicate field values in all other request headers are separated by commas.

r.headersOut{}

outgoing headers object, writable.

The “Foo” response header can be accessed with the syntax: headersOut.foo or headersOut['Foo'].

Field values of multi-value response headers (0.4.0) can be set with the syntax:

r.headersOut['Foo'] = ['a', 'b']

where the output will be:

Foo: a
Foo: b

All previous field values of the “Foo” response header will be deleted.

For standard response headers that accept only a single field value such as “Content-Type”, only the last element of the array will take effect. Field values of the “Set-Cookie” response header are always returned as an array. Duplicate field values in “Age”, “Content-Encoding”, “Content-Length”, “Content-Type”, “ETag”, “Expires”, “Last-Modified”, “Location”, “Retry-After” response headers are ignored. Duplicate field values in all other response headers are separated by commas.

r.httpVersion

HTTP version, read-only

r.internalRedirect(uri)

performs an internal redirect to the specified uri. If the uri starts with the “@” prefix, it is considered a named location. Redirected requests become internal and can access the internal locations. The actual redirect happens after the handler execution is completed.

After redirect, a new njs VM is started in the target location, the VM in the original location is stopped. Values of nginx variables are kept and can be used to pass information to the target location. Since 0.5.3, the variable declared with the js_var directive for http or stream can be used.

r.log(string)

writes a string to the error log on the info level of logging

r.method

HTTP method, read-only

r.parent

references the parent request object

r.remoteAddress

client address, read-only

r.requestBody

the property is deprecated since 0.5.0, the r.requestBuffer or r.requestText property should be used instead.

r.requestBuffer

client request body if it has not been written to a temporary file (since 0.5.0). To ensure that the client request body is in memory, its size should be limited by client_max_body_size, and a sufficient buffer size should be set using client_body_buffer_size. The property is available only in the js_content directive.

r.requestText

the same as r.requestBuffer, but returns a string. Note that it may convert bytes invalid in UTF-8 encoding into the replacement character.

r.rawHeadersIn{}

returns an array of key-value pairs exactly as they were received from the client (0.4.1).

For example, with the following request headers:

Host: localhost
Foo:  bar
foo:  bar2

the output of r.rawHeadersIn will be:

[
    ['Host', 'localhost'],
    ['Foo', 'bar'],
    ['foo', 'bar2']
]

All foo headers can be collected with the syntax:

r.rawHeadersIn.filter(v=>v[0].toLowerCase() == 'foo').map(v=>v[1])

the output will be:

['bar', 'bar2']

Header field names are not converted to lower case, duplicate field values are not merged.

r.rawHeadersOut{}

returns an array of key-value pairs of response headers (0.4.1). Header field names are not converted to lower case, duplicate field values are not merged.

r.responseBody

the property is deprecated since 0.5.0, the r.responseBuffer or the r.responseText property should be used instead.

r.responseBuffer

holds the subrequest response body, read-only (since 0.5.0). The size of r.responseBuffer is limited by the subrequest_output_buffer_size directive.

r.responseText

the same as r.responseBuffer but returns a string (since 0.5.0). Note that it may convert bytes invalid in UTF-8 encoding into the replacement character.

r.return(status[, string | Buffer])

sends the entire response with the specified status to the client. The response can be a string or Buffer (0.5.0).

It is possible to specify either a redirect URL (for codes 301, 302, 303, 307, and 308) or the response body text (for other codes) as the second argument

r.send(string | Buffer)

sends a part of the response body to the client. The data sent can be a string or Buffer (0.5.0)

r.sendBuffer(data[, options])

adds data to the chain of data chunks to be forwarded to the next body filter (0.5.2). The actual forwarding happens later, when the all the data chunks of the current chain are processed.

The data can be a string or Buffer. The options is an object used to override nginx buffer flags derived from an incoming data chunk buffer. The flags can be overridden with the following flags:

last

boolean, true if the buffer is the last buffer

flush

boolean, true if the buffer should have the flush flag

The method may be called only from the js_body_filter function.

r.sendHeader()

sends the HTTP headers to the client

r.status

status, writable

r.subrequest(uri[, options[, callback]])

creates a subrequest with the given uri and options, and installs an optional completion callback.

A subrequest shares its input headers with the client request. To send headers different from original headers to a proxied server, the proxy_set_header directive can be used. To send a completely new set of headers to a proxied server, the proxy_pass_request_headers directive can be used.

If options is a string, then it holds the subrequest arguments string. Otherwise, options is expected to be an object with the following keys:

args

arguments string, by default an empty string is used

body

request body, by default the request body of the parent request object is used

method

HTTP method, by default the GET method is used

detached

boolean flag (0.3.9), if true, the created subrequest is a detached subrequest. Responses to detached subrequests are ignored. Unlike ordinary subrequests, a detached subrequest can be created inside a variable handler. The detached flag and callback argument are mutually exclusive.

The completion callback receives a subrequest response object with methods and properties identical to the parent request object.

Since 0.3.8, if a callback is not provided, the Promise object that resolves to the subrequest response object is returned.

r.uri

current URI in request, normalized, read-only

r.rawVariables{}

nginx variables as Buffers, writable (since 0.5.0)

r.variables{}

nginx variables object, writable (since 0.2.8).

A variable is writable if:

• it was created using the js_var directive for http or stream (since 0.5.3)
• it is referenced in nginx configuration file

Even so, some embedded variables still cannot be assigned a value (for example, $http_).

r.warn(string)

writes a string to the error log on the warning level of logging

Stream Session

The stream session object is available only in the ngx_stream_js_module module. All string properties of the object are byte strings.

s.allow()

an alias to s.done(0) (0.2.4)

s.decline()

an alias to s.done(-5) (0.2.4)

s.deny()

an alias to s.done(403) (0.2.4)

s.done([code])

sets an exit code for the current phase handler to a code value, by default 0. The actual finalization happens when the js handler is completed and all pending events, for example, from ngx.fetch() or setTimeout(), are processed (0.2.4).

Possible code values:

• 0 — successful finalization, passing control to the next phase
• -5 — undecided, passing control to the next handler of the current phase (if any)
• 403 — access is forbidden

May be called only from a phase handler function: js_access or js_preread.

s.error(string)

writes a sent string to the error log on the error level of logging

s.log(string)

writes a sent string to the error log on the info level of logging

s.off(eventName)

unregisters the callback set by the s.on() method (0.2.4)

s.on(event, callback)

registers a callback for the specified event (0.2.4).

An event may be one of the following strings:

upload

new data (string) from a client

download

new data (string) to a client

upstream

new data (Buffer) from a client (since 0.5.0)

downstream

new data (Buffer) to a client (since 0.5.0)

The completion callback has the following prototype: callback(data, flags), where data is string or Buffer (depending on the event type) flags is an object with the following properties:

last

a boolean value, true if data is a last buffer.

s.remoteAddress

client address, read-only

s.rawVariables

nginx variables as Buffers, writable (since 0.5.0)

s.send(data[, options])

adds data to the chain of data chunks that will be forwarded in the forward direction: in download callback to a client; in upload to an upstream server (0.2.4). The actual forwarding happens later, when the all the data chunks of the current chain are processed.

The data can be a string or Buffer (0.5.0). The options is an object used to override nginx buffer flags derived from an incoming data chunk buffer. The flags can be overridden with the following flags:

last

boolean, true if the buffer is the last buffer

flush

boolean, true if the buffer should have the flush flag

The method can be called multiple times per callback invocation.

s.status

session status code, an alias to the $status variable, read only (since 0.5.2)

s.variables{}

nginx variables object, writable (since 0.2.8). A variable can be writable only if it is referenced in nginx configuration file. Even so, some embedded variables still cannot be assigned a value.

s.warn(string)

writes a sent string to the error log on the warning level of logging

Response

The Response interface is available since 0.5.1.

arrayBuffer()

Takes a Response stream and reads it to completion. Returns a Promise that resolves with an ArrayBuffer.

bodyUsed

A boolean value, true if the body was read.

headers

The Headers read-only object associated with the Response:

get(name)

returns a string containing the values of all headers with the specified name separated by a comma and a space

getAll(name)

returns an array containing the values of all headers with the specified name

has(name)

returns a boolean value indicating whether a header with the specified name exists

json()

Takes a Response stream and reads it to completion. Returns a Promise that resolves with the result of parsing the body text as JSON.

ok

A boolean value, true if the response was successful (status codes between 200–299).

redirected

A boolean value, true if the response is the result of a redirect.

status

The status code of the response.

statusText

The status message corresponding to the status code.

text()

Takes a Response stream and reads it to completion. Returns a Promise that resolves with a string.

type

The type of the response.

url

The URL of the response.

ngx

The ngx global object is available since 0.5.0.

ngx.fetch(url, [options])

Makes a request to fetch an URL (0.5.1), returns a Promise that resolves with the Response object. Only the http:// scheme is supported, redirects are not handled.

The options parameter is expected to be an object with the following keys:

body

request body, by default is empty

buffer_size

the buffer size for reading the response, by default is 4096

headers

request headers object

max_response_body_size

the maximum size of the response body in bytes, by default is 32768

method

HTTP method, by default the GET method is used

Example:

ngx.fetch('http://nginx.org/')
.then(reply => reply.text())
.then(body => r.return(200, body))
.catch(e => r.return(501, e.message))

ngx.log(level, message)

Writes a message to the error log with the specified level of logging. The level parameter specifies one of the log levels, the message parameter can be a string or Buffer. The following log levels can be specified: ngx.INFO, ngx.WARN, and ngx.ERR.

built-in objects

njs

The njs object is a global object that represents the current VM instance (since 0.2.0).

njs.version

Returns a string with the current version of njs (for example, “0.5.2”).

njs.dump(value)

Returns the pretty-print string representation for a value.

njs.on(event, callback)

Registers a callback for the specified VM event (since 0.5.2). An event may be one of the following strings:

exit

is called before the VM is destroyed. The callback is called without arguments.

process

The process object is a global object that provides information about the current process (0.3.3).

process.argv

Returns an array that contains the command line arguments passed when the current process was launched.

process.env

Returns an object containing the user environment.

By default, nginx removes all environment variables inherited from its parent process except the TZ variable. Use the env directive to preserve some of the inherited variables.

process.pid

Returns the PID of the current process.

process.ppid

Returns the PID of the current parent process.

String

There are two types of strings in njs: a Unicode string (default) and a byte string.

A Unicode string corresponds to an ECMAScript string which contains Unicode characters.

Byte strings contain a sequence of bytes and are used to serialize Unicode strings to external data and deserialize from external sources. For example, the toUTF8() method serializes a Unicode string to a byte string using UTF-8 encoding:

>> '£'.toUTF8().toString('hex')
'c2a3'  /* C2 A3 is the UTF-8 representation of 00A3 ('£') code point */

The toBytes() method serializes a Unicode string with code points up to 255 into a byte string, otherwise, null is returned:

>> '£'.toBytes().toString('hex')
'a3'  /* a3 is a byte equal to 00A3 ('£') code point  */

String.bytesFrom(array | string, encoding)

Creates a byte string either from an array that contains octets, or from an encoded string (0.2.3). The encoding can be hex, base64, and base64url. The method is deprecated since 0.4.4, the Buffer.from method should be used instead:

>> Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]).toString()
'buffer'

>> Buffer.from('YnVmZmVy', 'base64').toString()
'buffer'

String.prototype.fromBytes(start[, end])

Returns a new Unicode string from a byte string where each byte is replaced with a corresponding Unicode code point.

String.prototype.fromUTF8(start[, end])

Converts a byte string containing a valid UTF-8 string into a Unicode string, otherwise null is returned.

String.prototype.toBytes(start[, end])

Serializes a Unicode string to a byte string. Returns null if a character larger than 255 is found in the string.

String.prototype.toString(encoding)

Encodes a string to hex, base64, or base64url:

>>  'αβγδ'.toString('base64url')
'zrHOss6zzrQ'

Before version 0.4.3, only a byte string could be encoded:

>>  'αβγδ'.toUTF8().toString('base64url')
'zrHOss6zzrQ'

String.prototype.toUTF8(start[, end])

Serializes a Unicode string to a byte string using UTF-8 encoding.

>> 'αβγδ'.toUTF8().length
8
>> 'αβγδ'.length
4

web API

Text Decoder

The TextDecoder produces a stream of code points from a stream of bytes (0.4.3).

TextDecoder([[encoding], options])

Creates a new TextDecoder object for specified encoding, currently, only UTF-8 is supported. The options is TextDecoderOptions dictionary with the property:

fatal

boolean flag indicating if TextDecoder.decode() must throw the TypeError exception when a coding error is found, by default is false.

TextDecoder.prototype.encoding

Returns a string with the name of the encoding used by TextDecoder(), read-only.

TextDecoder.prototype.fatal

boolean flag, true if the error mode is fatal, read-only.

TextDecoder.prototype.ignoreBOM

boolean flag, true if the byte order marker is ignored, read-only.

TextDecoder.prototype.decode(buffer, [options])

Returns a string with the text decoded from the buffer by TextDecoder(). The buffer can be ArrayBuffer. The options is TextDecodeOptions dictionary with the property:

stream

boolean flag indicating if additional data will follow in subsequent calls to decode(): true if processing the data in chunks, and false for the final chunk or if the data is not chunked. By default is false.

>> (new TextDecoder()).decode(new Uint8Array([206,177,206,178]))
αβ

Text Encoder

The TextEncoder object produces a byte stream with UTF-8 encoding from a stream of code points (0.4.3).

TextEncoder()

Returns a newly constructed TextEncoder that will generate a byte stream with UTF-8 encoding.

TextEncoder.prototype.encode(string)

Encodes string into a Uint8Array with UTF-8 encoded text.

TextEncoder.prototype.encodeInto(string, uint8Array)

Encodes a string to UTF-8, puts the result into destination Uint8Array, and returns a dictionary object that shows the progress of the encoding. The dictionary object contains two members:

read

the number of UTF-16 units of code from the source string converted to UTF-8

written

the number of bytes modified in the destination Uint8Array

timers

clearTimeout(timeout)

Cancels a timeout object created by setTimeout().

setTimeout(function, milliseconds[, argument1, argumentN])

Calls a function after a specified number of milliseconds. One or more optional arguments can be passed to the specified function. Returns a timeout object.

function handler(v)
{
    // ...
}

t = setTimeout(handler, 12);

// ...

clearTimeout(t);

built-in modules

Buffer

Buffer.alloc(size[, fill[, encoding]]))

Allocates a new Buffer of a specified size. If fill is not specified, the Buffer will be zero-filled. If fill is specified, the allocated Buffer will be initialized by calling buf.fill(fill). If fill and encoding are specified, the allocated Buffer will be initialized by calling buf.fill(fill, encoding).

The fill parameter may be a string, Buffer, Uint8Array, or integer.

Buffer.allocUnsafe(size)

The same as Buffer.alloc(), with the difference that the memory allocated for the buffer is not initialized, the contents of the new buffer is unknown and may contain sensitive data.

Buffer.byteLength(value[, encoding])

Returns the byte length of a specified value, when encoded using encoding. The value can be a string, Buffer, TypedArray, DataView, or ArrayBuffer. If the value is a string, the encoding parameter is its encoding, can be utf8, hex, base64, base64url; by default is utf8.

Buffer.compare(buffer1, buffer2)

Compares buffer1 with buffer2 when sorting arrays of Buffer instances. Returns 0 if buffer1 is the same as buffer2, 1 if buffer2 should come before buffer1 when sorted, or -1 if buffer2 should come after buffer1 when sorted.

Buffer.concat(list[, totalLength])

Returns a new Buffer which is the result of concatenating all the Buffer instances in the list. If there are no items in the list or the total length is 0, a new zero-length Buffer is returned. If totalLength is not specified, it is calculated from the Buffer instances in list by adding their lengths. If totalLength is specified, it is coerced to an unsigned integer. If the combined length of the Buffers in list exceeds totalLength, the result is truncated to totalLength.

Buffer.from(array)

Allocates a new Buffer using an array of bytes in the range 0 – 255. Array entries outside that range will be truncated.

Buffer.from(arrayBuffer, byteOffset[, length]])

Creates a view of the ArrayBuffer without copying the underlying memory. The optional byteOffset and length arguments specify a memory range within the arrayBuffer that will be shared by the Buffer.

Buffer.from(buffer)

Copies the passed buffer data onto a new Buffer instance.

Buffer.from(object[, offsetOrEncoding[, length]])

For objects whose valueOf() function returns a value not strictly equal to object, returns Buffer.from(object.valueOf(), offsetOrEncoding, length).

Buffer.from(string[, encoding])

Creates a new Buffer with a string. The encoding parameter identifies the character encoding to be used when converting a string into bytes. The encoding can be utf8, hex, base64, base64url; by default is utf8.

Buffer.isBuffer(object)

A boolean value, returns true if object is a Buffer.

Buffer.isEncoding(encoding)

A boolean value, returns true if encoding is the name of a supported character encoding.

buffer[index]

The index operator that can be used to get and set the octet at position index in buffer. The values refer to individual bytes, so the legal value range is between 0 and 255 (decimal).

buf.buffer

The underlying ArrayBuffer object based on which this Buffer object is created.

buf.byteOffset

An integer, specifying the byteOffset of the Buffers underlying ArrayBuffer object.

buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])

Compares buffer with target and returns a number indicating whether buffer comes before, after, or is the same as target in sort order. Comparison is based on the actual sequence of bytes in each Buffer. The targetStart is an integer specifying the offset within target at which to begin comparison, by default is 0. The targetEnd is an integer specifying the offset within target at which to end comparison, by default is target.length. The sourceStart is an integer specifying the offset within buffer at which to begin comparison, by default is 0. The sourceEnd is an integer specifying the offset within buffer at which to end comparison (not inclusive), by default is buf.length.

buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])

Copies data from a region of buffer to a region in target, even if the target memory region overlaps with buffer. The target parameter is a Buffer or Uint8Array to copy into.

The targetStart is an integer specifying the offset within target at which to begin writing, by default is 0. The sourceStart is an integer specifying the offset within buffer from which to begin copying, by default is 0. The sourceEnd is an integer specifying the offset within buffer at which to stop copying (not inclusive) by default is buf.length.

buf.equals(otherBuffer)

A boolean value, returns true if both Buffer and otherBuffer have exactly the same bytes.

buf.fill(value[, offset[, end]][, encoding])

Fills the Buffer with the specified value. If the offset and end are not specified, the entire Buffer will be filled. The value is coerced to uint32 if it is not a string, Buffer, or integer. If the resulting integer is greater than 255, the Buffer will be filled with value and 255.

buf.includes(value[, byteOffset][, encoding])

Equivalent to buf.indexOf() !== -1, returns true if the value was found in Buffer.

buf.indexOf(value[, byteOffset][, encoding])

Returns an integer which is the index of the first occurrence of value in Buffer, or -1 if Buffer does not contain value. The value can be a string with specified encoding (by default utf8), Buffer, Unit8Array, or a number between 0 and 255.

buf.lastIndexOf(value[, byteOffset][, encoding])

The same as buf.indexOf(), except the last occurrence of the value is found instead of the first occurrence. The value can be a string, Buffer, or integer between 1 and 255. If the value is an empty string or empty Buffer, byteOffset will be returned.

buf.length

Returns the number of bytes in Buffer.

buf.readIntBE(offset, byteLength)

Reads the byteLength from buf at the specified offset and interprets the result as a big-endian, two's complement signed value supporting up to 48 bits of accuracy. The byteLength parameter is an integer between 1 and 6 specifying the number of bytes to read.

The similar methods are also supported: buf.readInt8([offset]), buf.readInt16BE([offset]), buf.readInt32BE([offset]).

buf.readIntLE(offset, byteLength)

Reads the byteLength from buf at the specified offset and interprets the result as a little-endian, two's complement signed value supporting up to 48 bits of accuracy. The byteLength parameter is an integer between 1 and 6 specifying the number of bytes to read.

The similar methods are also supported: buf.readInt8([offset]), buf.readInt16LE([offset]), buf.readInt32LE([offset]).

buf.readUIntBE(offset, byteLength)

Reads the byteLength from buf at the specified offset and interprets the result as a big-endian integer supporting up to 48 bits of accuracy. The byteLength parameter is an integer between 1 and 6 specifying the number of bytes to read.

The similar methods are also supported: buf.readUInt8([offset]), buf.readUInt16BE([offset]), buf.readUInt32BE([offset]).

buf.readUIntLE(offset, byteLength)

Reads the byteLength from buf at the specified offset and interprets the result as a little-endian integer supporting up to 48 bits of accuracy. The byteLength parameter is an integer between 1 and 6 specifying the number of bytes to read.

The similar methods are also supported: buf.readUInt8([offset]), buf.readUInt16LE([offset]), buf.readUInt32LE([offset]).

buf.readDoubleBE([offset])

Reads a 64-bit, big-endian double from buf at the specified offset.

buf.readDoubleLE([offset])

Reads a 64-bit, little-endian double from buf at the specified offset.

buf.readFloatBE([offset])

Reads a 32-bit, big-endian float from buf at the specified offset.

buf.readFloatLE([offset])

Reads a 32-bit, little-endian float from buf at the specified offset.

buf.subarray[start[, end]])

Returns a new buf that references the same memory as the original, but offset and cropped by start and end. If end is greater than buf.length, the same result as that of end equal to buf.length is returned.

buf.slice[start[, end]])

Returns a new buf that references the same memory as the original, but offset and cropped by the start and end values. The method is not compatible with the Uint8Array.prototype.slice(), which is a superclass of Buffer. To copy the slice, use Uint8Array.prototype.slice().

buf.swap16()

Interprets buf as an array of unsigned 16-bit numbers and swaps the byte order in-place. Throws an error if buf.length is not a multiple of 2.

buf.swap32()

Interprets buf as an array of unsigned 32-bit numbers and swaps the byte order in-place. Throws an error if buf.length is not a multiple of 4.

buf.swap64()

Interprets buf as an array of 64-bit numbers and swaps byte order in-place. Throws an error if buf.length is not a multiple of 8.

buf.toJSON()

Returns a JSON representation of buf. JSON.stringify() implicitly calls this function when stringifying a Buffer instance.

buf.toString([encoding[, start[, end]]])

Decodes buf to a string according to the specified character encoding which can be utf8, hex, base64, base64url. The start and end parameters may be passed to decode only a subset of Buffer.

buf.write(string[, offset[, length]][, encoding])

Writes a string to buf at offset according to the character encoding. The length parameter is the number of bytes to write. If Buffer did not contain enough space to fit the entire string, only part of string will be written, however, partially encoded characters will not be written. The encoding can be utf8, hex, base64, base64url.

buf.writeIntBE(value, offset, byteLength)

Writes byteLength bytes of value to buf at the specified offset as big-endian. Supports up to 48 bits of accuracy. The byteLength parameter is an integer between 1 and 6 specifying the number of bytes to read.

The following similar methods are also supported: buf.writeInt8, buf.writeInt16BE, buf.writeInt32BE.

buf.writeIntLE(value, offset, byteLength)

Writes byteLength bytes of value to buf at the specified offset as little-endian. Supports up to 48 bits of accuracy. The byteLength parameter is an integer between 1 and 6 specifying the number of bytes to read.

The following similar methods are also supported: buf.writeInt8, buf.writeInt16LE, buf.writeInt32LE.

buf.writeUIntBE(value, offset, byteLength)

Writes byteLength bytes of value to buf at the specified offset as big-endian. Supports up to 48 bits of accuracy. The byteLength parameter is an integer between 1 and 6 specifying the number of bytes to read.

The following similar methods are also supported: buf.writeUInt8, buf.writeUInt16BE, buf.writeUInt32BE.

buf.writeUIntLE(value, offset, byteLength)

Writes byteLength bytes of value to buf at the specified offset as little-endian. Supports up to 48 bits of accuracy. The byteLength parameter is an integer between 1 and 6 specifying the number of bytes to read.

The following similar methods are also supported: buf.writeUInt8, buf.writeUInt16LE, buf.writeUInt32LE.

buf.writeDoubleBE(value, [offset])

Writes the value to buf at the specified offset as big-endian.

buf.writeDoubleLE(value, [offset])

Writes the value to buf at the specified offset as little-endian.

buf.writeFloatBE(value, [offset])

Writes the value to buf at the specified offset as big-endian.

buf.writeFloatLE(value, [offset])

Writes the value to buf at the specified offset as little-endian.

Crypto

The Crypto module provides cryptographic functionality support. The Crypto module object is returned by require('crypto').

crypto.createHash(algorithm)

Creates and returns a Hash object that can be used to generate hash digests using the given algorithm. The algorithm can be md5, sha1, and sha256.

crypto.createHmac(algorithm, secret key)

Creates and returns an HMAC object that uses the given algorithm and secret key. The algorithm can be md5, sha1, and sha256.

Hash

hash.update(data)

Updates the hash content with the given data.

hash.digest([encoding])

Calculates the digest of all of the data passed using hash.update(). The encoding can be hex, base64, and base64url. If encoding is not provided, a Buffer object (0.4.4) is returned.

Before version (0.4.4), a byte string was returned instead of a Buffer object.

>> var cr = require('crypto')
undefined

>> cr.createHash('sha1').update('A').update('B').digest('base64url')
'BtlFlCqiamG-GMPiK_GbvKjdK10'

HMAC

hmac.update(data)

Updates the HMAC content with the given data.

hmac.digest([encoding])

Calculates the HMAC digest of all of the data passed using hmac.update(). The encoding can be hex, base64, and base64url. If encoding is not provided, a Buffer object (0.4.4) is returned.

Before version 0.4.4, a byte string was returned instead of a Buffer object.

>> var cr = require('crypto')
undefined

>> cr.createHmac('sha1', 'secret.key').update('AB').digest('base64url')
'Oglm93xn23_MkiaEq_e9u8zk374'

File System

The File System module provides operations with files.

The module object is returned by require('fs'). Since 0.3.9, promissified versions of file system methods are available through require('fs').promises object:

> var fs = require('fs').promises;
undefined
> fs.readFile("/file/path").then((data)=>console.log(data))
<file data>

accessSync(path[, mode])

Synchronously tests permissions for a file or directory specified in the path (0.3.9). If the check fails, an error will be returned, otherwise, the method will return undefined.

mode

by default is fs.constants.F_OK. The mode argument is an optional integer that specifies the accessibility checks to be performed.

try {
    fs.accessSync('/file/path', fs.constants.R_OK | fs.constants.W_OK);
    console.log('has access');
} catch (e) {
    console.log('no access');)
}

appendFileSync(filename, data[, options])

Synchronously appends specified data to a file with provided filename. The data is expected to be a string or a Buffer object (0.4.4). If the file does not exist, it will be created. The options parameter is expected to be an object with the following keys:

mode

mode option, by default is 0o666

flag

file system flag, by default is a

mkdirSync(path[, options])

Synchronously creates a directory at the specified path (0.4.2). The options parameter is expected to be an integer that specifies the mode, or an object with the following keys:

mode

mode option, by default is 0o777.

readdirSync(path[, options])

Synchronously reads the contents of a directory at the specified path (0.4.2). The options parameter is expected to be a string that specifies encoding or an object with the following keys:

encoding

encoding, by default is utf8. The encoding can be utf8 and buffer (0.4.4).

withFileTypes

if set to true, the files array will contain fs.Dirent objects, by default is false.

readFileSync(filename[, options])

Synchronously returns the contents of the file with provided filename. The options parameter holds string that specifies encoding. If an encoding is specified, a string is returned, otherwise, a Buffer object (0.4.4) is returned.

Before version 0.4.4, a byte string was returned if encoding was not specified.

Otherwise, options is expected to be an object with the following keys:

encoding

encoding, by default is not specified. The encoding can be utf8, hex (0.4.4), base64 (0.4.4), base64url (0.4.4).

flag

file system flag, by default is r

>> var fs = require('fs')
undefined
>> var file = fs.readFileSync('/file/path.tar.gz')
undefined
>> var gzipped = file.slice(0,2).toString('hex') === '1f8b'; gzipped
true

realpathSync(path[, options])

Synchronously computes the canonical pathname by resolving ., .. and symbolic links using realpath(3). The options argument can be a string specifying an encoding, or an object with an encoding property specifying the character encoding to use for the path passed to the callback (0.3.9).

renameSync(oldPath, newPath)

Synchronously changes the name or location of a file from oldPath to newPath (0.3.4).

>> var fs = require('fs')
undefined
>> var file = fs.renameSync('hello.txt', 'HelloWorld.txt')
undefined

rmdirSync(path)

Synchronously removes a directory at the specified path (0.4.2).

symlinkSync(target, path)

Synchronously creates the link called path pointing to target using symlink(2) (0.3.9). Relative targets are relative to the link’s parent directory.

unlinkSync(path)

Synchronously unlinks a file by path (0.3.9).

writeFileSync(filename, data[, options])

Synchronously writes data to a file with provided filename. The data is expected to be a string or a Buffer object (0.4.4). If the file does not exist, it will be created, if the file exists, it will be replaced. The options parameter is expected to be an object with the following keys:

mode

mode option, by default is 0o666

flag

file system flag, by default is w

>> var fs = require('fs')
undefined
>> var file = fs.writeFileSync('hello.txt', 'Hello world')
undefined

fs.Dirent

fs.Dirent is a representation of a directory entry — a file or a subdirectory. When readdirSync() is called with the withFileTypes option, the resulting array contains fs.Dirent objects.

• dirent.isBlockDevice() — returns true if the fs.Dirent object describes a block device.
• dirent.isCharacterDevice() — returns true if the fs.Dirent object describes a character device.
• dirent.isDirectory() — returns true if the fs.Dirent object describes a file system directory.
• dirent.isFIFO() — returns true if the fs.Dirent object describes a first-in-first-out (FIFO) pipe.
• dirent.isFile() — returns true if the fs.Dirent object describes a regular file.
• dirent.isSocket() — returns true if the fs.Dirent object describes a socket.
• dirent.isSymbolicLink() — returns true if the fs.Dirent object describes a symbolic link.
• dirent.name — the name of the file fs.Dirent object refers to.

File Access Constants

The access() method can accept the following flags. These flags are exported by fs.constants:

• F_OK — indicates that the file is visible to the calling process, used by default if no mode is specified
• R_OK — indicates that the file can be read by the calling process
• W_OK — indicates that the file can be written by the calling process
• X_OK — indicates that the file can be executed by the calling process

File System Flags

The flag option can accept the following values:

• a — open a file for appending. The file is created if it does not exist
• ax — the same as a but fails if the file already exists
• a+ — open a file for reading and appending. If the file does not exist, it will be created
• ax+ — the same as a+ but fails if the file already exists
• as — open a file for appending in synchronous mode. If the file does not exist, it will be created
• as+ — open a file for reading and appending in synchronous mode. If the file does not exist, it will be created
• r — open a file for reading. An exception occurs if the file does not exist
• r+ — open a file for reading and writing. An exception occurs if the file does not exist
• rs+ — open a file for reading and writing in synchronous mode. Instructs the operating system to bypass the local file system cache
• w — open a file for writing. If the file does not exist, it will be created. If the file exists, it will be replaced
• wx — the same as w but fails if the file already exists
• w+ — open a file for reading and writing. If the file does not exist, it will be created. If the file exists, it will be replaced
• wx+ — the same as w+ but fails if the file already exists

Query String

The Query String module provides support for parsing and formatting URL query strings (0.4.3). The Query String module object is returned by require('querystring').

querystring.decode()

is an alias for querystring.parse().

querystring.encode()

is an alias for querystring.stringify().

querystring.escape(string)

Performs URL encoding of the given string, returns an escaped query string. The method is used by querystring.stringify() and should not be used directly.

querystring.parse(string[, separator[, equal[, options]]])

Parses the query string URL and returns an object.

The separator parameter is a substring for delimiting key and value pairs in the query string, by default is “&”.

The equal parameter is a substring for delimiting keys and values in the query string, by default is “=”.

The options parameter is expected to be an object with the following keys:

decodeURIComponent function

Function used to decode percent-encoded characters in the query string, by default is querystring.unescape()

maxKeys number

the maximum number of keys to parse, by default is 1000. The 0 value removes limitations for counting keys.

By default, percent-encoded characters within the query string are assumed to use the UTF-8 encoding, invalid UTF-8 sequences will be replaced with the U+FFFD replacement character.

For example, for the following query string

'foo=bar&abc=xyz&abc=123'

the output will be:

{
  foo: 'bar',
  abc: ['xyz', '123']
}

querystring.stringify(object[, separator[, equal[, options]]])

Serializes an object and returns a URL query string.

The separator parameter is a substring for delimiting key and value pairs in the query string, by default is “&”.

The equal parameter is a substring for delimiting keys and values in the query string, by default is “=”.

The options parameter is expected to be an object with the following keys:

encodeURIComponent function

The function to use when converting URL-unsafe characters to percent-encoding in the query string, by default is querystring.escape().

By default, characters that require percent-encoding within the query string are encoded as UTF-8. If other encoding is required, then encodeURIComponent option should be specified.

For example, for the following command

querystring.stringify({ foo: 'bar', baz: ['qux', 'quux'], 123: '' });

the query string will be:

'foo=bar&baz=qux&baz=quux&123='

querystring.unescape(string)

Performs decoding of URL percent-encoded characters of the string, returns an unescaped query string. The method is used by querystring.parse() and should not be used directly.