The context.utils object

When writing JavaScript code for a filter, you always have the context.utils object available. This object has the following methods:

byte[] getUTF8BytesForString(string)

Returns the UTF-8 bytes for the given string. 

For example, to compute the hash for a string:

let sqlBytes = context.utils.getUTF8BytesForString(context.packet.sql);

let DigestUtils = Java.type("org.apache.commons.codec.digest.DigestUtils");

let sqlHash = DigestUtils.sha1Hex(sqlBytes);

string stringFromUTF8Bytes(byte[])

Builds a string from a byte array, which should contain UTF-8 encoded characters.

Example:

let byteArray = [72, 101, 108, 108, 111, 32, 119, 111, 114, 108, 100];

let str = context.utils.stringFromUTF8Bytes(byteArray);

string stringFromUTF8Bytes(byte[] bytes, int offset, int size)

Builds a string from a byte array, which should contain UTF-8 encoded characters.

Example:

let byteArray = [0, 0, 108, 108, 111, 32, 119, 111, 114, 108, 100, 0, 0, 0, 0];

let str = context.utils.stringFromUTF8Bytes(byteArray, 2, 9);

object createObject()

Creates a new empty object, which (unlike JavaScript objects) can be stored in long-lived contexts. For example:

context.connectionContext.qres = context.utils.createObject();

See the JavaScript environment page for details.

object createCache(int maxSize, int ttlSecs)

Creates a new cache object, which will contain up to maxSize objects. Key/value pairs may be purged if they have not been accessed for more than ttlSecs seconds, or if the cache reaches its maximum size (maxSize), at which points the least recently used key/value pairs will be removed from the cache.

context.filterContext.stmtCache = context.utils.createCache(100, 600);

context.filterContext.stmtCache.put("something to cache", something);

Keep in mind that JavaScript objects cannot be shared across invocations of a filter (primitives like strings, number and booleans are fine). You can use createObject() (see above) if you need an object that does not have that limitation.

string doPost(string url, string payload)

Makes a REST POST call to the specified URL, POSTing the given payload. Returns the response as a string if successful, null otherwise.

byte[] allocateByteArray(int)

Returns a byte array of the specified size.

let responseBytes = context.utils.allocateByteArray(5000);

let numRead = sock.getInputStream().read(responseBytes);

let responseStr = context.utils.stringFromUTF8Bytes(responseBytes, 0, numRead);

string getBinaryDump(byte[] bytes)

Returns a readable string for the specified set of bytes. This is useful for debugging mostly, e.g.:

let bytes = context.utils.getUTF8BytesForString("Four score and seven years ago, our forefathers");

log.debug(context.utils.getBinaryDump(bytes));

The returned string looks like:

46 6F 75 72 20 73 63 6F 72 65 20 61 6E 64 20 73   Four score and s
65 76 65 6E 20 79 65 61 72 73 20 61 67 6F 2C 20   even years ago,
6F 75 72 20 66 6F 72 65 66 61 74 68 65 72 73      our forefathers

string getBinaryDump(byte[] bytes, int offset, int length)

Returns a readable string for the specified set of bytes, starting at the specified offset, for the specified number of bytes. This is useful mostly for debugging.