Coder Encoding/encryption abstract base class

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Description

	Coder is an abstract base class that defines a common interface for general-purpose encryption and encoding of data. Coder-derived classes are used in conjunction with the htmlCgi class to perform automatic encryption and decryption of name/value pairs.
	html++ includes four Coder-derived classes:
	NullCoder
	XorCoder
	ScrambleCoder
	UrlCoder

Declaration

	#include <dcmicro/htmlpp/coder.h>

Hierarchy
See Also

	htmlServer, NullCoder, XorCoder, ScrambleCoder, UrlCoder

Related Constants/Definitions

	None.

Constructors

	Coder()

	Constructs an empty object.

Destructors

	virtual ~Coder()

	Destroys the object.

Member Methods

	ID	virtual int ID() const = 0

	Returns the integer identification of the algorithm. Valid ID values range from 0-99, and the range of 0-30 is reserved by html++. User-defined algorithms may use ID's in the range of 31-99. The htmlCgi class encodes the ID of an algorithm in it's output for later identification during decoding.

	Name	virtual String Name() const = 0

	Returns the name of the algorithm as a text string. This is for informational purposes only.

	Encode	virtual char * Encode( const char * unencoded, int& length ) = 0

	Encode the unencoded buffer of specified length bytes, allocating storage for the resulting buffer using 'new' and returning a pointer to it. The length reference is updated to reflect the number of bytes returned in the allocated buffer, which could be larger or smaller than the original value depending on the algorithm. It is the responsiblity of the calling routine to release the memory using 'delete'.
	NOTE: By convention, when subclassing Coder for user-defined algorithms, the size of the buffer allocated for the encoded result must be (length+1) bytes so that calling routines may optionally append a terminating null character.

	Decode	virtual char * Decode( const char * encoded, int& length ) = 0

	Decode the encoded buffer of specified length bytes, allocating storage for the resulting buffer using 'new' and returning a pointer to it. The length reference is updated to reflect the number of bytes returned in the allocated buffer, which could be larger or smaller than the original value depending on the algorithm. It is the responsiblity of the calling routine to release the memory using 'delete'.
	NOTE: As with the Encode() method, when subclassing Coder for user-defined algorithms, the size of the buffer allocated for the decoded result must be (length+1) bytes so that calling routines may optionally append a terminating null character.

Example Use

	The example below illustrates using the ScrambleCoder class to encrypt and then decrypt a buffer of text. In day-to-day use with html++, most applications simply instantiate a global copy of ScrambleCoder, passing it to htmlServer::Crypt() at startup for automatic encryption and decryption of name/value pairs.

	#include <stdio.h>
	#include <stdlib.h>
	#include <dcmicro/htmlpp/htmlpp.h>
	int main( void )
	{
	char *  orig = "The quick brown fox" ;
	char *  enc ;   //  encoded pointer
	char *  dec ;   //  decoded pointer
	int     length = strlen(orig) ;
	//  Set up a ScrambleCoder using a password,
	//  then use it to encrypt the original text.
	//  Note that the length parameter's value may
	//  be altered by the Encode() method.
	ScrambleCoder  s( "password" ) ;
	enc = s.Encode( orig, length ) ;
	enc[length] = '\0' ;  //  append term null
	cout << enc << "\n" ; //  display the encrypted data
	//  Now set up another ScrambleCoder to decrypt
	//  the data, using the same password.
	ScrambleCoder  s2( "password" ) ;
	dec = s2.Decode( enc, length ) ;
	dec[length] = '\0' ;  //  append term null
	cout << dec << "\n" ; //  display the result
	//  Release the buffers allocated
	//  by Encode() and Decode()
	delete enc ;
	delete dec ;
	return 0 ;
	}

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