Sink
| Documentation |
#include <cryptopp/simple.h>
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In the Pipelining paradigm, a Sink is the destination of transformed data. They accept transformed data from Filters, and they are the last member of a chain. Sinks serve the opposite role of Sources.
Sinks exist for different types of objects. Crypto++ provides the following stock Sinks:
You can swap different Sinks in and out. If you are writting data to a file through a FileSink, then you can swap in a StringSink to write the data to memory.
A StringSink requires no additional information to terminate the data chain. Other objects, such as FileSinks require additional information such as a filename.
An ArraySink is just a typedef for a StringSink using the {ptr, size} constructor.
Private keys and other sensitive material should not be save to a string using a StringSink. Many sample code uses a and snippets use StringSink and string to hold the sensitive material. Though convenient, the practice is not a very good idea - see Keys and Formats for details.
Examples
The following example demonstrates the creation of a StringSink.
string s; StringSink sink( s );
The following example demonstrates reading a file, and placing the contents of the file in a string. This is known as pipelining.
string s; FileSource file( filename, new StringSink( s ) ); cout << s << endl;
The following example performs the same operation as above, but without the variable file.
string s; FileSource( filename, true, new StringSink( s ) ); cout << s << endl;
A slightly more complicated example of pipelining is below. Before the FileSource is placed in the string, it is hex encoded.
string s; FileSource( filename, new HexEncoder( new StringSink( s ) ) ); cout << s << endl;
Note that the HexEncoder and StringSink created with new do not require explicit destruction - the FileSource will call delete on the HexEncoder, which in turns calls delete on the StringSink when it (the FileSource) is destroyed.
Finally, the example below places 4 random bytes of data into a StringSink after hex encoding using a random number source. As the chain gets longer, nesting the chaining structure as with if statements offers better readability.
string s;
AutoSeededRandomPool rng;
RandomNumberSource( rng, 4, true,
new HexEncoder(
new CryptoPP::StringSink( s )
) // HexEncoder
); // RandomNumberSource
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