public virtual ssize_t splice (InputStream source, OutputStreamSpliceFlags flags, Cancellable? cancellable = null) throws IOError

Splices an input stream into an output stream.

Example: ZLib-Compression:

private const ZlibCompressorFormat FORMAT = ZlibCompressorFormat.GZIP;

private void convert (File source, File dest, Converter converter) throws Error {
var src_stream = source.read ();
var dst_stream = dest.replace (null, false, 0);
var conv_stream = new ConverterOutputStream (dst_stream, converter);

// 'splice' pumps all data from an InputStream to an OutputStream
conv_stream.splice (src_stream, 0);

public int main (string[] args) {
if (args.length < 2) {
print ("Usage: %s FILE\n", args[0]);
return 0;

var infile = File.new_for_commandline_arg (args[1]);
if (!infile.query_exists ()) {
stderr.printf ("File '%s' does not exist.\n", args[1]);
return 1;

var zipfile = File.new_for_commandline_arg (args[1] + ".gz");
var outfile = File.new_for_commandline_arg (args[1] + "_out");

try {
convert (infile, zipfile, new ZlibCompressor (FORMAT));
convert (zipfile, outfile, new ZlibDecompressor (FORMAT));
} catch (Error e) {
stderr.printf ("%s\n", e.message);
return 1;

return 0;

valac --pkg gio-2.0 GLib.ZlibCompressor.vala



a OutputStream.


a InputStream.


a set of OutputStreamSpliceFlags.


optional Cancellable object, null to ignore.


a ssize_t containing the size of the data spliced, or -1 if an error occurred. Note that if the number of bytes spliced is greater than g_maxssize, then that will be returned, and there is no way to determine the actual number of bytes spliced.