Decompress gzip file to stdout

zcat.cc

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <string>
#include <vector>
#include <assert.h>
#include <zlib.h>

using namespace std;

int inflateString(const std::string& dataIn, std::string& dataOut)
{
	dataOut.clear();
	dataOut.reserve(dataIn.size() * 4);

	z_stream strm = {0};

	strm.next_in = (Bytef *) dataIn.c_str();
	strm.avail_in =
	strm.total_in = dataIn.size();

	vector<unsigned char> outBuf(4096);

	strm.next_out = &outBuf[0];
	strm.avail_out = outBuf.size();
	strm.total_out = 0;

	//15 window bits, and the +32 tells zlib to autodetect zlib/gzip
	int rc = inflateInit2(&strm, (15 + 32)); 

	while (rc == Z_OK || rc == Z_STREAM_END) {
		rc = inflate(&strm, Z_NO_FLUSH);
		if (rc == Z_OK || rc == Z_STREAM_END) {
			size_t outputLen = outBuf.size() - strm.avail_out;
			dataOut.append((char *) &outBuf[0], outputLen);

			if (rc == Z_OK) {
				// reset for more reads
				strm.next_out = &outBuf[0];
				strm.avail_out = outBuf.size();
			} else {
				return Z_OK;
			}
		}
	}

	return rc;
}

int main (int argc, char *argv[])
{
	string zdataIn;

	char buf[1024];
	size_t frc;

	while ((frc = fread(buf, 1, sizeof(buf), stdin)) > 0) {
		zdataIn.append(&buf[0], frc);

		if (frc < sizeof(buf))
			break;
	}

	string dataOut;
	int rc = inflateString(zdataIn, dataOut);
	assert(rc == Z_OK);

	write(STDOUT_FILENO, dataOut.c_str(), dataOut.size());
	return 0;
}