good good study, day day up!

vendor/gopl.io/ch13/bzip-print/bzip2.go

@@ -0,0 +1,96 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 362.
+// This is the version that appears in print,
+// but it does not comply with the proposed
+// rules for passing pointers between Go and C.
+// (https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md)
+// See gopl.io/ch13/bzip for an updated version.
+//!+
+
+// Package bzip provides a writer that uses bzip2 compression (bzip.org).
+package bzip
+
+/*
+#cgo CFLAGS: -I/usr/include
+#cgo LDFLAGS: -L/usr/lib -lbz2
+#include <bzlib.h>
+int bz2compress(bz_stream *s, int action,
+                char *in, unsigned *inlen, char *out, unsigned *outlen);
+*/
+import "C"
+
+import (
+	"io"
+	"unsafe"
+)
+
+type writer struct {
+	w      io.Writer // underlying output stream
+	stream *C.bz_stream
+	outbuf [64 * 1024]byte
+}
+
+// NewWriter returns a writer for bzip2-compressed streams.
+func NewWriter(out io.Writer) io.WriteCloser {
+	const (
+		blockSize  = 9
+		verbosity  = 0
+		workFactor = 30
+	)
+	w := &writer{w: out, stream: new(C.bz_stream)}
+	C.BZ2_bzCompressInit(w.stream, blockSize, verbosity, workFactor)
+	return w
+}
+
+//!-
+
+//!+write
+func (w *writer) Write(data []byte) (int, error) {
+	if w.stream == nil {
+		panic("closed")
+	}
+	var total int // uncompressed bytes written
+
+	for len(data) > 0 {
+		inlen, outlen := C.uint(len(data)), C.uint(cap(w.outbuf))
+		C.bz2compress(w.stream, C.BZ_RUN,
+			(*C.char)(unsafe.Pointer(&data[0])), &inlen,
+			(*C.char)(unsafe.Pointer(&w.outbuf)), &outlen)
+		total += int(inlen)
+		data = data[inlen:]
+		if _, err := w.w.Write(w.outbuf[:outlen]); err != nil {
+			return total, err
+		}
+	}
+	return total, nil
+}
+
+//!-write
+
+//!+close
+// Close flushes the compressed data and closes the stream.
+// It does not close the underlying io.Writer.
+func (w *writer) Close() error {
+	if w.stream == nil {
+		panic("closed")
+	}
+	defer func() {
+		C.BZ2_bzCompressEnd(w.stream)
+		w.stream = nil
+	}()
+	for {
+		inlen, outlen := C.uint(0), C.uint(cap(w.outbuf))
+		r := C.bz2compress(w.stream, C.BZ_FINISH, nil, &inlen,
+			(*C.char)(unsafe.Pointer(&w.outbuf)), &outlen)
+		if _, err := w.w.Write(w.outbuf[:outlen]); err != nil {
+			return err
+		}
+		if r == C.BZ_STREAM_END {
+			return nil
+		}
+	}
+}
+
+//!-close