Update to gobook@0a3e8d997823052c6a8575feca6e515ac6f8299d

This commit is contained in:
Alan Donovan 2015-11-30 22:37:52 -05:00
parent 84af1e6bd3
commit 34cd1719c0
7 changed files with 343 additions and 3 deletions

28
ch13/bzip-print/bzip2.c Normal file
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@ -0,0 +1,28 @@
// 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.
//!+
/* This file is gopl.io/ch13/bzip/bzip2.c, */
/* a simple wrapper for libbzip2 suitable for cgo. */
#include <bzlib.h>
int bz2compress(bz_stream *s, int action,
char *in, unsigned *inlen, char *out, unsigned *outlen) {
s->next_in = in;
s->avail_in = *inlen;
s->next_out = out;
s->avail_out = *outlen;
int r = BZ2_bzCompress(s, action);
*inlen -= s->avail_in;
*outlen -= s->avail_out;
return r;
}
//!-

96
ch13/bzip-print/bzip2.go Normal file
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@ -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

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@ -0,0 +1,40 @@
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
package bzip_test
import (
"bytes"
"compress/bzip2" // reader
"io"
"testing"
"gopl.io/ch13/bzip" // writer
)
func TestBzip2(t *testing.T) {
var compressed, uncompressed bytes.Buffer
w := bzip.NewWriter(&compressed)
// Write a repetitive message in a million pieces,
// compressing one copy but not the other.
tee := io.MultiWriter(w, &uncompressed)
for i := 0; i < 1000000; i++ {
io.WriteString(tee, "hello")
}
if err := w.Close(); err != nil {
t.Fatal(err)
}
// Check the size of the compressed stream.
if got, want := compressed.Len(), 255; got != want {
t.Errorf("1 million hellos compressed to %d bytes, want %d", got, want)
}
// Decompress and compare with original.
var decompressed bytes.Buffer
io.Copy(&decompressed, bzip2.NewReader(&compressed))
if !bytes.Equal(uncompressed.Bytes(), decompressed.Bytes()) {
t.Error("decompression yielded a different message")
}
}

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@ -17,6 +17,12 @@ int bz2compress(bz_stream *s, int action,
int r = BZ2_bzCompress(s, action);
*inlen -= s->avail_in;
*outlen -= s->avail_out;
/* "C code may store a Go pointer in C memory subject to rule 2:
* it must stop storing the pointer before it returns to Go." */
s->next_in = NULL;
s->next_out = NULL;
return r;
}

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@ -2,6 +2,20 @@
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 362.
// The version of this file that appears in the book 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)
// The rules forbid a C function like bz2compress from storing 'in' and
// 'out' (pointers to variables allocated by Go) into the Go variable 's',
// even temporarily.
//
// To comply with the rules, the bz_stream variable must be allocated
// by C code. We have introduced two C functions, bz2alloc and
// bz2free, to allocate and free instances of the bz_stream type.
// Also, we have changed bz2compress so that before it returns, it
// clears the fields of the bz_stream that contain point to Go
// variables.
//!+
// Package bzip provides a writer that uses bzip2 compression (bzip.org).
@ -11,8 +25,12 @@ package bzip
#cgo CFLAGS: -I/usr/include
#cgo LDFLAGS: -L/usr/lib -lbz2
#include <bzlib.h>
#include <stdlib.h>
bz_stream* bz2alloc() { return calloc(1, sizeof(bz_stream)); }
int bz2compress(bz_stream *s, int action,
char *in, unsigned *inlen, char *out, unsigned *outlen);
void bz2free(bz_stream* s) { return free(s); }
*/
import "C"
@ -34,9 +52,7 @@ func NewWriter(out io.Writer) io.WriteCloser {
verbosity = 0
workFactor = 30
)
// NOTE: This code may not work in future Go releases.
// See http://www.gopl.io/errata.html for explanation.
w := &writer{w: out, stream: new(C.bz_stream)}
w := &writer{w: out, stream: C.bz2alloc()}
C.BZ2_bzCompressInit(w.stream, blockSize, verbosity, workFactor)
return w
}
@ -75,6 +91,7 @@ func (w *writer) Close() error {
}
defer func() {
C.BZ2_bzCompressEnd(w.stream)
C.bz2free(w.stream)
w.stream = nil
}()
for {

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// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// Package tempconv performs Celsius and Fahrenheit temperature computations.
package tempconv
import (
"flag"
"fmt"
)
type Celsius float64
type Fahrenheit float64
func CToF(c Celsius) Fahrenheit { return Fahrenheit(c*9.0/5.0 + 32.0) }
func FToC(f Fahrenheit) Celsius { return Celsius((f - 32.0) * 5.0 / 9.0) }
func (c Celsius) String() string { return fmt.Sprintf("%g°C", c) }
/*
//!+flagvalue
package flag
// Value is the interface to the value stored in a flag.
type Value interface {
String() string
Set(string) error
}
//!-flagvalue
*/
//!+celsiusflag
// *celsiusFlag satisfies the flag.Value interface.
type celsiusFlag struct{ Celsius }
func (f *celsiusFlag) Set(s string) error {
var unit string
var value float64
fmt.Sscanf(s, "%f%s", &value, &unit) // no error check needed
switch unit {
case "C", "°C":
f.Celsius = Celsius(value)
return nil
case "F", "°F":
f.Celsius = FToC(Fahrenheit(value))
return nil
}
return fmt.Errorf("invalid temperature %q", s)
}
//!-celsiusflag
//!+Celsiusflag
// CelsiusFlag defines a Celsius flag with the specified name,
// default value, and usage, and returns the address of the flag variable.
// The flag argument must have a quantity and a unit, e.g., "100C".
func CelsiusFlag(name string, value Celsius, usage string) *Celsius {
f := celsiusFlag{value}
flag.CommandLine.Var(&f, name, usage)
return &f.Celsius
}
//!-Celsiusflag

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ch8/chat/chat.go.~master~ Normal file
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// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
//!+
// Chat is a server that lets clients chat with each other.
package main
import (
"bufio"
"fmt"
"log"
"net"
)
//!+broadcaster
type client chan<- string // an outgoing message channel
var (
entering = make(chan client)
leaving = make(chan client)
messages = make(chan string) // all incoming client messages
)
func broadcaster() {
clients := make(map[client]bool) // all connected clients
for {
select {
case msg := <-messages:
// Broadcast incoming message to all
// clients' outgoing message channels.
for cli := range clients {
cli <- msg
}
case cli := <-entering:
clients[cli] = true
case cli := <-leaving:
delete(clients, cli)
close(cli)
}
}
}
//!-broadcaster
//!+handleConn
func handleConn(conn net.Conn) {
ch := make(chan string) // outgoing client messages
go clientWriter(conn, ch)
who := conn.RemoteAddr().String()
entering <- ch
messages <- who + " has arrived"
input := bufio.NewScanner(conn)
for input.Scan() {
messages <- who + ": " + input.Text()
}
messages <- who + " has left"
leaving <- ch
conn.Close()
}
func clientWriter(conn net.Conn, ch <-chan string) {
for msg := range ch {
fmt.Fprintln(conn, msg)
}
}
//!-handleConn
//!+main
func main() {
listener, err := net.Listen("tcp", "localhost:8000")
if err != nil {
log.Fatal(err)
}
go broadcaster()
for {
conn, err := listener.Accept()
if err != nil {
log.Print(err)
continue
}
go handleConn(conn)
}
}
//!-main