src/lib/io/io.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This package provides basic interfaces to I/O primitives.
// Its primary job is to wrap existing implementations of such primitives,
// such as those in package os, into shared public interfaces that
// abstract the functionality.
// It also provides buffering primitives and some other basic operations.
package io

import (
	"os";
	"syscall";
)

// ErrEOF is the error returned by Readn and Copyn when they encounter EOF.
var ErrEOF = os.NewError("EOF")

// Read is the interface that wraps the basic Read method.
type Read interface {
	Read(p []byte) (n int, err *os.Error);
}

// Write is the interface that wraps the basic Write method.
type Write interface {
	Write(p []byte) (n int, err *os.Error);
}

// Close is the interface that wraps the basic Close method.
type Close interface {
	Close() *os.Error;
}

// ReadWrite is the interface that groups the basic Read and Write methods.
type ReadWrite interface {
	Read;
	Write;
}

// ReadClose is the interface that groups the basic Read and Close methods.
type ReadClose interface {
	Read;
	Close;
}

// WriteClose is the interface that groups the basic Write and Close methods.
type WriteClose interface {
	Write;
	Close;
}

// ReadWriteClose is the interface that groups the basic Read, Write and Close methods.
type ReadWriteClose interface {
	Read;
	Write;
	Close;
}

// Convert a string to an array of bytes for easy marshaling.
func StringBytes(s string) []byte {
	b := make([]byte, len(s));
	for i := 0; i < len(s); i++ {
		b[i] = s[i];
	}
	return b;
}

// WriteString writes the contents of the string s to w, which accepts an array of bytes.
func WriteString(w Write, s string) (n int, err *os.Error) {
	return w.Write(StringBytes(s))
}

// Readn reads r until the buffer buf is full, or until EOF or error.
func Readn(r Read, buf []byte) (n int, err *os.Error) {
	n = 0;
	for n < len(buf) {
		nn, e := r.Read(buf[n:len(buf)]);
		if nn > 0 {
			n += nn
		}
		if e != nil {
			return n, e
		}
		if nn <= 0 {
			return n, ErrEOF	// no error but insufficient data
		}
	}
	return n, nil
}

// Convert something that implements Read into something
// whose Reads are always Readn
type fullRead struct {
	r	Read;
}

func (fr *fullRead) Read(p []byte) (n int, err *os.Error) {
	n, err = Readn(fr.r, p);
	return n, err
}

// MakeFullReader takes r, an implementation of Read, and returns an object
// that still implements Read but always calls Readn underneath.
func MakeFullReader(r Read) Read {
	if fr, ok := r.(*fullRead); ok {
		// already a fullRead
		return r
	}
	return &fullRead{r}
}

// Copy n copies n bytes (or until EOF is reached) from src to dst.
// It returns the number of bytes copied and the error, if any.
func Copyn(src Read, dst Write, n int64) (written int64, err *os.Error) {
	buf := make([]byte, 32*1024);
	for written < n {
		l := len(buf);
		if d := n - written; d < int64(l) {
			l = int(d);
		}
		nr, er := src.Read(buf[0 : l]);
		if nr > 0 {
			nw, ew := dst.Write(buf[0 : nr]);
			if nw > 0 {
				written += int64(nw);
			}
			if ew != nil {
				err = ew;
				break;
			}
			if nr != nw {
				err = os.EIO;
				break;
			}
		}
		if er != nil {
			err = er;
			break;
		}
		if nr == 0 {
			err = ErrEOF;
			break;
		}
	}
	return written, err
}

// Copy copies from src to dst until EOF is reached.
// It returns the number of bytes copied and the error, if any.
func Copy(src Read, dst Write) (written int64, err *os.Error) {
	buf := make([]byte, 32*1024);
	for {
		nr, er := src.Read(buf);
		if nr > 0 {
			nw, ew := dst.Write(buf[0:nr]);
			if nw > 0 {
				written += int64(nw);
			}
			if ew != nil {
				err = ew;
				break;
			}
			if nr != nw {
				err = os.EIO;
				break;
			}
		}
		if er != nil {
			err = er;
			break;
		}
		if nr == 0 {
			break;
		}
	}
	return written, err
}