Source file src/cmd/internal/bio/buf.go

     1	// Copyright 2015 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	// Package bio implements common I/O abstractions used within the Go toolchain.
     6	package bio
     7	
     8	import (
     9		"bufio"
    10		"io"
    11		"log"
    12		"os"
    13	)
    14	
    15	// Reader implements a seekable buffered io.Reader.
    16	type Reader struct {
    17		f *os.File
    18		*bufio.Reader
    19	}
    20	
    21	// Writer implements a seekable buffered io.Writer.
    22	type Writer struct {
    23		f *os.File
    24		*bufio.Writer
    25	}
    26	
    27	// Create creates the file named name and returns a Writer
    28	// for that file.
    29	func Create(name string) (*Writer, error) {
    30		f, err := os.Create(name)
    31		if err != nil {
    32			return nil, err
    33		}
    34		return &Writer{f: f, Writer: bufio.NewWriter(f)}, nil
    35	}
    36	
    37	// Open returns a Reader for the file named name.
    38	func Open(name string) (*Reader, error) {
    39		f, err := os.Open(name)
    40		if err != nil {
    41			return nil, err
    42		}
    43		return &Reader{f: f, Reader: bufio.NewReader(f)}, nil
    44	}
    45	
    46	func (r *Reader) MustSeek(offset int64, whence int) int64 {
    47		if whence == 1 {
    48			offset -= int64(r.Buffered())
    49		}
    50		off, err := r.f.Seek(offset, whence)
    51		if err != nil {
    52			log.Fatalf("seeking in output: %v", err)
    53		}
    54		r.Reset(r.f)
    55		return off
    56	}
    57	
    58	func (w *Writer) MustSeek(offset int64, whence int) int64 {
    59		if err := w.Flush(); err != nil {
    60			log.Fatalf("writing output: %v", err)
    61		}
    62		off, err := w.f.Seek(offset, whence)
    63		if err != nil {
    64			log.Fatalf("seeking in output: %v", err)
    65		}
    66		return off
    67	}
    68	
    69	func (r *Reader) Offset() int64 {
    70		off, err := r.f.Seek(0, 1)
    71		if err != nil {
    72			log.Fatalf("seeking in output [0, 1]: %v", err)
    73		}
    74		off -= int64(r.Buffered())
    75		return off
    76	}
    77	
    78	func (w *Writer) Offset() int64 {
    79		if err := w.Flush(); err != nil {
    80			log.Fatalf("writing output: %v", err)
    81		}
    82		off, err := w.f.Seek(0, 1)
    83		if err != nil {
    84			log.Fatalf("seeking in output [0, 1]: %v", err)
    85		}
    86		return off
    87	}
    88	
    89	func (r *Reader) Close() error {
    90		return r.f.Close()
    91	}
    92	
    93	func (w *Writer) Close() error {
    94		err := w.Flush()
    95		err1 := w.f.Close()
    96		if err == nil {
    97			err = err1
    98		}
    99		return err
   100	}
   101	
   102	func (r *Reader) File() *os.File {
   103		return r.f
   104	}
   105	
   106	func (w *Writer) File() *os.File {
   107		return w.f
   108	}
   109	
   110	// Slice reads the next length bytes of r into a slice.
   111	//
   112	// This slice may be backed by mmap'ed memory. Currently, this memory
   113	// will never be unmapped. The second result reports whether the
   114	// backing memory is read-only.
   115	func (r *Reader) Slice(length uint64) ([]byte, bool, error) {
   116		if length == 0 {
   117			return []byte{}, false, nil
   118		}
   119	
   120		data, ok := r.sliceOS(length)
   121		if ok {
   122			return data, true, nil
   123		}
   124	
   125		data = make([]byte, length)
   126		_, err := io.ReadFull(r, data)
   127		if err != nil {
   128			return nil, false, err
   129		}
   130		return data, false, nil
   131	}
   132	
   133	// SliceRO returns a slice containing the next length bytes of r
   134	// backed by a read-only mmap'd data. If the mmap cannot be
   135	// established (limit exceeded, region too small, etc) a nil slice
   136	// will be returned. If mmap succeeds, it will never be unmapped.
   137	func (r *Reader) SliceRO(length uint64) []byte {
   138		data, ok := r.sliceOS(length)
   139		if ok {
   140			return data
   141		}
   142		return nil
   143	}
   144	

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