// 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. // Package io 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, plus some other related primitives. // // Because these interfaces and primitives wrap lower-level operations with // various implementations, unless otherwise informed clients should not // assume they are safe for parallel execution. package io import ( "errors" ) // Seek whence values. const ( SeekStart = 0 // seek relative to the origin of the file SeekCurrent = 1 // seek relative to the current offset SeekEnd = 2 // seek relative to the end ) // ErrShortWrite means that a write accepted fewer bytes than requested // but failed to return an explicit error. var ErrShortWrite = errors.New("short write") // ErrShortBuffer means that a read required a longer buffer than was provided. var ErrShortBuffer = errors.New("short buffer") // EOF is the error returned by Read when no more input is available. // Functions should return EOF only to signal a graceful end of input. // If the EOF occurs unexpectedly in a structured data stream, // the appropriate error is either ErrUnexpectedEOF or some other error // giving more detail. var EOF = errors.New("EOF") // ErrUnexpectedEOF means that EOF was encountered in the // middle of reading a fixed-size block or data structure. var ErrUnexpectedEOF = errors.New("unexpected EOF") // ErrNoProgress is returned by some clients of an io.Reader when // many calls to Read have failed to return any data or error, // usually the sign of a broken io.Reader implementation. var ErrNoProgress = errors.New("multiple Read calls return no data or error") // Reader is the interface that wraps the basic Read method. // // Read reads up to len(p) bytes into p. It returns the number of bytes // read (0 <= n <= len(p)) and any error encountered. Even if Read // returns n < len(p), it may use all of p as scratch space during the call. // If some data is available but not len(p) bytes, Read conventionally // returns what is available instead of waiting for more. // // When Read encounters an error or end-of-file condition after // successfully reading n > 0 bytes, it returns the number of // bytes read. It may return the (non-nil) error from the same call // or return the error (and n == 0) from a subsequent call. // An instance of this general case is that a Reader returning // a non-zero number of bytes at the end of the input stream may // return either err == EOF or err == nil. The next Read should // return 0, EOF. // // Callers should always process the n > 0 bytes returned before // considering the error err. Doing so correctly handles I/O errors // that happen after reading some bytes and also both of the // allowed EOF behaviors. // // Implementations of Read are discouraged from returning a // zero byte count with a nil error, except when len(p) == 0. // Callers should treat a return of 0 and nil as indicating that // nothing happened; in particular it does not indicate EOF. // // Implementations must not retain p. type Reader interface { Read(p []byte) (n int, err error) } // Writer is the interface that wraps the basic Write method. // // Write writes len(p) bytes from p to the underlying data stream. // It returns the number of bytes written from p (0 <= n <= len(p)) // and any error encountered that caused the write to stop early. // Write must return a non-nil error if it returns n < len(p). // Write must not modify the slice data, even temporarily. // // Implementations must not retain p. type Writer interface { Write(p []byte) (n int, err error) } // Closer is the interface that wraps the basic Close method. // // The behavior of Close after the first call is undefined. // Specific implementations may document their own behavior. type Closer interface { Close() error } // Seeker is the interface that wraps the basic Seek method. // // Seek sets the offset for the next Read or Write to offset, // interpreted according to whence: // SeekStart means relative to the start of the file, // SeekCurrent means relative to the current offset, and // SeekEnd means relative to the end. // Seek returns the new offset relative to the start of the // file and an error, if any. // // Seeking to an offset before the start of the file is an error. // Seeking to any positive offset is legal, but the behavior of subsequent // I/O operations on the underlying object is implementation-dependent. type Seeker interface { Seek(offset int64, whence int) (int64, error) } // ReadWriter is the interface that groups the basic Read and Write methods. type ReadWriter interface { Reader Writer } // ReadCloser is the interface that groups the basic Read and Close methods. type ReadCloser interface { Reader Closer } // WriteCloser is the interface that groups the basic Write and Close methods. type WriteCloser interface { Writer Closer } // ReadWriteCloser is the interface that groups the basic Read, Write and Close methods. type ReadWriteCloser interface { Reader Writer Closer } // ReadSeeker is the interface that groups the basic Read and Seek methods. type ReadSeeker interface { Reader Seeker } // WriteSeeker is the interface that groups the basic Write and Seek methods. type WriteSeeker interface { Writer Seeker } // ReadWriteSeeker is the interface that groups the basic Read, Write and Seek methods. type ReadWriteSeeker interface { Reader Writer Seeker } // ReaderFrom is the interface that wraps the ReadFrom method. // // ReadFrom reads data from r until EOF or error. // The return value n is the number of bytes read. // Any error except io.EOF encountered during the read is also returned. // // The Copy function uses ReaderFrom if available. type ReaderFrom interface { ReadFrom(r Reader) (n int64, err error) } // WriterTo is the interface that wraps the WriteTo method. // // WriteTo writes data to w until there's no more data to write or // when an error occurs. The return value n is the number of bytes // written. Any error encountered during the write is also returned. // // The Copy function uses WriterTo if available. type WriterTo interface { WriteTo(w Writer) (n int64, err error) } // ReaderAt is the interface that wraps the basic ReadAt method. // // ReadAt reads len(p) bytes into p starting at offset off in the // underlying input source. It returns the number of bytes // read (0 <= n <= len(p)) and any error encountered. // // When ReadAt returns n < len(p), it returns a non-nil error // explaining why more bytes were not returned. In this respect, // ReadAt is stricter than Read. // // Even if ReadAt returns n < len(p), it may use all of p as scratch // space during the call. If some data is available but not len(p) bytes, // ReadAt blocks until either all the data is available or an error occurs. // In this respect ReadAt is different from Read. // // If the n = len(p) bytes returned by ReadAt are at the end of the // input source, ReadAt may return either err == EOF or err == nil. // // If ReadAt is reading from an input source with a seek offset, // ReadAt should not affect nor be affected by the underlying // seek offset. // // Clients of ReadAt can execute parallel ReadAt calls on the // same input source. // // Implementations must not retain p. type ReaderAt interface { ReadAt(p []byte, off int64) (n int, err error) } // WriterAt is the interface that wraps the basic WriteAt method. // // WriteAt writes len(p) bytes from p to the underlying data stream // at offset off. It returns the number of bytes written from p (0 <= n <= len(p)) // and any error encountered that caused the write to stop early. // WriteAt must return a non-nil error if it returns n < len(p). // // If WriteAt is writing to a destination with a seek offset, // WriteAt should not affect nor be affected by the underlying // seek offset. // // Clients of WriteAt can execute parallel WriteAt calls on the same // destination if the ranges do not overlap. // // Implementations must not retain p. type WriterAt interface { WriteAt(p []byte, off int64) (n int, err error) } // ByteReader is the interface that wraps the ReadByte method. // // ReadByte reads and returns the next byte from the input. type ByteReader interface { ReadByte() (byte, error) } // ByteScanner is the interface that adds the UnreadByte method to the // basic ReadByte method. // // UnreadByte causes the next call to ReadByte to return the same byte // as the previous call to ReadByte. // It may be an error to call UnreadByte twice without an intervening // call to ReadByte. type ByteScanner interface { ByteReader UnreadByte() error } // ByteWriter is the interface that wraps the WriteByte method. type ByteWriter interface { WriteByte(c byte) error } // RuneReader is the interface that wraps the ReadRune method. // // ReadRune reads a single UTF-8 encoded Unicode character // and returns the rune and its size in bytes. If no character is // available, err will be set. type RuneReader interface { ReadRune() (r rune, size int, err error) } // RuneScanner is the interface that adds the UnreadRune method to the // basic ReadRune method. // // UnreadRune causes the next call to ReadRune to return the same rune // as the previous call to ReadRune. // It may be an error to call UnreadRune twice without an intervening // call to ReadRune. type RuneScanner interface { RuneReader UnreadRune() error } // stringWriter is the interface that wraps the WriteString method. type stringWriter interface { WriteString(s string) (n int, err error) } // WriteString writes the contents of the string s to w, which accepts a slice of bytes. // If w implements a WriteString method, it is invoked directly. // Otherwise, w.Write is called exactly once. func WriteString(w Writer, s string) (n int, err error) { if sw, ok := w.(stringWriter); ok { return sw.WriteString(s) } return w.Write([]byte(s)) } // ReadAtLeast reads from r into buf until it has read at least min bytes. // It returns the number of bytes copied and an error if fewer bytes were read. // The error is EOF only if no bytes were read. // If an EOF happens after reading fewer than min bytes, // ReadAtLeast returns ErrUnexpectedEOF. // If min is greater than the length of buf, ReadAtLeast returns ErrShortBuffer. // On return, n >= min if and only if err == nil. func ReadAtLeast(r Reader, buf []byte, min int) (n int, err error) { if len(buf) < min { return 0, ErrShortBuffer } for n < min && err == nil { var nn int nn, err = r.Read(buf[n:]) n += nn } if n >= min { err = nil } else if n > 0 && err == EOF { err = ErrUnexpectedEOF } return } // ReadFull reads exactly len(buf) bytes from r into buf. // It returns the number of bytes copied and an error if fewer bytes were read. // The error is EOF only if no bytes were read. // If an EOF happens after reading some but not all the bytes, // ReadFull returns ErrUnexpectedEOF. // On return, n == len(buf) if and only if err == nil. func ReadFull(r Reader, buf []byte) (n int, err error) { return ReadAtLeast(r, buf, len(buf)) } // CopyN copies n bytes (or until an error) from src to dst. // It returns the number of bytes copied and the earliest // error encountered while copying. // On return, written == n if and only if err == nil. // // If dst implements the ReaderFrom interface, // the copy is implemented using it. func CopyN(dst Writer, src Reader, n int64) (written int64, err error) { written, err = Copy(dst, LimitReader(src, n)) if written == n { return n, nil } if written < n && err == nil { // src stopped early; must have been EOF. err = EOF } return } // Copy copies from src to dst until either EOF is reached // on src or an error occurs. It returns the number of bytes // copied and the first error encountered while copying, if any. // // A successful Copy returns err == nil, not err == EOF. // Because Copy is defined to read from src until EOF, it does // not treat an EOF from Read as an error to be reported. // // If src implements the WriterTo interface, // the copy is implemented by calling src.WriteTo(dst). // Otherwise, if dst implements the ReaderFrom interface, // the copy is implemented by calling dst.ReadFrom(src). func Copy(dst Writer, src Reader) (written int64, err error) { return copyBuffer(dst, src, nil) } // CopyBuffer is identical to Copy except that it stages through the // provided buffer (if one is required) rather than allocating a // temporary one. If buf is nil, one is allocated; otherwise if it has // zero length, CopyBuffer panics. func CopyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) { if buf != nil && len(buf) == 0 { panic("empty buffer in io.CopyBuffer") } return copyBuffer(dst, src, buf) } // copyBuffer is the actual implementation of Copy and CopyBuffer. // if buf is nil, one is allocated. func copyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) { // If the reader has a WriteTo method, use it to do the copy. // Avoids an allocation and a copy. if wt, ok := src.(WriterTo); ok { return wt.WriteTo(dst) } // Similarly, if the writer has a ReadFrom method, use it to do the copy. if rt, ok := dst.(ReaderFrom); ok { return rt.ReadFrom(src) } if buf == nil { 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 = ErrShortWrite break } } if er != nil { if er != EOF { err = er } break } } return written, err } // LimitReader returns a Reader that reads from r // but stops with EOF after n bytes. // The underlying implementation is a *LimitedReader. func LimitReader(r Reader, n int64) Reader { return &LimitedReader{r, n} } // A LimitedReader reads from R but limits the amount of // data returned to just N bytes. Each call to Read // updates N to reflect the new amount remaining. // Read returns EOF when N <= 0 or when the underlying R returns EOF. type LimitedReader struct { R Reader // underlying reader N int64 // max bytes remaining } func (l *LimitedReader) Read(p []byte) (n int, err error) { if l.N <= 0 { return 0, EOF } if int64(len(p)) > l.N { p = p[0:l.N] } n, err = l.R.Read(p) l.N -= int64(n) return } // NewSectionReader returns a SectionReader that reads from r // starting at offset off and stops with EOF after n bytes. func NewSectionReader(r ReaderAt, off int64, n int64) *SectionReader { return &SectionReader{r, off, off, off + n} } // SectionReader implements Read, Seek, and ReadAt on a section // of an underlying ReaderAt. type SectionReader struct { r ReaderAt base int64 off int64 limit int64 } func (s *SectionReader) Read(p []byte) (n int, err error) { if s.off >= s.limit { return 0, EOF } if max := s.limit - s.off; int64(len(p)) > max { p = p[0:max] } n, err = s.r.ReadAt(p, s.off) s.off += int64(n) return } var errWhence = errors.New("Seek: invalid whence") var errOffset = errors.New("Seek: invalid offset") func (s *SectionReader) Seek(offset int64, whence int) (int64, error) { switch whence { default: return 0, errWhence case SeekStart: offset += s.base case SeekCurrent: offset += s.off case SeekEnd: offset += s.limit } if offset < s.base { return 0, errOffset } s.off = offset return offset - s.base, nil } func (s *SectionReader) ReadAt(p []byte, off int64) (n int, err error) { if off < 0 || off >= s.limit-s.base { return 0, EOF } off += s.base if max := s.limit - off; int64(len(p)) > max { p = p[0:max] n, err = s.r.ReadAt(p, off) if err == nil { err = EOF } return n, err } return s.r.ReadAt(p, off) } // Size returns the size of the section in bytes. func (s *SectionReader) Size() int64 { return s.limit - s.base } // TeeReader returns a Reader that writes to w what it reads from r. // All reads from r performed through it are matched with // corresponding writes to w. There is no internal buffering - // the write must complete before the read completes. // Any error encountered while writing is reported as a read error. func TeeReader(r Reader, w Writer) Reader { return &teeReader{r, w} } type teeReader struct { r Reader w Writer } func (t *teeReader) Read(p []byte) (n int, err error) { n, err = t.r.Read(p) if n > 0 { if n, err := t.w.Write(p[:n]); err != nil { return n, err } } return }