| // 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 or |
| // any error encountered. If ReadByte returns an error, no input |
| // byte was consumed, and the returned byte value is undefined. |
| 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 |
| } |
| |
| // WriteString writes the contents of the string s to w, which accepts a slice of bytes. |
| // If w implements a "WriteString(string) (int, error)" method, it is invoked directly. |
| // Otherwise, w.Write is called exactly once. |
| func WriteString(w Writer, s string) (n int, err error) { |
| return 0, nil |
| } |
| |
| // 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) { |
| return 0, nil |
| } |
| |
| // 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 0, nil |
| } |
| |
| // 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) { |
| return 0, nil |
| } |
| |
| // 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 0, 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) { |
| return 0, nil |
| } |
| |
| // 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 nil } |
| |
| // 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) { |
| return 0, nil |
| } |
| |
| // 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 nil |
| } |
| |
| // SectionReader implements Read, Seek, and ReadAt on a section |
| // of an underlying ReaderAt. |
| type SectionReader struct { |
| unexported struct{} |
| } |
| |
| func (s *SectionReader) Read(p []byte) (n int, err error) { |
| return 0, nil |
| } |
| |
| func (s *SectionReader) Seek(offset int64, whence int) (int64, error) { |
| return 0, nil |
| } |
| |
| func (s *SectionReader) ReadAt(p []byte, off int64) (n int, err error) { |
| return 0, nil |
| } |
| |
| // Size returns the size of the section in bytes. |
| func (s *SectionReader) Size() int64 { return 0 } |
| |
| // 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 nil |
| } |
| |
| // MultiReader returns a Reader that's the logical concatenation of |
| // the provided input readers. They're read sequentially. Once all |
| // inputs have returned EOF, Read will return EOF. If any of the readers |
| // return a non-nil, non-EOF error, Read will return that error. |
| func MultiReader(readers ...Reader) Reader { |
| return nil |
| } |
| |
| // MultiWriter creates a writer that duplicates its writes to all the |
| // provided writers, similar to the Unix tee(1) command. |
| func MultiWriter(writers ...Writer) Writer { |
| return nil |
| } |
| |
| // ErrClosedPipe is the error used for read or write operations on a closed pipe. |
| var ErrClosedPipe = errors.New("io: read/write on closed pipe") |
| |
| // A PipeReader is the read half of a pipe. |
| type PipeReader struct { |
| unexported struct{} |
| } |
| |
| // Read implements the standard Read interface: |
| // it reads data from the pipe, blocking until a writer |
| // arrives or the write end is closed. |
| // If the write end is closed with an error, that error is |
| // returned as err; otherwise err is EOF. |
| func (r *PipeReader) Read(data []byte) (n int, err error) { |
| return 0, nil |
| } |
| |
| // Close closes the reader; subsequent writes to the |
| // write half of the pipe will return the error ErrClosedPipe. |
| func (r *PipeReader) Close() error { |
| return nil |
| } |
| |
| // CloseWithError closes the reader; subsequent writes |
| // to the write half of the pipe will return the error err. |
| func (r *PipeReader) CloseWithError(err error) error { |
| return nil |
| } |
| |
| // A PipeWriter is the write half of a pipe. |
| type PipeWriter struct { |
| unexported struct{} |
| } |
| |
| // Write implements the standard Write interface: |
| // it writes data to the pipe, blocking until one or more readers |
| // have consumed all the data or the read end is closed. |
| // If the read end is closed with an error, that err is |
| // returned as err; otherwise err is ErrClosedPipe. |
| func (w *PipeWriter) Write(data []byte) (n int, err error) { |
| return 0, nil |
| } |
| |
| // Close closes the writer; subsequent reads from the |
| // read half of the pipe will return no bytes and EOF. |
| func (w *PipeWriter) Close() error { |
| return nil |
| } |
| |
| // CloseWithError closes the writer; subsequent reads from the |
| // read half of the pipe will return no bytes and the error err, |
| // or EOF if err is nil. |
| // |
| // CloseWithError always returns nil. |
| func (w *PipeWriter) CloseWithError(err error) error { |
| return nil |
| } |
| |
| // Pipe creates a synchronous in-memory pipe. |
| // It can be used to connect code expecting an io.Reader |
| // with code expecting an io.Writer. |
| // |
| // Reads and Writes on the pipe are matched one to one |
| // except when multiple Reads are needed to consume a single Write. |
| // That is, each Write to the PipeWriter blocks until it has satisfied |
| // one or more Reads from the PipeReader that fully consume |
| // the written data. |
| // The data is copied directly from the Write to the corresponding |
| // Read (or Reads); there is no internal buffering. |
| // |
| // It is safe to call Read and Write in parallel with each other or with Close. |
| // Parallel calls to Read and parallel calls to Write are also safe: |
| // the individual calls will be gated sequentially. |
| func Pipe() (*PipeReader, *PipeWriter) { |
| return nil, nil |
| } |