Source file src/io/io.go

     1  // Copyright 2009 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 io provides basic interfaces to I/O primitives.
     6  // Its primary job is to wrap existing implementations of such primitives,
     7  // such as those in package os, into shared public interfaces that
     8  // abstract the functionality, plus some other related primitives.
     9  //
    10  // Because these interfaces and primitives wrap lower-level operations with
    11  // various implementations, unless otherwise informed clients should not
    12  // assume they are safe for parallel execution.
    13  package io
    14  
    15  import (
    16  	"errors"
    17  	"sync"
    18  )
    19  
    20  // Seek whence values.
    21  const (
    22  	SeekStart   = 0 // seek relative to the origin of the file
    23  	SeekCurrent = 1 // seek relative to the current offset
    24  	SeekEnd     = 2 // seek relative to the end
    25  )
    26  
    27  // ErrShortWrite means that a write accepted fewer bytes than requested
    28  // but failed to return an explicit error.
    29  var ErrShortWrite = errors.New("short write")
    30  
    31  // errInvalidWrite means that a write returned an impossible count.
    32  var errInvalidWrite = errors.New("invalid write result")
    33  
    34  // ErrShortBuffer means that a read required a longer buffer than was provided.
    35  var ErrShortBuffer = errors.New("short buffer")
    36  
    37  // EOF is the error returned by Read when no more input is available.
    38  // (Read must return EOF itself, not an error wrapping EOF,
    39  // because callers will test for EOF using ==.)
    40  // Functions should return EOF only to signal a graceful end of input.
    41  // If the EOF occurs unexpectedly in a structured data stream,
    42  // the appropriate error is either [ErrUnexpectedEOF] or some other error
    43  // giving more detail.
    44  var EOF = errors.New("EOF")
    45  
    46  // ErrUnexpectedEOF means that EOF was encountered in the
    47  // middle of reading a fixed-size block or data structure.
    48  var ErrUnexpectedEOF = errors.New("unexpected EOF")
    49  
    50  // ErrNoProgress is returned by some clients of a [Reader] when
    51  // many calls to Read have failed to return any data or error,
    52  // usually the sign of a broken [Reader] implementation.
    53  var ErrNoProgress = errors.New("multiple Read calls return no data or error")
    54  
    55  // Reader is the interface that wraps the basic Read method.
    56  //
    57  // Read reads up to len(p) bytes into p. It returns the number of bytes
    58  // read (0 <= n <= len(p)) and any error encountered. Even if Read
    59  // returns n < len(p), it may use all of p as scratch space during the call.
    60  // If some data is available but not len(p) bytes, Read conventionally
    61  // returns what is available instead of waiting for more.
    62  //
    63  // When Read encounters an error or end-of-file condition after
    64  // successfully reading n > 0 bytes, it returns the number of
    65  // bytes read. It may return the (non-nil) error from the same call
    66  // or return the error (and n == 0) from a subsequent call.
    67  // An instance of this general case is that a Reader returning
    68  // a non-zero number of bytes at the end of the input stream may
    69  // return either err == EOF or err == nil. The next Read should
    70  // return 0, EOF.
    71  //
    72  // Callers should always process the n > 0 bytes returned before
    73  // considering the error err. Doing so correctly handles I/O errors
    74  // that happen after reading some bytes and also both of the
    75  // allowed EOF behaviors.
    76  //
    77  // If len(p) == 0, Read should always return n == 0. It may return a
    78  // non-nil error if some error condition is known, such as EOF.
    79  //
    80  // Implementations of Read are discouraged from returning a
    81  // zero byte count with a nil error, except when len(p) == 0.
    82  // Callers should treat a return of 0 and nil as indicating that
    83  // nothing happened; in particular it does not indicate EOF.
    84  //
    85  // Implementations must not retain p.
    86  type Reader interface {
    87  	Read(p []byte) (n int, err error)
    88  }
    89  
    90  // Writer is the interface that wraps the basic Write method.
    91  //
    92  // Write writes len(p) bytes from p to the underlying data stream.
    93  // It returns the number of bytes written from p (0 <= n <= len(p))
    94  // and any error encountered that caused the write to stop early.
    95  // Write must return a non-nil error if it returns n < len(p).
    96  // Write must not modify the slice data, even temporarily.
    97  //
    98  // Implementations must not retain p.
    99  type Writer interface {
   100  	Write(p []byte) (n int, err error)
   101  }
   102  
   103  // Closer is the interface that wraps the basic Close method.
   104  //
   105  // The behavior of Close after the first call is undefined.
   106  // Specific implementations may document their own behavior.
   107  type Closer interface {
   108  	Close() error
   109  }
   110  
   111  // Seeker is the interface that wraps the basic Seek method.
   112  //
   113  // Seek sets the offset for the next Read or Write to offset,
   114  // interpreted according to whence:
   115  // [SeekStart] means relative to the start of the file,
   116  // [SeekCurrent] means relative to the current offset, and
   117  // [SeekEnd] means relative to the end
   118  // (for example, offset = -2 specifies the penultimate byte of the file).
   119  // Seek returns the new offset relative to the start of the
   120  // file or an error, if any.
   121  //
   122  // Seeking to an offset before the start of the file is an error.
   123  // Seeking to any positive offset may be allowed, but if the new offset exceeds
   124  // the size of the underlying object the behavior of subsequent I/O operations
   125  // is implementation-dependent.
   126  type Seeker interface {
   127  	Seek(offset int64, whence int) (int64, error)
   128  }
   129  
   130  // ReadWriter is the interface that groups the basic Read and Write methods.
   131  type ReadWriter interface {
   132  	Reader
   133  	Writer
   134  }
   135  
   136  // ReadCloser is the interface that groups the basic Read and Close methods.
   137  type ReadCloser interface {
   138  	Reader
   139  	Closer
   140  }
   141  
   142  // WriteCloser is the interface that groups the basic Write and Close methods.
   143  type WriteCloser interface {
   144  	Writer
   145  	Closer
   146  }
   147  
   148  // ReadWriteCloser is the interface that groups the basic Read, Write and Close methods.
   149  type ReadWriteCloser interface {
   150  	Reader
   151  	Writer
   152  	Closer
   153  }
   154  
   155  // ReadSeeker is the interface that groups the basic Read and Seek methods.
   156  type ReadSeeker interface {
   157  	Reader
   158  	Seeker
   159  }
   160  
   161  // ReadSeekCloser is the interface that groups the basic Read, Seek and Close
   162  // methods.
   163  type ReadSeekCloser interface {
   164  	Reader
   165  	Seeker
   166  	Closer
   167  }
   168  
   169  // WriteSeeker is the interface that groups the basic Write and Seek methods.
   170  type WriteSeeker interface {
   171  	Writer
   172  	Seeker
   173  }
   174  
   175  // ReadWriteSeeker is the interface that groups the basic Read, Write and Seek methods.
   176  type ReadWriteSeeker interface {
   177  	Reader
   178  	Writer
   179  	Seeker
   180  }
   181  
   182  // ReaderFrom is the interface that wraps the ReadFrom method.
   183  //
   184  // ReadFrom reads data from r until EOF or error.
   185  // The return value n is the number of bytes read.
   186  // Any error except EOF encountered during the read is also returned.
   187  //
   188  // The [Copy] function uses [ReaderFrom] if available.
   189  type ReaderFrom interface {
   190  	ReadFrom(r Reader) (n int64, err error)
   191  }
   192  
   193  // WriterTo is the interface that wraps the WriteTo method.
   194  //
   195  // WriteTo writes data to w until there's no more data to write or
   196  // when an error occurs. The return value n is the number of bytes
   197  // written. Any error encountered during the write is also returned.
   198  //
   199  // The Copy function uses WriterTo if available.
   200  type WriterTo interface {
   201  	WriteTo(w Writer) (n int64, err error)
   202  }
   203  
   204  // ReaderAt is the interface that wraps the basic ReadAt method.
   205  //
   206  // ReadAt reads len(p) bytes into p starting at offset off in the
   207  // underlying input source. It returns the number of bytes
   208  // read (0 <= n <= len(p)) and any error encountered.
   209  //
   210  // When ReadAt returns n < len(p), it returns a non-nil error
   211  // explaining why more bytes were not returned. In this respect,
   212  // ReadAt is stricter than Read.
   213  //
   214  // Even if ReadAt returns n < len(p), it may use all of p as scratch
   215  // space during the call. If some data is available but not len(p) bytes,
   216  // ReadAt blocks until either all the data is available or an error occurs.
   217  // In this respect ReadAt is different from Read.
   218  //
   219  // If the n = len(p) bytes returned by ReadAt are at the end of the
   220  // input source, ReadAt may return either err == EOF or err == nil.
   221  //
   222  // If ReadAt is reading from an input source with a seek offset,
   223  // ReadAt should not affect nor be affected by the underlying
   224  // seek offset.
   225  //
   226  // Clients of ReadAt can execute parallel ReadAt calls on the
   227  // same input source.
   228  //
   229  // Implementations must not retain p.
   230  type ReaderAt interface {
   231  	ReadAt(p []byte, off int64) (n int, err error)
   232  }
   233  
   234  // WriterAt is the interface that wraps the basic WriteAt method.
   235  //
   236  // WriteAt writes len(p) bytes from p to the underlying data stream
   237  // at offset off. It returns the number of bytes written from p (0 <= n <= len(p))
   238  // and any error encountered that caused the write to stop early.
   239  // WriteAt must return a non-nil error if it returns n < len(p).
   240  //
   241  // If WriteAt is writing to a destination with a seek offset,
   242  // WriteAt should not affect nor be affected by the underlying
   243  // seek offset.
   244  //
   245  // Clients of WriteAt can execute parallel WriteAt calls on the same
   246  // destination if the ranges do not overlap.
   247  //
   248  // Implementations must not retain p.
   249  type WriterAt interface {
   250  	WriteAt(p []byte, off int64) (n int, err error)
   251  }
   252  
   253  // ByteReader is the interface that wraps the ReadByte method.
   254  //
   255  // ReadByte reads and returns the next byte from the input or
   256  // any error encountered. If ReadByte returns an error, no input
   257  // byte was consumed, and the returned byte value is undefined.
   258  //
   259  // ReadByte provides an efficient interface for byte-at-time
   260  // processing. A [Reader] that does not implement  ByteReader
   261  // can be wrapped using bufio.NewReader to add this method.
   262  type ByteReader interface {
   263  	ReadByte() (byte, error)
   264  }
   265  
   266  // ByteScanner is the interface that adds the UnreadByte method to the
   267  // basic ReadByte method.
   268  //
   269  // UnreadByte causes the next call to ReadByte to return the last byte read.
   270  // If the last operation was not a successful call to ReadByte, UnreadByte may
   271  // return an error, unread the last byte read (or the byte prior to the
   272  // last-unread byte), or (in implementations that support the [Seeker] interface)
   273  // seek to one byte before the current offset.
   274  type ByteScanner interface {
   275  	ByteReader
   276  	UnreadByte() error
   277  }
   278  
   279  // ByteWriter is the interface that wraps the WriteByte method.
   280  type ByteWriter interface {
   281  	WriteByte(c byte) error
   282  }
   283  
   284  // RuneReader is the interface that wraps the ReadRune method.
   285  //
   286  // ReadRune reads a single encoded Unicode character
   287  // and returns the rune and its size in bytes. If no character is
   288  // available, err will be set.
   289  type RuneReader interface {
   290  	ReadRune() (r rune, size int, err error)
   291  }
   292  
   293  // RuneScanner is the interface that adds the UnreadRune method to the
   294  // basic ReadRune method.
   295  //
   296  // UnreadRune causes the next call to ReadRune to return the last rune read.
   297  // If the last operation was not a successful call to ReadRune, UnreadRune may
   298  // return an error, unread the last rune read (or the rune prior to the
   299  // last-unread rune), or (in implementations that support the [Seeker] interface)
   300  // seek to the start of the rune before the current offset.
   301  type RuneScanner interface {
   302  	RuneReader
   303  	UnreadRune() error
   304  }
   305  
   306  // StringWriter is the interface that wraps the WriteString method.
   307  type StringWriter interface {
   308  	WriteString(s string) (n int, err error)
   309  }
   310  
   311  // WriteString writes the contents of the string s to w, which accepts a slice of bytes.
   312  // If w implements [StringWriter], [StringWriter.WriteString] is invoked directly.
   313  // Otherwise, [Writer.Write] is called exactly once.
   314  func WriteString(w Writer, s string) (n int, err error) {
   315  	if sw, ok := w.(StringWriter); ok {
   316  		return sw.WriteString(s)
   317  	}
   318  	return w.Write([]byte(s))
   319  }
   320  
   321  // ReadAtLeast reads from r into buf until it has read at least min bytes.
   322  // It returns the number of bytes copied and an error if fewer bytes were read.
   323  // The error is EOF only if no bytes were read.
   324  // If an EOF happens after reading fewer than min bytes,
   325  // ReadAtLeast returns [ErrUnexpectedEOF].
   326  // If min is greater than the length of buf, ReadAtLeast returns [ErrShortBuffer].
   327  // On return, n >= min if and only if err == nil.
   328  // If r returns an error having read at least min bytes, the error is dropped.
   329  func ReadAtLeast(r Reader, buf []byte, min int) (n int, err error) {
   330  	if len(buf) < min {
   331  		return 0, ErrShortBuffer
   332  	}
   333  	for n < min && err == nil {
   334  		var nn int
   335  		nn, err = r.Read(buf[n:])
   336  		n += nn
   337  	}
   338  	if n >= min {
   339  		err = nil
   340  	} else if n > 0 && err == EOF {
   341  		err = ErrUnexpectedEOF
   342  	}
   343  	return
   344  }
   345  
   346  // ReadFull reads exactly len(buf) bytes from r into buf.
   347  // It returns the number of bytes copied and an error if fewer bytes were read.
   348  // The error is EOF only if no bytes were read.
   349  // If an EOF happens after reading some but not all the bytes,
   350  // ReadFull returns [ErrUnexpectedEOF].
   351  // On return, n == len(buf) if and only if err == nil.
   352  // If r returns an error having read at least len(buf) bytes, the error is dropped.
   353  func ReadFull(r Reader, buf []byte) (n int, err error) {
   354  	return ReadAtLeast(r, buf, len(buf))
   355  }
   356  
   357  // CopyN copies n bytes (or until an error) from src to dst.
   358  // It returns the number of bytes copied and the earliest
   359  // error encountered while copying.
   360  // On return, written == n if and only if err == nil.
   361  //
   362  // If dst implements [ReaderFrom], the copy is implemented using it.
   363  func CopyN(dst Writer, src Reader, n int64) (written int64, err error) {
   364  	written, err = Copy(dst, LimitReader(src, n))
   365  	if written == n {
   366  		return n, nil
   367  	}
   368  	if written < n && err == nil {
   369  		// src stopped early; must have been EOF.
   370  		err = EOF
   371  	}
   372  	return
   373  }
   374  
   375  // Copy copies from src to dst until either EOF is reached
   376  // on src or an error occurs. It returns the number of bytes
   377  // copied and the first error encountered while copying, if any.
   378  //
   379  // A successful Copy returns err == nil, not err == EOF.
   380  // Because Copy is defined to read from src until EOF, it does
   381  // not treat an EOF from Read as an error to be reported.
   382  //
   383  // If src implements [WriterTo],
   384  // the copy is implemented by calling src.WriteTo(dst).
   385  // Otherwise, if dst implements [ReaderFrom],
   386  // the copy is implemented by calling dst.ReadFrom(src).
   387  func Copy(dst Writer, src Reader) (written int64, err error) {
   388  	return copyBuffer(dst, src, nil)
   389  }
   390  
   391  // CopyBuffer is identical to Copy except that it stages through the
   392  // provided buffer (if one is required) rather than allocating a
   393  // temporary one. If buf is nil, one is allocated; otherwise if it has
   394  // zero length, CopyBuffer panics.
   395  //
   396  // If either src implements [WriterTo] or dst implements [ReaderFrom],
   397  // buf will not be used to perform the copy.
   398  func CopyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {
   399  	if buf != nil && len(buf) == 0 {
   400  		panic("empty buffer in CopyBuffer")
   401  	}
   402  	return copyBuffer(dst, src, buf)
   403  }
   404  
   405  // copyBuffer is the actual implementation of Copy and CopyBuffer.
   406  // if buf is nil, one is allocated.
   407  func copyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {
   408  	// If the reader has a WriteTo method, use it to do the copy.
   409  	// Avoids an allocation and a copy.
   410  	if wt, ok := src.(WriterTo); ok {
   411  		return wt.WriteTo(dst)
   412  	}
   413  	// Similarly, if the writer has a ReadFrom method, use it to do the copy.
   414  	if rf, ok := dst.(ReaderFrom); ok {
   415  		return rf.ReadFrom(src)
   416  	}
   417  	if buf == nil {
   418  		size := 32 * 1024
   419  		if l, ok := src.(*LimitedReader); ok && int64(size) > l.N {
   420  			if l.N < 1 {
   421  				size = 1
   422  			} else {
   423  				size = int(l.N)
   424  			}
   425  		}
   426  		buf = make([]byte, size)
   427  	}
   428  	for {
   429  		nr, er := src.Read(buf)
   430  		if nr > 0 {
   431  			nw, ew := dst.Write(buf[0:nr])
   432  			if nw < 0 || nr < nw {
   433  				nw = 0
   434  				if ew == nil {
   435  					ew = errInvalidWrite
   436  				}
   437  			}
   438  			written += int64(nw)
   439  			if ew != nil {
   440  				err = ew
   441  				break
   442  			}
   443  			if nr != nw {
   444  				err = ErrShortWrite
   445  				break
   446  			}
   447  		}
   448  		if er != nil {
   449  			if er != EOF {
   450  				err = er
   451  			}
   452  			break
   453  		}
   454  	}
   455  	return written, err
   456  }
   457  
   458  // LimitReader returns a Reader that reads from r
   459  // but stops with EOF after n bytes.
   460  // The underlying implementation is a *LimitedReader.
   461  func LimitReader(r Reader, n int64) Reader { return &LimitedReader{r, n} }
   462  
   463  // A LimitedReader reads from R but limits the amount of
   464  // data returned to just N bytes. Each call to Read
   465  // updates N to reflect the new amount remaining.
   466  // Read returns EOF when N <= 0 or when the underlying R returns EOF.
   467  type LimitedReader struct {
   468  	R Reader // underlying reader
   469  	N int64  // max bytes remaining
   470  }
   471  
   472  func (l *LimitedReader) Read(p []byte) (n int, err error) {
   473  	if l.N <= 0 {
   474  		return 0, EOF
   475  	}
   476  	if int64(len(p)) > l.N {
   477  		p = p[0:l.N]
   478  	}
   479  	n, err = l.R.Read(p)
   480  	l.N -= int64(n)
   481  	return
   482  }
   483  
   484  // NewSectionReader returns a [SectionReader] that reads from r
   485  // starting at offset off and stops with EOF after n bytes.
   486  func NewSectionReader(r ReaderAt, off int64, n int64) *SectionReader {
   487  	var remaining int64
   488  	const maxint64 = 1<<63 - 1
   489  	if off <= maxint64-n {
   490  		remaining = n + off
   491  	} else {
   492  		// Overflow, with no way to return error.
   493  		// Assume we can read up to an offset of 1<<63 - 1.
   494  		remaining = maxint64
   495  	}
   496  	return &SectionReader{r, off, off, remaining, n}
   497  }
   498  
   499  // SectionReader implements Read, Seek, and ReadAt on a section
   500  // of an underlying [ReaderAt].
   501  type SectionReader struct {
   502  	r     ReaderAt // constant after creation
   503  	base  int64    // constant after creation
   504  	off   int64
   505  	limit int64 // constant after creation
   506  	n     int64 // constant after creation
   507  }
   508  
   509  func (s *SectionReader) Read(p []byte) (n int, err error) {
   510  	if s.off >= s.limit {
   511  		return 0, EOF
   512  	}
   513  	if max := s.limit - s.off; int64(len(p)) > max {
   514  		p = p[0:max]
   515  	}
   516  	n, err = s.r.ReadAt(p, s.off)
   517  	s.off += int64(n)
   518  	return
   519  }
   520  
   521  var errWhence = errors.New("Seek: invalid whence")
   522  var errOffset = errors.New("Seek: invalid offset")
   523  
   524  func (s *SectionReader) Seek(offset int64, whence int) (int64, error) {
   525  	switch whence {
   526  	default:
   527  		return 0, errWhence
   528  	case SeekStart:
   529  		offset += s.base
   530  	case SeekCurrent:
   531  		offset += s.off
   532  	case SeekEnd:
   533  		offset += s.limit
   534  	}
   535  	if offset < s.base {
   536  		return 0, errOffset
   537  	}
   538  	s.off = offset
   539  	return offset - s.base, nil
   540  }
   541  
   542  func (s *SectionReader) ReadAt(p []byte, off int64) (n int, err error) {
   543  	if off < 0 || off >= s.Size() {
   544  		return 0, EOF
   545  	}
   546  	off += s.base
   547  	if max := s.limit - off; int64(len(p)) > max {
   548  		p = p[0:max]
   549  		n, err = s.r.ReadAt(p, off)
   550  		if err == nil {
   551  			err = EOF
   552  		}
   553  		return n, err
   554  	}
   555  	return s.r.ReadAt(p, off)
   556  }
   557  
   558  // Size returns the size of the section in bytes.
   559  func (s *SectionReader) Size() int64 { return s.limit - s.base }
   560  
   561  // Outer returns the underlying [ReaderAt] and offsets for the section.
   562  //
   563  // The returned values are the same that were passed to [NewSectionReader]
   564  // when the [SectionReader] was created.
   565  func (s *SectionReader) Outer() (r ReaderAt, off int64, n int64) {
   566  	return s.r, s.base, s.n
   567  }
   568  
   569  // An OffsetWriter maps writes at offset base to offset base+off in the underlying writer.
   570  type OffsetWriter struct {
   571  	w    WriterAt
   572  	base int64 // the original offset
   573  	off  int64 // the current offset
   574  }
   575  
   576  // NewOffsetWriter returns an [OffsetWriter] that writes to w
   577  // starting at offset off.
   578  func NewOffsetWriter(w WriterAt, off int64) *OffsetWriter {
   579  	return &OffsetWriter{w, off, off}
   580  }
   581  
   582  func (o *OffsetWriter) Write(p []byte) (n int, err error) {
   583  	n, err = o.w.WriteAt(p, o.off)
   584  	o.off += int64(n)
   585  	return
   586  }
   587  
   588  func (o *OffsetWriter) WriteAt(p []byte, off int64) (n int, err error) {
   589  	if off < 0 {
   590  		return 0, errOffset
   591  	}
   592  
   593  	off += o.base
   594  	return o.w.WriteAt(p, off)
   595  }
   596  
   597  func (o *OffsetWriter) Seek(offset int64, whence int) (int64, error) {
   598  	switch whence {
   599  	default:
   600  		return 0, errWhence
   601  	case SeekStart:
   602  		offset += o.base
   603  	case SeekCurrent:
   604  		offset += o.off
   605  	}
   606  	if offset < o.base {
   607  		return 0, errOffset
   608  	}
   609  	o.off = offset
   610  	return offset - o.base, nil
   611  }
   612  
   613  // TeeReader returns a [Reader] that writes to w what it reads from r.
   614  // All reads from r performed through it are matched with
   615  // corresponding writes to w. There is no internal buffering -
   616  // the write must complete before the read completes.
   617  // Any error encountered while writing is reported as a read error.
   618  func TeeReader(r Reader, w Writer) Reader {
   619  	return &teeReader{r, w}
   620  }
   621  
   622  type teeReader struct {
   623  	r Reader
   624  	w Writer
   625  }
   626  
   627  func (t *teeReader) Read(p []byte) (n int, err error) {
   628  	n, err = t.r.Read(p)
   629  	if n > 0 {
   630  		if n, err := t.w.Write(p[:n]); err != nil {
   631  			return n, err
   632  		}
   633  	}
   634  	return
   635  }
   636  
   637  // Discard is a [Writer] on which all Write calls succeed
   638  // without doing anything.
   639  var Discard Writer = discard{}
   640  
   641  type discard struct{}
   642  
   643  // discard implements ReaderFrom as an optimization so Copy to
   644  // io.Discard can avoid doing unnecessary work.
   645  var _ ReaderFrom = discard{}
   646  
   647  func (discard) Write(p []byte) (int, error) {
   648  	return len(p), nil
   649  }
   650  
   651  func (discard) WriteString(s string) (int, error) {
   652  	return len(s), nil
   653  }
   654  
   655  var blackHolePool = sync.Pool{
   656  	New: func() any {
   657  		b := make([]byte, 8192)
   658  		return &b
   659  	},
   660  }
   661  
   662  func (discard) ReadFrom(r Reader) (n int64, err error) {
   663  	bufp := blackHolePool.Get().(*[]byte)
   664  	readSize := 0
   665  	for {
   666  		readSize, err = r.Read(*bufp)
   667  		n += int64(readSize)
   668  		if err != nil {
   669  			blackHolePool.Put(bufp)
   670  			if err == EOF {
   671  				return n, nil
   672  			}
   673  			return
   674  		}
   675  	}
   676  }
   677  
   678  // NopCloser returns a [ReadCloser] with a no-op Close method wrapping
   679  // the provided [Reader] r.
   680  // If r implements [WriterTo], the returned [ReadCloser] will implement [WriterTo]
   681  // by forwarding calls to r.
   682  func NopCloser(r Reader) ReadCloser {
   683  	if _, ok := r.(WriterTo); ok {
   684  		return nopCloserWriterTo{r}
   685  	}
   686  	return nopCloser{r}
   687  }
   688  
   689  type nopCloser struct {
   690  	Reader
   691  }
   692  
   693  func (nopCloser) Close() error { return nil }
   694  
   695  type nopCloserWriterTo struct {
   696  	Reader
   697  }
   698  
   699  func (nopCloserWriterTo) Close() error { return nil }
   700  
   701  func (c nopCloserWriterTo) WriteTo(w Writer) (n int64, err error) {
   702  	return c.Reader.(WriterTo).WriteTo(w)
   703  }
   704  
   705  // ReadAll reads from r until an error or EOF and returns the data it read.
   706  // A successful call returns err == nil, not err == EOF. Because ReadAll is
   707  // defined to read from src until EOF, it does not treat an EOF from Read
   708  // as an error to be reported.
   709  func ReadAll(r Reader) ([]byte, error) {
   710  	b := make([]byte, 0, 512)
   711  	for {
   712  		n, err := r.Read(b[len(b):cap(b)])
   713  		b = b[:len(b)+n]
   714  		if err != nil {
   715  			if err == EOF {
   716  				err = nil
   717  			}
   718  			return b, err
   719  		}
   720  
   721  		if len(b) == cap(b) {
   722  			// Add more capacity (let append pick how much).
   723  			b = append(b, 0)[:len(b)]
   724  		}
   725  	}
   726  }
   727  

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