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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-16 19:23:18 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-16 19:23:18 +0000 |
commit | 43a123c1ae6613b3efeed291fa552ecd909d3acf (patch) | |
tree | fd92518b7024bc74031f78a1cf9e454b65e73665 /src/bytes/buffer.go | |
parent | Initial commit. (diff) | |
download | golang-1.20-43a123c1ae6613b3efeed291fa552ecd909d3acf.tar.xz golang-1.20-43a123c1ae6613b3efeed291fa552ecd909d3acf.zip |
Adding upstream version 1.20.14.upstream/1.20.14upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'src/bytes/buffer.go')
-rw-r--r-- | src/bytes/buffer.go | 473 |
1 files changed, 473 insertions, 0 deletions
diff --git a/src/bytes/buffer.go b/src/bytes/buffer.go new file mode 100644 index 0000000..ee83fd8 --- /dev/null +++ b/src/bytes/buffer.go @@ -0,0 +1,473 @@ +// 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 bytes + +// Simple byte buffer for marshaling data. + +import ( + "errors" + "io" + "unicode/utf8" +) + +// smallBufferSize is an initial allocation minimal capacity. +const smallBufferSize = 64 + +// A Buffer is a variable-sized buffer of bytes with Read and Write methods. +// The zero value for Buffer is an empty buffer ready to use. +type Buffer struct { + buf []byte // contents are the bytes buf[off : len(buf)] + off int // read at &buf[off], write at &buf[len(buf)] + lastRead readOp // last read operation, so that Unread* can work correctly. +} + +// The readOp constants describe the last action performed on +// the buffer, so that UnreadRune and UnreadByte can check for +// invalid usage. opReadRuneX constants are chosen such that +// converted to int they correspond to the rune size that was read. +type readOp int8 + +// Don't use iota for these, as the values need to correspond with the +// names and comments, which is easier to see when being explicit. +const ( + opRead readOp = -1 // Any other read operation. + opInvalid readOp = 0 // Non-read operation. + opReadRune1 readOp = 1 // Read rune of size 1. + opReadRune2 readOp = 2 // Read rune of size 2. + opReadRune3 readOp = 3 // Read rune of size 3. + opReadRune4 readOp = 4 // Read rune of size 4. +) + +// ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer. +var ErrTooLarge = errors.New("bytes.Buffer: too large") +var errNegativeRead = errors.New("bytes.Buffer: reader returned negative count from Read") + +const maxInt = int(^uint(0) >> 1) + +// Bytes returns a slice of length b.Len() holding the unread portion of the buffer. +// The slice is valid for use only until the next buffer modification (that is, +// only until the next call to a method like Read, Write, Reset, or Truncate). +// The slice aliases the buffer content at least until the next buffer modification, +// so immediate changes to the slice will affect the result of future reads. +func (b *Buffer) Bytes() []byte { return b.buf[b.off:] } + +// String returns the contents of the unread portion of the buffer +// as a string. If the Buffer is a nil pointer, it returns "<nil>". +// +// To build strings more efficiently, see the strings.Builder type. +func (b *Buffer) String() string { + if b == nil { + // Special case, useful in debugging. + return "<nil>" + } + return string(b.buf[b.off:]) +} + +// empty reports whether the unread portion of the buffer is empty. +func (b *Buffer) empty() bool { return len(b.buf) <= b.off } + +// Len returns the number of bytes of the unread portion of the buffer; +// b.Len() == len(b.Bytes()). +func (b *Buffer) Len() int { return len(b.buf) - b.off } + +// Cap returns the capacity of the buffer's underlying byte slice, that is, the +// total space allocated for the buffer's data. +func (b *Buffer) Cap() int { return cap(b.buf) } + +// Truncate discards all but the first n unread bytes from the buffer +// but continues to use the same allocated storage. +// It panics if n is negative or greater than the length of the buffer. +func (b *Buffer) Truncate(n int) { + if n == 0 { + b.Reset() + return + } + b.lastRead = opInvalid + if n < 0 || n > b.Len() { + panic("bytes.Buffer: truncation out of range") + } + b.buf = b.buf[:b.off+n] +} + +// Reset resets the buffer to be empty, +// but it retains the underlying storage for use by future writes. +// Reset is the same as Truncate(0). +func (b *Buffer) Reset() { + b.buf = b.buf[:0] + b.off = 0 + b.lastRead = opInvalid +} + +// tryGrowByReslice is a inlineable version of grow for the fast-case where the +// internal buffer only needs to be resliced. +// It returns the index where bytes should be written and whether it succeeded. +func (b *Buffer) tryGrowByReslice(n int) (int, bool) { + if l := len(b.buf); n <= cap(b.buf)-l { + b.buf = b.buf[:l+n] + return l, true + } + return 0, false +} + +// grow grows the buffer to guarantee space for n more bytes. +// It returns the index where bytes should be written. +// If the buffer can't grow it will panic with ErrTooLarge. +func (b *Buffer) grow(n int) int { + m := b.Len() + // If buffer is empty, reset to recover space. + if m == 0 && b.off != 0 { + b.Reset() + } + // Try to grow by means of a reslice. + if i, ok := b.tryGrowByReslice(n); ok { + return i + } + if b.buf == nil && n <= smallBufferSize { + b.buf = make([]byte, n, smallBufferSize) + return 0 + } + c := cap(b.buf) + if n <= c/2-m { + // We can slide things down instead of allocating a new + // slice. We only need m+n <= c to slide, but + // we instead let capacity get twice as large so we + // don't spend all our time copying. + copy(b.buf, b.buf[b.off:]) + } else if c > maxInt-c-n { + panic(ErrTooLarge) + } else { + // Add b.off to account for b.buf[:b.off] being sliced off the front. + b.buf = growSlice(b.buf[b.off:], b.off+n) + } + // Restore b.off and len(b.buf). + b.off = 0 + b.buf = b.buf[:m+n] + return m +} + +// Grow grows the buffer's capacity, if necessary, to guarantee space for +// another n bytes. After Grow(n), at least n bytes can be written to the +// buffer without another allocation. +// If n is negative, Grow will panic. +// If the buffer can't grow it will panic with ErrTooLarge. +func (b *Buffer) Grow(n int) { + if n < 0 { + panic("bytes.Buffer.Grow: negative count") + } + m := b.grow(n) + b.buf = b.buf[:m] +} + +// Write appends the contents of p to the buffer, growing the buffer as +// needed. The return value n is the length of p; err is always nil. If the +// buffer becomes too large, Write will panic with ErrTooLarge. +func (b *Buffer) Write(p []byte) (n int, err error) { + b.lastRead = opInvalid + m, ok := b.tryGrowByReslice(len(p)) + if !ok { + m = b.grow(len(p)) + } + return copy(b.buf[m:], p), nil +} + +// WriteString appends the contents of s to the buffer, growing the buffer as +// needed. The return value n is the length of s; err is always nil. If the +// buffer becomes too large, WriteString will panic with ErrTooLarge. +func (b *Buffer) WriteString(s string) (n int, err error) { + b.lastRead = opInvalid + m, ok := b.tryGrowByReslice(len(s)) + if !ok { + m = b.grow(len(s)) + } + return copy(b.buf[m:], s), nil +} + +// MinRead is the minimum slice size passed to a Read call by +// Buffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond +// what is required to hold the contents of r, ReadFrom will not grow the +// underlying buffer. +const MinRead = 512 + +// ReadFrom reads data from r until EOF and appends it to the buffer, growing +// the buffer as needed. The return value n is the number of bytes read. Any +// error except io.EOF encountered during the read is also returned. If the +// buffer becomes too large, ReadFrom will panic with ErrTooLarge. +func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) { + b.lastRead = opInvalid + for { + i := b.grow(MinRead) + b.buf = b.buf[:i] + m, e := r.Read(b.buf[i:cap(b.buf)]) + if m < 0 { + panic(errNegativeRead) + } + + b.buf = b.buf[:i+m] + n += int64(m) + if e == io.EOF { + return n, nil // e is EOF, so return nil explicitly + } + if e != nil { + return n, e + } + } +} + +// growSlice grows b by n, preserving the original content of b. +// If the allocation fails, it panics with ErrTooLarge. +func growSlice(b []byte, n int) []byte { + defer func() { + if recover() != nil { + panic(ErrTooLarge) + } + }() + // TODO(http://golang.org/issue/51462): We should rely on the append-make + // pattern so that the compiler can call runtime.growslice. For example: + // return append(b, make([]byte, n)...) + // This avoids unnecessary zero-ing of the first len(b) bytes of the + // allocated slice, but this pattern causes b to escape onto the heap. + // + // Instead use the append-make pattern with a nil slice to ensure that + // we allocate buffers rounded up to the closest size class. + c := len(b) + n // ensure enough space for n elements + if c < 2*cap(b) { + // The growth rate has historically always been 2x. In the future, + // we could rely purely on append to determine the growth rate. + c = 2 * cap(b) + } + b2 := append([]byte(nil), make([]byte, c)...) + copy(b2, b) + return b2[:len(b)] +} + +// WriteTo writes data to w until the buffer is drained or an error occurs. +// The return value n is the number of bytes written; it always fits into an +// int, but it is int64 to match the io.WriterTo interface. Any error +// encountered during the write is also returned. +func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) { + b.lastRead = opInvalid + if nBytes := b.Len(); nBytes > 0 { + m, e := w.Write(b.buf[b.off:]) + if m > nBytes { + panic("bytes.Buffer.WriteTo: invalid Write count") + } + b.off += m + n = int64(m) + if e != nil { + return n, e + } + // all bytes should have been written, by definition of + // Write method in io.Writer + if m != nBytes { + return n, io.ErrShortWrite + } + } + // Buffer is now empty; reset. + b.Reset() + return n, nil +} + +// WriteByte appends the byte c to the buffer, growing the buffer as needed. +// The returned error is always nil, but is included to match bufio.Writer's +// WriteByte. If the buffer becomes too large, WriteByte will panic with +// ErrTooLarge. +func (b *Buffer) WriteByte(c byte) error { + b.lastRead = opInvalid + m, ok := b.tryGrowByReslice(1) + if !ok { + m = b.grow(1) + } + b.buf[m] = c + return nil +} + +// WriteRune appends the UTF-8 encoding of Unicode code point r to the +// buffer, returning its length and an error, which is always nil but is +// included to match bufio.Writer's WriteRune. The buffer is grown as needed; +// if it becomes too large, WriteRune will panic with ErrTooLarge. +func (b *Buffer) WriteRune(r rune) (n int, err error) { + // Compare as uint32 to correctly handle negative runes. + if uint32(r) < utf8.RuneSelf { + b.WriteByte(byte(r)) + return 1, nil + } + b.lastRead = opInvalid + m, ok := b.tryGrowByReslice(utf8.UTFMax) + if !ok { + m = b.grow(utf8.UTFMax) + } + b.buf = utf8.AppendRune(b.buf[:m], r) + return len(b.buf) - m, nil +} + +// Read reads the next len(p) bytes from the buffer or until the buffer +// is drained. The return value n is the number of bytes read. If the +// buffer has no data to return, err is io.EOF (unless len(p) is zero); +// otherwise it is nil. +func (b *Buffer) Read(p []byte) (n int, err error) { + b.lastRead = opInvalid + if b.empty() { + // Buffer is empty, reset to recover space. + b.Reset() + if len(p) == 0 { + return 0, nil + } + return 0, io.EOF + } + n = copy(p, b.buf[b.off:]) + b.off += n + if n > 0 { + b.lastRead = opRead + } + return n, nil +} + +// Next returns a slice containing the next n bytes from the buffer, +// advancing the buffer as if the bytes had been returned by Read. +// If there are fewer than n bytes in the buffer, Next returns the entire buffer. +// The slice is only valid until the next call to a read or write method. +func (b *Buffer) Next(n int) []byte { + b.lastRead = opInvalid + m := b.Len() + if n > m { + n = m + } + data := b.buf[b.off : b.off+n] + b.off += n + if n > 0 { + b.lastRead = opRead + } + return data +} + +// ReadByte reads and returns the next byte from the buffer. +// If no byte is available, it returns error io.EOF. +func (b *Buffer) ReadByte() (byte, error) { + if b.empty() { + // Buffer is empty, reset to recover space. + b.Reset() + return 0, io.EOF + } + c := b.buf[b.off] + b.off++ + b.lastRead = opRead + return c, nil +} + +// ReadRune reads and returns the next UTF-8-encoded +// Unicode code point from the buffer. +// If no bytes are available, the error returned is io.EOF. +// If the bytes are an erroneous UTF-8 encoding, it +// consumes one byte and returns U+FFFD, 1. +func (b *Buffer) ReadRune() (r rune, size int, err error) { + if b.empty() { + // Buffer is empty, reset to recover space. + b.Reset() + return 0, 0, io.EOF + } + c := b.buf[b.off] + if c < utf8.RuneSelf { + b.off++ + b.lastRead = opReadRune1 + return rune(c), 1, nil + } + r, n := utf8.DecodeRune(b.buf[b.off:]) + b.off += n + b.lastRead = readOp(n) + return r, n, nil +} + +// UnreadRune unreads the last rune returned by ReadRune. +// If the most recent read or write operation on the buffer was +// not a successful ReadRune, UnreadRune returns an error. (In this regard +// it is stricter than UnreadByte, which will unread the last byte +// from any read operation.) +func (b *Buffer) UnreadRune() error { + if b.lastRead <= opInvalid { + return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune") + } + if b.off >= int(b.lastRead) { + b.off -= int(b.lastRead) + } + b.lastRead = opInvalid + return nil +} + +var errUnreadByte = errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read") + +// UnreadByte unreads the last byte returned by the most recent successful +// read operation that read at least one byte. If a write has happened since +// the last read, if the last read returned an error, or if the read read zero +// bytes, UnreadByte returns an error. +func (b *Buffer) UnreadByte() error { + if b.lastRead == opInvalid { + return errUnreadByte + } + b.lastRead = opInvalid + if b.off > 0 { + b.off-- + } + return nil +} + +// ReadBytes reads until the first occurrence of delim in the input, +// returning a slice containing the data up to and including the delimiter. +// If ReadBytes encounters an error before finding a delimiter, +// it returns the data read before the error and the error itself (often io.EOF). +// ReadBytes returns err != nil if and only if the returned data does not end in +// delim. +func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) { + slice, err := b.readSlice(delim) + // return a copy of slice. The buffer's backing array may + // be overwritten by later calls. + line = append(line, slice...) + return line, err +} + +// readSlice is like ReadBytes but returns a reference to internal buffer data. +func (b *Buffer) readSlice(delim byte) (line []byte, err error) { + i := IndexByte(b.buf[b.off:], delim) + end := b.off + i + 1 + if i < 0 { + end = len(b.buf) + err = io.EOF + } + line = b.buf[b.off:end] + b.off = end + b.lastRead = opRead + return line, err +} + +// ReadString reads until the first occurrence of delim in the input, +// returning a string containing the data up to and including the delimiter. +// If ReadString encounters an error before finding a delimiter, +// it returns the data read before the error and the error itself (often io.EOF). +// ReadString returns err != nil if and only if the returned data does not end +// in delim. +func (b *Buffer) ReadString(delim byte) (line string, err error) { + slice, err := b.readSlice(delim) + return string(slice), err +} + +// NewBuffer creates and initializes a new Buffer using buf as its +// initial contents. The new Buffer takes ownership of buf, and the +// caller should not use buf after this call. NewBuffer is intended to +// prepare a Buffer to read existing data. It can also be used to set +// the initial size of the internal buffer for writing. To do that, +// buf should have the desired capacity but a length of zero. +// +// In most cases, new(Buffer) (or just declaring a Buffer variable) is +// sufficient to initialize a Buffer. +func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} } + +// NewBufferString creates and initializes a new Buffer using string s as its +// initial contents. It is intended to prepare a buffer to read an existing +// string. +// +// In most cases, new(Buffer) (or just declaring a Buffer variable) is +// sufficient to initialize a Buffer. +func NewBufferString(s string) *Buffer { + return &Buffer{buf: []byte(s)} +} |