github.com/dolthub/dolt/go@v0.40.5-0.20240520175717-68db7794bea6/libraries/utils/buffer/buffer.go (about)

     1  // Copyright 2021 Dolthub, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package buffer
    16  
    17  import (
    18  	"io"
    19  
    20  	"github.com/dolthub/dolt/go/libraries/utils/iohelp"
    21  )
    22  
    23  type DynamicBuffer struct {
    24  	blocks    [][]byte
    25  	blockSize int
    26  }
    27  
    28  func New(blockSize int) *DynamicBuffer {
    29  	return &DynamicBuffer{blockSize: blockSize}
    30  }
    31  
    32  func (buf *DynamicBuffer) Append(bytes []byte) {
    33  	blockIdx := len(buf.blocks) - 1
    34  
    35  	var space int
    36  	var pos int
    37  	if blockIdx >= 0 {
    38  		currBlock := buf.blocks[blockIdx]
    39  		pos = len(currBlock)
    40  		space = cap(currBlock) - pos
    41  	}
    42  
    43  	for len(bytes) > 0 {
    44  		if space == 0 {
    45  			for len(bytes) >= buf.blockSize {
    46  				buf.blocks = append(buf.blocks, bytes[:buf.blockSize])
    47  				bytes = bytes[buf.blockSize:]
    48  				blockIdx++
    49  			}
    50  
    51  			if len(bytes) == 0 {
    52  				return
    53  			}
    54  
    55  			buf.blocks = append(buf.blocks, make([]byte, 0, buf.blockSize))
    56  			pos = 0
    57  			space = buf.blockSize
    58  			blockIdx++
    59  		}
    60  
    61  		n := len(bytes)
    62  		if n > space {
    63  			n = space
    64  		}
    65  
    66  		buf.blocks[blockIdx] = buf.blocks[blockIdx][:pos+n]
    67  		copy(buf.blocks[blockIdx][pos:], bytes[:n])
    68  		bytes = bytes[n:]
    69  		space -= n
    70  		pos += n
    71  	}
    72  }
    73  
    74  func (buf *DynamicBuffer) Close() *BufferIterator {
    75  	itr := &BufferIterator{blocks: buf.blocks}
    76  	buf.blocks = nil
    77  
    78  	return itr
    79  }
    80  
    81  type BufferIterator struct {
    82  	blocks [][]byte
    83  	i      int
    84  }
    85  
    86  func (itr *BufferIterator) Next() ([]byte, error) {
    87  	if itr.i >= len(itr.blocks) {
    88  		return nil, io.EOF
    89  	}
    90  	next := itr.blocks[itr.i]
    91  	itr.i++
    92  
    93  	return next, nil
    94  }
    95  
    96  func (itr *BufferIterator) NumBlocks() int {
    97  	return len(itr.blocks)
    98  }
    99  
   100  func (itr *BufferIterator) FlushTo(wr io.Writer) error {
   101  	for {
   102  		data, err := itr.Next()
   103  
   104  		if err == io.EOF {
   105  			return nil
   106  		} else if err != nil {
   107  			return err
   108  		}
   109  
   110  		err = iohelp.WriteAll(wr, data)
   111  
   112  		if err != nil {
   113  			return err
   114  		}
   115  	}
   116  }
   117  
   118  func (itr *BufferIterator) AsReader() io.Reader {
   119  	return &bufferIteratorReader{
   120  		itr: itr,
   121  	}
   122  }
   123  
   124  type bufferIteratorReader struct {
   125  	itr      *BufferIterator
   126  	currBuff []byte
   127  }
   128  
   129  func (b *bufferIteratorReader) Read(dest []byte) (n int, err error) {
   130  	if len(b.currBuff) == 0 {
   131  		b.currBuff, err = b.itr.Next()
   132  
   133  		if err != nil {
   134  			return 0, err
   135  		}
   136  	}
   137  
   138  	destSize := len(dest)
   139  	toCopy := b.currBuff
   140  	if len(b.currBuff) > destSize {
   141  		toCopy = b.currBuff[:destSize]
   142  	}
   143  
   144  	n = copy(dest, toCopy)
   145  	b.currBuff = b.currBuff[n:]
   146  
   147  	return n, err
   148  }