go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/common/iotools/countingreader.go (about)

     1  // Copyright 2015 The LUCI Authors.
     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 iotools
    16  
    17  import (
    18  	"io"
    19  )
    20  
    21  // CountingReader is an io.Reader that counts the number of bytes that are read.
    22  type CountingReader struct {
    23  	io.Reader // The underlying io.Reader.
    24  
    25  	Count int64
    26  }
    27  
    28  var _ io.Reader = (*CountingReader)(nil)
    29  
    30  // Read implements io.Reader.
    31  func (c *CountingReader) Read(buf []byte) (int, error) {
    32  	amount, err := c.Reader.Read(buf)
    33  	c.Count += int64(amount)
    34  	return amount, err
    35  }
    36  
    37  // ReadByte implements io.ByteReader.
    38  func (c *CountingReader) ReadByte() (byte, error) {
    39  	// If our underlying reader is a ByteReader, use its ReadByte directly.
    40  	if br, ok := c.Reader.(io.ByteReader); ok {
    41  		b, err := br.ReadByte()
    42  		if err == nil {
    43  			c.Count++
    44  		}
    45  		return b, err
    46  	}
    47  
    48  	data := []byte{0}
    49  	amount, err := c.Reader.Read(data)
    50  	if amount != 0 {
    51  		c.Count += int64(amount)
    52  		return data[0], err
    53  	}
    54  	return 0, err
    55  }