minio/pkg/ioutil/delimited-reader.go

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/*
* Minio Cloud Storage, (C) 2018 Minio, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package ioutil
import (
"bufio"
"io"
)
var (
nByte byte = 10 // the byte that corresponds to the '\n' rune.
rByte byte = 13 // the byte that corresponds to the '\r' rune.
)
// DelimitedReader reduces the custom delimiter to `\n`.
type DelimitedReader struct {
r *bufio.Reader
delimiter []rune // Select can have upto 2 characters as delimiter.
assignEmpty bool // Decides whether the next read byte should be discarded.
}
// NewDelimitedReader detects the custom delimiter and replaces with `\n`.
func NewDelimitedReader(r io.Reader, delimiter []rune) *DelimitedReader {
return &DelimitedReader{r: bufio.NewReader(r), delimiter: delimiter, assignEmpty: false}
}
// Reads and replaces the custom delimiter with `\n`.
func (r *DelimitedReader) Read(p []byte) (n int, err error) {
n, err = r.r.Read(p)
if err != nil {
return
}
for i, b := range p {
if r.assignEmpty {
swapAndNullify(p, i)
r.assignEmpty = false
continue
}
if b == rByte && rune(b) != r.delimiter[0] {
// Replace the carriage returns with `\n`.
// Mac styled csv will have `\r` as their record delimiter.
p[i] = nByte
} else if rune(b) == r.delimiter[0] { // Eg, `\r\n`,`ab`,`a` are valid delimiters
if i+1 == len(p) && len(r.delimiter) > 1 {
// If the first delimiter match falls on the boundary,
// Peek the next byte and if it matches, discard it in the next byte read.
if nextByte, nerr := r.r.Peek(1); nerr == nil {
if rune(nextByte[0]) == r.delimiter[1] {
p[i] = nByte
// To Discard in the next read.
r.assignEmpty = true
}
}
} else if len(r.delimiter) > 1 && rune(p[i+1]) == r.delimiter[1] {
// The second delimiter falls in the same chunk.
p[i] = nByte
r.assignEmpty = true
} else if len(r.delimiter) == 1 {
// Replace with `\n` incase of single charecter delimiter match.
p[i] = nByte
}
}
}
return
}
// Occupy the first byte space and nullify the last byte.
func swapAndNullify(p []byte, n int) {
for i := n; i < len(p)-1; i++ {
p[i] = p[i+1]
}
p[len(p)-1] = 0
}