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package magic
import (
"bufio"
"bytes"
"encoding/csv"
"errors"
"io"
"sync"
)
// A bufio.Reader pool to alleviate problems with memory allocations.
var readerPool = sync.Pool{
New: func() any {
// Initiate with empty source reader.
return bufio.NewReader(nil)
},
}
func newReader(r io.Reader) *bufio.Reader {
br := readerPool.Get().(*bufio.Reader)
br.Reset(r)
return br
}
// Csv matches a comma-separated values file.
func Csv(raw []byte, limit uint32) bool {
return sv(raw, ',', limit)
}
// Tsv matches a tab-separated values file.
func Tsv(raw []byte, limit uint32) bool {
return sv(raw, '\t', limit)
}
func sv(in []byte, comma rune, limit uint32) bool {
in = dropLastLine(in, limit)
br := newReader(bytes.NewReader(in))
defer readerPool.Put(br)
r := csv.NewReader(br)
r.Comma = comma
r.ReuseRecord = true
r.LazyQuotes = true
r.Comment = '#'
lines := 0
for {
_, err := r.Read()
if errors.Is(err, io.EOF) {
break
}
if err != nil {
return false
}
lines++
}
return r.FieldsPerRecord > 1 && lines > 1
}
// dropLastLine drops the last incomplete line from b.
//
// mimetype limits itself to ReadLimit bytes when performing a detection.
// This means, for file formats like CSV for NDJSON, the last line of the input
// can be an incomplete line.
func dropLastLine(b []byte, readLimit uint32) []byte {
if readLimit == 0 || uint32(len(b)) < readLimit {
return b
}
for i := len(b) - 1; i > 0; i-- {
if b[i] == '\n' {
return b[:i]
}
}
return b
}
|
