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// Package csvvalue provides an efficient parser for a single line CSV value.
// It is more efficient than the standard library csv package for parsing many
// small values. For multi-line CSV parsing, the standard library is recommended.
package csvvalue
import (
"encoding/csv"
"errors"
"io"
"strings"
"unicode"
"unicode/utf8"
)
var errInvalidDelim = errors.New("csv: invalid field or comment delimiter")
var defaultParser = NewParser()
// Fields parses the line with default parser and returns
// slice of fields for the record. If dst is nil, a new slice is allocated.
func Fields(inp string, dst []string) ([]string, error) {
return defaultParser.Fields(inp, dst)
}
// Parser is a CSV parser for a single line value.
type Parser struct {
Comma rune
LazyQuotes bool
TrimLeadingSpace bool
}
// NewParser returns a new Parser with default settings.
func NewParser() *Parser {
return &Parser{Comma: ','}
}
// Fields parses the line and returns slice of fields for the record.
// If dst is nil, a new slice is allocated.
// For backward compatibility, a trailing newline is allowed.
func (r *Parser) Fields(line string, dst []string) ([]string, error) {
if !validDelim(r.Comma) {
return nil, errInvalidDelim
}
if cap(dst) == 0 {
// imprecise estimate, strings.Count is fast
dst = make([]string, 0, 1+strings.Count(line, string(r.Comma)))
} else {
dst = dst[:0]
}
const quoteLen = len(`"`)
var (
pos int
commaLen = utf8.RuneLen(r.Comma)
trim = r.TrimLeadingSpace
)
// allow trailing newline for compatibility
if n := len(line); n > 0 && line[n-1] == '\n' {
if n > 1 && line[n-2] == '\r' {
line = line[:n-2]
} else {
line = line[:n-1]
}
}
if len(line) == 0 {
return nil, io.EOF
}
parseField:
for {
if trim {
i := strings.IndexFunc(line, func(r rune) bool {
return !unicode.IsSpace(r)
})
if i < 0 {
i = len(line)
}
line = line[i:]
pos += i
}
if len(line) == 0 || line[0] != '"' {
// Non-quoted string field
i := strings.IndexRune(line, r.Comma)
var field string
if i >= 0 {
field = line[:i]
} else {
field = line
}
// Check to make sure a quote does not appear in field.
if !r.LazyQuotes {
if j := strings.IndexRune(field, '"'); j >= 0 {
return nil, parseErr(pos+j, csv.ErrBareQuote)
}
}
dst = append(dst, field)
if i >= 0 {
line = line[i+commaLen:]
pos += i + commaLen
continue
}
break
}
// Quoted string field
line = line[quoteLen:]
pos += quoteLen
halfOpen := false
for {
i := strings.IndexRune(line, '"')
if i >= 0 {
// Hit next quote.
if !halfOpen {
dst = append(dst, line[:i])
} else {
appendToLast(dst, line[:i])
}
halfOpen = false
line = line[i+quoteLen:]
pos += i + quoteLen
switch rn := nextRune(line); {
case rn == '"':
// `""` sequence (append quote).
appendToLast(dst, "\"")
line = line[quoteLen:]
pos += quoteLen
halfOpen = true
case rn == r.Comma:
// `",` sequence (end of field).
line = line[commaLen:]
pos += commaLen
continue parseField
case len(line) == 0:
break parseField
case r.LazyQuotes:
// `"` sequence (bare quote).
appendToLast(dst, "\"")
halfOpen = true
default:
// `"*` sequence (invalid non-escaped quote).
return nil, parseErr(pos-quoteLen, csv.ErrQuote)
}
} else {
if !r.LazyQuotes {
return nil, parseErr(pos, csv.ErrQuote)
}
// Hit end of line (copy all data so far).
dst = append(dst, line)
break parseField
}
}
}
return dst, nil
}
func validDelim(r rune) bool {
return r != 0 && r != '"' && r != '\r' && r != '\n' && utf8.ValidRune(r) && r != utf8.RuneError
}
func appendToLast(dst []string, s string) {
dst[len(dst)-1] += s
}
func nextRune(b string) rune {
r, _ := utf8.DecodeRuneInString(b)
return r
}
func parseErr(pos int, err error) error {
return &csv.ParseError{StartLine: 1, Line: 1, Column: pos + 1, Err: err}
}
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