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|
package logfmt
import (
"bufio"
"bytes"
"fmt"
"io"
"unicode/utf8"
)
// A Decoder reads and decodes logfmt records from an input stream.
type Decoder struct {
pos int
key []byte
value []byte
lineNum int
s *bufio.Scanner
err error
}
// NewDecoder returns a new decoder that reads from r.
//
// The decoder introduces its own buffering and may read data from r beyond
// the logfmt records requested.
func NewDecoder(r io.Reader) *Decoder {
dec := &Decoder{
s: bufio.NewScanner(r),
}
return dec
}
// ScanRecord advances the Decoder to the next record, which can then be
// parsed with the ScanKeyval method. It returns false when decoding stops,
// either by reaching the end of the input or an error. After ScanRecord
// returns false, the Err method will return any error that occurred during
// decoding, except that if it was io.EOF, Err will return nil.
func (dec *Decoder) ScanRecord() bool {
if dec.err != nil {
return false
}
if !dec.s.Scan() {
dec.err = dec.s.Err()
return false
}
dec.lineNum++
dec.pos = 0
return true
}
// ScanKeyval advances the Decoder to the next key/value pair of the current
// record, which can then be retrieved with the Key and Value methods. It
// returns false when decoding stops, either by reaching the end of the
// current record or an error.
func (dec *Decoder) ScanKeyval() bool {
dec.key, dec.value = nil, nil
if dec.err != nil {
return false
}
line := dec.s.Bytes()
// garbage
for p, c := range line[dec.pos:] {
if c > ' ' {
dec.pos += p
goto key
}
}
dec.pos = len(line)
return false
key:
const invalidKeyError = "invalid key"
start, multibyte := dec.pos, false
for p, c := range line[dec.pos:] {
switch {
case c == '=':
dec.pos += p
if dec.pos > start {
dec.key = line[start:dec.pos]
if multibyte && bytes.IndexRune(dec.key, utf8.RuneError) != -1 {
dec.syntaxError(invalidKeyError)
return false
}
}
if dec.key == nil {
dec.unexpectedByte(c)
return false
}
goto equal
case c == '"':
dec.pos += p
dec.unexpectedByte(c)
return false
case c <= ' ':
dec.pos += p
if dec.pos > start {
dec.key = line[start:dec.pos]
if multibyte && bytes.IndexRune(dec.key, utf8.RuneError) != -1 {
dec.syntaxError(invalidKeyError)
return false
}
}
return true
case c >= utf8.RuneSelf:
multibyte = true
}
}
dec.pos = len(line)
if dec.pos > start {
dec.key = line[start:dec.pos]
if multibyte && bytes.IndexRune(dec.key, utf8.RuneError) != -1 {
dec.syntaxError(invalidKeyError)
return false
}
}
return true
equal:
dec.pos++
if dec.pos >= len(line) {
return true
}
switch c := line[dec.pos]; {
case c <= ' ':
return true
case c == '"':
goto qvalue
}
// value
start = dec.pos
for p, c := range line[dec.pos:] {
switch {
case c == '=' || c == '"':
dec.pos += p
dec.unexpectedByte(c)
return false
case c <= ' ':
dec.pos += p
if dec.pos > start {
dec.value = line[start:dec.pos]
}
return true
}
}
dec.pos = len(line)
if dec.pos > start {
dec.value = line[start:dec.pos]
}
return true
qvalue:
const (
untermQuote = "unterminated quoted value"
invalidQuote = "invalid quoted value"
)
hasEsc, esc := false, false
start = dec.pos
for p, c := range line[dec.pos+1:] {
switch {
case esc:
esc = false
case c == '\\':
hasEsc, esc = true, true
case c == '"':
dec.pos += p + 2
if hasEsc {
v, ok := unquoteBytes(line[start:dec.pos])
if !ok {
dec.syntaxError(invalidQuote)
return false
}
dec.value = v
} else {
start++
end := dec.pos - 1
if end > start {
dec.value = line[start:end]
}
}
return true
}
}
dec.pos = len(line)
dec.syntaxError(untermQuote)
return false
}
// Key returns the most recent key found by a call to ScanKeyval. The returned
// slice may point to internal buffers and is only valid until the next call
// to ScanRecord. It does no allocation.
func (dec *Decoder) Key() []byte {
return dec.key
}
// Value returns the most recent value found by a call to ScanKeyval. The
// returned slice may point to internal buffers and is only valid until the
// next call to ScanRecord. It does no allocation when the value has no
// escape sequences.
func (dec *Decoder) Value() []byte {
return dec.value
}
// Err returns the first non-EOF error that was encountered by the Scanner.
func (dec *Decoder) Err() error {
return dec.err
}
func (dec *Decoder) syntaxError(msg string) {
dec.err = &SyntaxError{
Msg: msg,
Line: dec.lineNum,
Pos: dec.pos + 1,
}
}
func (dec *Decoder) unexpectedByte(c byte) {
dec.err = &SyntaxError{
Msg: fmt.Sprintf("unexpected %q", c),
Line: dec.lineNum,
Pos: dec.pos + 1,
}
}
// A SyntaxError represents a syntax error in the logfmt input stream.
type SyntaxError struct {
Msg string
Line int
Pos int
}
func (e *SyntaxError) Error() string {
return fmt.Sprintf("logfmt syntax error at pos %d on line %d: %s", e.Pos, e.Line, e.Msg)
}
|
