cdleo / go-sqldb

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.ContainsRune(dec.key, utf8.RuneError) {

					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.ContainsRune(dec.key, utf8.RuneError) {

					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.ContainsRune(dec.key, utf8.RuneError) {

			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)

}