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scanner.go
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scanner.go
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package influxql
import (
"bufio"
"bytes"
"errors"
"fmt"
"io"
"strings"
)
// Scanner represents a lexical scanner for InfluxQL.
type Scanner struct {
r *reader
}
// NewScanner returns a new instance of Scanner.
func NewScanner(r io.Reader) *Scanner {
return &Scanner{r: &reader{r: bufio.NewReader(r)}}
}
// Scan returns the next token and position from the underlying reader.
// Also returns the literal text read for strings, numbers, and duration tokens
// since these token types can have different literal representations.
func (s *Scanner) Scan() (tok Token, pos Pos, lit string) {
// Read next code point.
ch0, pos := s.r.read()
// If we see whitespace then consume all contiguous whitespace.
// If we see a letter, or certain acceptable special characters, then consume
// as an ident or reserved word.
if isWhitespace(ch0) {
return s.scanWhitespace()
} else if isLetter(ch0) || ch0 == '_' {
s.r.unread()
return s.scanIdent()
} else if isDigit(ch0) {
return s.scanNumber()
}
// Otherwise parse individual characters.
switch ch0 {
case eof:
return EOF, pos, ""
case '"':
s.r.unread()
return s.scanIdent()
case '\'':
return s.scanString()
case '.':
ch1, _ := s.r.read()
s.r.unread()
if isDigit(ch1) {
return s.scanNumber()
}
return DOT, pos, ""
case '+', '-':
return s.scanNumber()
case '*':
return MUL, pos, ""
case '/':
return DIV, pos, ""
case '=':
if ch1, _ := s.r.read(); ch1 == '~' {
return EQREGEX, pos, ""
}
s.r.unread()
return EQ, pos, ""
case '!':
if ch1, _ := s.r.read(); ch1 == '=' {
return NEQ, pos, ""
} else if ch1 == '~' {
return NEQREGEX, pos, ""
}
s.r.unread()
case '>':
if ch1, _ := s.r.read(); ch1 == '=' {
return GTE, pos, ""
}
s.r.unread()
return GT, pos, ""
case '<':
if ch1, _ := s.r.read(); ch1 == '=' {
return LTE, pos, ""
} else if ch1 == '>' {
return NEQ, pos, ""
}
s.r.unread()
return LT, pos, ""
case '(':
return LPAREN, pos, ""
case ')':
return RPAREN, pos, ""
case ',':
return COMMA, pos, ""
case ';':
return SEMICOLON, pos, ""
}
return ILLEGAL, pos, string(ch0)
}
// scanWhitespace consumes the current rune and all contiguous whitespace.
func (s *Scanner) scanWhitespace() (tok Token, pos Pos, lit string) {
// Create a buffer and read the current character into it.
var buf bytes.Buffer
ch, pos := s.r.curr()
_, _ = buf.WriteRune(ch)
// Read every subsequent whitespace character into the buffer.
// Non-whitespace characters and EOF will cause the loop to exit.
for {
ch, _ = s.r.read()
if ch == eof {
break
} else if !isWhitespace(ch) {
s.r.unread()
break
} else {
_, _ = buf.WriteRune(ch)
}
}
return WS, pos, buf.String()
}
func (s *Scanner) scanIdent() (tok Token, pos Pos, lit string) {
// Save the starting position of the identifier.
_, pos = s.r.read()
s.r.unread()
var buf bytes.Buffer
for {
if ch, _ := s.r.read(); ch == eof {
break
} else if ch == '"' {
tok0, pos0, lit0 := s.scanString()
if tok0 == BADSTRING || tok0 == BADESCAPE {
return tok0, pos0, lit0
}
return IDENT, pos, lit0
} else if isIdentChar(ch) {
s.r.unread()
buf.WriteString(ScanBareIdent(s.r))
} else {
s.r.unread()
break
}
}
lit = buf.String()
// If the literal matches a keyword then return that keyword.
if tok = Lookup(lit); tok != IDENT {
return tok, pos, ""
}
return IDENT, pos, lit
}
// scanString consumes a contiguous string of non-quote characters.
// Quote characters can be consumed if they're first escaped with a backslash.
func (s *Scanner) scanString() (tok Token, pos Pos, lit string) {
s.r.unread()
_, pos = s.r.curr()
var err error
lit, err = ScanString(s.r)
if err == errBadString {
return BADSTRING, pos, lit
} else if err == errBadEscape {
_, pos = s.r.curr()
return BADESCAPE, pos, lit
}
return STRING, pos, lit
}
func (s *Scanner) ScanRegex() (tok Token, pos Pos, lit string) {
_, pos = s.r.curr()
// Start & end sentinels.
start, end := '/', '/'
// Valid escape chars.
escapes := map[rune]rune{'/': '/'}
b, err := ScanDelimited(s.r, start, end, escapes, true)
if err == errBadEscape {
_, pos = s.r.curr()
return BADESCAPE, pos, lit
} else if err != nil {
return BADREGEX, pos, lit
}
return REGEX, pos, string(b)
}
// scanNumber consumes anything that looks like the start of a number.
// Numbers start with a digit, full stop, plus sign or minus sign.
// This function can return non-number tokens if a scan is a false positive.
// For example, a minus sign followed by a letter will just return a minus sign.
func (s *Scanner) scanNumber() (tok Token, pos Pos, lit string) {
var buf bytes.Buffer
// Check if the initial rune is a "+" or "-".
ch, pos := s.r.curr()
if ch == '+' || ch == '-' {
// Peek at the next two runes.
ch1, _ := s.r.read()
ch2, _ := s.r.read()
s.r.unread()
s.r.unread()
// This rune must be followed by a digit or a full stop and a digit.
if isDigit(ch1) || (ch1 == '.' && isDigit(ch2)) {
_, _ = buf.WriteRune(ch)
} else if ch == '+' {
return ADD, pos, ""
} else if ch == '-' {
return SUB, pos, ""
}
} else if ch == '.' {
// Peek and see if the next rune is a digit.
ch1, _ := s.r.read()
s.r.unread()
if !isDigit(ch1) {
return ILLEGAL, pos, "."
}
// Unread the full stop so we can read it later.
s.r.unread()
} else {
s.r.unread()
}
// Read as many digits as possible.
_, _ = buf.WriteString(s.scanDigits())
// If next code points are a full stop and digit then consume them.
if ch0, _ := s.r.read(); ch0 == '.' {
if ch1, _ := s.r.read(); isDigit(ch1) {
_, _ = buf.WriteRune(ch0)
_, _ = buf.WriteRune(ch1)
_, _ = buf.WriteString(s.scanDigits())
} else {
s.r.unread()
s.r.unread()
}
} else {
s.r.unread()
}
// Attempt to read as a duration if it doesn't have a fractional part.
if !strings.Contains(buf.String(), ".") {
// If the next rune is a duration unit (u,µ,ms,s) then return a duration token
if ch0, _ := s.r.read(); ch0 == 'u' || ch0 == 'µ' || ch0 == 's' || ch0 == 'h' || ch0 == 'd' || ch0 == 'w' {
_, _ = buf.WriteRune(ch0)
return DURATION_VAL, pos, buf.String()
} else if ch0 == 'm' {
_, _ = buf.WriteRune(ch0)
if ch1, _ := s.r.read(); ch1 == 's' {
_, _ = buf.WriteRune(ch1)
} else {
s.r.unread()
}
return DURATION_VAL, pos, buf.String()
}
s.r.unread()
}
return NUMBER, pos, buf.String()
}
// scanDigits consume a contiguous series of digits.
func (s *Scanner) scanDigits() string {
var buf bytes.Buffer
for {
ch, _ := s.r.read()
if !isDigit(ch) {
s.r.unread()
break
}
_, _ = buf.WriteRune(ch)
}
return buf.String()
}
// isWhitespace returns true if the rune is a space, tab, or newline.
func isWhitespace(ch rune) bool { return ch == ' ' || ch == '\t' || ch == '\n' }
// isLetter returns true if the rune is a letter.
func isLetter(ch rune) bool { return (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') }
// isDigit returns true if the rune is a digit.
func isDigit(ch rune) bool { return (ch >= '0' && ch <= '9') }
// isIdentChar returns true if the rune can be used in an unquoted identifier.
func isIdentChar(ch rune) bool { return isLetter(ch) || isDigit(ch) || ch == '_' }
// isIdentFirstChar returns true if the rune can be used as the first char in an unquoted identifer.
func isIdentFirstChar(ch rune) bool { return isLetter(ch) || ch == '_' }
// bufScanner represents a wrapper for scanner to add a buffer.
// It provides a fixed-length circular buffer that can be unread.
type bufScanner struct {
s *Scanner
i int // buffer index
n int // buffer size
buf [3]struct {
tok Token
pos Pos
lit string
}
}
// newBufScanner returns a new buffered scanner for a reader.
func newBufScanner(r io.Reader) *bufScanner {
return &bufScanner{s: NewScanner(r)}
}
// Scan reads the next token from the scanner.
func (s *bufScanner) Scan() (tok Token, pos Pos, lit string) {
return s.scanFunc(s.s.Scan)
}
// ScanRegex reads a regex token from the scanner.
func (s *bufScanner) ScanRegex() (tok Token, pos Pos, lit string) {
return s.scanFunc(s.s.ScanRegex)
}
// scanFunc uses the provided function to scan the next token.
func (s *bufScanner) scanFunc(scan func() (Token, Pos, string)) (tok Token, pos Pos, lit string) {
// If we have unread tokens then read them off the buffer first.
if s.n > 0 {
s.n--
return s.curr()
}
// Move buffer position forward and save the token.
s.i = (s.i + 1) % len(s.buf)
buf := &s.buf[s.i]
buf.tok, buf.pos, buf.lit = scan()
return s.curr()
}
// Unscan pushes the previously token back onto the buffer.
func (s *bufScanner) Unscan() { s.n++ }
// curr returns the last read token.
func (s *bufScanner) curr() (tok Token, pos Pos, lit string) {
buf := &s.buf[(s.i-s.n+len(s.buf))%len(s.buf)]
return buf.tok, buf.pos, buf.lit
}
// reader represents a buffered rune reader used by the scanner.
// It provides a fixed-length circular buffer that can be unread.
type reader struct {
r io.RuneScanner
i int // buffer index
n int // buffer char count
pos Pos // last read rune position
buf [3]struct {
ch rune
pos Pos
}
eof bool // true if reader has ever seen eof.
}
// ReadRune reads the next rune from the reader.
// This is a wrapper function to implement the io.RuneReader interface.
// Note that this function does not return size.
func (r *reader) ReadRune() (ch rune, size int, err error) {
ch, _ = r.read()
if ch == eof {
err = io.EOF
}
return
}
// UnreadRune pushes the previously read rune back onto the buffer.
// This is a wrapper function to implement the io.RuneScanner interface.
func (r *reader) UnreadRune() error {
r.unread()
return nil
}
// read reads the next rune from the reader.
func (r *reader) read() (ch rune, pos Pos) {
// If we have unread characters then read them off the buffer first.
if r.n > 0 {
r.n--
return r.curr()
}
// Read next rune from underlying reader.
// Any error (including io.EOF) should return as EOF.
ch, _, err := r.r.ReadRune()
if err != nil {
ch = eof
} else if ch == '\r' {
if ch, _, err := r.r.ReadRune(); err != nil {
// nop
} else if ch != '\n' {
_ = r.r.UnreadRune()
}
ch = '\n'
}
// Save character and position to the buffer.
r.i = (r.i + 1) % len(r.buf)
buf := &r.buf[r.i]
buf.ch, buf.pos = ch, r.pos
// Update position.
// Only count EOF once.
if ch == '\n' {
r.pos.Line++
r.pos.Char = 0
} else if !r.eof {
r.pos.Char++
}
// Mark the reader as EOF.
// This is used so we don't double count EOF characters.
if ch == eof {
r.eof = true
}
return r.curr()
}
// unread pushes the previously read rune back onto the buffer.
func (r *reader) unread() {
r.n++
}
// curr returns the last read character and position.
func (r *reader) curr() (ch rune, pos Pos) {
i := (r.i - r.n + len(r.buf)) % len(r.buf)
buf := &r.buf[i]
return buf.ch, buf.pos
}
// eof is a marker code point to signify that the reader can't read any more.
const eof = rune(0)
func ScanDelimited(r io.RuneScanner, start, end rune, escapes map[rune]rune, escapesPassThru bool) ([]byte, error) {
// Scan start delimiter.
if ch, _, err := r.ReadRune(); err != nil {
return nil, err
} else if ch != start {
return nil, fmt.Errorf("expected %s; found %s", string(start), string(ch))
}
var buf bytes.Buffer
for {
ch0, _, err := r.ReadRune()
if ch0 == end {
return buf.Bytes(), nil
} else if err != nil {
return buf.Bytes(), err
} else if ch0 == '\n' {
return nil, errors.New("delimited text contains new line")
} else if ch0 == '\\' {
// If the next character is an escape then write the escaped char.
// If it's not a valid escape then return an error.
ch1, _, err := r.ReadRune()
if err != nil {
return nil, err
}
c, ok := escapes[ch1]
if !ok {
if escapesPassThru {
// Unread ch1 (char after the \)
_ = r.UnreadRune()
// Write ch0 (\) to the output buffer.
_, _ = buf.WriteRune(ch0)
continue
} else {
buf.Reset()
_, _ = buf.WriteRune(ch0)
_, _ = buf.WriteRune(ch1)
return buf.Bytes(), errBadEscape
}
}
_, _ = buf.WriteRune(c)
} else {
_, _ = buf.WriteRune(ch0)
}
}
}
// ScanString reads a quoted string from a rune reader.
func ScanString(r io.RuneScanner) (string, error) {
ending, _, err := r.ReadRune()
if err != nil {
return "", errBadString
}
var buf bytes.Buffer
for {
ch0, _, err := r.ReadRune()
if ch0 == ending {
return buf.String(), nil
} else if err != nil || ch0 == '\n' {
return buf.String(), errBadString
} else if ch0 == '\\' {
// If the next character is an escape then write the escaped char.
// If it's not a valid escape then return an error.
ch1, _, _ := r.ReadRune()
if ch1 == 'n' {
_, _ = buf.WriteRune('\n')
} else if ch1 == '\\' {
_, _ = buf.WriteRune('\\')
} else if ch1 == '"' {
_, _ = buf.WriteRune('"')
} else if ch1 == '\'' {
_, _ = buf.WriteRune('\'')
} else {
return string(ch0) + string(ch1), errBadEscape
}
} else {
_, _ = buf.WriteRune(ch0)
}
}
}
var errBadString = errors.New("bad string")
var errBadEscape = errors.New("bad escape")
var errBadRegex = errors.New("bad regex")
// ScanBareIdent reads bare identifier from a rune reader.
func ScanBareIdent(r io.RuneScanner) string {
// Read every ident character into the buffer.
// Non-ident characters and EOF will cause the loop to exit.
var buf bytes.Buffer
for {
ch, _, err := r.ReadRune()
if err != nil {
break
} else if !isIdentChar(ch) {
r.UnreadRune()
break
} else {
_, _ = buf.WriteRune(ch)
}
}
return buf.String()
}
var errInvalidIdentifier = errors.New("invalid identifier")
// IsRegexOp returns true if the operator accepts a regex operand.
func IsRegexOp(t Token) bool {
return (t == EQREGEX || t == NEQREGEX)
}
// assert will panic with a given formatted message if the given condition is false.
func assert(condition bool, msg string, v ...interface{}) {
if !condition {
panic(fmt.Sprintf("assert failed: "+msg, v...))
}
}