caddy/caddyconfig/caddyfile/lexer.go

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// Copyright 2015 Matthew Holt and The Caddy Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package caddyfile
import (
"bufio"
"bytes"
"fmt"
"io"
"regexp"
"strings"
"unicode"
)
type (
// lexer is a utility which can get values, token by
// token, from a Reader. A token is a word, and tokens
// are separated by whitespace. A word can be enclosed
// in quotes if it contains whitespace.
lexer struct {
reader *bufio.Reader
token Token
line int
skippedLines int
}
// Token represents a single parsable unit.
Token struct {
File string
imports []string
Line int
Text string
wasQuoted rune // enclosing quote character, if any
heredocMarker string
snippetName string
}
)
// Tokenize takes bytes as input and lexes it into
// a list of tokens that can be parsed as a Caddyfile.
// Also takes a filename to fill the token's File as
// the source of the tokens, which is important to
// determine relative paths for `import` directives.
func Tokenize(input []byte, filename string) ([]Token, error) {
l := lexer{}
if err := l.load(bytes.NewReader(input)); err != nil {
return nil, err
}
var tokens []Token
for {
found, err := l.next()
if err != nil {
return nil, err
}
if !found {
break
}
l.token.File = filename
tokens = append(tokens, l.token)
}
return tokens, nil
}
// load prepares the lexer to scan an input for tokens.
// It discards any leading byte order mark.
func (l *lexer) load(input io.Reader) error {
l.reader = bufio.NewReader(input)
l.line = 1
// discard byte order mark, if present
firstCh, _, err := l.reader.ReadRune()
if err != nil {
return err
}
if firstCh != 0xFEFF {
err := l.reader.UnreadRune()
if err != nil {
return err
}
}
return nil
}
// next loads the next token into the lexer.
// A token is delimited by whitespace, unless
// the token starts with a quotes character (")
// in which case the token goes until the closing
// quotes (the enclosing quotes are not included).
// Inside quoted strings, quotes may be escaped
// with a preceding \ character. No other chars
// may be escaped. The rest of the line is skipped
// if a "#" character is read in. Returns true if
// a token was loaded; false otherwise.
func (l *lexer) next() (bool, error) {
var val []rune
var comment, quoted, btQuoted, inHeredoc, heredocEscaped, escaped bool
var heredocMarker string
makeToken := func(quoted rune) bool {
l.token.Text = string(val)
l.token.wasQuoted = quoted
l.token.heredocMarker = heredocMarker
return true
}
for {
// Read a character in; if err then if we had
// read some characters, make a token. If we
// reached EOF, then no more tokens to read.
// If no EOF, then we had a problem.
ch, _, err := l.reader.ReadRune()
if err != nil {
if len(val) > 0 {
if inHeredoc {
return false, fmt.Errorf("incomplete heredoc <<%s on line #%d, expected ending marker %s", heredocMarker, l.line+l.skippedLines, heredocMarker)
}
return makeToken(0), nil
}
if err == io.EOF {
return false, nil
}
return false, err
}
// detect whether we have the start of a heredoc
if !inHeredoc && !heredocEscaped && len(val) > 1 && string(val[:2]) == "<<" {
if ch == '<' {
return false, fmt.Errorf("too many '<' for heredoc on line #%d; only use two, for example <<END", l.line)
}
if ch == '\r' {
continue
}
// after hitting a newline, we know that the heredoc marker
// is the characters after the two << and the newline.
// we reset the val because the heredoc is syntax we don't
// want to keep.
if ch == '\n' {
heredocMarker = string(val[2:])
if !heredocMarkerRegexp.Match([]byte(heredocMarker)) {
return false, fmt.Errorf("heredoc marker on line #%d must contain only alpha-numeric characters, dashes and underscores; got '%s'", l.line, heredocMarker)
}
inHeredoc = true
l.skippedLines++
val = nil
continue
}
val = append(val, ch)
continue
}
// if we're in a heredoc, all characters are read as-is
if inHeredoc {
val = append(val, ch)
if ch == '\n' {
l.skippedLines++
}
// check if we're done, i.e. that the last few characters are the marker
if len(val) > len(heredocMarker) && heredocMarker == string(val[len(val)-len(heredocMarker):]) {
// set the final value
val, err = l.finalizeHeredoc(val, heredocMarker)
if err != nil {
return false, err
}
// set the line counter, and make the token
l.line += l.skippedLines
l.skippedLines = 0
return makeToken('<'), nil
}
// stay in the heredoc until we find the ending marker
continue
}
// track whether we found an escape '\' for the next
// iteration to be contextually aware
if !escaped && !btQuoted && ch == '\\' {
escaped = true
continue
}
if quoted || btQuoted {
if quoted && escaped {
// all is literal in quoted area,
// so only escape quotes
if ch != '"' {
val = append(val, '\\')
}
escaped = false
} else {
if (quoted && ch == '"') || (btQuoted && ch == '`') {
return makeToken(ch), nil
}
}
// allow quoted text to wrap continue on multiple lines
if ch == '\n' {
l.line += 1 + l.skippedLines
l.skippedLines = 0
}
// collect this character as part of the quoted token
val = append(val, ch)
continue
}
if unicode.IsSpace(ch) {
// ignore CR altogether, we only actually care about LF (\n)
if ch == '\r' {
continue
}
// end of the line
if ch == '\n' {
// newlines can be escaped to chain arguments
// onto multiple lines; else, increment the line count
if escaped {
l.skippedLines++
escaped = false
} else {
l.line += 1 + l.skippedLines
l.skippedLines = 0
}
// comments (#) are single-line only
comment = false
}
// any kind of space means we're at the end of this token
if len(val) > 0 {
return makeToken(0), nil
}
continue
}
// comments must be at the start of a token,
// in other words, preceded by space or newline
if ch == '#' && len(val) == 0 {
comment = true
}
if comment {
continue
}
if len(val) == 0 {
l.token = Token{Line: l.line}
if ch == '"' {
quoted = true
continue
}
if ch == '`' {
btQuoted = true
continue
}
}
if escaped {
// allow escaping the first < to skip the heredoc syntax
if ch == '<' {
heredocEscaped = true
} else {
val = append(val, '\\')
}
escaped = false
}
val = append(val, ch)
}
}
// finalizeHeredoc takes the runes read as the heredoc text and the marker,
// and processes the text to strip leading whitespace, returning the final
// value without the leading whitespace.
func (l *lexer) finalizeHeredoc(val []rune, marker string) ([]rune, error) {
stringVal := string(val)
// find the last newline of the heredoc, which is where the contents end
lastNewline := strings.LastIndex(stringVal, "\n")
// collapse the content, then split into separate lines
lines := strings.Split(stringVal[:lastNewline+1], "\n")
// figure out how much whitespace we need to strip from the front of every line
// by getting the string that precedes the marker, on the last line
paddingToStrip := stringVal[lastNewline+1 : len(stringVal)-len(marker)]
// iterate over each line and strip the whitespace from the front
var out string
for lineNum, lineText := range lines[:len(lines)-1] {
// find an exact match for the padding
index := strings.Index(lineText, paddingToStrip)
// if the padding doesn't match exactly at the start then we can't safely strip
if index != 0 {
return nil, fmt.Errorf("mismatched leading whitespace in heredoc <<%s on line #%d [%s], expected whitespace [%s] to match the closing marker", marker, l.line+lineNum+1, lineText, paddingToStrip)
}
// strip, then append the line, with the newline, to the output.
// also removes all "\r" because Windows.
out += strings.ReplaceAll(lineText[len(paddingToStrip):]+"\n", "\r", "")
}
// Remove the trailing newline from the loop
if len(out) > 0 && out[len(out)-1] == '\n' {
out = out[:len(out)-1]
}
// return the final value
return []rune(out), nil
}
func (t Token) Quoted() bool {
return t.wasQuoted > 0
}
// NumLineBreaks counts how many line breaks are in the token text.
func (t Token) NumLineBreaks() int {
lineBreaks := strings.Count(t.Text, "\n")
if t.wasQuoted == '<' {
// heredocs have an extra linebreak because the opening
// delimiter is on its own line and is not included in the
// token Text itself, and the trailing newline is removed.
lineBreaks += 2
}
return lineBreaks
}
var heredocMarkerRegexp = regexp.MustCompile("^[A-Za-z0-9_-]+$")
// isNextOnNewLine tests whether t2 is on a different line from t1
func isNextOnNewLine(t1, t2 Token) bool {
// If the second token is from a different file,
// we can assume it's from a different line
if t1.File != t2.File {
return true
}
// If the second token is from a different import chain,
// we can assume it's from a different line
if len(t1.imports) != len(t2.imports) {
return true
}
for i, im := range t1.imports {
if im != t2.imports[i] {
return true
}
}
// If the first token (incl line breaks) ends
// on a line earlier than the next token,
// then the second token is on a new line
return t1.Line+t1.NumLineBreaks() < t2.Line
}