+++ /dev/null
-/*
- Based on the "jsonpath" spec/concept.
-
- http://goessner.net/articles/JsonPath/
- https://code.google.com/p/json-path/
-*/
-
-package query
-
-import (
- "fmt"
-)
-
-const maxInt = int(^uint(0) >> 1)
-
-type queryParser struct {
- flow chan token
- tokensBuffer []token
- query *Query
- union []pathFn
- err error
-}
-
-type queryParserStateFn func() queryParserStateFn
-
-// Formats and panics an error message based on a token
-func (p *queryParser) parseError(tok *token, msg string, args ...interface{}) queryParserStateFn {
- p.err = fmt.Errorf(tok.Position.String()+": "+msg, args...)
- return nil // trigger parse to end
-}
-
-func (p *queryParser) run() {
- for state := p.parseStart; state != nil; {
- state = state()
- }
-}
-
-func (p *queryParser) backup(tok *token) {
- p.tokensBuffer = append(p.tokensBuffer, *tok)
-}
-
-func (p *queryParser) peek() *token {
- if len(p.tokensBuffer) != 0 {
- return &(p.tokensBuffer[0])
- }
-
- tok, ok := <-p.flow
- if !ok {
- return nil
- }
- p.backup(&tok)
- return &tok
-}
-
-func (p *queryParser) lookahead(types ...tokenType) bool {
- result := true
- buffer := []token{}
-
- for _, typ := range types {
- tok := p.getToken()
- if tok == nil {
- result = false
- break
- }
- buffer = append(buffer, *tok)
- if tok.typ != typ {
- result = false
- break
- }
- }
- // add the tokens back to the buffer, and return
- p.tokensBuffer = append(p.tokensBuffer, buffer...)
- return result
-}
-
-func (p *queryParser) getToken() *token {
- if len(p.tokensBuffer) != 0 {
- tok := p.tokensBuffer[0]
- p.tokensBuffer = p.tokensBuffer[1:]
- return &tok
- }
- tok, ok := <-p.flow
- if !ok {
- return nil
- }
- return &tok
-}
-
-func (p *queryParser) parseStart() queryParserStateFn {
- tok := p.getToken()
-
- if tok == nil || tok.typ == tokenEOF {
- return nil
- }
-
- if tok.typ != tokenDollar {
- return p.parseError(tok, "Expected '$' at start of expression")
- }
-
- return p.parseMatchExpr
-}
-
-// handle '.' prefix, '[]', and '..'
-func (p *queryParser) parseMatchExpr() queryParserStateFn {
- tok := p.getToken()
- switch tok.typ {
- case tokenDotDot:
- p.query.appendPath(&matchRecursiveFn{})
- // nested parse for '..'
- tok := p.getToken()
- switch tok.typ {
- case tokenKey:
- p.query.appendPath(newMatchKeyFn(tok.val))
- return p.parseMatchExpr
- case tokenLeftBracket:
- return p.parseBracketExpr
- case tokenStar:
- // do nothing - the recursive predicate is enough
- return p.parseMatchExpr
- }
-
- case tokenDot:
- // nested parse for '.'
- tok := p.getToken()
- switch tok.typ {
- case tokenKey:
- p.query.appendPath(newMatchKeyFn(tok.val))
- return p.parseMatchExpr
- case tokenStar:
- p.query.appendPath(&matchAnyFn{})
- return p.parseMatchExpr
- }
-
- case tokenLeftBracket:
- return p.parseBracketExpr
-
- case tokenEOF:
- return nil // allow EOF at this stage
- }
- return p.parseError(tok, "expected match expression")
-}
-
-func (p *queryParser) parseBracketExpr() queryParserStateFn {
- if p.lookahead(tokenInteger, tokenColon) {
- return p.parseSliceExpr
- }
- if p.peek().typ == tokenColon {
- return p.parseSliceExpr
- }
- return p.parseUnionExpr
-}
-
-func (p *queryParser) parseUnionExpr() queryParserStateFn {
- var tok *token
-
- // this state can be traversed after some sub-expressions
- // so be careful when setting up state in the parser
- if p.union == nil {
- p.union = []pathFn{}
- }
-
-loop: // labeled loop for easy breaking
- for {
- if len(p.union) > 0 {
- // parse delimiter or terminator
- tok = p.getToken()
- switch tok.typ {
- case tokenComma:
- // do nothing
- case tokenRightBracket:
- break loop
- default:
- return p.parseError(tok, "expected ',' or ']', not '%s'", tok.val)
- }
- }
-
- // parse sub expression
- tok = p.getToken()
- switch tok.typ {
- case tokenInteger:
- p.union = append(p.union, newMatchIndexFn(tok.Int()))
- case tokenKey:
- p.union = append(p.union, newMatchKeyFn(tok.val))
- case tokenString:
- p.union = append(p.union, newMatchKeyFn(tok.val))
- case tokenQuestion:
- return p.parseFilterExpr
- default:
- return p.parseError(tok, "expected union sub expression, not '%s', %d", tok.val, len(p.union))
- }
- }
-
- // if there is only one sub-expression, use that instead
- if len(p.union) == 1 {
- p.query.appendPath(p.union[0])
- } else {
- p.query.appendPath(&matchUnionFn{p.union})
- }
-
- p.union = nil // clear out state
- return p.parseMatchExpr
-}
-
-func (p *queryParser) parseSliceExpr() queryParserStateFn {
- // init slice to grab all elements
- start, end, step := 0, maxInt, 1
-
- // parse optional start
- tok := p.getToken()
- if tok.typ == tokenInteger {
- start = tok.Int()
- tok = p.getToken()
- }
- if tok.typ != tokenColon {
- return p.parseError(tok, "expected ':'")
- }
-
- // parse optional end
- tok = p.getToken()
- if tok.typ == tokenInteger {
- end = tok.Int()
- tok = p.getToken()
- }
- if tok.typ == tokenRightBracket {
- p.query.appendPath(newMatchSliceFn(start, end, step))
- return p.parseMatchExpr
- }
- if tok.typ != tokenColon {
- return p.parseError(tok, "expected ']' or ':'")
- }
-
- // parse optional step
- tok = p.getToken()
- if tok.typ == tokenInteger {
- step = tok.Int()
- if step < 0 {
- return p.parseError(tok, "step must be a positive value")
- }
- tok = p.getToken()
- }
- if tok.typ != tokenRightBracket {
- return p.parseError(tok, "expected ']'")
- }
-
- p.query.appendPath(newMatchSliceFn(start, end, step))
- return p.parseMatchExpr
-}
-
-func (p *queryParser) parseFilterExpr() queryParserStateFn {
- tok := p.getToken()
- if tok.typ != tokenLeftParen {
- return p.parseError(tok, "expected left-parenthesis for filter expression")
- }
- tok = p.getToken()
- if tok.typ != tokenKey && tok.typ != tokenString {
- return p.parseError(tok, "expected key or string for filter function name")
- }
- name := tok.val
- tok = p.getToken()
- if tok.typ != tokenRightParen {
- return p.parseError(tok, "expected right-parenthesis for filter expression")
- }
- p.union = append(p.union, newMatchFilterFn(name, tok.Position))
- return p.parseUnionExpr
-}
-
-func parseQuery(flow chan token) (*Query, error) {
- parser := &queryParser{
- flow: flow,
- tokensBuffer: []token{},
- query: newQuery(),
- }
- parser.run()
- return parser.query, parser.err
-}
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