Allow more escape runes to be skipped over when parsing string literal.

[hoonmin]

This PR makes Dgraph to allow more escape runes to be skipped over when parsing string literal.

• \v
• \xnn

Description

Hi. I'm trying to upgrade Dgraph to 1.0.10 for HasFunction improvement.
But when bulk-load exported RDF files, we'd got following errors.

2018/11/07 12:41:02 while lexing <_:uid1234> <text> "I'm\x02\vAlice"^^<xs:string> .: Invalid escape character : 'v' in literal
while parsing line "..."
github.com/dgraph-io/dgraph/dgraph/cmd/bulk.(*mapper).processRDF
        /ext-go/1/src/github.com/dgraph-io/dgraph/dgraph/cmd/bulk/mapper.go:188
github.com/dgraph-io/dgraph/dgraph/cmd/bulk.(*mapper).run
        /ext-go/1/src/github.com/dgraph-io/dgraph/dgraph/cmd/bulk/mapper.go:135
github.com/dgraph-io/dgraph/dgraph/cmd/bulk.(*loader).mapStage.func1
        /ext-go/1/src/github.com/dgraph-io/dgraph/dgraph/cmd/bulk/loader.go:237
runtime.goexit
        /usr/local/go/src/runtime/asm_amd64.s:1333

And found that lexLiteral function in state.go validates the escape characters.

if r == '\u005c' { // backslash
    r = l.Next()
    if l.IsEscChar(r) || lex.HasUChars(r, l) {
        continue // This would skip over the escaped rune.
    }
    return l.Errorf("Invalid escape character : '%c' in literal", r)
}

Currently Dgraph allows [tbnrf] characters for escaped runes, but I think 'v' should be added like strconv.
https://golang.org/src/strconv/quote.go

Also, there are chances to store \xnn form of HEX values just like \u or \U.
Actually our Dgraph server have stored them but it doesn't allow \xnn when retrieving.

Please check this out. Thanks!

---

This change is 

[CLAassistant]

All committers have signed the CLA.

[manishrjain]

Thanks for the PR.

Reviewable status: 0 of 4 files reviewed, all discussions resolved