fexpr 
fexpr is a filter query language parser that generates extremely easy to work with AST structure so that you can create safely SQL, Elasticsearch, etc. queries from user input.
Or in other words, transform the string "id > 1" into the struct [{&& {{identifier id} > {number 1}}}].
Supports parenthesis and various conditional expression operators (see Grammar).
Example usage
go get github.com/ganigeorgiev/fexpr
package main
import github.com/ganigeorgiev/fexpr
func main() {
result, err := fexpr.Parse("id=123 && status='active'")
// result: [{&& {{identifier id} = {number 123}}} {&& {{identifier status} = {text active}}}]
}
Note that each parsed expression statement contains a join/union operator (
&&or||) so that the result can be consumed on small chunks without having to rely on the group/nesting context.
See the package documentation for more details and examples.
Grammar
fexpr grammar resembles the SQL WHERE expression syntax. It recognizes several token types (identifiers, numbers, quoted text, expression operators, whitespaces, etc.).
You could find all supported tokens in
scanner.go.
Operators
=Equal operator (eg.a=b)!=NOT Equal operator (eg.a!=b)>Greater than operator (eg.a>b)>=Greater than or equal operator (eg.a>=b)<Less than or equal operator (eg.a)<=Less than or equal operator (eg.a<=b)~Like/Contains operator (eg.a~b)!~NOT Like/Contains operator (eg.a!~b)&&AND join operator (eg.a=b && c=d)||OR join operator (eg.a=b || c=d)()Parenthesis (eg.(a=1 && b=2) || (a=3 && b=4))
Numbers
Number tokens are any integer or decimal numbers. Example: 123, 10.50.
Identifiers
Identifier tokens are literals that start with a letter, _, @ or # and could contain further any number of digits or . (usually used as a separator). Example: id, a.b.c, @request.method, field2.
Quoted text
Text tokens are any literals that are wrapped by ' or " quotes. Example: 'Lorem ipsum dolor 123!', "escaped \"word\"", "mixed 'quotes' are fine".
Using only the scanner
The tokenizer (aka. fexpr.Scanner) could be used without the parser's state machine so that you can write your own custom tokens processing:
s := fexpr.NewScanner(strings.NewReader("id > 123"))
// scan single token at a time until EOF or error is reached
for {
t, err := s.Scan()
if t.Type == fexpr.TokenEOF || err != nil {
break
}
fmt.Println(t)
}
// Output:
// {identifier id}
// {whitespace }
// {sign >}
// {whitespace }
// {number 123}
5 Dec 12, 2022
100 Dec 22, 2021
0 Jan 7, 2022
2 May 10, 2022
1.4k Jan 1, 2023
0 Feb 2, 2022
148 Dec 1, 2022
35.7k Jan 9, 2023
12 Jun 4, 2019
59 Nov 17, 2022
2k Jan 7, 2023
460 Dec 19, 2022
710 Jan 6, 2023
0 Oct 20, 2021
52 Dec 30, 2022
12 Nov 2, 2022
31 Nov 3, 2022
24 Oct 26, 2022
0 Nov 10, 2021
2.5k Jan 1, 2023
276 Jan 2, 2023
105 Dec 12, 2022
2k Jan 8, 2023
3.9k Jan 2, 2023
260 Dec 31, 2022
58 Dec 20, 2022
22 Jul 10, 2022
0 Jan 8, 2022
0 Dec 29, 2021