fts5query.go

package main

import (
	"errors"
)

const (
	NONE = '\000'
	WS   = '\001' // ASCII SOH standing in for WS word separator
)

// Convert a Google search like query into a FTS5 query, i.e. to not
// trigger the column filter misfeature. We don't try to make invalid queries
// work, just make queries that would be interpreted as column filters or the
// like work.
//
// based on: https://github.com/fazalmajid/temboz/blob/master/tembozapp/fts5.py
//
// EBNF:
// query = word
// word = [not space]+
// query = phrase
// phrase = '"' [^"]* '"'
// query = "(" query ")"
// query = query "AND" query
// query = query "OR" query
// query = "NOT" query
func fts5_term(term string) (string, error) {
	in_q := false
	implicit_q := false
	out := ""
	expect := '\000'
	pending := ""
	for _, c := range term {
		if c == '\'' { // SQL injection guard
			if pending != "" {
				if !implicit_q {
					out = out + "\""
					implicit_q = true
				}
				out = out + pending
				pending = ""
			}
			out = out + "''"
			continue
		}
		if expect != NONE {
			if in_q {
				return "", errors.New("query parse error 1")
			}
			if (expect == WS && (c != ' ' && c != '\t' && c != '\n' && c != '(' && c != '"')) || (expect != WS && c != expect) {
				out = out + "\"" + pending
				implicit_q = true
				expect = NONE
				pending = ""
			} else if expect == WS {
				out = out + pending
				expect = NONE
				pending = ""
			} else {
				pending = pending + string(c)
				switch expect {
				case 'N':
					expect = 'D'
				case 'O':
					expect = 'T'
				case 'D', 'R', 'T':
					expect = WS
				default:
					return "", errors.New("query parse error 3")
				}
				continue
			}
		}
		if c == '"' {
			if implicit_q {
				implicit_q = false
				in_q = true
			} else {
				in_q = !in_q
				out = out + string(c)
			}
		} else if !in_q && !implicit_q && (c == 'A' || c == 'O' || c == 'N') {
			// start of AND, OR or NOT
			switch c {
			case 'A':
				expect = 'N'
			case 'O':
				expect = 'R'
			case 'N':
				expect = 'O'
			default:
				return "", errors.New("query parse error 4")
			}
			pending = string(c)
		} else if c == ' ' || c == '\t' || c == '\n' || c == '(' || c == ')' {
			if implicit_q {
				out = out + "\""
				implicit_q = false
				in_q = false
			}
			out = out + string(c)
		} else {
			if in_q || implicit_q {
				out = out + string(c)
			} else {
				in_q = true
				implicit_q = true
				out = out + "\"" + string(c)
			}
		}
	}
	out = out + pending
	if in_q || implicit_q {
		out = out + "\""
	}
	return out, nil
}