Crystal string and heredoc with escaped characters for JSON
TLDR: Clarify a problem why some JSON content could be not parsable via directives and how to fix it
Published in
2 min readJul 7, 2022
require "json"pp JSON.parse(%|{"example1": "string without new line"}|)
# > {"example1" => "string without new line"}pp JSON.parse <<-CONTENT
{
"example2": "heredoc without new line"
}
CONTENT
# > {"example2" => "heredoc without new line"}pp JSON.parse(%|{"example3": "string with new line\n"}|)
# > Unhandled exception: Unexpected char '
# ' at line 1, column 35 (JSON::ParseException)pp JSON.parse <<-CONTENT
{
"example4": "heredoc with new line\n"
}
CONTENT
# > Unhandled exception: Unexpected char '
# ' at line 1, column 35 (JSON::ParseException)
Review the command: JSON.parse(%|{“foo”: “string with new line\n”}|) . It produces prase error:
Unhandled exception: Unexpected char '
' at line 1, column 35 (JSON::ParseException)The error printed hidden character as new line. It gave a hint, that something is not escaped. It looks like, JSON does allow to close a string on next lines:
$ echo "{\"foo\": \"string with new line\n\"}" | jq .
parse error: Invalid string: control characters from U+0000 through U+001F must be escaped at line 2, column 1How to fix the problem
A heredoc and string generally allows interpolation and escapes.
Interpolation can be disabled by using a non-interpolating string literal like %q() or escaping backslash \\ .
The opening heredoc identifier is enclosed in single quotes.
pp JSON.parse(%q("example3": "string with new line\n"}))
# > {"example3" => "string with new line\n"}pp JSON.parse <<-'CONTENT'
{
"example4": "heredoc with new line\n"
}
CONTENT
# > {"example4" => "heredoc with new line\n"}
