Stingray
Problem with decoding backslash in JSON
I’m faced with a problem in websockets when I received a message with backslash. I escapes backslash with double ‘’ but error is raised.
So I decide to check how Poison lib is working in iex console:
Poison.decode! "{\"string\":\"a\\b\"}"
return me:
%{"string" => "a\b"}
and
Poison.decode! "{\"string\":\"a\\c\"}"
return me:
** (Poison.SyntaxError) Unexpected token: c
but I expect
%{"string" => "a\c"}
What wrong with my string?
Marked As Solved
Marcus
No, that is the representation of the string with the escaped backslash. If you print the string with IO.puts you get a\b.
Try the sigli ~S in iex.
iex(21)> ~S|{"string":"a\\c"}| # generates a string with no escaping
"{\"string\":\"a\\\\c\"}" # the string with escaping
iex(22)> Poison.decode(~S|{"string":"a\\c"}|) # escaped just for the parser
{:ok, %{"string" => "a\\c"}}
iex(23)> ~S|a\c|
"a\\c"
iex(24)> IO.puts("a\\c")
a\c
:ok
Also Liked
talentdeficit
you have two levels of escaping going on. one for iex and one for json
“{“string”:“a\\b”}” in iex is equivalent to the json string ‘{“string”:“a\b”}’ which is the literal character “a” followed by the escape sequence for a backspace
if you want the literal character “a” followed by the literal character “” followed by the literal character “b” you want the string ‘{“string”:“a\\b”}’ which written in iex/elixir is “{“string”:“a\\\\b”}”
arcanemachine
I was confused when this worked, even though I had already tried using the ~s sigil without success.
It turns out that the ~S sigil (with a capital ‘S’) doesn’t do any interpolation and ignores escape codes, which solved the problem for me:
https://hexdocs.pm/elixir/sigils.html#interpolation-and-escaping-in-string-sigils
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