Proper JSON Escaping in Clojure API

Question

I have a Clojure function that writes out the contents of a vector of URLs to JSON, and returns this from an API endpoint. This endpoint data is read by an Elm JSON Decoder on a frontend app. Running this Clojure function directly gives me the following:

(json/write-str ["http://www.example.com?param=value" "http://www.example2.com?param=value"])

Which returns:

"[\"http:\\/\\/www.example.com?param=value\",\"http:\\/\\/www.example2.com?param=value\"]"

Wonderful! If I input this result directly into an Elm Decoder such as this:

stringArrayDecoder : Json.Decoder.Decoder (List String)
stringArrayDecoder =
Json.Decoder.list Json.Decoder.string

It parses it happily with no error.

However, when I view the JSON response from the endpoint, it is losing some of the escaping and I get this:

["http:\/\/www.example.com?param=value","http:\/\/www.example2.com?param=value"]

Which my Elm decoder cannot read.

How do I avoid this? How can I get the fully escaped JSON values produced by my internal function through the API endpoint and into my Elm frontend Decoder?

Remy · Accepted Answer · 2020-09-16 07:12:44Z

4

JSON allows you to escape forward slashes / and other characters as to prevent stuff like </ from popping up in html.

write-str has an :escape-slash boolean option:

:escape-slash boolean

If true (default) the slash / is escaped as \/

Thus you can instead write

(json/write-str ["http://url.one" "http://url.two"] :escape-slash false)
=> "[\"http://url.one\",\"http://url.two\"]"

answered Sep 16, 2020 at 7:12

Remy

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4 Comments

cfrick Over a year ago

Valid workaround - yet i'd like to see this addressed in the elm side if it where my project.

Remy Over a year ago

I tried it out and that Elm decoder works... albeit the error > my = Json.Decode.decodeString (Json.Decode.list Json.Decode.string) j Ok ["example.com?param=value","http://… : Result Json.Decode.Error (List String)

P. Libby Over a year ago

Thank you for your help @Remy. I am able to parse the direct output of that updated write-str command as well, though I'm still seeing the issue I mentioned where it's losing the outside double quotes when returned from the API. I may ask a separate question regarding an Elm decoder that will work for the non-quoted JSON array, or better specifying my issue. However your answer was helpful in its own right so I've marked it as such!

Remy Over a year ago

Ah ok, now I understand the question better. Maybe the confusion is in what write-str actually does, which is different from what an API would return. I'd suggest you use write instead and build your decoder based on that.

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