JsonProvider failed to parse JSON from API written myself - f#

Question

I write an API using springMVC.It's a simple API, I just use it to test JsonProvider.
#ResponseBody
#RequestMapping(value = "/api/test", method = RequestMethod.GET)
public TestClass test(final HttpServletRequest request,
final HttpServletResponse response){
return new TestClass("cc");
}
class TestClass{
public TestClass(){
}
public TestClass(final String name) {
super();
this.name = name;
}
private String name;
public String getName() {
return name;
}
public void setName(final String name) {
this.name = name;
}
}
The API simply returns
But JsonProvider just throws a compile error.
Severity Code Description Project File Line
Error The type provider 'ProviderImplementation.JsonProvider' reported an error: Cannot read sample JSON from 'http://localhost/api/test': Invalid JSON starting at character 0, snippet =
----
"{\"name\":
-----
json =
------
"{\"name\":\"cc\"}"
------- JsonProcess c:\users\xx\documents\visual studio 2015\Projects\JsonProcess\JsonProcess\Program.fs 8
The F# code:
open FSharp.Data
[<Literal>]
let jsonValue = """
{"name":"cc"}
"""
type JsonData = JsonProvider<"http://localhost/api/test">
[<EntryPoint>]
let main argv =
0 // return an integer exit code
Use the String literal jsonValue as sample is ok.type JsonData = JsonProvider<jsonValue>

Answer 1

I checked the FSharp.Data source code (its the function asyncRead) to see how they download the JSON. It basically boils down to this:
let readString =
async {
let contentTypes = [ HttpContentTypes.Json ]
let headers = [
HttpRequestHeaders.UserAgent ("F# Data JSON Type Provider")
HttpRequestHeaders.Accept (String.concat ", " contentTypes)
]
let! text = Http.AsyncRequestString("http://www.kujiale.com/api/askinvitesearch?query=cc", headers = headers)
return text
}
If one runs this code against the url http://www.kujiale.com/api/askinvitesearch?query=cc we see something interesting about what's returned:
"[{\"linkToIdeaBook\":\"/u/3FO4K4UR89F1/huabao\",\"linkToDesi
Note that the content starts with " and that the "strings" are "escaped" with \. So it seems the JSON document is returned as an escaped string. According to json.org the root object must be either an object or array so the parser fails at character 0.
If one switches to contentType HttpContentTypes.Text it starts like this:
[{"linkToIdeaBook":"/u/3FO4K4UR89F1/huabao","linkToDesignCollect":"/u
Which actually turns out to be a valid JSON object.
To me it seems somewhat odd that if you ask for content with content type JSON you get an escaped string but that seems to be the root cause of the failure.
How to resolve it is more difficult to say. One way forward would be a PR to FSharp.Data to allow users to specify the content type used to download content.