Support to read raw json from Decoder object about rustc-serialize

[oli-obk]

I suggest using Json::from_str or from_reader since your issue is Json-specific and and afaik not what Encodable/Decodable are to be used for.

[rohitjoshi]

@oli-obk Issue is with limitation in the Decoder trait interface which doesn't allow to access underneath object for custom manipulation.

I tried using Json::from_str which doesn't work due to json string can have variable type of the value. e.g alert key value could be string or dictionary as per Apple Push Notification specifications.

e.g { "alert" : "Hello world!!" } or { "alert" : {"body": "Hello, world!", "action-loc-key": "Open"} }

I think this can be resolve by 3 way.

1. rustc_serialize::Decoder trait expose a method to return underline type. Not sure Rust would alllow this. e.g fn read<T>(&mut self)-> DecodeResult<T> {}

2. Modify read_str() in json.rs as below which will return string representation of the object

   fn read_str(&mut self) -> DecodeResult<string::String> {
     //expect!(self.pop(), String)
   match self.pop() {
         Json::String(v) => Ok(v),
         value => Ok(value.to_string()),
     }
    }
   

3. Add read_json() method for Decoder implementation for Json

`

impl Decoder {
     fn pop(&mut self) -> Json {
         self.stack.pop().unwrap()
     }
    // new method
     pub fn read_json(&mut self) -> Json {
         self.stack.pop().unwrap()
     }
 }

`

[oli-obk]

even if you use the 3rd version. The Decodable has no access to the actual decoder, only to the trait. Without negative trait bounds this won't work (not sure if it works with them)
The 1st version requires specialization of generics (which would allow a full rewrite to a nicer interface to the serialization lib).
The 2nd version breaks the contract with the function and would only serve your special case.

[rohitjoshi]

@oli-obk Thanks for the details. I am new to Rust and trying to understand.
Regarding 2nd version, instead of modifying existing read_str(), we might want to add read_as_string() which sets expectation of getting converted string response.

[oli-obk]

read_as_string() would not make sense in a binary decoder though. As the Binary might be something not representable as a string.
Basically you should assume that Decoder can only decode types with a derived RustcEncodable trait.

[rohitjoshi]

@oli-obk I guess it would be same issue for existing read_str() method in Decoder trait for binary decoder.

Don't you think suggested option 2 is better which will return string representation of object rather than returning error at runtime.

I wish Rust supported selective override of trait method. :)

[rohitjoshi]

@alexcrichton do you think some support will be added to either pop json object or read_str() will stringify the object and return as string. If you advise me one of these option, I can submit a PR.

[softprops]

was there any resolution on this?

[rohitjoshi]

No but I had forked and implemented custom function.

[alexcrichton]

I'm going to close this now that this crate is deprecated in favor of serde. We're discontinuing feature development in rustc-serialize but will still continue to merge bug fixes if they arise.