fix(http client): more user-friendly error messages when decoding fails (#853)

* fix(http client): serde_json::Value -> T

This PR changes the http client to decode the reponse as `Response<serde_json::Value> -> Response<R>`
In order to get a more user-friendly error message

Before:

```
response: Err(ParseError(Error("missing field `error`", line: 1, column: 3752798)))
```

After

```
2022-08-11T13:57:12.033043Z  INFO http: r: Parse error: invalid type: string "lo", expected u8
```

* address grumbles

* Update client/http-client/src/client.rs

* Update client/http-client/src/client.rs

client/http-client/src/client.rs

@@ -35,7 +35,7 @@ use jsonrpsee_core::client::{CertificateStore, ClientT, IdKind, RequestIdManager
 use jsonrpsee_core::params::BatchRequestBuilder;
 use jsonrpsee_core::tracing::RpcTracing;
 use jsonrpsee_core::traits::ToRpcParams;
-use jsonrpsee_core::{Error, TEN_MB_SIZE_BYTES};
+use jsonrpsee_core::{Error, JsonRawValue, TEN_MB_SIZE_BYTES};
 use jsonrpsee_types::error::CallError;
 use rustc_hash::FxHashMap;
 use serde::de::DeserializeOwned;
@@ -216,7 +216,9 @@ impl ClientT for HttpClient {
 				}
 			};
 
-			let response: Response<_> = match serde_json::from_slice(&body) {
+			// NOTE: it's decoded first to `JsonRawValue` and then to `R` below to get
+			// a better error message if `R` couldn't be decoded.
+			let response: Response<&JsonRawValue> = match serde_json::from_slice(&body) {
 				Ok(response) => response,
 				Err(_) => {
 					let err: ErrorResponse = serde_json::from_slice(&body).map_err(Error::ParseError)?;
@@ -224,8 +226,10 @@ impl ClientT for HttpClient {
 				}
 			};
 
+			let result = serde_json::from_str(response.result.get()).map_err(Error::ParseError)?;
+
 			if response.id == id {
-				Ok(response.result)
+				Ok(result)
 			} else {
 				Err(Error::InvalidRequestId)
 			}
@@ -264,7 +268,9 @@ impl ClientT for HttpClient {
 				Ok(Err(e)) => return Err(Error::Transport(e.into())),
 			};
 
-			let rps: Vec<Response<_>> =
+			// NOTE: it's decoded first to `JsonRawValue` and then to `R` below to get
+			// a better error message if `R` couldn't be decoded.
+			let rps: Vec<Response<&JsonRawValue>> =
 				serde_json::from_slice(&body).map_err(|_| match serde_json::from_slice::<ErrorResponse>(&body) {
 					Ok(e) => Error::Call(CallError::Custom(e.error_object().clone().into_owned())),
 					Err(e) => Error::ParseError(e),
@@ -277,7 +283,8 @@ impl ClientT for HttpClient {
 					Some(pos) => *pos,
 					None => return Err(Error::InvalidRequestId),
 				};
-				responses[pos] = rp.result
+				let result = serde_json::from_str(rp.result.get()).map_err(Error::ParseError)?;
+				responses[pos] = result;
 			}
 			Ok(responses)
 		}