Add FromResponse trait and ParseError

src/client/from_response.rs

@@ -0,0 +1,45 @@
+use std::error::Error;
+use std::fmt;
+
+use rustc_serialize::json::Json;
+
+/// Response parsing.
+pub trait FromResponse: Sized {
+    /// Parse a JSON response.
+    fn from_response(json: &Json) -> Result<Self, ParseError>;
+}
+
+/// Response parse errors.
+#[derive(Debug)]
+pub enum ParseError {
+    /// Expected response to be of type.
+    ExpectedType(&'static str),
+
+    /// Expected field to be of type.
+    ExpectedFieldType(&'static str, &'static str),
+
+    /// Expected field to equal value.
+    ExpectedFieldValue(&'static str, &'static str),
+
+    /// Expected field to not be present.
+    UnexpectedField(&'static str),
+}
+
+impl fmt::Display for ParseError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        match *self {
+            ParseError::ExpectedType(t) =>
+                write!(f, "Expected response of type {}", t),
+            ParseError::ExpectedFieldType(k, t) =>
+                write!(f, "Expected field {} of type {}", k, t),
+            ParseError::ExpectedFieldValue(k, v) =>
+                write!(f, "Expected field {} to equal {}", k, v),
+            ParseError::UnexpectedField(k) =>
+                write!(f, "Unexpected field {}", k),
+        }
+    }
+}
+
+impl Error for ParseError {
+    fn description(&self) -> &str { "response parse error" }
+}

src/client/mod.rs

@@ -7,6 +7,9 @@ use url::{self, form_urlencoded, Url};
 
 use provider::Provider;
 
+pub use self::from_response::{FromResponse, ParseError};
+mod from_response;
+
 /// OAuth 2.0 client.
 pub struct Client<P: Provider> {
     http_client: hyper::Client,