update json example and guide info

examples/json/src/main.rs

@@ -1,12 +1,14 @@
 extern crate actix;
 extern crate actix_web;
+extern crate bytes;
 extern crate futures;
 extern crate env_logger;
 extern crate serde_json;
 #[macro_use] extern crate serde_derive;
 
 use actix_web::*;
-use futures::Future;
+use bytes::BytesMut;
+use futures::{Future, Stream};
 
 #[derive(Debug, Serialize, Deserialize)]
 struct MyObj {
@@ -14,8 +16,10 @@ struct MyObj {
     number: i32,
 }
 
+/// This handler uses `HttpRequest::json()` for loading json object.
 fn index(mut req: HttpRequest) -> Box<Future<Item=HttpResponse, Error=Error>> {
-    req.json().from_err()
+    req.json()
+        .from_err()  // convert all errors into `Error`
         .and_then(|val: MyObj| {
             println!("model: {:?}", val);
             Ok(httpcodes::HTTPOk.build().json(val)?)  // <- send response
@@ -23,6 +27,38 @@ fn index(mut req: HttpRequest) -> Box<Future<Item=HttpResponse, Error=Error>> {
         .responder()
 }
 
+
+const MAX_SIZE: usize = 262_144;  // max payload size is 256k
+
+/// This handler manually load request payload and parse json
+fn index_manual(mut req: HttpRequest) -> Box<Future<Item=HttpResponse, Error=Error>> {
+    // readany() returns asynchronous stream of Bytes objects
+    req.payload_mut().readany()
+        // `Future::from_err` acts like `?` in that it coerces the error type from
+        // the future into the final error type
+        .from_err()
+
+        // `fold` will asynchronously read each chunk of the request body and
+        // call supplied closure, then it resolves to result of closure
+        .fold(BytesMut::new(), move |mut body, chunk| {
+            // limit max size of in-memory payload
+            if (body.len() + chunk.len()) > MAX_SIZE {
+                Err(error::ErrorBadRequest("overflow"))
+            } else {
+                body.extend_from_slice(&chunk);
+                Ok(body)
+            }
+        })
+        // `Future::and_then` can be used to merge an asynchronous workflow with a
+        // synchronous workflow
+        .and_then(|body| {
+            // body is loaded, now we can deserialize json
+            let obj = serde_json::from_slice::<MyObj>(&body)?;
+            Ok(httpcodes::HTTPOk.build().json(obj)?) // <- send response
+        })
+        .responder()
+}
+
 fn main() {
     ::std::env::set_var("RUST_LOG", "actix_web=info");
     let _ = env_logger::init();
@@ -32,6 +68,7 @@ fn main() {
         Application::new()
             // enable logger
             .middleware(middlewares::Logger::default())
+            .resource("/manual", |r| r.method(Method::POST).f(index_manual))
             .resource("/", |r| r.method(Method::POST).f(index))})
         .bind("127.0.0.1:8080").unwrap()
         .start();