ASP.NET Web API and HTTP Fundamentals

ASP.NET Web API
and HTTP Fundamentals
Ido Flatow

Senior Architect
Microsoft MVP
SELA Group

@idoFLATOW
http://bit.ly/flatow-blog

This presentation:
http://sdrv.ms/1eKAsRd

ASP.NET WEB API AND HTTP FUNDAMENTALS

CRAMMING YOUR BRAINS WITH
HTTP & ASP.NET WEB API


HTTP Fundamentals via Web API



Hosting



HTTP Messages



HTTP.SYS



URIs



IIS 101



Routing



HTTP compression



Verbs



Persisted Connections



Controllers and Actions



Web API Self Hosting



Status Codes



HttpRequestMessage
HttpResponseMessage



Error Handling



Content Negotiation



Media Type Formatters



OData



Validations



Dependency Resolver

www.devconnections.com



More HTTP and Web API


Caching



Concurrency



Security



Streaming



WebSockets & SignalR

2


ABOUT ME



Senior architect, Sela Group
Co-author of:






WCF 4 – Microsoft official course





Developing Windows Azure and Web Services –
Microsoft official course
Pro .NET Performance – Apress

Microsoft MVP
Focus on server, services, and cloud
technologies
Manager of the Israeli Web Developers User
Group



WHY IS HTTP IMPORTANT?


HTTP is a first class application layer protocol



Unlike other protocols it was created to
support a single information system



That system happened to be the largest and
main information system of the human race:


4


NO REALLY, WHY?
 Today's




systems face new challenges:

Internet scale applications

Cloud-based applications


5


NO REALLY, WHY?
 Today's


systems face new challenges:

Broader reach of clients


6


WHAT ABOUT ASP.NET WEB API?
 The

.NET platform never had a first class
framework for HTTP-based services

 WCF

was created as a SOAP-based
framework and never really matured to
support HTTP


7


THE HISTORY OF ASP.NET WEB API
6 Preview Versions

WCF Web API
on CodePlex

WCF WebHttp
Binding (.NET 4)


ASP.NET Web API 4
Release

ASP.NET is
Open Source

ASP.NET Web API 2
Release Candidate

ASP.NET Web API
(Beta)

8


HTTP MESSAGES 101
 HTTP

is a first class application protocol:



Widely supported across platforms and devices



Scalable



Simple

 Uses

the request-response messaging pattern

 Define

resource-based semantics and not
RPC (Remote Procedure Call) or methods


9


HTTP REQUEST MESSAGES
GET http://localhost:2300/api/agents/Bond HTTP/1.1
Accept: text/html, application/xhtml+xml, */*
Accept-Language: en-US,en;q=0.7,he;q=0.3
User-Agent: Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2;
WOW64; Trident/6.0)
Accept-Encoding: gzip, deflate
Host: localhost:2300
DNT: 1
Connection: Keep-Alive


10


HTTP RESPONSE MESSAGES
HTTP/1.1 200 OK
Cache-Control: public, max-age=300
Content-Type: application/json; charset=utf-8
ETag: "1"
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
Date: Mon, 19 Nov 2012 17:49:40 GMT
Content-Length: 142
{

}

"Id": "Bond",
"FullName": "James Bond",
"Alias": "007",
"Version": 1,
"Image": "http://localhost:2300/api/agents/Bond.jpg"


11


URIS
 HTTP

is not an RPC protocol

 HTTP

uses URIs to identify resources over
the network

 An

HTTP URI has the following basic
structure:
http://theagency.com:8080/agents?id=1
Schema


Host

Port

Absolute
Path

Query

12


CLEAN URLS AND ASP.NET


Using clean URLs can be a problem with IIS



IIS needs extensions to map requests to handlers



Without extensions, IIS is lost



ASP.NET Routing to the rescue with UrlRoutingModule



It’s all about patterns… and mapping them to handlers



The starting point of MVC, Dynamic Data, and Web API



System.Web.Routing.RouteTable.Routes.MapHttpRoute

RouteTable.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);

13


THE BASICS OF WEB API - ROUTING
DEMO


14


ROUTING WITH ATTRIBUTES
 Why

attributes over convention?



Child (sub) resources



Multiple type of parameters or return values



Versioning of actions and controllers

 Start


by enabling attribute routing

config.MapHttpAttributeRoutes();

[RoutePrefix("api/agents/{agentId}")]
public class ObservationsController : ApiController
{
// GET api/agents/bond/observations
[HttpGet("observations/{date}")]
public Observation Get(string agentId, DateTime date) { ... }
}


15


VERBS
 HTTP

defines a set of Methods or Verbs that
add an action-like semantics to requests

 Verbs

are defined as the first segment of the
request-line:
GET http://localhost:4392/travelers/1 HTTP/1.1

 There

are eight verbs defined in HTTP 1.1:

GET
POST
PUT
DELETE

HEAD
OPTIONS
TRACE
CONNECT
16


3, 2, 1, ACTIONS!
 Actions

are matched by HTTP verb
public names and the existence of parameters
class ProductsController : ApiController
{
public IEnumerable<Product> GetProducts() {...}
public Product GetProductById(int id) {...}
public HttpResponseMessage PostProduct(Product product) {...}
}

GET api/products
GET api/products/42
POST api/products

DELETE api/products/42


HANDLING VERBS IN ASP.NET WEB API
DEMO


18


STATUS CODES


Status codes describe the result of the server’s effort
to satisfy the request



Passed in the response's status-line as three digit
alongside a textual description called reason phrase



HTTP has five different categories of status-codes:


1xx – Informational (100 / 101)



2xx – Success

(200 – 206)



3xx – Redirection

(300 – 307)



4xx – Client Error

(400 – 417)



5xx – Server Error

(500 – 505)


19


STATUS CODE EXAMPLES


404?



401?



304?



503?



500?



200?



301?



302?


20


HTTP RESPONSE MESSAGE
 Returning

an HttpResponseMessage allows
more control over the response, including:


Status code



HTTP headers



Entity body

public HttpResponseMessage CreateAgent(Agent agent)
{
agent = _repository.Add(agent);
var response =
Request.CreateResponse<Agent>(HttpStatusCode.Created, agent);
response.Headers.Location = GetAgentLocation(agent.Id);
return response;
}

21


HANDLING STATUS CODES
DEMO


22


ERROR HANDLING


In HTTP services errors are handled by





Returning an appropriate status code
Returning an entity body explaining the error
(when applicable)

Web API allows you to handle exceptions by


Return an HttpResponseMessage with
appropriate status code (404, 500 …)



Throw an HttpResponseException



Create a general exception handler by using
Filters


23


HANDLING ERRORS
DEMO


24


MEDIA TYPES
 HTTP

was originally designed to transfer
Hypertext

 Hypertext

documents contain references to
other resources including images, video, etc.

 Multipurpose

Internet Mail Extensions (MIME)
Types or Media-types allow HTTP to express
different formats:
text/html; charset=UTF-8
Type


Subtype

Type specific parameters
25


CONTENT NEGOTIATION
 HTTP

defines a process to best match the
server’s response to the client’s expectation

 Negotiation

can be done using:



Headers:
Accept, Accept- Language, Accept- Charset,
Accept-Encoding



URI:
File extensions (.jpeg, .html), host-name: (com, org),
path and query


26


MEDIA TYPE FORMATTERS
 ASP.NET

Web API uses Media Type Formatters to
control serialization

 Each

media type formatter is associated with a
media type, file extension, or query string

 The

host is configured with a collection of
MediaTypeFormatter objects

 Create

custom formatters by deriving from:



MediaTypeFormatter – asynchronous read/write



BufferedMediaTypeFormatter – synchronous read/write


27


CONTENT NEGOTIATION IN WEB API
DEMO


28


VALIDATING USER INPUT


Use System.ComponentModel.DataAnnotations
on entity classes to add validation rules



Validation rules can be check by calling
ModelState.IsValid



When validation fails, return a Bad Request (400)



ModelState is a dictionary of property name &
errors, use it to construct a meaningful response


29


public class Contact {
[Required]
public string FullName { get; set;}
[Email]
public string Email { get; set;}
}
if (!this.ModelState.IsValid) {
var errors = this.ModelState.Where(s => s.Value.Errors.Count > 0)
.Select(s => new KeyValuePair<string, string>
(s.Key, s.Value.Errors.First().ErrorMessage));
response = Request.CreateResponse(
HttpStatusCode.BadRequest, errors);

}


30


DEMO


31


ODATA QUERYABLE ACTIONS
 The

Open Data Protocol (OData) provides a
RESTful standard for exposing data models

 OData

uses URIs to perform query operations:



Entity projection – $select, $expand



Sorting – $orderby



Entity sub-setting – $top, $skip



Filtering – $filter, logical operators: eq, ne, gt, lt


32


DEFINING ODATA ACTIONS


Install the Microsoft.AspNet.WebApi.OData NuGet
package



Define an action with the following characteristics:


Returns IQueryable<T> or IEnumerable<T>



Decorated with the [Queryable] attribute

[Queryable]

public IQueryable<Agent> GetAgents()
{
}


33


WEB API AND ODATA
[Queryable]
public IQueryable<Agent> GetAgents()
{
return repository.GetAll().AsQueryable();
}
api/agents?$orderby=Name
api/agents?$skip=10
api/agents?$skip=50&$top=10

api/agents?$filter=salary gt 50000


ODATA ACTIONS
DEMO


35


ODATA MODELS
 OData

also provides a mechanism for
exposing entity models:


Publishing the models metadata



Exposing relations between entities using the
Atom media-type


36


CREATING AND EXPOSING ODATA
MODELS
 Exposing

an OData model requires the
following configuration:


Creating an EDM model using the
ODataConventionModelBuilder class



Adding a route using the MapODataRoute
method

 In

addition, any controller exposed in the
model should derive from the
ODataController or
EntitySetController<TEntity, TKey> classes


37


CONSUMING ODATA SERVICES


Add a service reference to the OData service



Create a new instance of the generated
Container class



Use LINQ to query the container

var client = new MyODataService.Container(new Uri("…"));
var agent = (from a in client.Agents
where a.Id == "Bond"
select a).Single();


38


ODATA MODELS
DEMO


39


DEPENDENCY RESOLVER
AND THE API CONTROLLER


To be testable, the ApiController should
support dependency injection



Web API supports dependency injection with
the IDependencyResolver interface



Implement your custom resolver or use it to
wrap a known IoC Container (Castle, Unity,
MEF, Ninject…)



Register the dependency resolver through
Web API global configuration



And Voilà!


40
40


HTTP.SYS, WHAT’S THAT?


It’s the thing that handles HTTP on your machine



It’s a kernel mode device driver



Ever since Windows XP SP2 / Windows Server 2003



Responsible of



Kernel mode SSL (full support as of Windows Server 2008)



Caching responses in kernel mode





Routing requests to the correct application

Implementing QoS, such as connection limits and timeouts

Want to know more? netsh http show


41


IIS 101



Web application hosting
Comes in two flavors






IIS Express

Full IIS (or simply IIS)

Provides


Reliability



Manageability



Security



Performance



Scalability


42


ENABLING COMPRESSION WITH IIS



Compression is something the client needs to
request
Requests are not normally compressed



Accept-Encoding: gzip,deflate
Server is not obligated to compress the response



Content-Encoding: gzip / deflate



IIS Compression
Modes
Dynamic
Compression
Static Compression

Scenarios

Considerations

Small number of requests

Uses CPU and memory

Limited network bandwidth

Not cached

Improve transmission times

Can be cached

Graphic-heavy sites

Uses some CPU

43


HTTP PERSISTENT CONNECTION
IT’S ALIVE



Beginning with HTTP 1.1, clients and servers
must support persistent connections
Persistent is good



Fewer TCP connections = less congestion





Single connection can pipeline HTTP requests





Less simultaneous opened connections = less CPU

No re-handshaking = reduced latency

Send Connection: Keep-Alive in request and response
headers to keep the underlying TCP connection open
Connection is dropped if either end lacks sending the
Keep-Alive header – Implementation Dependent


44


KEEPING IT ALIVE!
DEMO


45


KEEP IT ALIVE, BUT FOR HOW LONG?







IIS by default adds Keep-Alive to every response
HTTP.SYS has a default timeout of 120 seconds for idle
connections
When expecting many clients with a small number of
request, Keep-Alive may have an overhead
For short visits, consider disabling Keep-Alive or reduce
the idle timeout to a couple of seconds (5? 2? 1?)
Use logs to check visits and frequency of idle
connections:


IIS log files: C:inetpublogsLogFiles



HTTP.SYS log files: %windir%system32LogFilesHTTPERR


46


WHO NEEDS IIS? WE HAVE SELF-HOSTING
IIS is the natural hosting environment for the
ASP.NET web stack, Web API included
 When IIS is not an option or unwanted, use a
self-hosted Web API
 Just follow three basic steps:





Create host configuration and routing rules





Install the Microsoft ASP.NET Web API Self Host
NuGet package
Start the self-hosted server

Under the covers, Web API self-hosting is
handled by WCF


47


CACHING
 HTTP

caches store copies of responses to
reduce network traffic

 HTTP

caches reduces call latency and
increases server throughput

 Caches

are a main factor for scalability
on the web


48


TYPES OF CACHES


Browser/Client Cache
Stores representations locally on the computer’s
hard drive



Proxy Cache
Corporates and ISPs provide shared proxies
providing shared cache on their network



Gateway (Reverse Proxy) Cache
Stores representations on behalf of the server.
Content Delivery Networks (CDNs) use gateway
cache distributed around the web


49


CONTROLLING CACHE
 HTTP

headers can be used to control
cache behaviors

 HTTP

provides method the avoid
staleness of cached data


Expiration



Validation



Invalidation


50


CONTROLLING CACHE
DEMO


51


ETAG: VERSIONING & CONCURRENCY





When caching content, we need to identify when
content has changed
The ETag (entity tag) header represents the version of
the content
ETags are sent to the client with the response, and are
re-sent to the server on subsequent requests
In the action, compare received and existing ETags,
and return either:





A new entity if they are different
An HTTP 304 (Not Modified) if they are identical

When updating entities using POST/PUT, use the ETag
for concurrency (version) checks



ETAG VERSIONING
public HttpResponseMessage Get(int id)
{
HttpResponseMessage response;
var etag = Request.Headers.IfNoneMatch.FirstOrDefault();
Agent agent = _manager.GetAgentById(id);
if (etag != null &&
etag.ToString().Replace(@"""", "") == agent.Version)
{
response = new HttpResponseMessage(HttpStatusCode.NotModified);
}
else
{
response = Request.CreateResponse(HttpStatusCode.OK, agent);
response.Headers.ETag = new EntityTagHeaderValue(
string.Format(@"""{0}""", agent.Version));
}
return response;
53
}


SECURITY


HTTP messages are clear text, in order to
have any form of secured connection they
must be encrypted



This is what SSL is for



Once encrypted there are still several
challenges remaining:


Authentication



Persisting authentication throughout the
conversation



Authorization


54


HTTPS - HOW SECURE SOCKETS LAYER WORKS
3. Client verifies certificate’s
authenticity
1. Client requests a secured session
2. Server responds with an X.509 certificate
4. Client sends a symmetric encryption key

(encrypted with the server’s public key)
6. Client and server exchange encrypted messages

(encrypted with the symmetric key)

5. Server decrypts the encryption
key with its private key


CLASSIC HTTP AUTHENTICATION


HTTP uses the Authorization header to pass
authentication data:

Authorization: Basic eWFuaXY6eWFuaXY=


According to specs, HTTP supports only two
schemas:





Basic (plain text)
Digest (hashed password)

Nowadays, it is common to find other schemas:


NTLM / Negotiate (Windows authentication)



Certificate



OAuth


56


BASIC AUTHENTICATION
DEMO


57


HTTP STREAMING


Advantages



Message can be handled before received completely





Less large memory allocation and buffering
Connection can remain opened for a long time

Useful for





File download/upload
Live data feed (notifications, video streams, …)

It’s a chunking mechanism


Uses a persistent HTTP connection



The Content-Length HTTP header is omitted



Each chunk is sent as size + chunk



Chunk size can vary



Stream ends when last chunk is sent with size 0 (zero)


58


HTTP STREAMING AND WEB API


Reading a streamed request





Request.Content.ReadAsStreamAsync (File Stream )
Request.Content.ReadAsMultipartAsync (Multi-part
Stream)

Writing a streamed response


Do you want to pull from an existing stream? Or push
your own data down the stream?



Pull : StreamContent(inputStream)



Push: PushStreamContent(contentWritingAction)



When pushing data use Stream.Flush() to chunk


59


STREAMING WITH WEB API
DEMO


60


DUPLEX COMMUNICATION
WITH HTTP


HTTP is a request-response protocol



Updates are through server polling





Periodic polling (Anything new?)
Long polling (I’m waiting for you!)

Many disadvantages


Periodic polling inflicts high-latency on updates



Long polling is hard to implement



Can cause bandwidth overhead if used
improperly


61


WEBSOCKETS IN A GLANCE
 Bi-directional
 Supports

both HTTP and HTTPS (SSL)

 Accessible
 Supports

TCP channel (full-duplex)

through JavaScript API

cross-domain calls

 Client-side

- IE10, Chrome, Firefox, .NET 4.5

 Server-side

– IIS 8, ASP.NET 4.5, SignalR

 Standardization


is still in progress!!


ASP.NET SIGNALR 101
 Real-time,

over HTTP

persistent connection abstraction

 Useful

for dashboards & monitoring,
collaborative work, job progress, gaming…

 SignalR

works everywhere



WebSockets



Server Sent Events



Forever Frame



Long Polling


63


ASP.NET SIGNALR 101
 Supported

clients:



Desktop applications using .NET 4/4.5



Web browsers using JavaScript



Windows Store and Windows Phone Apps

 Supports

scaling servers to Web farm with
Windows Azure Service Bus, Redis, and SQL
Server


64


SIGNALR API, CHOOSE WHAT WORKS
FOR YOU
 Connections


Low level



Raw strings up and down (the “old way”)



Broadcast to all clients, groups, or individuals



Connect, reconnect & disconnect semantics

 Hubs


Built on top of connections



Client-Server and Server-Client RPC



Automatic client proxy generation for JavaScript


65


ASP.NET SIGNALR
DEMO


66


SO WHAT DID WE LEARN TODAY?


HTTP Fundamentals via Web API



Hosting

You are now an HTTP ninja
Rank 1. Just 4 more ranks to go!!


HTTP Messages



HTTP.SYS



URIs



IIS 101



Routing



HTTP compression



Verbs



Persisted Connections



Controllers and Actions



Web API Self Hosting



Status Codes



HttpRequestMessage
HttpResponseMessage



Error Handling



Content Negotiation



Media Type Formatters



OData



Validations



Dependency Resolver




More HTTP and Web API


Caching



Concurrency



Security



Streaming



WebSockets & SignalR

67


RESOURCES


HTTP




www.ietf.org/rfc/rfc2616.txt

REST




www.ics.uci.edu/~fielding/pubs/dissertation/top.htm

ASP.NET Web API


www.asp.net/web-api



www.asp.net/web-api/videos





This Presentation:
sdrv.ms/1eKAsRd

webapibloggers.com (without www)

Fiddler


www.fiddler2.com



www.youtube.com/watch?v=7Tw5EHvTERc



“Debugging the Web with Fiddler”, Tuesday 2:00PM


68

ASP.NET Web API and HTTP Fundamentals

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