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Hidden Gems in HTTP Ben Ramsey ■ Atlanta PHP ■ 5 Nov 2009

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Why HTTP?

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Because you are a Web developer.

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HTTP is the Web.

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That’s all I have to say about that.

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Some properties of HTTP…

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■ A client-server architecture ■ Atomic ■ Cacheable ■ A uniform interface ■ Layered ■ Code on demand

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Now, what does that sound like?

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REST!

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And, that’s all I have to say about that, too.

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Our focus today…

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■ Semantic HTTP ■ Methods you’ve never used ■ Status codes you didn’t know existed ■ Working with HTTP in PHP

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Semantics are important.

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1 User requests page above their authorization level.

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2 User is redirected to a login page where they are prompted to increase their authorization level.

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GET /protected/content/1234 HTTP/1.1 Host: example.org HTTP/1.1 302 Found Date: Tue, 05 Nov 2009 17:34:24 GMT Server: Apache/2.2.14 (Unix) PHP/5.3.0 X-Powered-By: PHP/5.3.0 Location: /login Content-Length: 0 Content-Type: text/html; charset=utf-8

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The resource requested is found at another location?

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No, no, no. That’s not what we

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The semantics are all wrong.

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Methods you’ve never used…

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Well, not really never.

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■ You know GET ■ Retrieval of information ■ Transfers a representation of a resource from the server to the client ■ Safe & idempotent GET

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GET /user/ramsey HTTP/1.1 Host: atom.example.org HTTP/1.1 200 OK Date: Tue, 22 Sep 2009 17:28:14 GMT Server: Apache/2.2.11 (Unix) DAV/2 PHP/5.3.0 X-Powered-By: PHP/5.3.0 Content-Length: 594 Content-Type: application/atom+xml;type=entry ramsey ...

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He just thinks he’s funny.

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Stop laughing. You’re just encouraging him.

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POST ■ You know POST ■ The body content should be accepted as a new subordinate of the resource ■ Append, annotate, paste after ■ Not safe or idempotent

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POST /user HTTP/1.1 Host: atom.example.org Content-Type: application/atom+xml;type=entry Content-Length: 474 ramsey ... HTTP/1.1 201 Created Date: Tue, 22 Sep 2009 17:39:06 GMT Server: Apache/2.2.11 (Unix) DAV/2 PHP/5.3.0 X-Powered-By: PHP/5.3.0 Location: http://atom.example.org/user/ramsey Content-Length: 133 Content-Type: text/html; charset=utf-8
The content was created at the location http://atom.example.org/user/ramsey

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HEAD ■ Identical to GET, except… ■ Returns only the headers, not the body ■ Useful for getting details about a resource representation before retrieving the full representation ■ Safe & idempotent

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HEAD /content/1234.mp4 HTTP/1.1 Host: atom.example.org HTTP/1.1 200 OK Date: Tue, 22 Sep 2009 17:28:14 GMT Server: Apache/2.2.11 (Unix) DAV/2 PHP/5.3.0 X-Powered-By: PHP/5.3.0 Content-Length: 12334753 Content-Type: application/mp4

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PUT ■ Opposite of GET ■ Storage of information ■ Transfers a representation of a resource from the client to the server ■ Not safe ■ Idempotent

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PUT /user/ramsey/ HTTP/1.1 Host: atom.example.org Content-Type: application/atom+xml;type=entry Content-Length: 594 ramsey ... HTTP/1.1 200 OK Date: Tue, 22 Sep 2009 17:47:27 GMT Server: Apache/2.2.11 (Unix) DAV/2 PHP/5.3.0 X-Powered-By: PHP/5.3.0 Content-Length: 594 Content-Type: application/atom+xml;type=entry ramsey ...

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DELETE ■ Requests that the resource identified be removed from public access ■ Not safe ■ Idempotent

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DELETE /content/1234/ HTTP/1.1 Host: example.org HTTP/1.1 204 No Content Date: Tue, 22 Sep 2009 18:06:37 GMT Server: Apache/2.2.11 (Unix) DAV/2 PHP/5.3.0 X-Powered-By: PHP/5.3.0 Content-Length: 0 Content-Type: text/html; charset=utf-8

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What the hell are safe & idempotent methods?

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Safe methods ■ GET & HEAD should not take action other than retrieval ■ These are considered safe ■ Allows agents to represent POST, PUT, & DELETE in a special way

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Idempotence ■ Side-effects of N > 0 identical requests is the same as for a single request ■ GET, HEAD, PUT and DELETE share this property ■ OPTIONS and TRACE are inherently idempotent

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Status codes you didn’t know existed

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■ Informational (1xx) ■ Successful (2xx) ■ Redirection (3xx) ■ Client error (4xx) ■ Server error (5xx)

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The look-before- you-leap request (LBYL)

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1.Client sends a request without a body and includes the Expect: 100-continue header and all other headers 2.Server determines whether it will accept the request and responds with 100 Continue (or a 4xx code on error) 3.Client sends the request again with the body and without the Expect header

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1 POST /content/videos HTTP/1.1 Host: example.org Content-Type: video/mp4 Content-Length: 115910000 Authorization: Basic bWFkZTp5b3VfbG9vaw== Expect: 100-continue

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2 HTTP/1.1 413 Request Entity Too Large Date: Thu, 21 May 2009 23:05:15 GMT Server: Apache/2.2.11 (Unix) DAV/2 PHP/5.3.0 X-Powered-By: PHP/5.3.0 Content-Length: 0 Connection: close Content-Type: text/html Failure state

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2 HTTP/1.1 100 Continue Date: Thu, 21 May 2009 23:05:15 GMT Server: Apache/2.2.11 (Unix) DAV/2 PHP/5.3.0 X-Powered-By: PHP/5.3.0 Content-Length: 0 Content-Type: text/html Success state

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3 POST /content/videos HTTP/1.1 Host: example.org Content-Type: video/mp4 Content-Length: 115910000 Authorization: Basic bWFkZTp5b3VfbG9vaw== {binary video data}

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4 HTTP/1.1 201 Created Date: Thu, 21 May 2009 23:05:34 GMT Server: Apache/2.2.11 (Unix) DAV/2 PHP/5.3.0 X-Powered-By: PHP/5.3.0 Content-Length: 119 Content-Type: text/html Location: http://example.org/content/videos/1234

Video uploaded! Go here to see it.

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■ There are some problems with supporting 100 Continue from PHP through Apache ■ One suggestion is to use X-Expect instead of Expect ■ But there are still odd problems occurring that I can’t explain Caveat

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The created at another location response

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1 POST /content/videos HTTP/1.1 Host: example.org Content-Type: video/mp4 Content-Length: 115910000 Authorization: Basic bWFkZTp5b3VfbG9vaw== {binary video data}

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2 HTTP/1.x 201 Created Date: Thu, 21 May 2009 23:05:34 GMT Server: Apache/2.2.11 (Unix) DAV/2 PHP/5.3.0 X-Powered-By: PHP/5.3.0 Content-Length: 120 Content-Type: text/html Location: http://example.org/content/videos/1234

Video uploaded! Go here to see it.

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The “it’s not you it’s me” response

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i.e. I’ve accepted it but might have to do more processing

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2 HTTP/1.x 202 Accepted Date: Thu, 21 May 2009 23:05:34 GMT Server: Apache/2.2.11 (Unix) DAV/2 PHP/5.3.0 X-Powered-By: PHP/5.3.0 Content-Length: 137 Content-Type: text/html Location: http://example.org/content/videos/1234/status

Video processing! Check here for the status.

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The “I have nothing to say to you” response…

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…but you were still successful

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1 DELETE /content/videos/1234 HTTP/1.1 Host: example.org Authorization: Basic bWFkZTp5b3VfbG9vaw==

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2 HTTP/1.x 204 No Content Date: Thu, 21 May 2009 23:28:34 GMT

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The ranged request

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■ Used when requests are made for ranges of bytes from a resource ■ Determine whether a server supports range requests by checking for the Accept-Ranges header with HEAD

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1 HEAD /2390/2253727548_a413c88ab3_s.jpg HTTP/1.1 Host: farm3.static.flickr.com

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2 HTTP/1.0 200 OK Date: Mon, 05 May 2008 00:33:14 GMT Server: Apache/2.0.52 (Red Hat) Accept-Ranges: bytes Content-Length: 3980 Content-Type: image/jpeg

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3 GET /2390/2253727548_a413c88ab3_s.jpg HTTP/1.1 Host: farm3.static.flickr.com Range: bytes=0-999

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4 HTTP/1.0 206 Partial Content Date: Mon, 05 May 2008 00:36:57 GMT Server: Apache/2.0.52 (Red Hat) Accept-Ranges: bytes Content-Length: 1000 Content-Range: bytes 0-999/3980 Content-Type: image/jpeg {binary data}

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The GET me from another location response

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■ 303 See Other ■ The response to your request can be found at another URL identified by the Location header ■ The client should make a GET request on that URL ■ The Location is not a substitute for this URL

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1 POST /contact HTTP/1.1 Host: example.org Content-Type: application/x-www-form-urlencoded Content-Length: 1234 {url-encoded form values from a contact form}

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2 HTTP/1.1 303 See Other Date: Tue, 22 Sep 2009 23:41:33 GMT Server: Apache/2.2.11 (Unix) DAV/2 PHP/5.3.0 X-Powered-By: PHP/5.3.0 Location: http://example.org/thankyou Content-Length: 0

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The find me temporarily at this place response

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■ 307 Temporary Redirect ■ The resource resides temporarily at the URL identified by the Location ■ The Location may change, so don’t update your links ■ If the request is not GET or HEAD, then you must allow the user to confirm the action

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The permanent forwarding address response

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■ 301 Moved Permanently ■ The resource has moved permanently to the URL indicated by the Location header ■ You should update your links accordingly ■ Great for forcing search engines, etc. to index the new URL instead of this one

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But what about just finding the resource at another location?

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■ 302 Found ■ The resource has been found at another URL identified by the Location header ■ The new URL might be temporary, so the client should continue to use this URL ■ Redirections SHOULD be confirmed by the user (in practice, browsers don’t respect this)

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The data validation error response

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■ 400 Bad Request ■ Generic error message ■ The client sent malformed syntax ■ The client needs to modify the request before sending it again (to fix errors)

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POST /user/ HTTP/1.1 Host: atom.example.org Content-Type: application/atom+xml;type=entry Content-Length: 474 r@msey ... HTTP/1.1 400 Bad Request Date: Tue, 22 Sep 2009 23:51:00 GMT Server: Apache/2.2.11 (Unix) DAV/2 PHP/5.3.0 X-Powered-By: PHP/5.3.0 Content-Length: 123 Connection: close Content-Type: text/html; charset=utf-8
The following errors occurred:
  • Title contained invalid characters

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The login required response

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1 User requests page above their authorization level. Remember this? GET /protected/content/1234 HTTP/1.1 Host: example.org

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2 User is redirected to a login page where they are prompted to increase their authorization level. HTTP/1.1 302 Found Date: Tue, 05 Nov 2009 17:34:24 GMT Server: Apache/2.2.14 (Unix) PHP/5.3.0 X-Powered-By: PHP/5.3.0 Location: /login Content-Length: 0 Content-Type: text/html; charset=utf-8

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A more semantic way:

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1 GET /protected/content/1234 HTTP/1.1 Host: example.org

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2 HTTP/1.1 401 Unauthorized Date: Tue, 05 Nov 2009 18:31:33 GMT Server: Apache/2.2.14 (Unix) PHP/5.3.0 X-Powered-By: PHP/5.3.0 WWW-Authenticate: HTML form="login" Content-Length: 421 Content-Type: text/html; charset=utf-8

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You must log in Username Password

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■ Doesn’t imply the resource exists at another location ■ Tells clients the resource requires authorization ■ Clearly tells crawlers they can’t access the resource ■ Was originally in HTML5:
 http://blog.whatwg.org/this-week-in-html-5-episode-14 ■ No longer in HTML5, but it works

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But wait! There’s more…

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Working with HTTP in PHP

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■ header() function
 http://php.net/header ■ Client URL library (cURL)
 http://php.net/curl ■ Streams
 http://php.net/streams ■ HTTP extension (pecl/http)
 http://php.net/http

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Questions? ■ My website is benramsey.com ■ @ramsey on Twitter ■ Read the HTTP spec at
 tools.ietf.org/html/rfc2616 ■ My company is Schematic
 schematic.com

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Hidden Gems in HTTP Copyright © Ben Ramsey. Some rights reserved. This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License. For uses not covered under this license, please contact the author.