- Introduction to HTTP 1:22
- Building a Case for HTTP 2:41
- Intro to HTTP 2 questions
- HTTP Requests Using Telnet 7:08
- HTTP Request Format 3:01
- HTTP Headers 1 question
- HTTP Response Format 3:42
- HTTP Response Format 1 question
- Sending Data with a GET Request 4:11
- Sending Data with a GET Request 1 question
- Sending Data with a POST Request 5:57
- Sending Data with a POST Request 1 question
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Sending Data with a POST Request
5:57There are many times in which HTTP is used to send a request whose purpose is to modify data on the server. POST requests are used for this purpose and are constructed a bit differently than GET requests that send data. In a POST request, data is sent in the request payload instead of in the URI. This video shows you exactly how this is accomplished.
Using the query string in a URI to pass
additional data with a GET request
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is a nice way to fine tune your
request and the subsequent response.
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For example, a server can make sure
that a request to the /search resource,
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is fully accommodated by reading
the query string parameter you passed.
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Which would probably contain your
search string, say the string Chicago.
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In putting together its response
the server would include
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only search results related to Chicago.
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This is a nice feature of HTTP but its use
is limited to the fetching of results,
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that is these get requests
are essentially read only.
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But what if we want to update a resource
to incorporate the data that we pass it?
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This requires a different kind of request,
a POST request.
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As you recall,
in contrast to a GET request,
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the purpose of a POST request is
to make a change on the server.
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Maybe update a database record,
upload a new file to the server or
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possibly delete data from the server.
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In short, POST requests lead
to a change on the server and
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in particular, a change to the resource
listed in the URI of the request.
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Recall the scenario mentioned
in the previous video
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where you might be editing a context
first name using an html form.
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A server receiving this request should
update the context associated record
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on the database with the new
first name provided.
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I want to be clear that we won't
be looking at how to actually
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change the resource requested.
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That's up to the developer of the web
application that lives on the server and
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captures your request.
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We'll focus here on just the request
itself and how it's formatted in http.
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Let's have a look.
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In a POST request,
additional considerations need to be made.
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Remember in our HTTP responses
we saw content length header?
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As a reminder, this specified the number
of bytes included in the response body.
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Now it turns out that in a POST request,
we'll be transmitting data
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in the request body or payload and not in
the URI like we did in the GET request.
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Which means we'll need to include
a content like header in our request
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to indicate the number of
bytes we are transmitting.
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For purposes of this demo, I'll simply
count the number of characters that I'm
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using in the data and use that as the
number of bytes for the content length.
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I tell you in the teachers notes why
this works for the demo, so here we go.
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Well, telnet to httpbin.org and
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issue a POST requesting
using HTTP version 1.1.
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Again, the host is httpbin.org.
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And the content length header,
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I'll specify 32 bytes because
I'll be passing 32 characters.
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Make sure to leave a blank line in
between the content length header and
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the request body or payload.
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Let me just pass a couple
pieces of information here.
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I'll pass my first name and
I'll pass a language.
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Now I'm sending a POST request to
the /post resource here because I
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know that httpbin.org is expecting
a POST request at this resource.
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Usually the name of
the resource won't be post.
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Okay let's make this request,
we'll press Enter there.
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Now, I can see that the server received
my request and read my data because
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that data was used in the response
that was sent back right here.
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first name = Chris and language = English.
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Cool stuff!
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Now, lemme show you an example of
what might happen if you miscalculate
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the number of bytes in the request.
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Let me clear my screen.
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And I will again telnet to httpbin.org and
make a POST request.
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This time, indicating the Content-Length
header as 30 bytes instead of the 32 that
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I will pass it.
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I'll pass it the same data
that I did last time.
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Now, when I hit Enter,
the response I get is actually not okay.
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The status listed is 400.
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Bad request,
remember the 400 level codes indicate
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an error in the client's HTTP request.
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In this case, it happened because I
sent more data, 32 bytes of data,
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than what I indicated in the
Content-Length header, which was 30 bytes.
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Now you've seen two ways to send
data to the resource listed
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in the URI you've requested.
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With a GET request, you'll send
the data in query string format by
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appending it to the URI,
starting with a question mark.
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These GET requests are meant to
be read only in that they make
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no changes to the server and
only return existing data.
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We also saw how to send
data with a POST request.
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For this, we drop the data into
the request body in query string format,
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after the blank line
that follows the headers.
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Speaking of which, we need to add
a content length header that indicates
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exactly how many bytes
are included in our POST data.
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And remember, POST requests are intended
to modify the resource requested.
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All that said, I'm exhausted.
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When it comes down to it, navigating
the web and sending data using our manual
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method is time consuming,
error prone and just plain boring.
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Wouldn't it be nice if
there were a GUI for HTTP?
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During the remaining part of this course,
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we'll look at how a web browser gives
the everyday web surfer the ability
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to communicate with HTTP without ever
having to look at the protocol itself.
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