1. Bob’s computer sends along a stream of 1 and 0 bits, indicated by high and low
voltages on a wire. These bits form some information, containing a header and
body. The header contains an immediate destination of his local router’s MAC
address, with a final destination of Alice’s IP address. The body contains his
request for Alice’s server application.
2.
Bob’s local router receives all these 1’s and 0’s and interprets them as a packet,
from Bob’s own MAC address, and destined for Alice’s IP address. His router
stamps its own IP address on the packet as the “from” IP address, and sends it off
across the Internet.
3. Bob’s packet traverses several intermediary servers, which direct his packet
toward the correct physical/wired path, on to Alice’s server.
4. Alice’s server receives the packet, at her IP address.
5. Alice’s server reads the packet port destination (almost always port 80 for web
applications, this can be thought of as something like an “apartment number” for
packet data, where the IP address is the “street address”), in the header, and
passes it off to the appropriate application – the web server application.
6. The web server application receives a stream of data from the server processor.
This data says something like:
- This is a GET request
- The following file is requested: index.html
7. The web server locates the correct HTML file, bundles it up into a new packet to
send to Bob, and sends it through to its local router, for transport back to Bob’s
machine, through the same process.
And voilà! We have The Internet.
So, where in this exchange did the web browser come into play? Absolutely nowhere.
In fact, browsers are a relatively recent invention in the history of the Internet, when
Nexus was released in 1990.
Yes, the web browser is a very useful application for creating these packets of infor‐
mation, sending them off, and interpreting the data you get back as pretty pic‐
tures, sounds, videos, and text. However, a web browser is just code, and code can be
taken apart, broken into its basic components, re-written, re-used, and made to do
anything we want. A web browser can tell the processor to send some data to the
application that handles your wireless (or wired) interface, but many languages have
libraries that can do that just as well.
Let’s take a look at how this is done in Python:
from urllib.request import urlopen
html = urlopen("http://pythonscraping.com/pages/page1.html")
print(html.read())
You can save this code as scrapetest.py and run it in your terminal using the com‐
mand:
4 | Chapter 1: Your First Web Scraper
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