URLs

• Uniform
• Resource
• Locator

URL Diagram

(via DoePud)

URL Breakdown

protocol://host:port/path?query#fragment

• some parts are optional

Protocol

• http - the basics
• https - "S" means "Secure"
• file - local filesystem

many others...

Host

in http://www.example.com

the host is www.example.com

the host is a domain name

the browser will use that name to locate the host server, using DNS (*domain name service*) to translate from text to an IP address, then use TCP/IP to connect to that host and begin an HTTP session

Port

in http://localhost:8080

8080 is a port number

it identifies the HTTP service running on the server

the default port for HTTP is 80 (but developers often run servers on other ports, especially on their local machine)

Path

in http://musical-notes.com/bands/heart

the path is /bands/heart

the path helps the service locate the specific resource that the client wants

(this is the "R" in "URL")

the final part of the path ("heart") is called the slug and is used for search engine optimization (SEO)

Queries

in http://musical-notes.com/bands/search?heart

the path is /bands/search

the query is ?heart

this was the original way to do searches on the Web, but was soon enhanced...

Query Parameters

Query Parameters use the same URL slot as normal queries, but use a particular format to encode multiple parameters into a single string

Inside the query string, URLs use delimiters:

• & to separate parameters from each other
• = to separate individual parameter names from values

in http://musical-notes.com/bands/search?category=folk&date=1977

the query is ?category=folk&date=1977

the query parameters are

Percent Encoding

any funky characters in a URL are "escaped" (encoded) as hexadecimal using percent-encoding

"funky" includes...

• space (which turns into + or %20)
• plus signs (%2B) and percent signs (%25)
• some other punctuation marks
• non-ASCII Unicode characters

e.g. http://example.com/引き割り.html becomes http://example.com/%E5%BC%95%E3%81%8D%E5%89%B2%E3%82%8A.html

Query Parameter Encoding

Combining query parameter encoding and percent-encoding can lead to some confusing URLs. For instance...

in http://musical-notes.com/bands/search?category=80%27s+Rock+Bands&page=2

the query is ?category=80%27s+Rock+Bands&page=2

• the first parameter is category=80%27s+Rock+Bands
• the %27 means "apostrophe"
• the + means "space"

so the decoded query parameters are

...it's confusing but it makes sense if you break it down

fragment

in the URL http://example.com/users/alex#profile

#profile called the fragment or anchor

the fragment is a hint to the browser and is not sent to the server with the rest of the URL

in normal pages, it asks the browser to scroll to a location inside the document, after the page has loaded

in Single-Page Apps (SPAs) it is used to determine which pseudo-page to display