Unit 3: Headers · Lesson 1 of 5 · 16 min
Reading headers
Headers are name and value lines, and Linux tools slice them easily.
mission
- You are
- The analyst reviewing the shop.
- Situation
- Developers will ask you for exact header values, not screenshots.
- Goal
- Pull single headers out of responses with grep and cut.
- Hand in
- The Server, Content-Type and Cache-Control values of three pages.
A response as a labelled parcel
One header by name
Header names are not case sensitive, so always grep with -i.
curl -sI http://127.0.0.1:8000/ | grep -i '^server'
Server: shop/1.4
you should see Server: shop/1.4.
curl- Sends web requests and prints the response. Built into Linux, macOS and Windows 10 and later.
grep- Prints the lines of text that match a pattern. Built into Linux and macOS.
Just the value
curl -sI http://127.0.0.1:8000/api/products | grep -i '^content-type' | cut -d' ' -f2-
application/json
you should see application/json with no name in front.
cut- Keeps only chosen columns or characters from each line. Built into Linux and macOS.
Only the names
A list of names is handy for comparing two pages side by side.
curl -sI http://127.0.0.1:8000/shop | cut -d: -f1
HTTP/1.1 200 OK
Server
Date
Content-Type
Content-Length
X-Content-Type-Options
X-Frame-Options
Referrer-Policy
Content-Security-Policy
you should see The status line, then one header name per line.
Spot the difference between two pages
diff <(curl -sI http://127.0.0.1:8000/ | cut -d: -f1) <(curl -sI http://127.0.0.1:8000/shop | cut -d: -f1)
6a7,9
> X-Frame-Options
> Referrer-Policy
> Content-Security-Policy
you should see Three headers only /shop sends.
defender tip Frameworks set headers per route. Diffing the head of two pages is the quickest way to find routes that missed a setting.
diff- Shows the lines that differ between two files. Built into Linux and macOS.
What a defender takes away
- 1
grep -ifinds a header;cuttrims it to the value. - 2Header names are case insensitive, values usually are not.
- 3Diff the headers of two routes to find gaps.
Questions
0 of 3 solved
Answer each one from what you find on your lab machine.