1. Network Programming (3)
CSE 132

2. iClicker/WUTexter Question
How many of the following IP addresses are properly formed (i.e., legal IP addresses)?
A: 1 B: 2 C: 3 D: 4 E: 5
@wucse132 <letter> XX

3. Today’s Outline
Observability
Protocols

4. Observability What is really going on?
Option 1: stare at the code until inspired
When that doesn’t work, make random change
Option 2: don’t assume the code you actually wrote does what you think it does!
Alter code so that you discover what it really does
PCS system is great for this
What about network code?
Is issue on client or server?

5. Observability for Network Code
Need to know what is really going across the network
On server, client, or maybe both:
Display what is going out the output stream
Display what is coming in the input stream
Support multiple interpretations of the raw data
Studio 7 today is about building these tools
Do a good job and it will help you the rest of the semester!

6. Protocols What is poor about the Lab W protocol? At least 3 things:
Inefficient use of network bandwidth (verbose)
Uninformative response(s) in the case of an error
Poor recovery from client mistake

7. Better Protocols What might I do about these protocol weaknesses?
Use shorter command names
Provide return error codes or strings
Start all msgs with magic number
Insert ‘!’ (ASCII 33) as magic number up front

8. iClicker/WUTexter Question
What is wrong with the message below?
Nothing is wrong, the message is fine
The first character is not the “magic number”
The count should be least significant digit first
The count is in decimal format
Characters take 2 bytes each in Java
@wucse132 <letter> XX