1. Network Server Programming Expression Evaluation Tutorial #10 CPSC 261

2. Socket calls in sequence (TCP) Server side Socket Bind Listen Accept Recv Send Close

3. listen() Indicates that the socket is to be used for accepting incoming connections Done on the “server” side only Returns 0 on success Returns -1 on error – errno is set to indicate why

4. listen() listen(socket, backlog) socket: a file descriptor returned from socket() backlog: the number of incoming connection requests to allow to queue

5. accept() Accepts an incoming connection – waits for an incoming connection request Done on the “server” side only Returns a new socket file descriptor on success Returns -1 on error – errno is set to indicate why

6. accept() accept(socket, addr, addrlen) socket: a file descriptor returned from socket() addr: a pointer to a struct sockaddr addrlen: a pointer to the length of the addr, changed by the call

7. The general pattern s = socket(AF_INET, SOCK_STREAM, 0); bind(s,...); listen(s, 5); while ((news = accept(s, addr, &len)) >= 0) { // communicate with client via news close(news); }

8. Multiple clients at once? How do you modify the general pattern if you want to be able to talk to multiple clients at the same time? Create a thread to deal with each one Or, if isolation matters, create a process to deal with each one

9. Expression evaluation The lab requires you to evaluate strings like: – “4+20” – “34/2”

10. Useful library functions isdigit(int c) strtol(char *p, char **end, 10)

11. If you want the bonus Arithmetic expressions are defined as: – Expr ::= Term { [+|-] Term }* – Term ::= Factor { [*|/] Factor }* – Factor ::= Literal | ( Expr ) Examples: – 2+5 – 4*6 – 3+5*7 – 2+5-4*6/(7+1)

12. Parsing Parsing is the process of determining the structure of a string It can often be done using a collection of mutually recursive functions; one for each non-terminal in the grammar

13. Parsing expressions Write functions named: – Expr() – Term() – Factor() – Literal() They will share the input string – In C, this pretty much has to be in a global variable

14. Literal() long Literal() { long answer = 0; if (isdigit(*input)) { answer = strtol(input, &input, 10); } else { Error("Literal", "Expected digit"); } Trace("Literal", answer); return answer; }

15. Term() pseudocode long Term() { call Factor(); while looking at ‘*’ or ‘/’ { remember the operator and skip it call Factor(); calculate the answer } return answer; }

16. Expr() Is pretty much like Term()

17. Factor() Has to choose between Literal() and Expr() in parentheses You can decide which to call based on the first character of the input – digit -> Literal – ( -> Expr After skipping over the (