Advanced UNIX programming

1. Advanced UNIX programming Fall 2002 Instructor: Ashok Srinivasan Lecture 28 Acknowledgements: The syllabus and power point presentations are modified versions of those by T. Baker and X. Yuan

2. Announcements • Reading assignment • Chapter 14 • Sections 14.1, 14.2, 14.4, and 14.5 • Chapter 23 • Quiz Monday • Project: Outline due Monday • Midterm 2 • Bonus points test • 20 Nov 2002

3. Week 10 Topics • Advanced UDP sockets • Reliable communication over UDP • Time out • Sequence numbers • Unix domain protocols • Address structure • Client-server

4. Unix domain protocols • Used for client-server communication on a single machine • Use same API as with regular client-server • Both stream and datagram sockets are supported • Why do we need this? • Efficiency • Passing file descriptors • More security checks

5. Address structure • Open a socket using UNIX domain socket socket(AF_LOCAL, SOCK_STREAM, 0) socket(AF_LOCAL, SOCK_DGRAM, 0) • Use AF_UNIX instead of AF_LOCAL for portability • UNIX domain socket address structure #include <sys/un.h> struct sockaddr_un { uint8_t sun_len; sa_family_t sun_family; /*AF_LOCAL or AF_UNIX */ char sun_path[104]; /* path name */ }

6. Binding a Unix domain socket • example1.c • Use absolute path for path name • bind will fail if the file exists • Pathname can potentially overrun the sun_path buffer • Otherwise, it is very similar to a TCP socket

7. Client-server • example2.c and example3.c • connect needs a pathname that is currently bound to an open UNIX domain socket of the same type • Permission test for connect is the same as that for open with write-only access • connect will fail if the listening queue is full • UNIX domain datagram sockets are similar to UDP sockets • Sender must bind first for the receiver to reply