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Network Programming with Sockets ECE 255 Douglas C. Schmidt Http

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Network Programming with Sockets ECE 255 Douglas C. Schmidt Http Intro duction The So cket Interface cont'd So ckets are a lo cal and remote OS IPC abstraction de ned in 4.2 BSD UNIX and beyond Originally, so ckets were implemented as a set of system calls { Now part of most major op erating systems, in- cluding Windows and Win32 systems { For eciency, they were tightly-coupled with the BSD networking architecture in the OS kernel So ckets were originally develop ed for TCP/IP proto cols Recent versions of so ckets are implemented { Later generalized to include other proto col fam- as a library of functions in user-space ilies { e.g., SVR4 UNIX and Win32 e.g., Novell IPX/SPX, TP4, ATM User-space implementations improve ex- So cket routine control communication be- tween pro cesses and proto cols ibility and portability at the exp ense of some p erformance { Also provide bu ering between synchronous ap- plication domain and the asynchronous kernel domain 2 4 The So cket Interface cont'd work Programming with Net DISTRIBUTEDAPPLICATION DISTRIBUTEDAPPLICATION DISTRIBUTEDAPPLICATION PROCESS 3592 PROCESS 4183 PROCESS 8729 APPLICATION 1 APPLICATION 2 APPLICATION 3 So ckets USER SPACE 255 ECE BSDSOCKET SOCKET SSYSTEMYSTEM V APIAPI TLITLI APIAPI OS KERNEL KERNEL C. Schmidt Douglas PROTOCOL SERVICES SPACE (TCP/IP, OSI, ETC.) http://www.ece.uci.edu/schmidt/ NETWORK INTERFACE [email protected] University of California, Irvine An application pro cess using TCP/IP pro- to cols resides in its own address space 1 3 Communication Domains cont'd Internet domain or TCP/IP PF INET Communication Domains cont'd { Communicate across network or on same ma- chine uses \dotted-decimal Internet addresses" e.g., "128.195.1.1 @ port 21" UNIX domain PF UNIX { Communicate only with a pro cess on the same { General-purp ose addressing, but existing ver- machine sions don't scale well due to xed-sized ad- dressing Uses UNIX lenames for rendezvous between This is xed in IPv6 client and server pro cesses { e.g., TCP, UDP, IP, ftp, rlogin, telnet { Really a form of intra-machine IPC, similar to SVR4 STREAM pip es STREAM and Supp orts b oth reliable SOCK Xerox XNS later evolved into Novell IPX unreliable SOCK DGRAM lo cal IPC { SPP, PEX, IDP Used for lo cal X-windows trac::: ISO OSI { e.g., TP4-TP1, CLNS, CONS 8 6 Communication Domains Communication domains are a key struc- turing concept in the BSD networking ar- chitecture Communication Domains cont'd { e.g., Internet domain and UNIX domain UNIX cont'd UNIX domain PF Domains sp ecify: { 4.3 BSD and SunOS 4.1.x implement pip es via \lob otomized" connection-oriented Unix domain 1. The scop e over which two pro cesses may com- so cket proto col implementations municate { SVR4-based UNIX systems use the STREAMS { e.g., lo cal only vs. lo cal/remote facility 2. How names and addresses are formed and in- In general, UNIX domain so ckets have b een terpreted in subsequent so cket calls subsumed by STREAM-pip es and connld in SVR4 { e.g., pathnames vs. IP/p ort numb ers { Not surprisingly, Win32 do es not supp ort UNIX domain so ckets Most so cket implementations provide sev- eral domains represented as \proto col fam- ilies" { The socket interface is used for all these pro- to col family domains 7 5 Stream So cket Typ e of service Reliably-delivered Message So cket { Reliable i.e., sequenced, non-duplicated, non- corrupted bi-directional delivery of byte-stream data Typ e of service { Reliable datagram Metaphor { A \network pip e" Metaphor { Sending a registered letter e.g., INET, SOCK STREAM, 0; int s = so cket PF e.g., /* Note, s is an internal id:::*/ int s = so cket PF NS, SOCK RDM, 0; Note, we'll use int as the so cket typ e, al- though Win32 uses SOCKET:: : 12 10 So cket Typ es Datagram So cket There are ve Typ es of So ckets 1. Stream So cket Typ e of service { Unreliable, unsequenced datagram 2. Datagram So cket 3. Reliably-delivered Message So cket Metaphor 4. Sequenced Packet Stream So cket { Sending a letter 5. Raw So ckets e.g., SOCK STREAM and SOCK DGRAM are INET, SOCK DGRAM, 0; int s = so cket PF the most common typ es of so ckets::: 9 11 So cket Addresses cont'd Raw So ckets General Format Typ e of service { Allows user-de ned proto cols that interface with struct so ckaddr f u short sa family; char sa data[14]; g; IP UNIX Domain { Requires ro ot access struct so ckaddr un f short sun family; char sun path[108]; g; Metaphor { Playing with an erector set:::;- Internet Domain addr f unsigned long s addr; g; struct in struct so ckaddr in f e.g., short sin family; u short sin port; struct in addr sin addr; char sin zero[8]; INET, SOCK RAW, 0; int s = so cket PF g; 14 16 So cket Addresses UNIX supp orts multiple communication do- Sequenced Packet Stream So cket mains, proto col families, and address fam- ilies Typ e of service { The so cket API provides a single address in- terface for all these families { Reliable, bi-directional delivery of record-oriented data The typ e of sockaddr structure used with Metaphor accept, bind, connect, sendto, and recvfrom di ers according to the domain UNIX vs. { Record-oriented TCP e.g., TP4 and XTP Internet vs. XNS e.g., The addressing API has a somewhat con- fusing and error-prone design int s = so cket PF NS, SOCK SEQPACKET, 0; { Motivation was to save space for the \common case":: : 15 13 So cket Op erations Connection-oriented So cket Lo cal context management Usage int so cket int domain, int typ e, int proto col; bind int fd, struct so ckaddr *, int len; int 2: ACTIVE 1: PASSIVE listen int fd, int backlog; int ROLE ROLE close int fd; int socket() socket() getp eername int fd, struct so ckaddr *, int *len; int bind() (optional) bind() getso ckname int fd, struct so ckaddr *, int *len; int connect() listen() accept() send()/recv() Connection establishment and termination send()/recv() close() 3: SERVICE PROCESSING close() int connect int fd, struct so ckaddr *, int len; int accept int fd, struct so ckaddr *, int *len; int shutdown int fd, int how; CLIENT SERVER Option management NETWORK int io ctl int fd, int request, char *arg; int fcntl int fd, int cmd, int arg; int getso ckopt int, int, int, char *, int *; int setso ckopt int, int, int, char *, int; 18 20 So cket Op erations So cket Addresses cont'd Data transfer General usage for Internet-domain service: int read int fd, void *buf, int len; struct so ckaddr in addr; int write int fd, void *buf, int len; int send int fd, void *buf, int len, int ags; memset &addr, 0, sizeof addr; int recv int fd, void *buf, int len, int * ags; addr.sin family = AF INET; int readv int fd, struct iovec [], int len; addr.sin port = htons p ort numb er; int writev int fd, struct iovec [], int len; addr.sin addr.s addr = htonl INADDR ANY; int sendto int fd, void *buf, int len, int ags, struct so ckaddr *, int len; int recvfrom int fd, void *buf, int len, int ags, if bind sd, struct so ckaddr * &addr, sizeof addr struct so ckaddr *, int *len; == 1 int sendmsg int fd, struct msghdr *msg, int ags; :::; int recvmsg int fd, struct msghdr *msg, int ags; Note the use of a cast Event demultiplexing { In C++, this whole mess can be cleaned-up via inheritance and dynamic binding! int select int maxfdp1, fd set *rdfds, fd set *wrfds, fd set *exfds, struct timeval *; 17 19 Client and Server Op erations Client and Server Op erations cont'd close socket { Close a so cket { Creates and op ens a so cket and returns a de- { int close int s; scriptor Note, there are subtle semantics related to { int s = so cket int domain, int typ e, int pro- \grace termination:::" of proto cols to col; domain ! PF UNIX, PF INET shutdown { Shutdown part or all of full-duplex connection typ e of service ! SOCK STREAM, SOCK DGRAM { int shutdown int s, int how; proto col ! generally 0, but could be TCP, how is 0, then further receives will be disal- VMTP, NETBLT, XTP lowed how is 1, then further sends will be disal- lowed Note, this call only lls in the rst part of how is 2, then further sends and receives will the 5-tuple asso ciation be disallowed { Note, shutdown do es not close the descriptor::: 24 22 Client and Server Op erations cont'd Connectionless So cket Usage bind Asso ciates a lo cal address e.g., an IP address, 2: ACTIVE { family, and port numb er to an un- ROLE 1: PASSIVE address so cket socket() ROLE named socket() bind() (optional) int bind int s, struct so ckaddr *addr, int ad- bind() { sendto()/ drlen; recvfrom() sendto()/ addr ! lo cal address e.g., p oints to an In- recvfrom() addr or a UNIX domain addr close() 3: SERVICE ternet PROCESSING close() addrlen ! length of address { Note CLIENT SERVER bind is not necessary for clients which im- NETWORK plicitly allo cate transient port numb ers ANY is a wildcard for The address INADDR any server host/network interface Always \zero-out" the address structure be- fore using it::: 21 23 Typical Server Op erations accept Typical Client Op erations { Returns a unique descriptor to the next avail- able completed connection from the connec- tion queue connect { int accept int s, struct so ckaddr *addr, int *addrlenptr; { Sp ecify foreign/remote destination address e.g., IP/p ort numb ers and joins two so ckets for addr ! address of remote server I/O: addrlenptr ! ptr to length of address { int connect int s, struct so ckaddr *addr, int addrlen; Returns new so cket descriptor sp ecifying the addr ! address of remote client full asso ciation addrlen ! length of address { Notes: 1.
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