COMP 117 Ping Demonstration Programs & Makefile / C++ Hints

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1 COMP 150-IDS: Internet Scale Distributed Systems (Spring 2018) COMP 117 Ping Demonstration Programs & Makefile / C++ Hints Noah Mendelsohn Tufts University noah@cs.tufts.edu Web: Copyright 2012, 2013, 2015, 2017 & 2018 Noah Mendelsohn

2 What you should get from today s session A quick look at some details you ll need to do our programming assignment, including: The framework we re using C++ Exceptions A tiny bit about inheritance Makefiles C/C++ tips and tricks 2

3 Working through the Demo Client 3

4 Preamble Include Framework and Debug code #include "c150dgmsocket.h" #include "c150debug.h" #include <fstream> using namespace std; using namespace C150NETWORK; // for C++ std library 4

5 Preamble #include "c150dgmsocket.h" #include "c150debug.h" #include <fstream> IMPORTANT! Needed for COMP150IDS Framework! using namespace std; using namespace C150NETWORK; // for C++ std library 5

6 Main pingclient Logic 6

7 Client logic try { C150DgmSocket *sock = new C150DgmSocket(); sock -> setservername(argv[serverarg]); This is not an ordinary socket it s a smart wrapper around a socket Establishes us as a client and identifies the server ports set based on login id sock -> write(argv[msgarg], strlen(argv[msgarg])+1); readlen = sock -> read(incomingmessage, sizeof(incomingmessage)); checkandprintmessage(readlen, incomingmessage, sizeof(incomingmessage)); catch (C150NetworkException e) { cerr << argv[0] << ": caught C150NetworkException: " << e.formattedexplanation() << endl; 7

8 Client logic try { Clients write, then read C150DgmSocket *sock = new C150DgmSocket(); sock -> setservername(argv[serverarg]); sock -> write(argv[msgarg], strlen(argv[msgarg])+1); readlen = sock -> read(incomingmessage, sizeof(incomingmessage)); checkandprintmessage(readlen, incomingmessage, sizeof(incomingmessage)); catch (C150NetworkException e) { cerr << argv[0] << ": caught C150NetworkException: " << e.formattedexplanation() << endl; 8

9 Demo Server 9

10 Server logic Nasty versions of interfaces introduce errors! nastiness = atoi(argv[1]); // convert command line string to integer try { C150DgmSocket *sock = new C150NastyDgmSocket(nastiness); c150debug->printf(c150application,"ready to accept messages"); while(1) { readlen = sock -> read(incomingmessage, sizeof(incomingmessage)-1); // WORK WITH MESSAGE HERE string response = SOME RESPONSE HERE ; sock -> write(response.c_str(), response.length()+1); catch (C150NetworkException e) { c150debug->printf(c150alwayslog,"caught C150NetworkException: %s\n", e.formattedexplanation().c_str()); 10

11 Server logic Servers read, then write nastiness = atoi(argv[1]); // convert command line string to integer try { C150DgmSocket *sock = new C150NastyDgmSocket(nastiness); c150debug->printf(c150application,"ready to accept messages"); while(1) { readlen = sock -> read(incomingmessage, sizeof(incomingmessage)-1); // WORK WITH MESSAGE HERE string response = SOME RESPONSE HERE ; sock -> write(response.c_str(), response.length()+1); catch (C150NetworkException e) { c150debug->printf(c150alwayslog,"caught C150NetworkException: %s\n", e.formattedexplanation().c_str()); 11

12 Server logic nastiness = atoi(argv[1]); try { // convert command line string to integer C150DgmSocket *sock = new C150NastyDgmSocket(nastiness); c150debug->printf(c150application,"ready to accept messages"); while(1) { readlen = sock -> read(incomingmessage, sizeof(incomingmessage)-1); // WORK WITH MESSAGE HERE string response = SOME RESPONSE HERE ; sock -> write(response.c_str(), response.length()+1); catch (C150NetworkException e) { c150debug->printf(c150alwayslog,"caught C150NetworkException: %s\n", e.formattedexplanation().c_str()); Framework assumes responses go to server/port from which we read 12

13 Inferring who is a server and who is a client nastiness = atoi(argv[1]); try { // convert command line string to integer C150DgmSocket *sock = new C150NastyDgmSocket(nastiness); c150debug->printf(c150application,"ready to accept messages"); while(1) { NOTE: The socket class imposes a simple notion of client/server on UDP It decides whether you re a server or client based on which methods you call first readlen = sock -> read(incomingmessage, sizeof(incomingmessage)-1); // WORK WITH MESSAGE HERE string response = SOME RESPONSE HERE ; 1) client calls setserver name then writes sock -> write(response.c_str(), response.length()+1); 2) server starts by doing a read. Not a very robust approach for production code, but handy for these simple programs. catch (C150NetworkException e) { c150debug->printf(c150alwayslog,"caught C150NetworkException: %s\n", e.formattedexplanation().c_str()); 13

14 C++ Inheritance 14

15 A super-simple look at C++ Inheritance class Shape { private: Point position; public: Point getposition(); virtual void draw() = 0; ; Base class Shape has draw() method with no implementation (=0) 15

16 A super-simple look at C++ Inheritance class Shape { private: Point position; public: Point getposition(); virtual void draw() = 0; ; Class Circle : public Shape { public: virtual void draw(); ; Each subclass provides its own implementation of draw() Class Square : public Shape { public: virtual void draw(); ; 16

17 A super-simple look at C++ Inheritance Class shape { private: Point position; public: Point getposition(); virtual void draw() = 0; ; Shape *shapearray[2]; int i; Both classes inherit postion() method from parent Class Circle : public Shape { public: virtual void draw(); ; Class Square : public Shape { public: virtual void draw(); ; shapearray[0] = new Circle(); shapearray[1] = new Square(); for(i=0; i<2; i++) { cout << shapearray[i] -> position; shapearray[i] -> draw(); 17

18 A super-simple look at C++ Inheritance Class shape { private: Point position; public: Point getposition(); virtual void draw() = 0; ; Shape *shapearray[2]; int i; First time calls Circle::draw, second time calls Square::draw Class Circle : public Shape { public: virtual void draw(); ; Class Square : public Shape { public: virtual void draw(); ; shapearray[0] = new Circle(); shapearray[1] = new Square(); for(i=0; i<2; i++) { cout << shapearray[i] -> position; shapearray[i] -> draw(); 18

19 Inheritance and nasty sockets logic The C150NastyDgmSocket class inherits from try { C150DgmSocket *sock = new C150NastyDgmSocket(nastiness); c150debug->printf(c150application,"ready to accept messages"); while(1) { readlen = sock -> read(incomingmessage, sizeof(incomingmessage)-1); // WORK WITH MESSAGE HERE string response = SOME RESPONSE HERE ; sock -> write(response.c_str(), response.length()+1); catch (C150NetworkException e) { C150DgmSocket. You can use either type here, unless you want to call methods specific to the nasty class. c150debug->printf(c150alwayslog,"caught C150NetworkException: %s\n", e.formattedexplanation().c_str()); 19

20 C++ Exceptions 20

21 C++ Exceptions try { C++ has try/catch/throw for Exceptions try clause runs first C150DgmSocket *sock = new C150DgmSocket(); sock -> setservername(argv[serverarg]); sock -> write(argv[msgarg], strlen(argv[msgarg])+1); Any network exception in try block or methods called by try block takes us here readlen = sock -> read(incomingmessage, sizeof(incomingmessage)); checkandprintmessage(readlen, incomingmessage, sizeof(incomingmessage)); catch (C150NetworkException e) { e is of whatever type was thrown cerr << argv[0] << ": caught C150NetworkException: " << e.formattedexplanation() << endl; 21

22 C++ Exceptions Exceptions are particularly useful for network code no need to percolate return codes through layers of method calls Standard COMP 150IDS Exception Class: throw throw C150NetworkException("Client received message that was not null terminated"); When an error occurs, throw an Exception (same as raise in other langs): throw C150NetworkException (or other class) Exception classes form a hierarchy based on class inheritance (no need for you to worry about that if you don t know C++ inheritance) 22

23 Makefiles Dependency based Command Execution 23

24 Makefile variables # Do all C++ compies with g++ CPP = g++ CPPFLAGS = -g -Wall -Werror -I$(C150LIB) # Where the COMP 150 shared utilities live, including c150ids.a and userports.csv # Note that environment variable COMP150IDS must be set for this to work! Variables defined this way or from environment (this is one reason you setenv COMP117 /comp/117) C150LIB = $(COMP117)/files/c150Utils/ [ several lines skipped ] pingclient: pingclient.o $(C150AR) $(INCLUDES) $(CPP) -o pingclient pingclient.o used this way 24

25 Targets and dependencies # Do all C++ compies with g++ CPP = g++ CPPFLAGS = -g -Wall -Werror -I$(C150LIB) # Where the COMP 150 shared utilities live, including c150ids.a and userports.csv # Note that environment variable COMP150IDS must be set for this to work! The pingclient target depends on pingclient.o (and include files, etc.) C150LIB = $(COMP117)/files/c150Utils/ [ several lines skipped ] pingclient: pingclient.o $(C150AR) $(INCLUDES) $(CPP) -o pingclient pingclient.o 25

26 What gets run # Do all C++ compies with g++ CPP = g++ CPPFLAGS = -g -Wall -Werror -I$(C150LIB) When pingclient is older than pingclient.o, etc. # Where the COMP 150 shared utilities live, including c150ids.a and userports.csv # Note that environment variable COMP150IDS must be set for this to work! C150LIB = $(COMP150IDS)/files/c150Utils/ [ several lines skipped ] pingclient: pingclient.o $(C150AR) $(INCLUDES) $(CPP) -o pingclient pingclient.o..use g++ to relink it 26

27 Fancier dependencies Each xxx.o file depends on xxx.cpp %.o:%.cpp $(INCLUDES) $(CPP) -c $(CPPFLAGS) $< and is compiled from that.cpp file 27

28 C cs. C++ Strings 28

29 C vs C++ Strings we use both! C++ provides automatic allocation and useful concatenation operations C char[] arrays needed for formatting message packets File and socket APIs defined in terms of C byte arrays Also preference For some purposes, printf/scanf are handier than C++ << Etc. 29

30 Some hints on strings Won t try a full tutorial here but, remember that you can convert: char cstring[4] = abc ; // remember the null! string newstring(cstring); // initialize C++ string // from C string char *fromcplusplus = newstring.c_str(); // IMPORTANT: fromcplusplus // is stable ONLY until // next change to newstring Our focus is on the distributed system design performance matters some, but do what s easy and clean 30

31 Stringstreams: useful for formatting and conversions C++ strings do not support <<, but stringstreams do include <sstream> include <iostream> // for stringstream // for cout stringstream ss; int answer = 25; // empty stringstream ss << The answer is << answer << pounds << endl; cout << ss.str(); // get string from stringstream 31

32 What I Do (mostly) I mostly use C++ strings: automatic allocation I use or convert to char[] if I m using APIs that need them I use either printf or stringstreams for formatting or concatenate strings with + (slower, and edge cases where it doesn t work) Not all the framework code makes good choices internally you ll find some stuff that probably should be cleaned up (e.g. excess conversions) 32

COMP 117 Ping Demonstration Programs & Makefile / C++ Hints

COMP 150-IDS: Internet Scale Distributed Systems (Spring 2017) COMP 117 Ping Demonstration Programs & Makefile / C++ Hints Noah Mendelsohn Tufts University Email: noah@cs.tufts.edu Web: http://www.cs.tufts.edu/~noah