User manual - ROSS Home page
Contents
1. e 14 2 4 2 Compile and link da o a a 6 Eas ee Ee 14 3 Developer s manual 15 3 1 The data abstraction layer si a PA e Goh A ERE 15 So The Data clasg crs ini O ARS A eee 15 dla Le Record class s oi a Dili Bn dt BES 16 agli Whe Recordset class aa pesa o E a a 17 3 2 Threads and synchronization 2 2 aa IL PALE ole ARL 18 pull he Thread Class Das eye As dalai 18 3 224 Phe Synchro Classy ioni eo beh ot a OE eR IOS BS 19 3 9 Database access ute af a a a ee ae cw Saran Bee a a ere Re Be 20 digli PheDBConn class ca finite ce ala eheh 20 3 3 2 The Query class Locana ek oa eek Pea ee ee YE 21 CONTENTS CONTENTS 4 The MCS server 22 4 1 Architecture of an MCS based system 00 22 4 1 1 Database server e pi colo ht eS a ae delia dei 22 4 1 2 Application server MCS based o 22 4 1 3 External programs ali cedri ie a a Be See ee a eg 22 lena IN A ai A E u 23 4 2 The MCS server i o bd dl lee le ie ii e ae 23 4 2 1 Comparison with a shell a 2052 Late Ue eee fhe 4 23 4 2 2 Temporal sequence of events during a connection 24 Ao Bas commands die sa lee a date Lena Ge een ee len ee A 25 DIL AMES e dy decd Ahk ee de BGR AE RA a a a 28 4 3 Running the MCS server Lu ile Be ala hw a A E aed 28 4 3 1 The configuration file taa de bea use do Beata aa ee es 28 4 4 Customize the MCS server 28 4 4 1 Adding external programs sal SHS ke DA eS as 28 4 4 2 Adding SQL script2. data In this case the different data are the different sockets connected to different clients That s how the server can process requests from several clients simultaneously As soon as the new thread is ready it will send a welcome message through the socket Receiving this message indicates that the server is ready to process client requests From now on the server will wait for commands to arrive while the client will enter a loop to send all necessary commands and receiving the related answers When the server receives a command it will check if it is a BYE command that is a command to close the connection If this is the case then the thread will destroy itself In all other cases the server will process the request and send the answer to the client until a BYE command is received 4 2 3 Base commands Users can request a service from an MCS based application server using commands There are two types of commands a base commands are those implemented in MCS itself b custom commands are those implemented by the users see Sect Developer s manual A command is a sequence of characters terminated by a newline character very similar to the ones used in a typical UNIX shell They are composed of a keyword the command itself zero or more options with a minus sign and zero or more arguments depending on the command The command keyword and the options are case insensitive whereas arguments are not Options and ar
3. distinct class for each possible VOTable node so that the C code will be very close to the XML counterpart Another important Astronomy feature is DIF Dynamic Indexing Facility which integrates the HTM and HEALPix indexing facilities inside database tables This means that a query involving spherical coordinates both in 2D or 3D environments can take advantage from the database built in indexing mechanisms to speed up execution of a query 1 3 Using MCS from other programming languages MCS also provides an interface to use some of its classes from programming languages other than C The features exported through this interface are e the possibility to use the database related classes together with the data abstraction layer e the possibility to connect to an MCS server Due to the fact that not all languages support the object oriented programming paradigm what is exported are just functions An interesting feature of these functions is that they all have the same names in all languages Supported programming languages are eC e Fortran 77 e PHP http www ivoa net Documents latest VOT html Shttp ross iasfbo inaf it votpp http ross iasfbo inaf it dif Shttp www sdss jhu edu htm http healpix jpl nasa gov 1 4 License issues 1 INTRODUCTION e Python e IDL Support for Java and Perl will be added soon 1 4 License issues MCS is distributed free of charge and according to the G
4. is the file name If no parameter is passed then the file out will be retrieved 27 4 3 Running the MCS server 4 THE MCS SERVER Command PUT lt file_name gt lt size gt Store a file into the work directory on the server Parameters are the file name and the file size in byte 4 2 4 Grants TO BE WRITTEN 4 3 Running the MCS server TO BE WRITTEN 4 3 1 The configuration file TO BE WRITTEN 4 4 Customize the MCS server One of the main feature of MCS as its acronym suggests is the possibility to be cus tomized adapting the server behaviour to specific needs tasks MCS can be customized in several ways e adding external programs either real external applications or batch lists of MCS commands e adding SQL programs to be executed on the database server e adding customized commands deriving the UserThread class e modifying the behaviour of the local thread deriving the LocalThread class We ll explain in detail how to customize the MCS server in the following sections 4 4 1 Adding external programs TO BE WRITTEN 4 4 2 Adding SQL scripts TO BE WRITTEN 4 4 3 Adding BATCH scripts TO BE WRITTEN 4 4 4 Adding custom commands TO BE WRITTEN 28 5 CONNECTING TO AN MCS SERVICE 5 Connecting to an MCS service To connect to an MCS service you can use one of the available interfaces for the various languages C C Fortran IDL PHP or Python Perl and Java will be added They already impl
5. C command home directory work directory Table 1 shell comparison 23 42 The MCS server 4 THE MCS SERVER 4 2 2 Temporal sequence of events during a connection In this section we ll explain the temporal sequence of events during an MCS session using Fig 2 The arrow indicates the time flow as we can see different blocks on client and CLIENT SERVER START Y WAI CONNECTION OPEN Cda SOCKET Y THRE CREATION SEND WELCOME MS RECEIVING r WELCOME MS z WAIT COMMAND SEND COMMAND z THREAD BYE gt DESTRUCTION F Y PROCESSING REQUEST SEND ANSWER RECEIVE ANSWER Figure 2 Flow diagram of a typical MCS session server aren t contemporaries Furthermore we see that while for the client the start and end points are well defined for the server we don t have such points because we suppose it is executed indefinitely Usually the server waits for a client to open a TCP socket when such a socket is opened the server creates a new thread of execution and assigns the connection to it We can notice point labeled A in Fig 2 that at this point the execution path of the server is split in two one of them returns to wait for another 24 42 The MCS server 4 THE MCS SERVER client while the other starts processing client requests on another thread Threads are basically identical programs working on different
6. MCS My Customizable Server GIORGIO CALDERONE IFC INAF PALERMO ITALY LUCIANO NICASTRO IASF INAF BOLOGNA ITALY June 11 2011 Ver 0 3 3 alpha3 http ross iasfbo inaf it mcs This page intentionally left blank CONTENTS CONTENTS Contents 1 Introduction 1 E Motivations a eda ose ieri bara be KD Be Te 1 1 2 MES features e id ia ke be te ak ae de ea Pene i 2 1 2 1 Multithreading applications usa aoe ated 3 1 2 2 Network applications ala de a PA SRA wo A 3 1 2 3 The MCS data abstraction layer lt a dgr dea ge ta 3 1 2 4 Database access E iaia ae a 3 1 2 5 FITS file access A A AS ae ee 3 1 2 6 Application server plotone ela 4 1 2 7 Other facilities e be ak Be e ea ee 4 1 2 8 Facilities included in previous releases 4 1 3 Using MCS from other programming languages 5 T4 censo issues eo nd eee es la ra a a 6 1 5 Some simple examples la Pea a thes ee a 6 1 6 About this document sie li a o ear de e A T 2 MCS installation and usage 11 241 Dependencies ss atea irana eS Reo Odes orale 11 22 Minstalline MES ici Ws a ie ere ace lira BOE diga 12 Til Configure Lodi Ro ke ge Ae O 12 222 Complex spad den de ad pao de AS i 13 DDB Stall e A ES AAA AR e alt de A 13 2 3 Troubleshooting e aeia a he ds ed he oh ae A a 13 2 3 1 Problems with Python isla Deidad era en 14 2 4 Using the MCS library ss o e e ile e ipa leeks kos en De a a 14 2 4 1 Include MCS header o
7. NU General Public License This means that you may copy this software and distribute it free of charge as well as modify it provided that you retain this note and mention the authors name The GNU General Public License comes with this package in a file named COPYING for more information about this license visit http www gnu org 1 5 Some simple examples The directory share examples in the MCS package contains several examples that can be compiled and executed once MCS has been installed To compile the examples simply execute make in that directory This section is aimed at giving a first sight at the code you should deal with if you decide to use MCS Some aspects may appear unclear here but these are just examples Check the following sections for further and more complete references In the first example see List 1 we ll show how to set and retrieve information from a Data object which is the object upon which is built the entire data abstraction layer Note in particular how the Data object takes care of all the necessary conversions between different data type In the second example see List 2 we ll execute a query on a database table and print the result on standard output We ll also show how to retrieve data through the data abstraction layer which in this case is implemented by the Query class from line 15 to the end In the third example see List 3 we ll build the simplest MCS application server with out any
8. a certain table or a table column he can access all records of that table or that table column MyRO lets you specify grants on a record level so a user can access only those records it is allowed to A consequence of this is that different users reading the same table will see different records The grants mechanism provided by MyRO is similar to that of a Unix file system that is each record has an owner and a group to which the record belongs Furthermore it has three sets of permissions for the owner the group and all other users that specify if http ross iasfbo inaf it myro 1 3 Using MCS from other programming languages 1 INTRODUCTION that record can be read and or written The software components of MyRO are a Perl script used to perform administrative tasks a C library and a set of MySQL functions The process of protecting tables is completely transparent to the final user that is once MyRO has been installed and configured by the database administrator users can access the database without even know that MyRO is working Astronomy related facilities The most important Astronomy facility is the possibility to read VOTable through the VOTPP VOTable C Parser library VOTable files can be read using the Parser_Stream or the Parser_Tree class that is using the SAX model read one node at a time or the DOM model read the entire file and build a browseable tree in memory Note that VOTPP provides a
9. as follows configure Anyway configure has a lot of options and switches type configure help for a list to customize the compilation step The options like with PACKAGE PATH can be used to specify the path where the configure script should search to find that package default is usr local Some of these options are specific to MCS e prefix PATH the directory under which all include files libraries and other files relative to MCS will be installed if this option is not used usr local is assumed e enable debug disable debug if enabled then the g and 00 flags will be added to the compiler command line these are needed to include debugging information in the library and to discard any optimization By default this option is disabled e enable all by default all optional facilities are disabled you can enable them with the relative options discussed below or you can enable all of them with this option Note also that if you want to enable all option except say the interface to Python you can simply use the following arguments configure enable all disable python e with pcre PATH if the PCRE package which is mandatory is not installed in a standard location typically usr local then you can provide the correct path with this option e with curl PATH if the cURL package which is mandatory is not installed in a standard location typically usr local then you can provide the correct pat
10. ascal language or the struct in C C indeed a Record object can contain any number of Data objects of any base type Creating and populating a Record is quite simple Create a Record object Record rec Create some Data objects Data dl STRING 20 Data d2 INT Data d3 TIME o ON Oo A e N _ Give a name to the Data objects dl setName A_String 16 3 1 The data abstraction layer 3 DEVELOPER S MANUAL 1 d2 setName An_Integer 12 d3 setName A_Float 13 14 Add the Data objects to the Record objects 15 rec addField dl 16 rec addField d2 ir rec addField d3 18 19 Now we can refer to each Data object using the syntar we would use with any C C array o 20 21 rec 0 Hello 22 rec 1 123 23 rec 2 1 23 24 Data amp tmp rec 0 25 26 We can also refer to a Data object using its name 27 string s rec A_String sval 28 int i rec An_Integer ival 29 float f rec A_Float fval As can be seen from the example a Record object can be used like a usual C C array that is using square brackets Another interesting feature which links the Data and Record classes is the possibility to give a name to the Data object and use that name to search the object inside a Record object see line 27 in previous example 3 1 3 The RecordSet class The third level of hierarchy is the RecordSet class which is a dynamica
11. c cli CID help 0 for i 0 i lt Record_count Client_out cli i printf s n Data_sval Record_field Client_out cli i Client_exec cli qry SELECT FROM mcstest 0 printf Number of rows d n RecordSet_nRows cli for i 0 i lt RecordSet_nFields cli i printf s t Data_name Record_field RecordSet_metarec cli i printf n while RecordSet_eof cli for i 0 i lt RecordSet_nFields cli i printf s t Data_sval Record_field RecordSet_rec cli i printf n RecordSet_setNext cli if ifd_got_error printf ERROR s n ifd_last_error ifd_reset_error Client _exec cli BYE 0 del_Client cli return 0 Listing 5 Source of client_c c 35 6 8 The Fortran int6rfabSING MCS WITH OTHER PROGRAMMING LANGUAGES 6 8 The Fortran interface To use the Fortran interface you should include two files e mcs_fortran inc wrappers implementation e mcs_facility inc functions declaration These files are located in the same directory as the main include file mcs hh see Sect 2 2 1 To compile and link your program follow these steps 77 mcs config cflags Wno unused variable c f_test f 77 o f_test f_test o mcs config libs The Wno unused variable is used here because in the mcs_facility inc there is a declaration for each function of the MCS interface without that option the compiler will annoy the
12. cstest test If the connection or authentication fails an exception will be thrown 3 3 2 The Query class Once a connection to the database has been estblished it is possible to execute SQL queries on it through the Query class 1 Query qry amp db 2 qry prepare SELECT FROM mcstest 3 qry execute In this case the query produce a result set which can be retrieved through the data ab straction layer because Query derives from RecordSet 1 Loop through the resulting record set 2 while qry eof 3 Get a reference to current record a Record amp rec qry rec el For each field print its value 7 for int i 0 i lt rec count i 8 cout lt lt rec i sval lt lt Xt 9 cout lt lt endl 10 u Move to next record 12 qry setNext 13 21 4 THE MCS SERVER 4 The MCS server 4 1 Architecture of an MCS based system An MCS based system has four main components see Fig 1 A a lt gt HA a 2 gt Database server MCS server Client C C Fortran IDL PHP Shell script IDL SQL Perl Figure 1 Main components of an MCS based system 4 1 1 Database server The database server is used to handle clients authentication to store all application specific data and anything else necessary to the application itself Th
13. customization but with all base features available authentication support base commands database access file download and upload access to external programs Finally in our fourth example see List 4 we use the Client class to connect to a running MCS server like the one in the previous example issue some commands to upload and download a file and finally execute a query on the remote database and print the result on standard output You should notice that lines from 24 to the end are exactly the same as those in listing 2 lines from 15 to the end This is due to the fact that both the Client and Query classes implement the data abstraction layer thus these classes provide the same interfaces to retrieve data even if in one case data are being read from a database and in the other data have been packed sent through the network and then unpacked 1 6 About this document 1 INTRODUCTION o N Q A e N y 10 12 13 14 15 16 z 18 19 20 21 22 include lt mcs hh gt us in ing namespace mcs t main Data d STRING 20 Assign an integer d 12 int i d ival Assigning a floating point number di 152 float f d fval Assign a date time data d 2007 03 19 13 30 time t t d tval Assign a string d My name is Giorgio string s d sval Listing 1 Source of datal cc 1 6 About this document This document gives an overview of the MCS facilities an
14. d focuses on some of the basic topics of MCS It is divided in several sections so that you can read only the information you need MCS installation and usage it provides information about the configuration of the package against all optional dependencies the compilation and installation furthermore it shows how to link against the MCS library Developer s manual it introduces the reader to some of the MCS basic concepts like the data abstraction layer thread handling database connections etc and focuses on various techniques to develop applications with MCS The MCS server it shows how to implement customize execute and administrate an MCS server Client s manual it shows how to connect to an MCS server Using MCS with other programming languages describes all the available interfaces to connect to MCS through other languages 1 6 About this document 1 INTRODUCTION include lt mcs hh gt using namespace mcs int main Connect to the database server DBConn db o On Q A e Ww N e Execute a query through the opened connection Query qry amp db qry prepare SELECT FROM mcstest qry execute e H H WN e o Loop through the resulting record set while qry eof e oa e o Get a reference to current record Record rec qry rec DOH PR N For each field print its value for int i 0 i lt rec count i cout lt lt rec i sval lt l
15. ement all the features of the MCS protocol like handling connection and data transfer either as a file or as record sets One of the main features of these interfaces as shown below is that the syntax except for the C interface is almost identical for all languages 5 1 The Client class The Client class is the main interface to MCS all other interfaces are implemented through it We recommend to read the reference documentation for the classes we ll men tion The Client class constructor line 9 accepts parameters about a the CLIPATH directory see Fig 3 b the host address of the host whose running the MCS service c the port on which the server is listening Once you are connected to the server you can use the login method line 11 to perform authentication and the exec method line 12 to issue commands In this examples we issued the CID command to retrieve the client identifier Each data exchanged between client and server passes through one of the public Record members of the Class client In this case the client identifier is contained into a Data object in the aux member line 14 As an example of another Record member we can require a brief help message about a command line 16 17 18 Then we can perform a query on the database and print all records line 20 to 33 Finally we close the connection and delete the Client object line 35 and 36 Note that all the code is in a try catch block to eventually catch exc
16. eptions that may be thrown MCS code throws only exception based on the class Event 5 2 User environment Once a user has connected and logged in see Sect 5 3 to an MCS service he she has a dedicated environment consisting of e a work directory where the user can upload or download files e a database connection so that a user can perform database queries as well as create temporary tables visible only to the user itself In this document we will refer to the work directory on the server with CLIPATH With the same name we ll refer to the directory on the client side from to which files are uploaded or downloaded see Fig 3 Figure 3 shows a directory called SRVPATH above CLIPATH this is the server main directory which contains all work directories 29 5 3 Login 5 CONNECTING TO AN MCS SERVICE Client side Server side Lo CLIPATH SRVPATH CLIPATH Figure 3 Directories in an MCS based system 5 3 Login The authentication should be made just after the connection using the USR PWD DBN optional and CON commands Some commands QRY FETCH EXEC etc require the user to be logged in otherwise a permission error will occur 5 4 Logout To logout simply issue the command BYE then close the socket It is important that the client closes the socket first otherwise the resource on the server will remain locked When a user closes its connection the server will close the database connection destroy t
17. et class has been used to implement the Client class which can connect to an MCS server 1 23 The MCS data abstraction layer The Data Record and RecordSet classes can be used as a high level abstraction layers upon data Basically these classes offer a unique interface to access data from different sources database files information sent by the MCS server etc Furthermore they provide facilities to convert data between different formats serialize data structures im plement thread safe queues etc These classes are intensively used to pass data between MCS classes See Sect 3 1 1 2 4 Database access The DBConn and Query classes provide the possibility to connect to a database server actually only MySQL is supported but other database server may be supported in the future and execute queries on it Data can be read from the database and written on it using the MCS data abstraction layer 1 2 5 FITS file access The FITSReader class can be used to read a FITS file Data will be read through the data abstraction layer http www mysql com 3http heasarc gsfc nasa gov docs heasarc fits html 1 2 MCS features 1 INTRODUCTION 1 2 6 Application server An application server is an application that provides a service over the network Typically a user connects to the service and issues a query that will be executed on the server then the resulting data will be sent back to the user using a dedicated communicatio
18. et classes see Sect 3 1 MCS is the evolution of a software named SDAMS SPOrt Data Archiving and Man agement System that was implemented to support the SPOrt experiment an Italian Space Agency ASI funded project which has been frozen because of the problems with the Columbus module on the International Space Station At that time the approach used to build SDAMS seemed to be easily portable to other experiments so its features and usability have been generalized until it became the actual MCS In fact it is now used to manage the data collected by the optical and infrared cameras ROSS REMIR mounted on the robotic telescope REM at La Silla Chile Although MCS has been developed to build an information server to support an astronomical project it is completely general purpose and can be used in the same manner in many other kind of projects 1 2 MCS features The MCS classes can be used to simplify application development in a variety of situations Anyway we have to warn the reader about the fact that the MCS library is not supposed to be used as a system library replacement if your application needs a low level control upon processes threads sockets database connections data conversions and memory allocation you simply have to use the system libraries Only in this way indeed you can dispose of all the possibilities offered by the operative systems and the C language However this kind of applications are just a minor part of al
19. f this is unlikely to occur both threads could read the same data from the queue and start the elaboration of the same file thus probably leading to an error This bug can be removed using the Synchro class to implement protected sections that are sections of code that can be executed by only one thread at a time The changes in the code are as follows class MyThread public Thread 1 2 Use the same Synchro object in all parallel threads 3 static Synchro syn 4 5 void run 6 for 7 if queue count 8 syn enter Enter the protected section 9 string fn queue pop sval 10 syn leave Leave the protected section 11 perform some task on the file 12 13 sleep_ms 1000 wait for one second 14 1s 16 As you can see the global variable now is being used inside a protected section thus the previous bug cannot occur anymore Note also that the protected section is leaved before working on the file that is because otherwise the other thread couldn t advance until the first has ended its job 3 3 Database access THe MCS library can be used to execute SQL queries on a MySQL database The classes involved are DBConn Query and Table 3 3 1 The DBConn class This class is used to open a database connection and perform authentication as in the following example 1 DBConn db 20 3 3 Database access 3 DEVELOPER S MANUAL 2 db connect mcstest m
20. ge In this case all successive calls will return immediately This way you can check if an error occurred only at the very end of a sequence of instructions as in the following example 33 6 7 The C interface6 USING MCS WITH OTHER PROGRAMMING LANGUAGES Call MCS function 1 Call MCS function 2 Call MCS function 3 if ifd_got_error handle error print ifd_last_error ifd_reset_error As you can see the check for the error is performed at the very end not after each function call Once you handled the error you may decide to continue execution in this case you should reset the status information with a call to the ifd_reset_error function as shown above 6 7 The C interface To use the C interface you should include the mcs_c h file in your source code it is located in the same directory as the main include file mcs hh see Sect 2 2 1 To compile and link your program follow the same step as with any other MCS based program cc mcs config cflags c myprog c cc 0o myprog myprog o mcs config libs As an example see Fig 5 in which we implemented in C the program we developed in C Fig 4 Some line needs a comment first of all note lines 7 9 10 in which the number of arguments is different from the corresponding C code that s because C cannot handle default argument values so we have to specify them all At lines 13 19 26 2 you can see that the syntax is in reverse o
21. guments are separated by one or more blanks and can be enclosed in double quotes to be considered as a single argument a single argument The actual argument anyway won t contain the double quotes If an argument must contain a double quote it can be escaped with a backslash The Tab 2 shows a list of available base commands Any base command provides the help option which will produce a brief explanation of the command usage A command can be executed each time the MCS server sends a prompt there can be three kinds of prompt e 0 last command executed successfully e 0W last command report a warning e 0E last command report an error Options common to all commands There are a number of options that are common to all commands so we report them here e help show a brief explanation about the command usage and doesn t execute the command e force continue execution of commands even if an error occurred e werr Turns all warning into errors so that a warning can stop the execution 25 42 The MCS server 4 THE MCS SERVER Table 2 MCS Command codes Command code Meaning CID Retrieve the CID Client Identifier CLINFO Retrieve information about all connected clients NOP A do nothing command USR Supply user name PWD Supply password DBN Supply application name CON Login BYE Close the connection GET Download a file from work directory PUT Upload a fi
22. h with this option e enable mysql disable mysql with mysql PATH enable or disable the compilation of MySQL facilities by default this option is en abled e enable openssl disable openssl with openss1 PATH enable or disable the compilation of Openssl facilities by default this option is dis abled 12 2 3 Troubleshooting 2 MCS INSTALLATION AND USAGE e enable cfitsio disable cfitsio with cfitsio PATH enable or disable the compilation of CFITSIO facilities by default this option is disabled e enable idl disable idl with id1l PATH enable or disable the compilation of IDL to MCS interface by default this option is disabled e enable php disable php with php PATH enable or disable the compilation of PHP to MCS interface by default this option is disabled e enable python disable python with python PATH enable or disable the compilation of Python to MCS interface by default this option is disabled There are several other options and switches available for further documentation see the INSTALL file 2 2 2 Compile To compile MCS once the configure script has been correctly executed simply issue the command make If you got errors while compiling check Sect 2 2 1 and the INSTALL file 2 2 3 Install If MCS has been correctly compiled you can install with the command make install If your account doesn t have the permission to write in the path where it s
23. hat it exploits the C capabilities in developing high level tasks but does not require the developer to deal with networking threading database code or in general low level code Furthermore some repetitive tasks like converting data between different types or creating and manipulating dynamically allocated data structures can be easily accomplished using the MCS classes MCS has been developed on the GNU Linux platform and it is released under the GPL license It can be freely downloaded from the site http ross iasfbo inaf it mcs This site contains all news updates documentation and downloadable software packages The site is still under development so check for updates The MCS project was developed at IFC INAF Palermo Italy by Giorgio Calderone and Luciano Nicastro now at IASF INAF Bologna 1 1 Motivations Information services can be separated in two classes those in which the information pro duced are addressed to humans and those in which they are meant for the use by other software applications In the former case there is a quite standardized way to develop such an information service essentially based upon a web server a database server a scripting language and HTML pages In the latter case instead there is no such standardization and this is one of the reasons why MCS My Customizable Server was implemented Thanks to its communication protocol indeed MCS can be used to easily develop information ser vices that ca
24. he thread associated with the client and optionally delete all files in the user work directory MCS will use the MyRO package to handle grants 30 6 USING MCS WITH OTHER PROGRAMMING LANGUAGES 6 Using MCS with other programming languages An MCS session is quite similar to a telnet client so user can connect to the server also with a simple telnet program But to take advantage of all the feature of the MCS protocol you ll need to use one of the available interfaces MCS is written in C so most of its facilities are available as classes In the following sections we ll assume that the reader has a minimum knowledge of the object oriented paradigm as well as the C syntax Furthermore we ll mention some of the MCS classes whose reference documentation can be found at http ross iasfbo inaf it mcs A user which connects to an MCS server needs to deal with the following classes e Client the interface to connect to an MCS server e Data the base class by which data are exchanged between client and server e Record a collection of Data objects e RecordSet a collection of Record objects Furthermore the following set of classes may be useful to a client program e DBConn connect to a database server e Query execute queries and retrieve results e Table perform direct access on a database table e Conf reads configuration files In Sect 5 1 we ll explain how to write a program which connects to an MCS server using
25. hould be installed then you ll get an error In this case you should login as root and retry 2 3 Troubleshooting In this section we show solution to the most common problems encountered while config uring and compiling MCS 13 2 4 Using the MCS library 2 MCS INSTALLATION AND USAGE 2 3 1 Problems with Python To build the Python to MCS interface the Python include files are required These are available in the Python source distribution or in the Python devel package of your distribution e The header Python h has not been found a symbolic link named python must point to the actual Python includes directory and it must be located either in usr include or usr local include 2 4 Using the MCS library Once you have installed the MCS library see Sect 2 2 you can use it in your C code as described here 2 4 1 Include MCS header All MCS classes and functions are defined inside the mcs namespace to avoid conflict with other libraries you may use To use the MCS facilities you must include the MCS header in your C source code as follows include lt mcs hh gt using namspace mcs To use the MCS library with other programming languages see Sect 6 2 4 2 Compile and link The MCS package installs a script named mcs config which can be used to retrieve several information regarding the installation itself for example the location of the include files and of the libraries as well as the list of the
26. in a separate thread you should derive the Thread class and overload its virtual run method This will become the body of execution of the separate thread Suppose you want to implement an application which reads file names from standard input and contemporary perform some task on the given files The derived class would be as in the following example 1 A global queue while file names are read from stdin they 2 are stored in this queue 18 3 2 Threads and synchronization 3 DEVELOPER S MANUAL 3 Record queue 4 5 Derive the Thread class s class MyThread public Thread 7 s void run 9 for 10 If there s at least one file name in the queue 11 if queue count 12 string fn queue pop sval 13 perform some task on the file 14 15 sleep_ms 1000 wait for one second 16 mi 18 As you can see this thread waits until there are file names in a queue and once the data arrive it will take the file name and perform some task on the file The main program should read the file names from stdin as in the following example int main Create the thread object and start it MyThread t t start string s while cin gt gt s Read from standand input queue push s Insert the string in the queue 1 2 3 4 5 6 7 8 9 This program will always be alive that is it will always react when you type a filename on s
27. ion del_CLASS addr These functions don t need any specific parameter but only the address of the object to be destroyed Note that you should call the appropriate destructor the one belonging to the same class with which the object was created otherwise you will surely get a segmentation fault These functions doesn t return any value 6 5 Methods Methods follow the name convention retval CLASS_methodname addr lt PARAMETERS gt where the parameters are the ones needed by the method Note that because overloading is not supported only one method with a certain name can exist The type and meaning of the returned values depend on the method called check the class documentation 6 6 Error handling Many MCS classes use exceptions to handle errors but this mechanism is not available in C nor in other languages for which we have an interface Because we didn t want to use the C Style error handling that is checking the returned value of a function after each call to see if an error occurred we implemented another mechanism the MCS library maintains an internal status structure which tells if an error occurred or not This status is checked each time an interface function is called if an error occurred in a previous call the function will return immediately otherwise the function will do its job If an error occurs during the execution of the function the status will be updated with an error messa
28. ion 6 4 or later e cURL http curl haxx se version 7 12 or later Typically these packages are already installed in the system if this is not the case you should install them before continuing However there are a lot of MCS facilities which depend on other optional packages e MySQL http www mysql com version 5 1 or later used to connect and manage a database to handle client authentications and grants e Openssl http www openssl org version 0 9 7 or later used to implement secure connections through sockets e CFITSIO http www cfitsio org version 0 9 7 or later used to read data in FITS format e IDL http www ittvis com idl version 5 6 or later used to implement the IDL to MCS interface e PHP http www php net version 5 0 5 or later used to implement the PHP to MCS interface e Python http www python org version 2 3 or later used to implement the Python to MCS interface You can enable or disable the compilation of each facility with the corresponding option of the configure script see Sect 2 2 1 11 2 2 Installing MCS 2 MCS INSTALLATION AND USAGE 2 2 Installing MCS 2 2 1 Configure Configuring MCS means checking your system for compatibilities search for include files and libraries and finally produce all necessary Makefiles needed to compile MCS This is done automatically by the distributed configure script Typically you can use this script without any option
29. is server isn t accessible directly from the clients but it is visible only to the application server At the moment the only supported database server is MySQL 14 In the future other servers may become accessible through MCS 4 1 2 Application server MCS based The application server is the core of the information system It implements the client server model a client opens a TCP socket towards the host running MCS and sends a request then the server computes an answer eventually querying the database and or executing some external programs and sends it back to the client The behaviour of the MCS server can be customized deriving some classes 4 1 3 External programs External programs are software applications written in any language which interact with the application server via command line and the standard output Support to these pro M4http www mysql com 22 42 The MCS server 4 THE MCS SERVER grams was added to easily integrate already existing applications within MCS 4 1 4 Clients Clients are programs which access the MCS service over the network Such programs can be written in any language and run on any platform provided that they implement the MCS protocol Interfaces that implement the MCS protocol are provided by the MCS library for the following languages on the Linux platform C C Fortran IDL PHP Python Support for other languages such as Java and Perl and the Windows platform
30. l the applications thus if your application needs to deal with this topics from a higher level then you can use the higher level MCS classes instead of the low level system routines The tasks that can be accomplished by the MCS classes can be subdivided in the following categories 1 2 MCS features 1 INTRODUCTION 1 2 1 Multithreading applications The Thread class can be used to create threads that are separate path of execution run ning in the same process memory space To create a separate thread you simply have to derive the Thread and implement the run method which will became the body of execu tion of the separate thread Synchronization between separate threads can be accomplished using the Synchro class This class is also used as parent class for other classes such as Record which acts as a shared resource between different threads 1 2 2 Network applications MCS provides several classes to develop network applications The HostInfo class can be used to retrieve information about a network host such as its IP address while the Net Interface class can be used to retrieve information about the network interfaces installed on a computer The Socket class is capable to open TCP sockets against remote hosts and send data through it The ServerSocket can be used to open a server socket that is a socket that waits on a specified port for incoming user connections This class has been used to implement the MCS server while Sock
31. le to the work directory GETDATA Retrieve a Data object PUTDATA Send a Data object QRY Execute an SQL query QRES Send the query result as a file FETCH Retrieve the record at the specified position EXEC Execute an external command or script with parameter Command USR lt username gt Used to supply the user name to the MCS server during authentication The user name identifies a list of grants Example usr giorgio Command PWD lt password gt Used to supply the password for a specific account Exam ple pwd my_password Command DBN lt application_name gt Used to select the application to which the user wants to connect This command can be used when a single MCS server implements different applications otherwise it is not useful Example dbn test This way you will access the application named test 26 42 The MCS server 4 THE MCS SERVER Command CON This command doesn t need any parameter and it is used to finalize the authentication process It must be used after the USR PWD and optionally the DBN com mands If the user authenticates successfully the following command will be automatically executed exec auto The MCS server administrator may use the auto script to initialize the user environ ment Command BYE Logout and close the connection Command CID Every client has a Client identifier that is a unique integer number that identifies the associated thread This command can be used to re
32. libraries to link to mcs config cflags mcs config libs For all other options type mcs config help To compile and link a program whose source file is say myprog cc against the MCS library you can issue the commands cpp mcs config cflags c myprog cc cpp 0o myprog myprog o mcs config libs or with a single command cpp mcs config cflags myprog cc o myprog mcs config libs Note that the single quotes are reversed single quotes ASCII decimal code 96 14 3 DEVELOPER S MANUAL 3 Developer s manual This section is aimed at showing to the reader some of the MCS basic concepts like the data abstraction layer thread handling database connections etc and focuses on various techniques to develop applications with MCS We will often refer to classes methods and function whose complete documentation can be found in the MCS library reference 13 3 1 The data abstraction layer The data abstraction layer is a set of classes aimed at providing a uniform access to data coming from different sources and to easily manipulate and transmit those data Namely the classes involved are Data Record and RecordSet with each one representing a different level of data hierarchy 3 1 1 The Data class The first level corresponds to the Data class which can be used to store a single data that is a number a string a date time a binary object etc The main feature of a Data object is it
33. lly sized container of Record objects It is not required that all contained objects have the same structure that is the same sequence of base type for Data objects Using a RecordSet object is quite similar to using a file handler indeed there is a current Record object pointed by a cursor like a pointer to a record in a file that can be moved forward and backward in the file to search for the required data The following example shows how to populate a RecordSet object and how to visit all the contained Record objects Create a RecordSet object RecordSet rset Bow No Insert the Record object created in the previous example rset insert rec Insert other Record objects as needed rset insert o On nu 1 o Visit all Record objects To visit all Record objects we have to move to the first Record object in the set rset setFirst 1 N 1 w Bl A 17 3 2 Threads and synchronization 3 DEVELOPER S MANUAL 15 16 Loop through all Record objects in the set 17 while rset eof is Get a reference to the current Record object 19 Record amp r rset rec 20 21 Use the record in some way 22 23 Move to the next Record object in the set 24 rset setNext 25 The previous example however shows a quite rare usage of the RecordSet class in fact it would be useless to populate a record and read it again inside the same programming unit The
34. most common way to populate a RecordSet is to derive the class and overload the fetch virtual method As an example see the code of the FileReader class It is worth to mention that while the names record and recordset are often used in database terminology the Record and RecordSet classes are not limited to database access instead they are designed to be general purpose For example the RecordSet is the parent class of the Parser_Table class which is used to read VOTable files Of course these classes are also used to perform database access in particular the result of a query inside the MCS library is presented as a RecordSet object a record of the result is presented as a Record object and a field of the record is presented as a Data object Another important feature of these classes is that they implement the Serializable interface so they can be easily sent through the network using the Socket class Indeed all message passing between client and server during an MCS session is performed using these objects to incapsulate the information being sent 3 2 Threads and synchronization Threads are essentially identical copies of a code which run on different data and let your program perform several contemporary tasks MCS lets you implement code that runs in separate threads and it provides a way to synchronize those threads using the Thread and Synchro classes 3 2 1 The Thread class To implement a code which runs
35. n be accessed from other software applications Furthermore MCS provides several mechanisms to customize the server behaviour and integrate already existing appli cations So MCS is an attempt to standardize the developing of these kind of applications through the VOTPP package 1 2 MCS features 1 INTRODUCTION By comparison MCS and its protocol are for software applications what a web server and HTTP are for the WWW a simple way to access data Another reason that drove the development of MCS is the need in today s astronomical projects of computational systems capable to store and analyze large amounts of scientific data to effectively share data with other research Institutes and to easily implement infor mation services to present data for different purposes scientific maintenance outreach etc Due to the wide scenario of astronomical projects there isn t yet a standardized ap proach to implement the software needed to support all the requirements of a project The new approach we propose here is the use of a unified model where all data are stored into the same database becoming available in different forms to different users with different privileges Finally MCS has been developed with the goal to simplify C developing through the use of high level classes that relieve the developers from repetitive tasks One of the most remarkable example of this higher level abstraction layer are the Data Record and RecordS
36. n protocol This process is very similar to the request of a web page The MCS library provides an already working multithreaded TCP server like many others but the MCS one has two interesting feature e the server behaviour is customizable that s the reason for its name that is the kind of queries that can be executed can be tuned on developer s needs e the communication protocol is perfectly integrated with the MCS data abstraction layer so that data sent back from the server are in a well defined format not like those of a web page and thus it is very simple to implement an application that can access the service 1 2 7 Other facilities MCS has also a lot of minor features that help the developers to deal with common problems Two of these facilities are e CommandParser a class to parse a command line with option and arguments support e Conf a class to read and write configuration files like the Windows INI files 1 2 8 Facilities included in previous releases A number of other facilities had been part of MCS in previous releases Now these facilities had become separate projects because they don t depend upon MCS except for VOTPP MyRO My Record Oriented privilege system MyRO is the name we use to refer to a technique used to implement a database privilege system on a per record basis Actually all database servers implement privilege systems based on tables or columns that is if a user has grants to access
37. ocumentation to see if a method is wrapped or not To use the interface you should therefore create an object call one or more of its methods and finally destroy him Before using an object you must call the appropriate wrapper to the constructor which returns the memory address where the object has been allocated You should not modify this address neither modify the type of the variable where the address has been stored for those languages that let you do this otherwise the object will become unreachable We recommend to destroy objects when they are no longer needed You can do this by calling the appropriate wrapper to the destructor and passing the address of the object to be destroyed The memory address you got from the constructor must also be passed to all the wrappers to methods of that class Important note What is returned by the wrapper to constructor routine is just a memory address so the language you are using even C doesn t know anything about the type of object that has been created For this reason if you use this address with a wrapper of another class your compiler won t give you any compilation or syntax error but you will likely get a segmentation fault when the program is running There is only one exception to this rule if an object derives from other classes then you can use the address of that object also with wrappers of parent classes In the following sections we ll explain the naming c
38. on 36 6 11 The IDL interf amp ceUSING MCS WITH OTHER PROGRAMMING LANGUAGES 6 11 The IDL interface The IDL interface will be available only if the option was enable when you executed the configuration script To use the IDL interface you should execute the id12mcs script in the directory where you ll store your source code this will create symbolic links to the files needed For efficiency reasons all interface functions will be available as IDL Dynamically Loadable Modules DLMs rather than functions and procedures No further action is required from the user to use these functions in the IDL code The comments relative to the C language apply here as well 37
39. onvention for a generic class named CLASS Arguments in brackets lt gt are specific to a function or method Arguments named addr are the memory address of an object 6 2 Constructors Constructors follow the name convention addr new_CLASS 0 lt PARAMETERS gt where the parameters are the ones needed by the constructor The first parameter is reserved for future use Note that only one constructor can be wrapped so check the documentation to see which one is used These functions return the memory address where the object has been allocated You must use this address in the subsequent methods call In all interfaces this memory address is stored in a numeric variable you should avoid changing its value or the type of the variable 6 3 Copying constructors Copying constructors follows the name convention 32 6 4 Destructors 6 USING MCS WITH OTHER PROGRAMMING LANGUAGES newaddr copy_CLASS addr These functions don t need any specific parameter but only the address of the object to be copied Note that you should call the appropriate copy constructor the one belonging to the same class with which the object was created otherwise you will surely get a segmentation fault These functions return the memory address of the newly created object Note actually only the Data class has a copy constructor implemented in the interfaces at the moment 6 4 Destructors Destructors follows the name convent
40. ption of the MCS library implementation It is produced using Doxygen The MCS documentation is work in progress so you should always look for the last version If you find any errors we d appreciate if you could send us an email A users mailing list is being prepared so please contact us if you are a potential user Thanks in advance available only in HTML format at http ross iasfbo inaf it mcs http www stack nl dimitri doxygen 12Giorgio Calderone lt gcalderone ifc inaf it gt Luciano Nicastro lt nicastro iasfbo inaf it gt 10 2 MCS INSTALLATION AND USAGE 2 MCS installation and usage The MCS software library is distributed in a tar gz package You can find the latest version at http ross iasfbo inaf it mcs To unpack the package simply issue the command tar xvzf mcs x y z tar gz where x y z are the version number namely the first number is the major revision the second number is the version and third number is the subversion A directory named mcs x y z will be created containing all sources code as well as the documentation and the scripts needed to install MCS Before installing MCS you should check that all mandatory dependencies are satisfied see Sect 2 1 then you must follow a three step procedure Configure Compile and Install 2 1 Dependencies The only mandatory packages required by MCS are e Perl http www perl com version 5 8 5 or later e PCRE http www pcre org vers
41. rder in respect to the C code let s examine the line 13 in detail cli gt aux 0 ivalQ C Data_ival Record_field Client_aux cli 0 C In either cases we are calling the Data ival method of the object returned by the Record operator at position 0 of the aux member of a Client object But the operator doesn t have any equivalent in the C language so it has been substituted by the Record_field function see reference documentation Furthermore the order in which members are called in C is reversed in the C language At line 38 there is a check to see if an error occurred and eventually the message is printed and the status is restored Finally note at lines 24 and 29 that we passed the address of the Client object to a wrapper for the RecordSet class this is allowed only because Client derives from Recordset 34 6 7 The C interface6 USING MCS WITH OTHER PROGRAMMING LANGUAGES o N Q wn e N NON N NN H EBH BP HO HO HKHH A U N E 0 7 O U dA GV N E OO 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 include lt stdio h gt include lt mcs _c h gt int main int argc char argv int i 2 IFD_OBJP cli new_Client 0 localhost 6523 0 10000 Client_login cli mcstest mcstest Client_exec cli CID 0 printf Client identifier is d n Data_ival Record_field Client_aux cli 0 Client_exe
42. s asa iii IA 28 4 4 3 Adding BATCH scripts oaa a 28 AAA Adding custom commands iau pere a 28 5 Connecting to an MCS service 29 5 1 The Client class ote oe a oe ah 29 9 2 User environment scali A A A Se 29 dd OST A E E A E E 30 SA TNO SOU peas G S gees Os Whe ae SB che a hae ee a She ee pra 30 6 Using MCS with other programming languages 31 6 1 Interface usage and naming convention 240 31 622 CONSUELA ac ce alii A tea a ca ice rele 32 6 3 Copying Constructors ooo ele dor eek Sk bea de e Ad 32 Ost DeStructors Losi as tess fida sede ita dee Es Pe e 33 Gio Methods corner aLe ata ri 33 0 6 Error handle esigia s a we ds i io dala aoe lire he ES a 33 OU The antenas oil ei ie eo en oe ee oa em Bnd 34 6 8 The Fortran interface ke ki tek eh an ke ES Ee PA 36 6 9 The PHP interface ass A ei E AR lh a 36 6 10 The Python interface io a bei nk AAA A A 36 0511 The TD interne acacia ea e he ee ea ere ba 37 1 INTRODUCTION 1 Introduction MCS is a collection of high level C classes and functions designed to easily implement the following kind of applications e multi thread applications e network applications through TCP database MySQL applications information servers VOTable and or FITS access Aside from these tasks MCS provides several other features that can be used to solve common problems when developing applications in C The greatest advantage in using MCS is t
43. s capability of performing conversions between different types of data that is you can assign to a Data object different types of data as in the following example Create a Data object Data mydata STRING 20 Assign an integer mydata 12 Assign a floating point number mydata 1 2 o IO e Ww N Rp Assign a string s My name is Giorgio pi As you can assign different type of data to a Data object you can also assign a Data object value to different types of variable as in the following example Assign to an integer variable int i mydata ival 1 2 3 4 Assign to a floating point variable 5 float f mydata fval 6 7 8 Assign to a string variable string s mydata sval You should have noticed that in this case a simple assignment is not allowed so you have to call the appropriate val method of the Data class in which the first character is i for 13http ross iasfbo inaf it mes 15 3 1 The data abstraction layer 3 DEVELOPER S MANUAL integers f for single precision floating point numbers s for strings etc Note however that a Data object is not a dynamic type object like those of other programming languages such as Perl PHP IDL indeed it always has a base type that determines the size of its internal buffer and the behaviour of the different conversion routines in the last example the base type is a string 20 charac
44. t Xt cout lt lt endl YN N N N O NNA Move to next record qry setNext Y N N N o N Q A gt gt Listing 2 Source of dbl cc include lt mcs hh gt using namespace mcs int main int argc char xargv Start the server daemon mcsStart simplest N Qa da wn eh Listing 3 Source of serverl cc db connect mcstest mcstest test 192 168 1 5 1 6 About this document 1 INTRODUCTION o On Q A e N 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 include lt mcs hh gt using namespace mcs int main int argc char xargv Connect to the MCS server Client cli localhost 6523 Perform authentication cli login mcstest mcstest test Upload a file cli exec PUT myfile Download a file cli exec GET myfile Execute a query on remote database cli exec QRY SELECT FROM mcstest Retrieve the result set cli exec QRES Loop through the resulting record set while cli eof Get a reference to current record Record amp rec cli rec For each field print its value for int i 0 i lt rec count i cout lt lt rec i sval lt lt Xt cout lt lt endl Move to next record cli setNext Listing 4 Source of client1 cc 1 6 About this document 1 INTRODUCTION e libmcs reference technical descri
45. tdin even if it is working on a file in a separate thread The Thread class is used inside MCS to implement the multithreaded server In the simplest case when a user connects to the server it will create an instance of a class named UserThread which derives Thread which will listen for user commands and eventually will send back the requested data Thus the main server program can continue to listen for new users connections Also if other users are already connected they will have their own thread to work with This way the server can provide services to different users at the same time 3 2 2 The Synchro class Once you have different threads running in your application you may need to synchronize them A typical example occurs when the threads need to access a global variable Suppose that in the previous example the computation inside the thread is very time consuming and you want to elaborate two files in parallel This can be easily done creating two or even more instances of the MyThread class in the main program 19 3 3 Database access 3 DEVELOPER S MANUAL Create two instances of the MyThread class 1 2 MyThread tl 3 MyThread t2 4 5 Start separate threads e tl start 7 t2 start That s all is needed to implement the parallel elaboration of two files But there s is a hidden bug in this code what would happen if both threads try to read from the global queue at the same time Even i
46. ters long A consequence of this fact is that an assignment can also lead to an error just because the base type cannot change during the use of the object and some conversions do not make sense In our previous example assigning a string more than 20 characters long would have led to an error Let s examine another case where an assignment could lead to an error 1 Create a Data object with base type INT 2 Data mydata INT 3 almydata 12 Ok s mydata 1 2 Ok will be rounded to 1 el mydata 1 5 Ok will be rounded to 2 7 s mydata A string Error 9 mydata 123 That is correct 10 ufint i mydata ival Ok i 123 12 string s mydata sval Ok s 123 As you can see the assignment in line 8 doesn t make any sense you can t assign a generic string to an integer base type On the other hand the assignment in line 9 is perfectly allowed because that string can be converted to an integer Finally the last two assignment are allowed even if in the first case the variable will be set to a value of 123 as an integer whereas in the second the variable will be set to the string 123 whose memory representation is quite different from the integer in the first case 3 1 2 The Record class On the second level of hierarchy there is the Record class which can be seen as a dynamically sized array of Data objects Here the word record is meant in the sense of a record in the P
47. these classes and the C language If a user wishes to use another language to connect to MCS he can use one of the available interfaces which are simply wrappers to the classes mentioned above For this reason the code to connect to MCS is quite similar in all languages and we recommend to read Sect 5 1 also if you don t plan to use C Successive sections will report information specific to each language As already mentioned the languages actually supported are C Fortran IDL PHP and Python In the near future interfaces will be developed for Java and Perl 6 1 Interface usage and naming convention In this section we describe how to use the interfaces for languages others than C and the naming convention used For a detailed description of all the classes involved and their methods check the reference manual as well as Sect 5 1 As mentioned above the interfaces are simply wrappers around C classes so when you re calling a function of the interface in your favourite language you are actually calling a method of a C object that lives in the heap dynamic memory That s the reason 31 6 2 Constructors 6 USING MCS WITH OTHER PROGRAMMING LANGUAGES why there isn t a reference documentation for each interface the main reference for the MCS classes contains all the information you need Note that not all the class members are wrapped in the various interfaces because only C supports overloading check the classes d
48. trieve such a number Command QRY sqascii sqfits lt query gt Execute SQL queries directly on the database DB server The query doesn t need to be quoted and you can use the quotes inside the query itself If it is a selection it will return information about the record set if it is not will return the number of affected records If the option sqascii or sqfits are given then the result of the query will be written into a file in the work directory respectively in ASCII or FITS format Example qry SELECT FROM table Notice you don t need to supply the at the end of the query like you would do with the MySQL client Command QRES This command prepare an ASCII file containing all records from the last query then it will send the file to the client Command EXEC lt name gt PARS This command executed an external program an SQL script or a batch file The name of external programs and or script are specified on the server in the configuration file If you re executing an external program the parameters will be passed on the command line and its standard output and error will be written into the work directory in the out and err file respectively If you re executing an SQL or batch script the parameters will be substituted inside the script where a placeholder like 1 2 etc is found Command GET lt file name gt Retrieve a file located into the work directory on the server The parameter
49. user with a lot of warnings The comments relative to the C language apply here as well furthermore notice that for some functions like Client_exec RecordSet_setNext we used a dummy variable for the return value This is necessary because these are really functions not procedures like del_Client even if the return value is of no interest 6 9 The PHP interface The PHP interface will be available only if the option was enabled when you executed the configuration script Starting from MCS version 0 3 1 it is not required anymore to use the php2mcs script in order to be able to use the PHP interface You still must include the file php2mcs php in your code require php2mcs php The comments relative to the C language apply here as well furthermore notice that instead of passing 0 to those parameters whose C counterparts require a NULL value we used the ifd_null function 6 10 The Python interface The Python interface will be available only if the option was enabled when you executed the configuration script Starting from MCS version 0 3 2 it is not required anymore to use the python2mcs script in order to be able to use the Python interface You still must import the file python2mcs py in your code from python2mcs import The comments relative to the C language apply here as well furthermore notice that instead of passing 0 to those parameters whose C counterparts require a NULL value we used the ifd_null functi
50. will be available soon we hope 4 2 The MCS server The MCS server is an application server that is an application that waits on a TCP port until a client gets connected When a client is connected the server provides an information service that is the possibility to request information to the server Data are transmitted using the MCS protocol which must be implemented by the clients This protocol is flexible enough to transmit binary data and files but also to let a client access the service offered by MCS from a simple telnet client Due to the flexibility of the protocol MCS is the natural solution to implement communication between different software tools running on different hosts through the network So MCS can also perform IPC Inter Process Communication 4 2 1 Comparison with a shell Using interactively an MCS server resemble very closely the usage of a classic Unix shell that is a command line interface with a prompt on which users can execute commands in their own environment and wait for the output before a new command can be issued It is therefore possible to make a comparison between the components of a shell and the ones from an MCS connection see Tab 1 The concepts listed herein will be described in details later Unix shell MCS server stdin e stdout bidirectional TCP socket system account MySQL account internal commands base commands programs shell scripts external programs EXE
Download Pdf Manuals
Related Search