Chapter 51. Parsing and URIs
Elements of the NSCL acquisition system are named with Universal Resource Locators, or URIs. For the purposes of the NSCLDAQ, a URI is not really distinguishable from a URL (Universal Resource Locator). It has the form: protocol://host:port/path, or protocol://host:port
- protocol
Is the means used to talk with a resource. For nscldaq this is most often tcp
- host
Is the system that hosts the resource that is identified by the URI. The host can either be a dotted IP address, or the DNS name of a host on the network.
- path
Identifies the resource within the host. This identification may differ depending on what the resource is. For a ring buffer, for example, the path is the name of the ring buffer.
- port
Identifes the network port number used to contact the server that provides the resource to the network.
The URI library is a class that parses URI's and provides member functions that return the elements of a URI. Here's a trivial example of the URI library in use:
Example 51-1. Sample URI library program
#include <URL.h>
#include <URIFormatException.h>
#include <iostream>
#include <stdlib.h>
int main(int argc, char** argv)
{
if (argc != 2) {
cerr << "Usage:\n";
cerr << " urltest URI\n"; 
exit(-1);
}
try { 
URL uri(argv[1]); 
cout << "Protocol: " << uri.getProto()
<< " host : " << uri.getHostName()
<< " path: " << uri.getPath() 
<< " port: " << uri.getPort() << endl;
}
catch(CURIFormatException& error) {
cerr << "URI was not valid: "
<< except.ReasonText() 
<< endl;
exit(-1);
}
exit(0);
}
- The test program accepts the URL to parse as its command line parameter. If the user does not provide a URL or provides too many parameters, the progrm's usage is printed on stderr before the program exits.
-
The
URLconstructor parses the URI. If, however the URI is not valid syntax, or refers to a host that does not exist, it will throw an exception (CUIRFormatException). The construction and manipulation of the URI is therefore wrapped in a try/catch block. - This section of code takes the parsed URI and demonstrates how to pull the elements of the URI out and print them.
-
This code catches errors that may be thrown by the URI
parse. The reason for the error is printed out.
For more information see
the
CURIFormatExceptionreference page.
To incorporate the URI library into your source code, you must compile with an appropriate set of switches to allow the compiler to locat your header files, and the linker to locate the URL library both at link time and at load time. If the example program above is called urltest.cpp and if you have an environment variable DAQROOT that points to the top level directory of the NSCLDAQ install tree the command below will compile and link the program.