Arc::DataHandle Class Reference

This class is a wrapper around the DataPoint class. More...

#include <DataHandle.h>

Public Member Functions
	DataHandle (const URL &url, const UserConfig &usercfg)
	~DataHandle ()
DataPoint *	operator-> ()
const DataPoint *	operator-> () const
DataPoint &	operator* ()
const DataPoint &	operator* () const
bool	operator! () const
	operator bool () const
Static Public Member Functions
static DataPoint *	GetPoint (const URL &url, const UserConfig &usercfg)

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Detailed Description

This class is a wrapper around the DataPoint class.

It simplifies the construction, use and destruction of DataPoint objects and should be used instead of DataPoint classes directly. The appropriate DataPoint subclass is created automatically and stored internally in DataHandle. A DataHandle instance can be thought of as a pointer to the DataPoint instance and the DataPoint can be accessed through the usual dereference operators. A DataHandle cannot be copied.

This class is main way to access remote data items and obtain information about them. Below is an example of accessing last 512 bytes of files stored at GridFTP server.

 #include <iostream>
 #include <arc/data/DataPoint.h>
 #include <arc/data/DataHandle.h>
 #include <arc/data/DataBuffer.h>
 
 using namespace Arc;
 
 int main(void) {
   #define DESIRED_SIZE 512
   Arc::UserConfig usercfg;
   URL url("gsiftp://localhost/files/file_test_21");
   DataPoint* handle = DataHandle::GetPoint(url,usercfg);
   if(!handle) {
     std::cerr<<"Unsupported URL protocol or malformed URL"<<std::endl;
     return -1;
   };
   FileInfo info;
   if(!handle->Stat(info)) {
     std::cerr<<"Failed Stat"<<std::endl;
     return -1;
   };
   unsigned long long int fsize = handle->GetSize();
   if(fsize == (unsigned long long int)-1) {
     std::cerr<<"file size is not available"<<std::endl;
     return -1;
   };
   if(fsize == 0) {
     std::cerr<<"file is empty"<<std::endl;
     return -1;
   };
   unsigned long long int foffset;
   if(fsize > DESIRED_SIZE) {
     handle->Range(fsize-DESIRED_SIZE,fsize-1);
   };
   unsigned int wto;
   DataBuffer buffer;
   if(!handle->PrepareReading(10,wto)) {
     std::cerr<<"Failed PrepareReading"<<std::endl;
     return -1;
   };
   if(!handle->StartReading(buffer)) {
     std::cerr<<"Failed StopReading"<<std::endl;
     return -1;
   };
   for(;;) {
     int n;
     unsigned int length;
     unsigned long long int offset;
     if(!buffer.for_write(n,length,offset,true)) {
       break;
     };
     std::cout<<"BUFFER: "<<offset<<": "<<length<<" :"<<std::string((const char*)(buffer[n]),length)<<std::endl;
     buffer.is_written(n);
   };
   if(buffer.error()) {
     std::cerr<<"Transfer failed"<<std::endl;
   };
   handle->StopReading();
   handle->FinishReading();
   return 0;
 }

And the same example in python

 import arc
 
 desired_size = 512
 usercfg = arc.UserConfig()
 url = arc.URL("gsiftp://localhost/files/file_test_21")
 handle = arc.DataHandle.GetPoint(url,usercfg)
 info = arc.FileInfo("")
 handle.Stat(info)
 print "Name: ", info.GetName()
 fsize = info.GetSize()
 if fsize > desired_size:
     handle.Range(fsize-desired_size,fsize-1)
 buffer = arc.DataBuffer()
 res, wto = handle.PrepareReading(10)
 handle.StartReading(buffer)
 while True:
     n = 0
     length = 0
     offset = 0
     ( r, n, length, offset, buf) = buffer.for_write(True)
     if not r: break
     print "BUFFER: ", offset, ": ", length, " :", buf
     buffer.is_written(n);

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Member Function Documentation

static DataPoint* Arc::DataHandle::GetPoint	(	const URL &	url,
		const UserConfig &	usercfg
	)			[inline, static]

Returns a pointer to new DataPoint object corresponding to URL. This static method is mostly for bindings to other languages and if availability scope of obtained DataPoint is undefined.

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The documentation for this class was generated from the following file:

• DataHandle.h