[protobuf] Re: Issue 689 in protobuf: Repeated fields do not serialize the 'size' into the file. Hence deserialize of repeated expects an unending sequence of repeated fields

[protobuf]

Comment #2 on issue 689 by narayan....@gmail.com: Repeated fields do not  
serialize the 'size' into the file. Hence deserialize of repeated expects  
an unending sequence of repeated fields
https://code.google.com/p/protobuf/issues/detail?id=689
Thank you for the response. This is what I am doing - i.e., adding the size  
before sending the protobuf on the wire (file descriptor of a file or  
socket) - then serializing-to-array and parsing-from-array.

Since there are many protobuf message structures like this in my college  
project, I ended up writing a template methods as follows (where T is the  
type of the protobuf object and My::Size itself is another protobuf object  
with a single int64 field in it, named size).

The request here is : Can we do something better?

---------------------
The template function:
---------------------
namespace My
{
    ///
    /// @brief
    /// Handy template to read a protobuf message object
    /// along with its byte size from a file descriptor.
    ///
    /// @param[out] rObj
    /// Reference to the protobuf object.
    ///
    /// @param[in] iFd
    /// The file descriptor.
    ///
    template <class T> void ReadProtobufWithSizeFromFileDescriptor(T &rObj,  
int iFd)
    {
        My::Size objSize;

        objSize.set_size(0);

        char *pByteArray = new char[objSize.ByteSize()];

        if (!pByteArray)
        {
            ERRORprintf("Unable allocate memory.");
            MY_THROW("Allocate Error.");
        }

        int iResult = read(iFd, pByteArray, objSize.ByteSize());

        if (iResult < objSize.ByteSize())
        {
            ERRORprintf("Unable to read from file.");
            delete [] pByteArray;
            MY_THROW("File Read Error.");
        }

        // Get the object size first.
        bool bResult = objSize.ParseFromArray(pByteArray,  
objSize.ByteSize());
        if (!bResult)
        {
            ERRORprintf("Unable to read from file.");
            MY_THROW("File Read Error.");
        }

        delete [] pByteArray;

        pByteArray = new char[objSize.size()];

        if (!pByteArray)
        {
            ERRORprintf("Unable allocate memory.");
            MY_THROW("Allocate Error.");
        }

        iResult = read(iFd, pByteArray, objSize.size());

        if (iResult < objSize.size())
        {
            ERRORprintf("Unable to read from file.");
            delete [] pByteArray;
            MY_THROW("File Read Error.");
        }

        bResult = rObj.ParseFromArray(pByteArray, objSize.size());

        if (!bResult)
        {
            ERRORprintf("Unable to read from file.");
            delete [] pByteArray;
            MY_THROW("File Read Error.");
        }

        delete [] pByteArray;
    }

    ///
    /// @brief
    /// Handy template to read a protobuf message object
    /// along with its byte size from a file descriptor.
    ///
    /// @param[out] rObj
    /// Reference to the protobuf object.
    ///
    /// @param[in] iFd
    /// The file descriptor.
    ///
    template <class T> void WriteProtobufWithSizeToFileDescriptor(T &rObj,  
int iFd)
    {
        My::Size objSize;

        objSize.set_size(rObj.ByteSize());

        char *pByteArray = new char[objSize.ByteSize()];

        if (!pByteArray)
        {
            ERRORprintf("Unable allocate memory.");
            MY_THROW("Allocate Error.");
        }

        // Write the object size first.
        bool bResult = objSize.SerializeToArray(pByteArray,  
objSize.ByteSize());

        if (!bResult)
        {
            ERRORprintf("Unable to write to file.");
            MY_THROW("File Write Error.");
        }

        int iResult = write(iFd, pByteArray, objSize.ByteSize());

        if (iResult < objSize.ByteSize())
        {
            ERRORprintf("Unable to write to file.");
            delete [] pByteArray;
            MY_THROW("File Write Error.");
        }

        delete [] pByteArray;

        pByteArray = new char[objSize.size()];

        if (!pByteArray)
        {
            ERRORprintf("Unable allocate memory.");
            MY_THROW("Allocate Error.");
        }

        bResult = rObj.SerializeToArray(pByteArray, objSize.size());

        if (!bResult)
        {
            ERRORprintf("Unable to write to file.");
            delete [] pByteArray;
            MY_THROW("File Write Error.");
        }

        iResult = write(iFd, pByteArray, objSize.size());

        if (iResult < objSize.size())
        {
            ERRORprintf("Unable to write to file.");
            delete [] pByteArray;
            MY_THROW("File Write Error.");
        }

        delete [] pByteArray;
    }
}

--------------------------


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