native messaging example in c++ for windows

[Rajesh Katalkar]

I am making a native messaging host using vc++ 2010 console app ...It is working but does not take read big json strings...
If i pass the same value to sample made in python ...it works there.....

following is roughly how i read

while(1)
{
   cnt = 0;
   zeromem len;;
   cin.read(len,4);
   for(i=0;i<4;i++)
    cnt += len[i];

  cin,read(buff,cnt);

//also below is how i write
    unsigned int len = response.length();
        cout << char(((len>>0) & 0xFF))
            << char(((len>>8) & 0xFF))
            << char(((len>>16) & 0xFF))
            << char(((len>>24) & 0xFF));

        cout<<response<<flush;   
}

I could not find a working eg of c++ anywhere



   

[Lambros Lambrou]

I think you're missing a line to shift "cnt" 8 bits before adding len[i] inside the loop:

cnt << 8;

cnt += len[i];

Lambros

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[Rajesh Katalkar]

message ={"text":"asasdasdasdasdasdasd","text1":"asasdasdasdasdasdasd","text2":"asasdasdasdasdasdasd","text3":"asasdasdasdasdasdasd","text4":"asasdasdasdasdasdasd"};

are you saying cnt = cnt<<8;
i tried it no use...
additionally i get a negative value of length in buff read

[Lambros Lambrou]

Yes you're right, I did mean cnt <<= 8;

Also, on an x86 system, the number is stored as little-endian, so you'll need to reverse the loop: for (i = 3; i >=0; i--)

Have a look at our implementation here: https://code.google.com/p/chromium/codesearch#chromium/src/remoting/host/native_messaging/native_messaging_reader.cc&q=NativeMessagingReader&sq=package:chromium&type=cs&l=78

This technique (using reinterpret_cast<char*>) has the advantage of working on little-endian and big-endian platforms.

[Rajesh Katalkar]

[Rajesh Katalkar]

i am using win7 64bit
my native host is 32bit

 i get "›" in len[0] which is -101

following is what i did
            for(int i=3;i>=0;i--)
            {  
                leng <<= 8;
                leng += (len[i]);
            }

i am still getting -101
where to put the reinterpret.....
I did not understand the chromium code,,,,it was sending message_length as buff to read from  but its a typedef of unit32 which has nothing

    MessageLengthType message_length;
    int read_result = read_stream_.ReadUntilComplete(
        reinterpret_cast<char*>(&message_length), kMessageHeaderSize);

can you please update my sample give me exact code so that i can try it

[Rajesh Katalkar]

I think i understood the code and what you want to say..
below is updated code which works fine for me now ,,for both 32 and 64bit version of native host....
i will test this more tomorrow as i will sleep now,,,
but please confirm the below logic is right or wrong..

while(1)
{
   int cnt = 0;

   cin.read(reinterpret_cast<char*>(&cnt) ,4);


  cin,read(buff,cnt);

[Lambros Lambrou]

Your "len" array was signed char[] rather than unsigned char[], which was messing up your arithmetic. Replacing "leng += len[i]" with "leng |= len[i]" would fix this, I think.

The reinterpret_cast version looks OK. Though it's better to use an explicit 32-bit type such as uint32_t instead of int.

[Vikas Pushkar]

Hi,

I am trying to do the same thing but i am recieving length as 0

i am using following code:

 while (1){
             int cnt = 0;
             std::cin.read(reinterpret_cast<char*>(&cnt) ,4);
             std::cin.read(buff,cnt);
             sprintf(Log_str," %d and %s \n",cnt,buff);
             LOG(Log_str);//LOG writes it to a opened file.

the output is "0  and   "

On Tuesday, 3 December 2013 22:50:13 UTC+5:30, Rajesh Katalkar wrote: