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digitalmars.D.learn - Receiving data into a type using sockets

reply Jonathan Sternberg <jonathansternberg gmail.com> writes:
I'm trying to learn how to do some networking code in D. In C, if I wanted to
read 4 bytes into an integer, I could just do (ignoring any error detection):

int foo;
recv(sockfd, &foo, sizeof(int), 0);

How do I do this with D? The receive function takes in a void [] parameter and
doesn't take in a number of bytes to read. Is there anyway to accomplish this
in D?
Jun 05 2011
parent reply David Nadlinger <see klickverbot.at> writes:
On 6/5/11 8:51 PM, Jonathan Sternberg wrote:

 I'm trying to learn how to do some networking code in D. In C, if I wanted to
 read 4 bytes into an integer, I could just do (ignoring any error detection):

 int foo;
 recv(sockfd,&foo, sizeof(int), 0);

 How do I do this with D? The receive function takes in a void [] parameter and
 doesn't take in a number of bytes to read. Is there anyway to accomplish this
 in D?


auto socket = new Socket(…);
…
int foo;
socket.receive((&foo)[0..1]);

---

void[] is like an array of bytes, with the difference to ubyte[] being 
that it can contain pointers which must be taken into account by the GC, 
and implicit convertibility. However, all the socket functions should 
operate on ubyte[] instead of void[] by current guidelines – the socket 
module is really old, this will definitely be changed when it will be 
overhauled/replaced.

David
Jun 05 2011
parent reply Jonathan Sternberg <jonathansternberg gmail.com> writes:
Cool. It compiles, but it doesn't seem to be doing exactly what I want. Say I
send
2 integers from the server to the client. When I do this on the client, it seems
to do the wrong thing.

int first, second;
auto sock = new TcpSocket();
sock.connect(new InternetAddress("localhost", 10000));

writeln( sock.receive((&first)[0..int.sizeof]) );
writeln( sock.receive((&second)[0..int.sizeof] );

This seems to print 8 and then block on the second call to receive. I thought
that
D was supposed to recognize that the array was only 4 bytes long and read only
that much. (note: on a 32-bit machine, so int comes out to 4 bytes)

When I do:

writeln( (&first)[0..int.sizeof].length );

It prints 4 as it's supposed to.
Jun 05 2011
parent reply David Nadlinger <see klickverbot.at> writes:
On 6/5/11 9:49 PM, Jonathan Sternberg wrote:

 Cool. It compiles, but it doesn't seem to be doing exactly what I want. Say I
send
 2 integers from the server to the client. When I do this on the client, it
seems
 to do the wrong thing.

 int first, second;
 auto sock = new TcpSocket();
 sock.connect(new InternetAddress("localhost", 10000));

 writeln( sock.receive((&first)[0..int.sizeof]) );
 writeln( sock.receive((&second)[0..int.sizeof] );

 This seems to print 8 and then block on the second call to receive. I thought
that
 D was supposed to recognize that the array was only 4 bytes long and read only
 that much. (note: on a 32-bit machine, so int comes out to 4 bytes)

 When I do:

 writeln( (&first)[0..int.sizeof].length );

 It prints 4 as it's supposed to.


&first is of type int*, so (&first)[0..int.sizeof] returns a slice 
pointing to int.sizeof (i.e. 4) ints, not a single one as you intend to. 
Just use »(&first)[0..1]« as per my original reply, and you should be fine.

David
Jun 05 2011
parent Andrew Wiley <wiley.andrew.j gmail.com> writes:
On Sun, Jun 5, 2011 at 12:55 PM, David Nadlinger <see klickverbot.at> wrote=
:


 On 6/5/11 9:49 PM, Jonathan Sternberg wrote:


 Cool. It compiles, but it doesn't seem to be doing exactly what I want.
 Say I send
 2 integers from the server to the client. When I do this on the client, =




it

 seems
 to do the wrong thing.

 int first, second;
 auto sock =3D new TcpSocket();
 sock.connect(new InternetAddress("localhost", 10000));

 writeln( sock.receive((&first)[0..int.sizeof]) );
 writeln( sock.receive((&second)[0..int.sizeof] );

 This seems to print 8 and then block on the second call to receive. I
 thought that
 D was supposed to recognize that the array was only 4 bytes long and rea=




d

 only
 that much. (note: on a 32-bit machine, so int comes out to 4 bytes)

 When I do:

 writeln( (&first)[0..int.sizeof].length );

 It prints 4 as it's supposed to.


 &first is of type int*, so (&first)[0..int.sizeof] returns a slice pointi=


ng

 to int.sizeof (i.e. 4) ints, not a single one as you intend to. Just use
 =BB(&first)[0..1]=AB as per my original reply, and you should be fine.


Also, note that receive is basically a direct call to C's receive, which
means that it has the same behavior with regards to buffer filling. Calling
sock.receive((&first)[0..1]) returns the number of bytes read, which may be
less than 4. I've handled this in the past by writing a template function
that takes a primitive type and loops until it has read all the bytes it
needs.
Oh, and D's int is always 32 bits, on 32 bit or 64 bit platforms. size_t is
an alias that switches from uint on 32 bit to ulong on 64 bit, and there's
another alias somewhere for signed types (ssize_t, I believe). The primitiv=
e
types always have the same sizes until you get into things like cent.
Jun 05 2011