GET (TCP/IP command) - how it works?

[dajan]

Hello programmers,

I am trying to get a little into the network things, and there is something i don't get about the GET network command, maybe someone experienced could explain it.
Here's the situation in fragment of code:

Code: QB64: [Select]

1. TYPE someType
2.     x AS INTEGER
3.     y AS INTEGER
4.     s AS STRING * 10
5.     '...
6. END TYPE
7.  
8. DIM someVar(1 TO 999) AS someType
9. DIM someOtherVar AS someOtherType 'any type, doesnt matter
10.  
11. clientHandle& = _OPENCLIENT("TCP/IP:1234:localhost")
12.  
13. DO
14.     GET clientHandle#, , someVar()
15.     '...other code that deals with somevar()
16.     IF NOT EOF(clientHandle) THEN GET clientHandle#, , someOtherVar
17. LOOP UNTIL EOF(clientHandle)
18.  
19. '...and another code that deals with somevar() and someOtherVar
20.  
21.  

My questions are:
1. after GET reads someVar() from client, how can I tell, if it has actually read it? I understand, that GET reads someVar only if there are enough bytes in clientHandle. But what tells me it did? GET does not return anything like status, from what I know.

2. If GET doesn't put anything into someVar (e.g. there is nothing or few to read), will the original content of someVar() be destroyed or preserved?

Thanks.

[Petr]

Hi. I didn't celebrate success with networking ... but ....
If one party sends information about the start of the transmission, it is good to wait for the set time (set yoursefl by your program) to confirm. Then the sending party sends the amount of data it wants to transfer. He waits for confirmation from the counterparty and then begins to send data and waits for a specified amount of time to confirm receipt from the counterparty. Preferably, the counterparty sends the size of the received data. If it does not send anything within the set limit, you must resolve it in the program so that both parties resume the new transmission (transfer reset). You'll never get the data you won't catch. These are my experiences gained when writing a network version of BattleShip game, that worked on the network .... 3x correctly and then stuck, just because I waited for the client to receive data in infinite time...  (my version not check the time)  And be careful. What works in localhost mode perfectly, may not work in the actual network.

[Petr]

Here I found one old program to transfer the image over the network. Again - it does not watch the time, so it will be unreliable in the real network.

Code: QB64: [Select]

1.  
2. DIM SHARED Host AS LONG, Client AS LONG
3. DIM Buffer AS _MEM, Offset AS _OFFSET, lastOffset AS _OFFSET
4.  
5. I_am = Network("localhost")
6. image& = _SCREENIMAGE '_LOADIMAGE("so.jpg", 32)
7. 'Image& = _LOADIMAGE("3.jpg", 32)
8.  
9. SELECT CASE I_am
10.     CASE 1 'HOST   -    in this demo HOST send image to client
11.         _TITLE "Host"
12.  
13.         Res$ = MKL$(_WIDTH(image&)) + MKL$(_HEIGHT(image&)) + MKL$(_PIXELSIZE(image&))
14.         PUT #Host, , Res$
15.  
16.  
17.         Buffer = _MEMIMAGE(image&)
18.         Offset = Buffer.OFFSET
19.         lastOffset = Buffer.OFFSET + _WIDTH(image&) * _HEIGHT(image&) * 4
20.         imageData$ = SPACE$(lastOffset - Offset)
21.         _MEMGET Buffer, Offset, imageData$
22.         _MEMFREE Buffer
23.         LOCATE 1, 1: PRINT "Sending picture data:"
24.  
25.         PUT #Host, , imageData$
26.         _DELAY .05
27.         PRINT "Waiting for confirm": _DISPLAY
28.         message$ = Transfer$(Host&, 6)
29.  
30.         DO
31.             IF message$ = "ALL OK" THEN LOCATE 2, 1: PRINT "Image transferred   ": _DISPLAY: END
32.             _DISPLAY
33.             _LIMIT 25
34.         LOOP
35.  
36.  
37.     CASE 2 'CLIENT - in this demo receive picture and show it on the screen
38.         _TITLE "Client"
39.         Head$ = Transfer$(Client&, 12)
40.         W& = CVL(MID$(Head$, 1, 4))
41.         H& = CVL(MID$(Head$, 5, 4))
42.         D& = CVL(MID$(Head$, 9, 4))
43.         SELECT CASE D&
44.             CASE 0: PRINT "Textmode not supported": END
45.             CASE 1: clrs = 256
46.             CASE 4: clrs = 32
47.         END SELECT
48.  
49.         imageData$ = Transfer$(Client&, (W& * H& * D&))
50.         receivedImage& = _NEWIMAGE(W&, H&, clrs) 'use the width and height you transferred before here
51.         Buffer = _MEMIMAGE(receivedImage&)
52.         _MEMPUT Buffer, Buffer.OFFSET, imageData$
53.         _MEMFREE Buffer
54.         SCREEN receivedImage&
55.         confirm$ = "ALL OK" '6 bytes
56.         PUT #Client&, , confirm$
57.         END
58. END SELECT
59.  
60.  
61. FUNCTION Transfer$ (channel AS LONG, lenght)
62.     Transfer$ = ""
63.     DO
64.         GET #channel&, , T$
65.         IF LEN(T$) THEN Transfer$ = Transfer$ + T$
66.         '  IF _CONNECTED(channel&) = 0 THEN PRINT "Connection failure.": END
67.     LOOP WHILE LEN(Transfer$) < lenght
68. END FUNCTION
69.  
70. FUNCTION Network (IP AS STRING)
71.     _AUTODISPLAY
72.     Client& = _OPENCLIENT("TCP/IP:3455:" + LTRIM$(IP$))
73.     IF Client& THEN
74.         Network = 2 'client
75.     ELSE
76.         PRINT "No host found"
77.         _DELAY 1
78.         Client& = _OPENHOST("TCP/IP:3455")
79.         IF Client& THEN
80.             PRINT "Host created!"
81.             DO
82.                 i& = _KEYHIT
83.                 IF i& = 27 THEN EXIT FUNCTION
84.                 Host& = _OPENCONNECTION(Client&)
85.                 _DISPLAY
86.             LOOP UNTIL Host&
87.             Network = 1
88.         END IF
89.     END IF
90. END FUNCTION
91.  
92.  

I forgot .... you have to run it twice to try this program. The first run creates a HOST, lets you run it and starts it again, the second run creates a client and sends a screenshot between them, the client will also show it for you, when the transfer is complete.