Difference between revisions of "TWSocket.Receive"
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== Definition == | == Definition == | ||
| − | ''' | + | '''function''' Receive(Buffer:Pointer; BufferSize:Integer): '''integer'''; |
== Description == | == Description == | ||
'''Receive''' is used in the [[TWSocket.OnDataAvailable|OnDataAvailable]]-Event to actually fetch the received data. The parameters needed are a buffer where the data will be placed and the size of that buffer. The return value of Receive specifies how many bytes where actually read and put in the buffer. If the buffer is too small, OnDataAvailable will occur again until all data is received. | '''Receive''' is used in the [[TWSocket.OnDataAvailable|OnDataAvailable]]-Event to actually fetch the received data. The parameters needed are a buffer where the data will be placed and the size of that buffer. The return value of Receive specifies how many bytes where actually read and put in the buffer. If the buffer is too small, OnDataAvailable will occur again until all data is received. | ||
| + | |||
| + | If the return value is 0 the connection the data shall be read from has been closed and a value of less than 0 means that an error occured. The SOCKET_ERROR constant's value will be returned in this case. In order to retrieve the real error code you need to check the LastError property immediately, before any other call might lead to yet another error. | ||
| + | |||
| + | If the LastError error code is WSAE_WOULD_BLOCK, it means that Receive has been called at a point in time where the system wasn't ready to process it. Most likely you can ignore this error condition. | ||
== Example == | == Example == | ||
| Line 17: | Line 21: | ||
if ErrCode <> 0 then exit; | if ErrCode <> 0 then exit; | ||
len:=Receive(@buf, sizeof(buf)); | len:=Receive(@buf, sizeof(buf)); | ||
| − | // here your procesing of the data will take place | + | |
| + | if (len > 0) then | ||
| + | // here your procesing of the data will take place | ||
end; | end; | ||
== Best practices == | == Best practices == | ||
| + | * never do any message processing like Application.ProcessMessages or GetMessage inside a eventhandler, since it will raise the same event again for the very same data! | ||
| + | * if the data received needs lengthy processing a separate thread for this might be a good idea since further data can only be received after the event has been processed completely. In most cases a separate thread is not necessary though. | ||
== How to == | == How to == | ||
Latest revision as of 17:04, 24 April 2015
Main page -> ICS component reference -> TWSocket -> Receive
Definition
function Receive(Buffer:Pointer; BufferSize:Integer): integer;
Description
Receive is used in the OnDataAvailable-Event to actually fetch the received data. The parameters needed are a buffer where the data will be placed and the size of that buffer. The return value of Receive specifies how many bytes where actually read and put in the buffer. If the buffer is too small, OnDataAvailable will occur again until all data is received.
If the return value is 0 the connection the data shall be read from has been closed and a value of less than 0 means that an error occured. The SOCKET_ERROR constant's value will be returned in this case. In order to retrieve the real error code you need to check the LastError property immediately, before any other call might lead to yet another error.
If the LastError error code is WSAE_WOULD_BLOCK, it means that Receive has been called at a point in time where the system wasn't ready to process it. Most likely you can ignore this error condition.
Example
procedure WSocket1OnDataAvailable(Sender: TObject; ErrCode: Word);
var buf:array[1..64] of byte;
len:Integer;
begin
if ErrCode <> 0 then exit;
len:=Receive(@buf, sizeof(buf));
if (len > 0) then
// here your procesing of the data will take place
end;
Best practices
- never do any message processing like Application.ProcessMessages or GetMessage inside a eventhandler, since it will raise the same event again for the very same data!
- if the data received needs lengthy processing a separate thread for this might be a good idea since further data can only be received after the event has been processed completely. In most cases a separate thread is not necessary though.
