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ProtocolReader.d

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00001 /*******************************************************************************
00002 
00003         @file ProtocolReader.d
00004         
00005         Copyright (c) 2004 Kris Bell
00006         
00007         This software is provided 'as-is', without any express or implied
00008         warranty. In no event will the authors be held liable for damages
00009         of any kind arising from the use of this software.
00010         
00011         Permission is hereby granted to anyone to use this software for any 
00012         purpose, including commercial applications, and to alter it and/or 
00013         redistribute it freely, subject to the following restrictions:
00014         
00015         1. The origin of this software must not be misrepresented; you must 
00016            not claim that you wrote the original software. If you use this 
00017            software in a product, an acknowledgment within documentation of 
00018            said product would be appreciated but is not required.
00019 
00020         2. Altered source versions must be plainly marked as such, and must 
00021            not be misrepresented as being the original software.
00022 
00023         3. This notice may not be removed or altered from any distribution
00024            of the source.
00025 
00026         4. Derivative works are permitted, but they must carry this notice
00027            in full and credit the original source.
00028 
00029 
00030                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
00031 
00032 
00033         @version        Initial version, July 2004      
00034         @author         Kris
00035 
00036 
00037 *******************************************************************************/
00038 
00039 module mango.cluster.qos.socket.ProtocolReader;
00040 
00041 private import  mango.io.Exception,
00042                 mango.io.PickleReader,
00043                 mango.io.EndianReader;
00044 
00045 private import  mango.cluster.model.ICluster;
00046 
00047 /*******************************************************************************
00048         
00049         Objects passed around a cluster are prefixed with a header, so the 
00050         receiver can pick them apart correctly. This header consists of:
00051 
00052         - the packet size, including the header (16 bits)
00053         - a command code (8 bits)
00054         - the length of the channel name (8 bits)
00055         - the channel name
00056         - the payload (an IPickle class)
00057 
00058         Everything is written in Network order (big endian).
00059 
00060 *******************************************************************************/
00061 
00062 class ProtocolReader : PickleReader
00063 {
00064         /***********************************************************************
00065         
00066                 Construct a ProtocolReader upon the given buffer. As
00067                 Objects are serialized, their content is written to this
00068                 buffer. The buffer content is then typically flushed to 
00069                 some external conduit, such as a file or socket.
00070 
00071                 Note that serialized data is always in Network order.
00072 
00073         ***********************************************************************/
00074         
00075         this (IBuffer buffer)
00076         in {
00077            assert (buffer);
00078            }
00079         body
00080         {
00081                 super (buffer);
00082         }
00083 
00084         /***********************************************************************
00085         
00086                 Return the payload if there was one, null otherwise.
00087 
00088         ***********************************************************************/
00089 
00090         IPayload getPayload (inout char[] channel, inout char[] element, inout ubyte cmd)
00091         {
00092                 int position = buffer.getPosition;
00093 
00094                 ushort size;
00095                 ubyte  versn;
00096 
00097                 get (size);
00098                 get (cmd);
00099                 get (versn);
00100 
00101                 // avoid allocation for these two strings
00102                 get (channel);
00103                 get (element);
00104 
00105                 // is there a payload attached?
00106                 if (size > (buffer.getPosition - position))
00107                     return cast(IPayload) thaw ();
00108 
00109                 return null;
00110         }
00111 
00112         /***********************************************************************
00113         
00114                 Return a duplicated slice of the buffer representing the 
00115                 recieved payload. This is a bit of a hack, but eliminates
00116                 a reasonable amount of overhead. Note that the channel/key
00117                 text is retained right at the start of the buffer, allowing
00118                 the writer to toss the whole thing back without any further
00119                 munging. 
00120 
00121         ***********************************************************************/
00122 
00123         ClusterContent getPacket (inout char[] channel, inout char[] element, inout ubyte cmd)
00124         {
00125                 ushort  size;
00126                 ubyte   versn;
00127 
00128                 // load up the length first.
00129                 get (size);
00130                 //printf ("size: %d\n", cast(int) size);
00131 
00132                 // read the header 
00133                 get (cmd);
00134 
00135                 // read the version stamp
00136                 get (versn);
00137 
00138                 // subtract header size
00139                 size -= buffer.getPosition;
00140                 
00141                 // may throw an exception if the payload is too large to fit
00142                 // completely inside the buffer!
00143                 buffer.get (size, false);
00144 
00145                 // duplicate the remaining packet (with channel/key text)
00146                 ClusterContent content = cast(ClusterContent) buffer.toString().dup;
00147 
00148                 // get a slice upon the channel name. Note this is 
00149                 // dup'd as part of the payload
00150                 get (channel);
00151 
00152                 // get a slice upon the element name. Note this is 
00153                 // dup'd as part of the payload
00154                 get (element);
00155 
00156                 // return the dup'd payload (including channel/key text)
00157                 return content;
00158         }
00159 }
00160 

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