DC_PLUG_READ

Section: distcache (2)
Updated: 2004.03.23
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NAME

DC_PLUG_read, DC_PLUG_consume, DC_PLUG_write, DC_PLUG_write_more, DC_PLUG_commit, DC_PLUG_rollback - DC_PLUG read/write functions

SYNOPSIS

 #include <distcache/dc_plug.h>

 int DC_PLUG_read(DC_PLUG *plug, int resume, unsigned long *request_uid,
                  DC_CMD *cmd, const unsigned char **payload_data,
                  unsigned int *payload_len);
 int DC_PLUG_consume(DC_PLUG *plug);
 int DC_PLUG_write(DC_PLUG *plug, int resume, unsigned long request_uid,
                   DC_CMD cmd, const unsigned char *payload_data,
                   unsigned int payload_len);
 int DC_PLUG_write_more(DC_PLUG *plug, const unsigned char *data,
                        unsigned int data_len);
 int DC_PLUG_commit(DC_PLUG *plug);
 int DC_PLUG_rollback(DC_PLUG *plug);

 typedef enum {
         DC_CMD_ERROR,
         DC_CMD_ADD,
         DC_CMD_GET,
         DC_CMD_REMOVE,
         DC_CMD_HAVE
 } DC_CMD;

DESCRIPTION

DC_PLUG_read() will attempt to open the next distcache message received by plug for reading. This message will block the reading of any other received messages remain until DC_PLUG_consume() is called. If a message has already been opened for reading inside plug, then DC_PLUG_read() will fail unless resume is set to non-zero in which case it will simply re-open the message that was already being read. If DC_PLUG_read() succeeds, request_uid, cmd, payload_data and payload_len are populated with the message's data. Note that payload_data points to the original data stored inside plug and this pointer is only valid until the next call to DC_PLUG_consume().

DC_PLUG_consume() will close the message currently opened for reading in plug, and will allow a future call to DC_PLUG_read() to succeed if there any subsequent (complete) messages received from the plug object's connection.

DC_PLUG_write() will attempt to open a distcache message for writing in plug. If successful, this message will block the writing of any other messages until the message is committed with DC_PLUG_commit() or discarded with DC_PLUG_rollback(). If a message has already been opened for writing, DC_PLUG_write() will fail unless resume is non-zero in which case the message will be re-opened and will overwrite the settings from the previous DC_PLUG_write() call. This is equivalent to DC_PLUG_rollback() followed immediately by DC_PLUG_write() with a zero resume value. Note that payload_len can be zero (and thus payload_data can be NULL) even if the message will eventually have payload data - this can be supplemented afterwards using the DC_PLUG_write_more() function. request_uid and cmd, on the other hand, must be specified at once in DC_PLUG_write().

DC_PLUG_write_more() will attempt to add more payload data to the message currently opened for writing in plug. This data will be concatenated to the end of any payload data already provided in prior calls to DC_PLUG_write() or DC_PLUG_write_more().

DC_PLUG_commit() will close the message currently opened for writing, and queue it for serialisation out on the plug object's connection.

DC_PLUG_rollback() will discard the message currently opened for writing.

RETURN VALUES

All these DC_PLUG functions return zero on failure, otherwise non-zero.

AUTHOR

This toolkit was designed and implemented by Geoff Thorpe for Cryptographic Appliances Incorporated. Since the project was released into open source, it has a home page and a project environment where development, mailing lists, and releases are organised. For problems with the software or this man page please check for new releases at the project web-site below, mail the users mailing list described there, or contact the author at geoff@geoffthorpe.net.