Add manual pages to RTD as individual files

[ric-plt/lib/rmr.git] / docs / rmr_realloc_payload.3.rst

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+ 
+.. This work is licensed under a Creative Commons Attribution 4.0 International License. 
+.. SPDX-License-Identifier: CC-BY-4.0 
+.. CAUTION: this document is generated from source in doc/src/rtd. 
+.. To make changes edit the source and recompile the document. 
+.. Do NOT make changes directly to .rst or .md files. 
+ 
+ 
+============================================================================================ 
+Man Page: rmr_realloc_payload 
+============================================================================================ 
+ 
+RMR Library Functions 
+============================================================================================ 
+ 
+ 
+NAME 
+-------------------------------------------------------------------------------------------- 
+ 
+rmr_realloc_payload 
+ 
+SYNOPSIS 
+-------------------------------------------------------------------------------------------- 
+ 
+ 
+:: 
+  
+ #include <rmr/rmr.h>
+ extern rmr_mbuf_t* rmr_realloc_payload( rmr_mbuf_t* msg, int new_len, int copy, int clone );
+ 
+ 
+ 
+DESCRIPTION 
+-------------------------------------------------------------------------------------------- 
+ 
+The rmr_realloc_payload function will return a pointer to an 
+RMR message buffer struct (rmr_mbuf_t) which has a payload 
+large enough to accomodate *new_len* bytes. If necessary, the 
+underlying payload is reallocated, and the bytes from the 
+original payload are copied if the *copy* parameter is true 
+(1). If the message passed in has a payload large enough, 
+there is no additional memory allocation and copying. 
+ 
+Cloning The Message Buffer 
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
+ 
+This function can also be used to generate a separate copy of 
+the original message, with the desired payload size, without 
+destroying the original message buffer or the original 
+payload. A standalone copy is made only when the *clone* 
+parameter is true (1). When cloning, the payload is copied to 
+the cloned message **only** if the *copy* parameter is true. 
+ 
+Message Buffer Metadata 
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
+ 
+The metadata in the original message buffer (message type, 
+subscription ID, and payload length) will be preserved if the 
+*copy* parameter is true. When this parameter is not true 
+(0), then these values are set to the uninitialised value 
+(-1) for type and ID, and the length is set to 0. 
+ 
+RETURN VALUE 
+-------------------------------------------------------------------------------------------- 
+ 
+The rmr_realloc_payload function returns a pointer to the 
+message buffer with the payload which is large enough to hold 
+*new_len* bytes. If the *clone* option is true, this will be 
+a pointer to the newly cloned message buffer; the original 
+message buffer pointer may still be used to reference that 
+message. It is the calling application's responsibility to 
+free the memory associateed with both messages using the 
+rmr_free_msg() function. 
+ 
+When the *clone* option is not used, it is still good 
+practice by the calling application to capture and use this 
+reference as it is possible that the message buffer, and not 
+just the payload buffer, was reallocated. In the event of an 
+error, a nil pointer will be returned and the value of 
+*errno* will be set to reflect the problem. 
+ 
+ERRORS 
+-------------------------------------------------------------------------------------------- 
+ 
+These value of *errno* will reflect the error condition if a 
+nil pointer is returned: 
+ 
+ 
+ 
+ENOMEM 
+   
+  Memory allocation of the new payload failed. 
+   
+ 
+EINVAL 
+   
+  The pointer passed in was nil, or refrenced an invalid 
+  message, or the required length was not valid. 
+ 
+ 
+EXAMPLE 
+-------------------------------------------------------------------------------------------- 
+ 
+The following code bit illustrates how this function can be 
+used to reallocate a buffer for a return to sender 
+acknowledgement message which is larger than the message 
+received. 
+ 
+ 
+:: 
+  
+   if( rmr_payload_size( msg ) < ack_sz ) {              // received message too small for ack
+     msg = rmr_realloc_payload( msg, ack_sz, 0, 0 );     // reallocate the message with a payload big enough
+     if( msg == NULL ) {
+       fprintf( stderr, "[ERR] realloc returned a nil pointer: %s\\n", strerror( errno ) );
+     } else {
+       // populate and send ack message
+     }
+ }
+ 
+ 
+ 
+SEE ALSO 
+-------------------------------------------------------------------------------------------- 
+ 
+rmr_alloc_msg(3), rmr_free_msg(3), rmr_init(3), 
+rmr_payload_size(3), rmr_send_msg(3), rmr_rcv_msg(3), 
+rmr_rcv_specific(3), rmr_rts_msg(3), rmr_ready(3), 
+rmr_fib(3), rmr_has_str(3), rmr_set_stimeout(3), 
+rmr_tokenise(3), rmr_mk_ring(3), rmr_ring_free(3)