I need to call some Foundation code from a new external PostgreSQL function, how to set-up my make files and how to avoid the compilation errors when including Foundation headers ?
The errors at compile time are generated by a conflictingSize data type declared both by PosgreSQL (in header "c.h") and by MacTypes.h.
The only way to solve the problem is to split your code in two parts: a glue file will contain all your PostgreSQL specific code (the entry points of your library) that will pop the arguments and cast/convert them to external functions that will do the real job (calling Foundation). These functions will be in another source files and of course must not depend on PostgreSQL headers. The result of the functions will be converted (if needed) back into the expected result type for the PostgreSQL backend.
Example with an external function generating an Universal ID:
The PostgreSQL glue:
#include "fmgr.h" /* for argument/result macros */
#include "cfuuid.h" /* our "real" job functions */
BpChar *result = (BpChar *) palloc( sizeof(int) + 60 ); // 60 is big enough for a CFUUID string
cfuuid_createstr( result->vl_dat, 60 ) ;
result->vl_len = strlen( result->vl_dat ) ;
The header declaring our "real" function:
void cfuuid_createstr(char *outBuffer, int inLen);
You install the uuid.so dynamic library as usual for your set-up (example: sudo cp uuid.so /usr/local/pgsql/lib).
The installation of the function in a database is as usual: (change /usr/local/pgsql/lib/ to where you put the library on your system) CREATE FUNCTION uuid_createstr() RETURNS character AS '/usr/local/pgsql/lib/uuid' LANGUAGE C IMMUTABLE STRICT ;
Executing select uuid_createstr(); will return something like 2AE61F94-D108-11D8-B8D6-0003933F0AB6.