Example of a pg_gethostname() function. Feedback?

[bricklen <bricklen@xxxxxxxxx>]

I had a need recently to get the server hostname of some databases
that we were unit-testing and couldn't find a built-in function for
it. One of my coworkers put together a C function that seems to work
well.
Does anyone have any suggestions or improvements to the code below?

Some testing was done with both 9.0 and and 9.1, linux, x86_64

To use:

select pg_gethostname();


/*
        A PostgreSQL function for getting the hostname.

        File: `pg_config --libdir`/pg_gethostname.c

        To compile:
                //gcc -fpic -c pg_gethostname.c
                //gcc -shared -o pg_gethostname.so pg_gethostname.o

        Note: the compile options above did work, amended steps:
                // make sure pg_config is in your path
                gcc  -I`pg_config --includedir-server` -fpic -c
pg_gethostname.c -L`pg_config --libdir`
                gcc -shared -o pg_gethostname.so pg_gethostname.o

        To create the function in PostgreSQL.

        //DROP FUNCTION IF EXISTS pg_gethostname();
        CREATE OR REPLACE FUNCTION pg_gethostname() RETURNS text
                AS 'pg_gethostname'
                LANGUAGE C IMMUTABLE STRICT;

*/

#include "postgres.h"
#include <unistd.h>
#include <string.h>
#include "fmgr.h"

#include "utils/palloc.h"
#include "utils/elog.h"
#include "storage/bufpage.h"

#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif

#define MAX_HOSTNAME_LENGTH 255


PG_FUNCTION_INFO_V1( pg_gethostname );

Datum pg_gethostname( PG_FUNCTION_ARGS );

Datum pg_gethostname( PG_FUNCTION_ARGS )
{
        text *t;
        char server_hostname[MAX_HOSTNAME_LENGTH];
        size_t length;

        if ( gethostname( server_hostname, MAX_HOSTNAME_LENGTH ) != 0 )
        {
                // things are not okay
                strncpy( server_hostname, "UNKNOWN", MAX_HOSTNAME_LENGTH );
        }

        length = strnlen( server_hostname, MAX_HOSTNAME_LENGTH );
        t = (text *) palloc(VARHDRSZ + length );
        SET_VARSIZE( t, VARHDRSZ + length );
        memcpy( VARDATA(t), server_hostname, length );

        PG_RETURN_TEXT_P( t );
}

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