Load-balance YSQL connections to YugabyteDB using vanilla C (libpq)

				
					// c_lbpq_demo.c
// Build: gcc c_lbpq_demo.c -o c_lbpq_demo -lpq
// Run:   ./c_lbpq_demo --count 12 --conn "host=h1,h2,h3 port=5433 dbname=yugabyte user=yugabyte sslmode=require load_balance_hosts=random"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libpq-fe.h>

static void die(const char *msg) {
  fprintf(stderr, "%s\n", msg);
  exit(EXIT_FAILURE);
}

static void check_ok(PGconn *c) {
  if (PQstatus(c) != CONNECTION_OK) {
    fprintf(stderr, "Connection failed: %s\n", PQerrorMessage(c));
    PQfinish(c);
    exit(EXIT_FAILURE);
  }
}

int main(int argc, char **argv) {
  const char *conninfo = NULL;
  int count = 6;

  // super simple flag parse
  for (int i = 1; i < argc; i++) {
    if (!strcmp(argv[i], "--count") && i+1 < argc) {
      count = atoi(argv[++i]);
    } else if (!strcmp(argv[i], "--conn") && i+1 < argc) {
      conninfo = argv[++i];
    }
  }

  if (!conninfo) {
    fprintf(stderr, "Usage: %s --count N --conn \"<libpq conn string>\"\n", argv[0]);
    fprintf(stderr, "Example conn: host=h1,h2,h3 port=5433 dbname=yugabyte user=yugabyte sslmode=require load_balance_hosts=random\n");
    return EXIT_FAILURE;
  }

  for (int i = 0; i < count; i++) {
    PGconn *c = PQconnectdb(conninfo);
    check_ok(c);

    // Show where we landed
    PGresult *r = PQexec(c, "select inet_server_addr(), inet_server_port(), pg_backend_pid()");
    if (PQresultStatus(r) != PGRES_TUPLES_OK) {
      fprintf(stderr, "Query failed: %s\n", PQerrorMessage(c));
      PQclear(r);
      PQfinish(c);
      return EXIT_FAILURE;
    }

    char *addr = PQgetvalue(r, 0, 0);
    char *port = PQgetvalue(r, 0, 1);
    char *pid  = PQgetvalue(r, 0, 2);

    printf("#%02d -> server=%s:%s backend_pid=%s\n", i+1, addr, port, pid);

    PQclear(r);
    PQfinish(c);
  }

  return EXIT_SUCCESS;
}