Read a line from stdin into a malloc'd buffer

readline.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *read_line_malloc(void) {
  size_t sz = 64;

  char *buf = malloc(sz);
  if (!fgets(buf, sz, stdin)) {
    *buf = '\0';
    return buf;
  }
  size_t len = strlen(buf);

  while (buf[len - 1] != '\n') {
    sz *= 2;
    buf = realloc(buf, sz);
    if (!fgets(buf + len, sz - len, stdin)) {
      return buf;
    }
    len += strlen(buf + len);
  }

  buf[len - 1] = '\0';
  return buf;
}