Address Robert's feedback

*** 99,108 ****
--- 99,112 ----
  static boolean_t
  str_reserve(str_t *s, size_t amt)
  {
          size_t newlen = s->str_len + amt;
  
+         /* overflow check */
+         if (newlen < s->str_len || newlen < amt)
+                 return (B_FALSE);
+ 
          if ((amt > 0) && (s->str_len + amt <= s->str_size))
                  return (B_TRUE);
  
          size_t newsize = roundup(newlen, STR_CHUNK_SZ);
          void *temp;
*** 161,171 ****
          dest->str_len += src->str_len;
          return (B_TRUE);
  }
  
  boolean_t
! str_append_c(str_t *s, int c)
  {
          if (!str_reserve(s, 1))
                  return (B_FALSE);
  
          s->str_s[s->str_len++] = c;
--- 165,175 ----
          dest->str_len += src->str_len;
          return (B_TRUE);
  }
  
  boolean_t
! str_append_c(str_t *s, char c)
  {
          if (!str_reserve(s, 1))
                  return (B_FALSE);
  
          s->str_s[s->str_len++] = c;
*** 207,219 ****
          }
  
          if (!str_reserve(dest, src->str_len))
                  return (B_FALSE);
  
!         /* Unlike some programmers, *I* can read manpages. */
          (void) memmove(dest->str_s + idx + src->str_len, dest->str_s + idx,
              dest->str_len - idx);
          (void) memcpy(dest->str_s + idx, src->str_s, src->str_len);
          dest->str_len += src->str_len;
  
          return (B_TRUE);
  }
--- 211,233 ----
          }
  
          if (!str_reserve(dest, src->str_len))
                  return (B_FALSE);
  
!         /*
!          * Shift the contents of dest over at the insertion point.  Since
!          * src and dest ranges will overlap, and unlike some programmers,
!          * *I* can read man pages - memmove() is the appropriate function
!          * to this.
!          */
          (void) memmove(dest->str_s + idx + src->str_len, dest->str_s + idx,
              dest->str_len - idx);
+ 
+         /*
+          * However the content to insert does not overlap with the destination
+          * so memcpy() is fine here.
+          */
          (void) memcpy(dest->str_s + idx, src->str_s, src->str_len);
          dest->str_len += src->str_len;
  
          return (B_TRUE);
  }