We present a type inference algorithm, in the style of compositional
analysis, for the language TRAFFIC---a specification language for flow
composition applications proposed in [BUCS-TR-2005-014]---and prove that
this algorithm is correct: the typings it infers are principal typings, and
the typings agree with syntax-directed type checking on closed flow
specifications. This algorithm is capable of verifying partial flow
specifications, which is a significant improvement over syntax-directed
type checking algorithm presented in [BUCS-TR-2005-015]. We also show that
this algorithm runs efficiently, i.e., in low-degree polynomial time.