Walls

Walls is a Japanese logic puzzle. Build “walls” through the white cells; the total length of each wall is given in the dark cells.

Rules: Draw some straight lines through the grid. The lines run horizontally and vertically through the centres of orthogonally adjacent cells. Exactly one line must run through each white cell.
A number in a dark cell indicates the total length of lines that end at the edges of that cell. Not every line must end in a dark cell; a line can end in a dark cell at both ends.