Should the random_on_hemisphere() function be used for Lambertian reflection in section 9.4?

[whenyd]

When I read the new line of code:
vec3 direction = rec.normal + random_unit_vector();
I'm confused. According to the descreption, we want to select the tangent unit sphere that is on the same side of the surface as the ray origin.
The random_on_hemisphere() function takes into account the reflection on the side of the incident light, while the random_unit_vector() function may get the light pointing inside the sphere.
And I got a picture more shadow under the small sphere. But I'm sorry the picture failed to upload.

[PoneyUHC]

rec.normal points outside the sphere if the incoming ray hits the sphere from outside.
It is also normalized, ie it has a magnitude of 1.
If you add a random_unit_vector to it, the result is on a unit_sphere outside the sphere we collide with, but for a single point that is P, which is the point of contact of those 2 spheres.
S will thus always be on this unit sphere outside the colliding sphere, and the vector PS will always be constructed so that its direction is going away from the sphere