Unclear why if (self == NULL) in 2 of the 4 functions. Suggest none or all 4.

A comment in stack.h concerning the meaning of the return value would be useful. Assume user of Stack does not have access to stack.c

Using Node and node is a bit too similar - differentiating only on 1 letter case.

Maybe want to add a stack_empty()?

typedef struct Node is not needed in stack.h.

Maybe allow stack_pop(Stack* self, int* data) where data is NULL to pop without saving.

Unclear why if (self == NULL) in 2 of the 4 functions. Suggest none or all 4.

A comment in stack.h concerning the meaning of the return value would be useful. Assume user of Stack does not have access to stack.c. Not clear is success happens with true or false.

Using Node and node is a bit too similar - differentiating only on 1 letter case.

Maybe want to add a stack_empty() query?

typedef struct Node is not needed in stack.h. Suggest moving to stack.c

Maybe allow stack_pop(Stack* self, int* data) where data is NULL to pop without saving.