The role of libraries and librarians keeps changing. Libraries are free to define the roles they will fulfill, but these roles should always be in response to the needs of their communities.
For some libraries this may mean offering services and assistance to their community’s homeless. 
Being a Librarian Now Means Also Being at Least a Part Time Social Worker is such an excellent article, that I really have nothing to add. It may seem long but it is very readable, and really worth the time it takes. It talks about not only the problem of homelessness, but also describes how some current libraries are working with the homeless. But my favorite part of the article is the little looks into the lives of those homeless who are using their public libraries.
I’ll leave you with just two quotes. I could easily have chosen twenty.
“It is a profession where you are helping people, not trying to sell them things they don’t need.”
“Anyone can become homeless. I’ve seen ex-doctors and bankers in here. You never know when you might need the help you can find at the library.”
A Life in Libraries 