How to handle a colleague who hasn't pulled their weight
When students come to me with problems like these, I very rarely just take the side of the active student against the "lazy" one.
If you work in a group, you're both responsible when the dynamic doesn't work. And keeping the group dynamic healthy is something every student should learn. I know how difficult it is, I've been both the lazy student and the active one.
It may feel to you like there's nothing you possibly could've done. But that's never true. You started the project by immediately splitting the work load, and reducing the level of necessary communication to a bare minimum. He took the easy half, because he was busy. When his work started to lag behind, you began to write specifications for him.
All this combined probably sapped his motivation. Every step along the way took the challenge out of his part, while he still had those thousands of lines of code to get through. Meanwhile you felt like you were doing more than your share, but you were getting things done, and things that you designed, problems you solved.
In a healthy project, you communicate and you meet often. You don't divide the workload to minimize communication, you use your shared expertise and you design together. That way, you both stay motivated, because you both feel like it's still your project.
What you're doing now is focusing on everything that he could be doing differently. That may be the fair option (cause you're doing all the work), but it's not a productive option, cause that's not a dimension you control. You should be asking yourself what you could've done differently. It may feel unfair, but it's something you can actually implement, so you'll feel a lot less powerless.
Anyway, that's a lesson for the next project. For this one, I'd say remain detached. It's not your responsibility to make sure John learns something, and you'll get the same grade either way. Talk to him, tell him you're unhappy with the way the project's gone and ask if you could've done anything differently to get him more motivated. Let him know you don't expect to be working with him on future project and you're better off as friends than as collaborators.
Just make sure you don't get angry with him. Anger might've been productive halfway down the project, but you're too late now.
Do not attempt to talk to the prof about it, as in my comment above. There are too many ways that that could go wrong for all of you, and surely not giving "satisfaction", such as it would be, to you.
The goal of not having someone get credit for a thing they didn't earn is dubious for fairly obvious reasons, and even though it's more understandable that you'd not want someone else to "get credit" for something you did, in overtime, ... the situation of collaboration with a partner chosen by you tends to put you in a situation of having little ground to stand on. And the rest of your life will provide you with very many more examples of people aiming for, and receiving, more credit than they earn.
Lesson: good friends are not necessarily good collaborators. Indeed, in the future, consider that a botched collaboration might ruin a friendship, thus, do not hastily choose collaborators from among friends. (Pity, I know...)
The possibility that you get less credit than you earned is also just a presagement of many events. Although one should generally avoid such situations, especially if one has bills to pay and such, it is unavoidable... So keep your internally-generated stress level as low as possible, even while recognizing the failings of many people... e.g., one's friends.
I had a similar experience in a programming course. My partner started to claim to have some problems doing it, so when I finished my part, he decided I should take part of his task. After a few iterations, he was left with a quite trivial piece of code, plus the documentation (easy, but boring).
Long story short, I ended up doing it all by myself. For orthogonal reasons, the relationship with my friend was quite delicate, so a frontal confrontation would have been messy. Instead, I submitted it without making comments, but every file had the auto-generated header including author:@David. A few days later, the lecturer asked me why was this, and I just explained what happened.
In retrospect, my handling was not so good, as I didn't try hard enough to solve the problem before the deadline was biting. But it is too late now. If he is your friend, and you want to keep it, you should talk to him first, don't let the problem rot. Now you have to decide if he has enough time to make it up to you, or if you should inform the grader (together) and reach an agreement (for example, split the grade).