- You can use a reaction on your own turn
- The charge is not interrupted
- The charging creature gains no bonus on the opportunity attack
So, to clarify the scenario, we have three creatures. I'll give them names:
- Bob, the charger
- Jane, the target of the charge
- Nelly, with the readied action to move
Bob charges, Jane. But Nelly has readied an action to move. As soon as Nelly sees Bob, she wants to run across his path directly in front of him. What happens?
First, a "charge" is not a discrete action. The Charger feat, PHB p. 165, says:
When you use your action to Dash, you can use a bonus action to make one melee weapon attack or to shove a creature.
If you move at least 10 feet in a straight line immediately before taking this bonus action, you either gain a +5 bonus to the attack’s damage roll (if you chose to make a melee attack and hit) or push the target up to 10 feet away from you (if you chose to shove and you succeed).
So Bob has taken the Dash action. Normally, Bob would attack Jane using a bonus action after finishing his move.
However, in this case, as soon as Nelly sees Bob, she interrupts Bob's move:
Page 193, PHB:
When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger.
So, in this case, the "trigger" was "as soon as Nelly sees Bob". So, she moves, crossing his path directly in front of him, and provokes an attack of opportunity in the process.
Nelly, is the one moving at this point, so only Bob gets an attack of opportunity, not Nelly.
Even though it is Bob's turn, he can still take his reaction to make an opportunity attack, p. 190 of the Player's Handbook:
Certain special abilities, spells, and situations allow you to take a special action called a reaction. A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else’s.
The charge feat allows Bob to make an attack as a bonus action, and possibly gain a bonus to that attack. It does not grant a bonus to any other actions, or attacks. So, Bob does not get a bonus to his opportunity attack.
From the Charger feat:
If you move at least 10 feet in a straight line immediately before taking this bonus action, you ... gain a +5 bonus to the attack’s damage roll
Next, after Bob makes the opportunity attack, Nelly completes her movement, and Bob's turn resumes.
Bob may continue his movement toward Jane, and use his bonus action to make an attack as granted by the Charger feat.