Green’s Dictionary of Slang

happy, cheerful; generous (cf. chuffy adj. (2)).

1695		E. Ravenscroft Canterbury Guests 57: Therefore I will give four Hundred a Year upon that Condition, whether any here will or nill, and let me see who'll say me nay. I can be as chuff as any of you.
1835		G. Kent Modern Flash Dict. 9: chuff – jolly, merry.
1837		‘Sam Weller’s Adventures!’ in C. Hindley James Catnach (1878) 278: Now I hopes you’re all hearty and chuff.
1848		Flash Dict. in Sinks of London Laid Open.
1908		A.N. Lyons Arthur’s 11: But she looked up, quite chuff.