Returns an object containing various state info regarding block chain processing.

"chain": "xxxx", (string) current network name as defined in BIP70 (main, test, regtest)
"blocks": xxxxxx, (numeric) the current number of blocks processed in the server
"headers": xxxxxx, (numeric) the current number of headers we have validated
"bestblockhash": "...", (string) the hash of the currently best block
"difficulty": xxxxxx, (numeric) the current difficulty
"verificationprogress": xxxx, (numeric) estimate of verification progress [0..1]
"chainwork": "xxxx" (string) total amount of work in active chain, in hexadecimal
"softforks": [ (array) status of softforks in progress
"id": "xxxx", (string) name of softfork
"version": xx, (numeric) block version
"enforce": { (object) progress toward enforcing the softfork rules for new-version blocks
"status": xx, (boolean) true if threshold reached
"found": xx, (numeric) number of blocks with the new version found
"required": xx, (numeric) number of blocks required to trigger
"window": xx, (numeric) maximum size of examined window of recent blocks
"reject": { ... } (object) progress toward rejecting pre-softfork blocks (same fields as "enforce")
}, ...

> bitcoin-cli getblockchaininfo
> curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "getblockchaininfo", "params": [] }' -H 'content-type: text/plain;'
Don't trust. Verify. Docs extracted from src/rpcblockchain.cpp#L498-L530.