cmd/faucet: fix genesis flag and improve documentation (ethereum#24735)

cmd/faucet/README.md

@@ -10,38 +10,40 @@ The `faucet` is a single binary app (everything included) with all configuration
 
 First thing's first, the `faucet` needs to connect to an Ethereum network, for which it needs the necessary genesis and network infos. Each of the following flags must be set:
 
-- `--genesis` is a path to a file containin the network `genesis.json`
-- `--network` is the devp2p network id used during connection
-- `--bootnodes` is a list of `enode://` ids to join the network through
+- `-genesis` is a path to a file containin the network `genesis.json`. or using:
+  - `-goerli` with the faucet with Görli network config
+  - `-rinkeby` with the faucet with Rinkeby network config
+- `-network` is the devp2p network id used during connection
+- `-bootnodes` is a list of `enode://` ids to join the network through
 
 The `faucet` will use the `les` protocol to join the configured Ethereum network and will store its data in `$HOME/.faucet` (currently not configurable).
 
 ## Funding
 
 To be able to distribute funds, the `faucet` needs access to an already funded Ethereum account. This can be configured via:
 
-- `--account.json` is a path to the Ethereum account's JSON key file
-- `--account.pass` is a path to a text file with the decryption passphrase
+- `-account.json` is a path to the Ethereum account's JSON key file
+- `-account.pass` is a path to a text file with the decryption passphrase
 
 The faucet is able to distribute various amounts of Ether in exchange for various timeouts. These can be configured via:
 
-- `--faucet.amount` is the number of Ethers to send by default
-- `--faucet.minutes` is the time to wait before allowing a rerequest
-- `--faucet.tiers` is the funding tiers to support  (x3 time, x2.5 funds)
+- `-faucet.amount` is the number of Ethers to send by default
+- `-faucet.minutes` is the time to wait before allowing a rerequest
+- `-faucet.tiers` is the funding tiers to support  (x3 time, x2.5 funds)
 
 ## Sybil protection
 
 To prevent the same user from exhausting funds in a loop, the `faucet` ties requests to social networks and captcha resolvers.
 
 Captcha protection uses Google's invisible ReCaptcha, thus the `faucet` needs to run on a live domain. The domain needs to be registered in Google's systems to retrieve the captcha API token and secrets. After doing so, captcha protection may be enabled via:
 
-- `--captcha.token` is the API token for ReCaptcha
-- `--captcha.secret` is the API secret for ReCaptcha
+- `-captcha.token` is the API token for ReCaptcha
+- `-captcha.secret` is the API secret for ReCaptcha
 
 Sybil protection via Twitter requires an API key as of 15th December, 2020. To obtain it, a Twitter user must be upgraded to developer status and a new Twitter App deployed with it. The app's `Bearer` token is required by the faucet to retrieve tweet data:
 
-- `--twitter.token` is the Bearer token for `v2` API access
-- `--twitter.token.v1` is the Bearer token for `v1` API access
+- `-twitter.token` is the Bearer token for `v2` API access
+- `-twitter.token.v1` is the Bearer token for `v1` API access
 
 Sybil protection via Facebook uses the website to directly download post data thus does not currently require an API configuration. 
 

cmd/faucet/faucet.go

@@ -147,7 +147,7 @@ func main() {
 		log.Crit("Failed to render the faucet template", "err", err)
 	}
 	// Load and parse the genesis block requested by the user
-	genesis, err := getGenesis(*goerliFlag, *rinkebyFlag, *tanenbaumFlag, *syscoinFlag)
+	genesis, err := getGenesis(*genesisFlag, *goerliFlag, *rinkebyFlag, *tanenbaumFlag, *syscoinFlag)
 	if err != nil {
 		log.Crit("Failed to parse genesis config", "err", err)
 	}
@@ -928,8 +928,12 @@ func authNoAuth(url string) (string, string, common.Address, error) {
 }
 
 // getGenesis returns a genesis based on input args
-func getGenesis(goerliFlag bool, rinkebyFlag bool, tanenbaumFlag bool, syscoinFlag bool) (*core.Genesis, error) {
+func getGenesis(genesisFlag string, goerliFlag bool, rinkebyFlag bool, tanenbaumFlag bool, syscoinFlag bool) (*core.Genesis, error) {
 	switch {
+	case genesisFlag != "":
+		var genesis core.Genesis
+		err := common.LoadJSON(genesisFlag, &genesis)
+		return &genesis, err
 	case goerliFlag:
 		return core.DefaultGoerliGenesisBlock(), nil
 	case rinkebyFlag: