cmd: Add config file support

[leszko]

What does this pull request do? Explain your changes. (required)
Add a possibility to configure Livepeer using a config file instead of flags.

Sample usage:

$ livepeer -config livepeer.conf

Sample livepeer.conf

broadcaster
cliAddr :7937
httpAddr :8938
orchAddr 127.0.0.1:8935,127.0.0.1:8936
v 6

Specific updates (required)
Used the library https://github.com/peterbourgon/ff, which allows using config file for the flags.

How did you test each of these updates (required)

1. Created a sample config file and checked if it works
2. Checked if both config files and flags are defined if flags take precedence over config file

Does this pull request close any open issues?
fix #101

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[hthillman]

Checked if both config files and flags are defined if flags take precedence over config file

Just to be super clear here - if flags are defined, they'll override the config?

[yondonfu]

Looks good! Just one minor question related to a comment.

I also think it would be great to add a short guide for configuring livepeer using a config file in https://github.com/livepeer/livepeer-org/tree/master (the repo for https://livepeer.org/docs). Maybe a section called "Configuring Livepeer" under the "Installation" header...

Also, just want to confirm my understanding of the ff package:

Since the package will parse flags, env vars and the config file the following should be true right?

• If -maxGasPrice is specified in all three, the value used in the flag takes precedence
• If -maxGasPrice is not specified in flags, but other flags are specified and the config file specifies -maxGasPrice then the value from the config file will be used

EDIT: Regarding the above question - just read your testing steps! 😓

[leszko]

Checked if both config files and flags are defined if flags take precedence over config file

Just to be super clear here - if flags are defined, they'll override the config?

Yes, they'll override the config.

[leszko]

I also think it would be great to add a short guide for configuring livepeer using a config file in https://github.com/livepeer/livepeer-org/tree/master (the repo for https://livepeer.org/docs). Maybe a section called "Configuring Livepeer" under the "Installation" header...

Yes, working on this together with @hthillman in the branch docs-config-updates of the https://github.com/livepeer/livepeer-org repo. I think we can merge this PR and later merge the doc-related PR.

Also, just want to confirm my understanding of the ff package:

Since the package will parse flags, env vars and the config file the following should be true right?

• If -maxGasPrice is specified in all three, the value used in the flag takes precedence
• If -maxGasPrice is not specified in flags, but other flags are specified and the config file specifies -maxGasPrice then the value from the config file will be used

EDIT: Regarding the above question - just read your testing steps! 😓

Yeah, it works exactly as you described. One more thing is that after the comment from @iameli , we added the env variables. So the priority here is (from the highest):

• flags
• env variables
• config file

[yondonfu]

LGTM!

The ability to use env vars for config is a bonus - nice!

[iameli]

LGTM!