rpc: Input-from-stdin mode for bitcoin-cli

[laanwj]

Implements #7442 by adding an option -stdin which reads additional arguments from standard in, one per line.

For example

$ echo -e "mysecretcode\n120" | src/bitcoin-cli -stdin walletpassphrase
$ echo -e "walletpassphrase\nmysecretcode\n120" | src/bitcoin-cli -stdin
$ src/bitcoin-cli -stdin walletpassphrase
mysecretcode
120
^D

This is the simplest implementation and avoids escaping issues by using newline as separator instead of space, I first had another implementation: laanwj/bitcoin@1f73b8e that reuses parseCommandLine from the GUI debug console, but I think this is more useful in practice as most use of cli is probably script-driven.

[paveljanik]

Brilliant idea!

ACK laanwj/bitcoin@c97198d

pavel$ echo -e "getblockhash\n0" | bitcoin-7550/src/bitcoin-cli -stdin
000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
pavel$ 

[jonasschnelli]

Nice!
Concept ACK. Plans to test this soon.

[jonasschnelli]

what about adding a magic work as ^D alternative? Something like "end" or "quit"?

[laanwj]

I've thought about that. The problem is that anything could be a valid argument. I've chosen the line-per-argument, until EOL to avoid that kind of escaping issues.
It's easy for scripting but yes for a user interface it's not very friendly.

master...laanwj:2016_02_cli_stdin is better in that regard, but what makes it an easier user interface is annoying/dangerous for scripting (as you'd have to quote ' "" etc to prevent one argument from spilling into the next)

[jonasschnelli]

Maybe adding a little ">>>" prompt and or giving a one-line-help-instruction when using -stdin (something like "enter command, arguments and use Ctrl-D to quit/execute")?

Allow quitting over "quit()" and if "exit" or "quit" has been typed, show little help line?
Though, a simple one-line-help-message would probably do the job.

Python example:

:~ jonasschnelli$ python
Python 2.7.10 (default, Sep 23 2015, 04:34:14) 
[GCC 4.2.1 Compatible Apple LLVM 7.0.0 (clang-700.0.72)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> quit
Use quit() or Ctrl-D (i.e. EOF) to exit

[laanwj]

That would be awesome for an "interactive mode" (see #3122), but -stdin is explicitly not meant to be that, it's just to have a way to input data (say, from scripts) that isn't exposed on the command line. Printing more text will make it harder to parse the output.

[jonasschnelli]

Agree. Was nitpick territory anyway (does not affect my tested ACK I already gave).

[laanwj]

Right, for now, I've added a EOF/Ctrl-D mention to the -help message at least.

[jonasschnelli]

Tested ACK c97198db769954c4ad2b57eaf7e5335578badc00

Post-merge actions: add to the docs/release notes, maybe add a little test script (though, not sure if we have a test entry point for bitcoin-cli at all).

[jonasschnelli]

Re-ACK 92bcca3