ExecUtil.executeCommandLine() is broken

[ivmarkov]

I assume that the semantics of e.g. ExecUtil.executeCommandLine("ls .") is to execute the command "ls" with a parameter ".".

(There is some sort of "extra safety" variant where I can pass "ls@@." and it will tokenize it etc. to workaround some "issues" on Mac, as it says. Looks a bit smelly, but anyways.)

The problem is when the caller does NOT use the "@@" trick. Passing "ls ." (i.e. where regular whitespace is used) will not do the right thing anymore, because someone has switched the implementation to ProcessBuilder on master several months ago. ProcessBuilder (unlike Runtime.exec() which was seemingly used in 2.5) does not accept a single command-line string where the command and its arguments are separated by whitespace.

Calling new ProcessBuilder(cmdLine) deceptively seems to work because the class does have a constructor with (String... commands) signature so it takes a single String parameter, but that parameter is supposed to be the command ONLY, not the whole command-line.

At least one binding in 3.0 (SamsungTV) seems to be broken because of this issue.

[ivmarkov]

By the way, there could be another issue: you are (trying to) exhaust the input stream (= stdout) of the child process after calling waitFor(). If memory serves me right, you have to do it before you are stuck in waitFor, or the child process might block when it fills its buffer and starts waiting on you to read it. And you need to exhaust stderr as well.

Quick googling here seems to confirm this: https://www.xspdf.com/help/50395592.html

So it will work where the child process returns only a handful of characters. Try it with a child which dumps gobs of info on stdout and it will block.

[kaikreuzer]

Sounds like a regression then - I'll put it to the openHAB 3 project, so that it is tracked.

[andrewfg]

By the way, there could be another issue: you are (trying to) exhaust the input stream (= stdout) of the child process after calling waitFor(). If memory serves me right, you have to do it before you are stuck in waitFor, or the child process might block when it fills its buffer and starts waiting on you to read it. And you need to exhaust stderr as well.

@ivmarkov / @kaikreuzer -- I think there is still an issue here.

• If you run executeCommandLine() on a "fast" command such as ls then it does return the full console output, but
• If you run it on a "slow" command (such as wget or curl) it does NOT return the full console output; it returns an empty string

https://community.openhab.org/t/oh3-migrated-rule-executecommandline-command-fails/114027

[openhab-bot]

This issue has been mentioned on openHAB Community. There might be relevant details there:

https://community.openhab.org/t/oh3-migrated-rule-executecommandline-command-fails/114027/7