[jira] [Issue Comment Deleted] (MESOS-3035) As a Developer I would like a standard way to run a Subprocess in libprocess

["Marco Massenzio (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MESOS-3035?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Marco Massenzio updated MESOS-3035:
-----------------------------------
    Comment: was deleted

(was: When reviewing the code in [r/36425|https://reviews.apache.org/r/36425/] [~benjaminhindman] noticed that there is a better abstraction that is possible to introduce for {{os::shell()}} that will simplify the caller's life.

Instead of having to handle all possible outcomes, we propose to refactor {{os::shell()}} as follows:

{code}
/**
 * Returns the output from running the specified command with the shell.
 */
Try<std::string> shell(const string& command)
{
  // Actually handle the WIFEXITED, WIFSIGNALED here!
}
{code}

where the returned string is {{stdout}} and, should the program be signaled, or exit with a non-zero exit code, we will simply return a {{Failure}} with an error message that will encapsulate both the returned/signaled state, and, possibly {{stderr}}.

And some test driven development:
{code}
EXPECT_ERROR(os::shell("false"));
EXPECT_SOME(os::shell("true"));

EXPECT_SOME_EQ("hello world", os::shell("echo hello world"));
{code}

Alternatively, the caller can ask to have {{stderr}} conflated with {{stdout}}:
{code}
Try<string> outAndErr = os::shell("myCmd --foo 2>&1");
{code}

However, {{stderr}} will be ignored by default:
{code}
// We don't read standard error by default.
EXPECT_SOME_EQ("", os::shell("echo hello world 1>&2"));

// We don't even read stderr if something fails (to return in Try::error).
Try<string> output = os::shell("echo hello world 1>&2 && false");
EXPECT_ERROR(output);
EXPECT_FALSE(strings::contains(output.error(), "hello world"));
{code}

An analysis of existing usage shows that in almost all cases, the caller only cares {{if not error}}; in fact, the actual exit code is read only once, and even then, in a test case.

We believe this will simplify the API to the caller, and will significantly reduce the length and complexity at the calling sites (<6 LOC against the current 20+).)

> As a Developer I would like a standard way to run a Subprocess in libprocess
> ----------------------------------------------------------------------------
>
>                 Key: MESOS-3035
>                 URL: https://issues.apache.org/jira/browse/MESOS-3035
>             Project: Mesos
>          Issue Type: Story
>          Components: libprocess
>            Reporter: Marco Massenzio
>            Assignee: Marco Massenzio
>
> As part of MESOS-2830 and MESOS-2902 I have been researching the ability to run a {{Subprocess}} and capture the {{stdout / stderr}} along with the exit status code.
> {{process::subprocess()}} offers much of the functionality, but in a way that still requires a lot of handiwork on the developer's part; we would like to further abstract away the ability to just pass a string, an optional set of command-line arguments and then collect the output of the command (bonus: without blocking).



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