Marco Massenzio created MESOS-3142:
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Summary: As a Developer I want a better way to run shell commands
Key: MESOS-3142
URL: https://issues.apache.org/jira/browse/MESOS-3142
Project: Mesos
Issue Type: Story
Components: stout
Affects Versions: 0.23.0
Reporter: Benjamin Hindman
Assignee: Marco Massenzio
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+).
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