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thaJeztah merged 2 commits into from
Mar 9, 2023
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stack/loader: Ignore cmd.exe special env variables #4081

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stack/loader: Ignore cmd.exe special env variables
vvoland Mar 9, 2023
012b779
stack: Change unexpected environment variable error
vvoland Mar 9, 2023
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16 changes: 15 additions & 1 deletion cli/command/stack/loader/loader.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ import (
"io"
"os"
"path/filepath"
"runtime"
"sort"
"strings"

Expand Down Expand Up @@ -104,9 +105,22 @@ func GetConfigDetails(composefiles []string, stdin io.Reader) (composetypes.Conf
func buildEnvironment(env []string) (map[string]string, error) {
result := make(map[string]string, len(env))
for _, s := range env {
if runtime.GOOS == "windows" && len(s) > 0 {
// cmd.exe can have special environment variables which names start with "=".
// They are only there for MS-DOS compatibility and we should ignore them.
// See TestBuildEnvironment for examples.
//
// https://ss64.com/nt/syntax-variables.html
// https://devblogs.microsoft.com/oldnewthing/20100506-00/?p=14133
// https://github.com/docker/cli/issues/4078
if s[0] == '=' {
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@vvoland vvoland Mar 9, 2023 •
edited
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I didn't make this one an explicit blacklist of variables, because:

  1. MS documentation explicitly states that:

The name of an environment variable cannot include an equal sign (=).
https://learn.microsoft.com/en-us/windows/win32/procthread/environment-variables

so user can't deliberately set such variable nor anyone other than cmd.exe should actually set such variables.

  1. I don't think we want to implement the parser for the drive-specific CWD format (or hardcode every possible drive letter).
  2. We don't want to play whack-a-mole if there are some other undocumented variables that can start with =.

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@thaJeztah thaJeztah Mar 9, 2023

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  1. MS documentation explicitly states that:

The name of an environment variable cannot include an equal sign (=).
https://learn.microsoft.com/en-us/windows/win32/procthread/environment-variables

Interesting, thanks!

So;

  • Perhaps we should include that link (and description that a user cannot set it) in the comment
  • From the above, I wonder indeed if this is something that os.Environ() should take into account (if that would make sense) and possibly filter out those "env-vars" (might be worth opening a ticket for in Golang, and see if there's opinions on that)

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@twinter-amosfivesix twinter-amosfivesix Mar 9, 2023

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There look to be existing Golang issues related to this:

continue
}
}

k, v, ok := strings.Cut(s, "=")
if !ok || k == "" {
Comment on lines 121 to 122
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@thaJeztah thaJeztah Mar 9, 2023

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I was wondering if the case above could also be checked as;

if ok && k == "" && runtime.GOOS == "windows" {
    // windows handling here

But not sure if that would make it actually more readable than your implementation, and won't give us a performance benefice, so .. bad suggestion I guess 😂

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@neersighted neersighted Mar 9, 2023

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I think the version as written is better as it makes the intention more obvious.

return result, errors.Errorf("unexpected environment %q", s)
return result, errors.Errorf("unexpected environment variable '%s'", s)
}
// value may be set, but empty if "s" is like "K=", not "K".
result[k] = v
Expand Down
32 changes: 32 additions & 0 deletions cli/command/stack/loader/loader_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@ package loader
import (
"os"
"path/filepath"
"runtime"
"strings"
"testing"

Expand Down Expand Up @@ -45,3 +46,34 @@ services:
assert.Check(t, is.Equal("3.0", details.ConfigFiles[0].Config["version"]))
assert.Check(t, is.Len(details.Environment, len(os.Environ())))
}

func TestBuildEnvironment(t *testing.T) {
inputEnv := []string{
"LEGIT_VAR=LEGIT_VALUE",
"EMPTY_VARIABLE=",
}

if runtime.GOOS == "windows" {
inputEnv = []string{
"LEGIT_VAR=LEGIT_VALUE",

// cmd.exe has some special environment variables which start with "=".
// These should be ignored as they're only there for MS-DOS compatibility.
"=ExitCode=00000041",
"=ExitCodeAscii=A",
`=C:=C:\some\dir`,
`=D:=D:\some\different\dir`,
`=X:=X:\`,
`=::=::\`,

"EMPTY_VARIABLE=",
}
}

env, err := buildEnvironment(inputEnv)
assert.NilError(t, err)

assert.Check(t, is.Len(env, 2))
assert.Check(t, is.Equal("LEGIT_VALUE", env["LEGIT_VAR"]))
assert.Check(t, is.Equal("", env["EMPTY_VARIABLE"]))
}