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ssh/tailssh: add logic for matching against AcceptEnv patterns (#13466)
Add logic for parsing and matching against our planned format for AcceptEnv values. Namely, this supports direct matches against string values and matching where * and ? are treated as wildcard characters which match against an arbitrary number of characters and a single character respectively. Actually using this logic in non-test code will come in subsequent changes. Updates https://github.com/tailscale/corp/issues/22775 Signed-off-by: Mario Minardi <mario@tailscale.com>
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Mario Minardi
GitHub
parent
9eb59c72c1
commit
c90c9938c8
110
ssh/tailssh/accept_env.go
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110
ssh/tailssh/accept_env.go
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@ -0,0 +1,110 @@
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package tailssh
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import (
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"slices"
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"strings"
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)
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// filterEnv filters a passed in environ string slice (a slice with strings
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// representing environment variables in the form "key=value") based on
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// the supplied slice of acceptEnv values.
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//
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// acceptEnv is a slice of environment variable names that are allowlisted
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// for the SSH rule in the policy file.
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//
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// acceptEnv values may contain * and ? wildcard characters which match against
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// zero or one or more characters and a single character respectively.
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func filterEnv(acceptEnv []string, environ []string) []string {
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var acceptedPairs []string
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for _, envPair := range environ {
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envVar := strings.Split(envPair, "=")[0]
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// Short circuit if we have a direct match between the environment
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// variable and an AcceptEnv value.
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if slices.Contains(acceptEnv, envVar) {
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acceptedPairs = append(acceptedPairs, envPair)
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continue
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}
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// Otherwise check if we have a wildcard pattern that matches.
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if matchAcceptEnv(acceptEnv, envVar) {
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acceptedPairs = append(acceptedPairs, envPair)
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continue
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}
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}
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return acceptedPairs
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}
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// matchAcceptEnv is a convenience function that wraps calling matchAcceptEnvPattern
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// with every value in acceptEnv for a given env that is being matched against.
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func matchAcceptEnv(acceptEnv []string, env string) bool {
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for _, pattern := range acceptEnv {
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if matchAcceptEnvPattern(pattern, env) {
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return true
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}
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}
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return false
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}
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// matchAcceptEnvPattern returns true if the pattern matches against the target string.
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// Patterns may include * and ? wildcard characters which match against zero or one or
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// more characters and a single character respectively.
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func matchAcceptEnvPattern(pattern string, target string) bool {
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patternIdx := 0
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targetIdx := 0
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for {
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// If we are at the end of the pattern we can only have a match if we
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// are also at the end of the target.
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if patternIdx >= len(pattern) {
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return targetIdx >= len(target)
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}
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if pattern[patternIdx] == '*' {
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// Optimization to skip through any repeated asterisks as they
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// have the same net effect on our search.
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for patternIdx < len(pattern) {
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if pattern[patternIdx] != '*' {
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break
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}
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patternIdx++
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}
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// We are at the end of the pattern after matching the asterisk,
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// implying a match.
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if patternIdx >= len(pattern) {
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return true
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}
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// Search through the target sequentially for the next character
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// from the pattern string, recursing into matchAcceptEnvPattern
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// to try and find a match.
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for ; targetIdx < len(target); targetIdx++ {
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if matchAcceptEnvPattern(pattern[patternIdx:], target[targetIdx:]) {
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return true
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}
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}
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// No match after searching through the entire target.
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return false
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}
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if targetIdx >= len(target) {
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return false
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}
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if pattern[patternIdx] != '?' && pattern[patternIdx] != target[targetIdx] {
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return false
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}
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patternIdx++
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targetIdx++
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}
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}
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140
ssh/tailssh/accept_env_test.go
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140
ssh/tailssh/accept_env_test.go
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@ -0,0 +1,140 @@
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package tailssh
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import (
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"fmt"
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"testing"
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"github.com/google/go-cmp/cmp"
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)
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func TestMatchAcceptEnvPattern(t *testing.T) {
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testCases := []struct {
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pattern string
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target string
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match bool
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}{
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{pattern: "*", target: "EXAMPLE_ENV", match: true},
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{pattern: "***", target: "123456", match: true},
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{pattern: "?", target: "A", match: true},
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{pattern: "?", target: "123", match: false},
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{pattern: "?*", target: "EXAMPLE_2", match: true},
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{pattern: "?*", target: "", match: false},
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{pattern: "*?", target: "A", match: true},
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{pattern: "*?", target: "", match: false},
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{pattern: "??", target: "CC", match: true},
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{pattern: "??", target: "123", match: false},
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{pattern: "*?*", target: "ABCDEFG", match: true},
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{pattern: "*?*", target: "C", match: true},
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{pattern: "*?*", target: "", match: false},
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{pattern: "?*?", target: "ABCDEFG", match: true},
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{pattern: "?*?", target: "A", match: false},
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{pattern: "**?TEST", target: "_TEST", match: true},
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{pattern: "**?TEST", target: "_TESTING", match: false},
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{pattern: "TEST**?", target: "TEST_", match: true},
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{pattern: "TEST**?", target: "A_TEST_", match: false},
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{pattern: "TEST_*", target: "TEST_A", match: true},
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{pattern: "TEST_*", target: "TEST_A_LONG_ENVIRONMENT_VARIABLE_NAME", match: true},
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{pattern: "TEST_*", target: "TEST", match: false},
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{pattern: "EXAMPLE_?_ENV", target: "EXAMPLE_A_ENV", match: true},
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{pattern: "EXAMPLE_?_ENV", target: "EXAMPLE_ENV", match: false},
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{pattern: "EXAMPLE_*_ENV", target: "EXAMPLE_aBcd2231---_ENV", match: true},
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{pattern: "EXAMPLE_*_ENV", target: "EXAMPLEENV", match: false},
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{pattern: "COMPLICA?ED_PATTERN*", target: "COMPLICATED_PATTERN_REST", match: true},
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{pattern: "COMPLICA?ED_PATTERN*", target: "COMPLICATED_PATT", match: false},
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{pattern: "COMPLICAT???ED_PATT??ERN", target: "COMPLICAT123ED_PATTggERN", match: true},
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{pattern: "COMPLICAT???ED_PATT??ERN", target: "COMPLICATED_PATTERN", match: false},
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{pattern: "DIRECT_MATCH", target: "DIRECT_MATCH", match: true},
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{pattern: "DIRECT_MATCH", target: "MISS", match: false},
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// OpenSSH compatibility cases
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// See https://github.com/openssh/openssh-portable/blob/master/regress/unittests/match/tests.c
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{pattern: "", target: "", match: true},
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{pattern: "aaa", target: "", match: false},
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{pattern: "", target: "aaa", match: false},
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{pattern: "aaaa", target: "aaa", match: false},
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{pattern: "aaa", target: "aaaa", match: false},
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{pattern: "*", target: "", match: true},
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{pattern: "?", target: "a", match: true},
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{pattern: "a?", target: "aa", match: true},
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{pattern: "*", target: "a", match: true},
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{pattern: "a*", target: "aa", match: true},
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{pattern: "?*", target: "aa", match: true},
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{pattern: "**", target: "aa", match: true},
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{pattern: "?a", target: "aa", match: true},
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{pattern: "*a", target: "aa", match: true},
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{pattern: "a?", target: "ba", match: false},
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{pattern: "a*", target: "ba", match: false},
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{pattern: "?a", target: "ab", match: false},
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{pattern: "*a", target: "ab", match: false},
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}
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for _, tc := range testCases {
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name := fmt.Sprintf("pattern_%s_target_%s", tc.pattern, tc.target)
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if tc.match {
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name += "_should_match"
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} else {
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name += "_should_not_match"
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}
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t.Run(name, func(t *testing.T) {
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match := matchAcceptEnvPattern(tc.pattern, tc.target)
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if match != tc.match {
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t.Errorf("got %v, want %v", match, tc.match)
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}
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})
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}
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}
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func TestFilterEnv(t *testing.T) {
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testCases := []struct {
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name string
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acceptEnv []string
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environ []string
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expectedFiltered []string
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}{
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{
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name: "simple direct matches",
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acceptEnv: []string{"FOO", "FOO2", "FOO_3"},
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environ: []string{"FOO=BAR", "FOO2=BAZ", "FOO_3=123", "FOOOO4-2=AbCdEfG"},
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expectedFiltered: []string{"FOO=BAR", "FOO2=BAZ", "FOO_3=123"},
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},
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{
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name: "bare wildcard",
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acceptEnv: []string{"*"},
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environ: []string{"FOO=BAR", "FOO2=BAZ", "FOO_3=123", "FOOOO4-2=AbCdEfG"},
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expectedFiltered: []string{"FOO=BAR", "FOO2=BAZ", "FOO_3=123", "FOOOO4-2=AbCdEfG"},
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},
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{
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name: "complex matches",
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acceptEnv: []string{"FO?", "FOOO*", "FO*5?7"},
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environ: []string{"FOO=BAR", "FOO2=BAZ", "FOO_3=123", "FOOOO4-2=AbCdEfG", "FO1-kmndGamc79567=ABC", "FO57=BAR2"},
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expectedFiltered: []string{"FOO=BAR", "FOOOO4-2=AbCdEfG", "FO1-kmndGamc79567=ABC"},
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},
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}
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for _, tc := range testCases {
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t.Run(tc.name, func(t *testing.T) {
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filtered := filterEnv(tc.acceptEnv, tc.environ)
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if diff := cmp.Diff(tc.expectedFiltered, filtered); diff != "" {
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t.Errorf("unexpected filter result (-got,+want): \n%s", diff)
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}
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})
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}
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}
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