do not mutate defaults in replaceOrAppendEnvValues

Signed-off-by: Andrey Kolomentsev <andrey.kolomentsev@docker.com>

oci/spec_opts.go

@@ -141,8 +141,10 @@ func WithEnv(environmentVariables []string) SpecOpts {
 // replaced by env key or appended to the list
 func replaceOrAppendEnvValues(defaults, overrides []string) []string {
 	cache := make(map[string]int, len(defaults))
+	results := make([]string, 0, len(defaults))
 	for i, e := range defaults {
 		parts := strings.SplitN(e, "=", 2)
+		results = append(results, e)
 		cache[parts[0]] = i
 	}
 
@@ -150,7 +152,7 @@ func replaceOrAppendEnvValues(defaults, overrides []string) []string {
 		// Values w/o = means they want this env to be removed/unset.
 		if !strings.Contains(value, "=") {
 			if i, exists := cache[value]; exists {
-				defaults[i] = "" // Used to indicate it should be removed
+				results[i] = "" // Used to indicate it should be removed
 			}
 			continue
 		}
@@ -158,21 +160,21 @@ func replaceOrAppendEnvValues(defaults, overrides []string) []string {
 		// Just do a normal set/update
 		parts := strings.SplitN(value, "=", 2)
 		if i, exists := cache[parts[0]]; exists {
-			defaults[i] = value
+			results[i] = value
 		} else {
-			defaults = append(defaults, value)
+			results = append(results, value)
 		}
 	}
 
 	// Now remove all entries that we want to "unset"
-	for i := 0; i < len(defaults); i++ {
-		if defaults[i] == "" {
-			defaults = append(defaults[:i], defaults[i+1:]...)
+	for i := 0; i < len(results); i++ {
+		if results[i] == "" {
+			results = append(results[:i], results[i+1:]...)
 			i--
 		}
 	}
 
-	return defaults
+	return results
 }
 
 // WithProcessArgs replaces the args on the generated spec

oci/spec_opts_test.go

@@ -31,6 +31,49 @@ import (
 	specs "github.com/opencontainers/runtime-spec/specs-go"
 )
 
+func TestReplaceOrAppendEnvValues(t *testing.T) {
+	t.Parallel()
+
+	defaults := []string{
+		"o=ups", "p=$e", "x=foo", "y=boo", "z", "t=",
+	}
+	overrides := []string{
+		"x=bar", "y", "a=42", "o=", "e", "s=",
+	}
+	expected := []string{
+		"o=", "p=$e", "x=bar", "z", "t=", "a=42", "s=",
+	}
+
+	defaultsOrig := make([]string, len(defaults))
+	copy(defaultsOrig, defaults)
+	overridesOrig := make([]string, len(overrides))
+	copy(overridesOrig, overrides)
+
+	results := replaceOrAppendEnvValues(defaults, overrides)
+
+	for i, x := range defaultsOrig {
+		if defaults[i] != x {
+			t.Fatal("defaults slice was mutated")
+		}
+	}
+
+	for i, x := range overridesOrig {
+		if overrides[i] != x {
+			t.Fatal("overrides slice was mutated")
+		}
+	}
+
+	if len(expected) != len(results) {
+		t.Fatalf("expected %s, but found %s", expected, results)
+	}
+
+	for i, x := range expected {
+		if results[i] != x {
+			t.Fatalf("expected %s, but found %s", expected, results)
+		}
+	}
+}
+
 func TestWithEnv(t *testing.T) {
 	t.Parallel()