Docker run -e FOO should erase FOO if FOO isn't set in client env

See #10141 for more info, but the main point of this is to make sure
that if you do "docker run -e FOO ..." that FOO from the current env
is passed into the container.  This means that if there's a value, its
set.  But it also means that if FOO isn't set then it should be unset in
the container too - even if it has to remove it from the env.  So,
   unset HOSTNAME
   docker run -e HOSTNAME busybox env
should _NOT_ show HOSTNAME in the list at all

Closes #10141

Signed-off-by: Doug Davis <dug@us.ibm.com>
Upstream-commit: 9ab73260f8e4662e7321b257c636928892f023cf
Component: engine

components/engine/utils/utils.go

@@ -401,7 +401,17 @@ func ReplaceOrAppendEnvValues(defaults, overrides []string) []string {
 		parts := strings.SplitN(e, "=", 2)
 		cache[parts[0]] = i
 	}
+
 	for _, value := range overrides {
+		// 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
+			}
+			continue
+		}
+
+		// Just do a normal set/update
 		parts := strings.SplitN(value, "=", 2)
 		if i, exists := cache[parts[0]]; exists {
 			defaults[i] = value
@@ -409,9 +419,28 @@ func ReplaceOrAppendEnvValues(defaults, overrides []string) []string {
 			defaults = append(defaults, 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:]...)
+			i--
+		}
+	}
+
 	return defaults
 }
 
+func DoesEnvExist(name string) bool {
+	for _, entry := range os.Environ() {
+		parts := strings.SplitN(entry, "=", 2)
+		if parts[0] == name {
+			return true
+		}
+	}
+	return false
+}
+
 // ReadSymlinkedDirectory returns the target directory of a symlink.
 // The target of the symbolic link may not be a file.
 func ReadSymlinkedDirectory(path string) (string, error) {