config: add env_merge support to containers.conf

Allow users to set default env_merge values in containers.conf.
Works the same as the --env-merge CLI option.

Fixes: containers/podman#28410
Signed-off-by: Jiwoo Ahn <ikwydls1314@gmail.com>

Author: jiwahn

common/docs/containers.conf.5.md

@@ -226,6 +226,14 @@ overwriting values specified on the command line when the container was created.
 
 Pass all host environment variables into the container.
 
+**env_merge**=[]
+
+Preprocess default environment variables for the container.
+Works the same as the **--env-merge** command line option.
+The value of existing variables in the image will be used for substitution.
+
+Example: `env_merge=["PATH=${PATH}:/custom/bin"]`
+
 **host_containers_internal_ip**=""
 
 Set the IP address the container should expect to connect to the host. The IP

common/pkg/config/config.go

@@ -142,6 +142,9 @@ type ContainersConfig struct {
 	// EnvHost Pass all host environment variables into the container.
 	EnvHost bool `toml:"env_host,omitempty"`
 
+	// EnvMerge preprocess the environment variables list for the container.
+	EnvMerge configfile.Slice `toml:"env_merge,omitempty"`
+
 	// HostContainersInternalIP is used to set a specific host.containers.internal ip.
 	HostContainersInternalIP string `toml:"host_containers_internal_ip,omitempty"`
 

common/pkg/config/config_local_test.go

@@ -664,4 +664,15 @@ var _ = Describe("Config Local", func() {
 		// Then
 		gomega.Expect(err).To(gomega.HaveOccurred())
 	})
+	It("should parse env_merge from config file", func() {
+		// Given
+		config, err := newLocked(&Options{}, testConfigPath(""))
+		gomega.Expect(err).ToNot(gomega.HaveOccurred())
+		gomega.Expect(config.Containers.EnvMerge.Get()).To(gomega.BeEmpty())
+		// When
+		config2, err := newLocked(&Options{}, testConfigPath("testdata/containers_default.conf"))
+		// Then
+		gomega.Expect(err).ToNot(gomega.HaveOccurred())
+		gomega.Expect(config2.Containers.EnvMerge.Get()).To(gomega.Equal([]string{"FOO=bar"}))
+	})
 })

common/pkg/config/containers.conf

@@ -137,6 +137,10 @@ default_sysctls = [
 #
 #env_host = false
 
+# Preprocess default environment variables for the container.
+#
+#env_merge = []
+
 # Set the IP address the container should expect to connect to the host. The IP
 # address is used by Podman to automatically add the `host.containers.internal`
 # and `host.docker.internal` hostnames to the container's `/etc/hosts` file. It

common/pkg/config/default.go

@@ -223,6 +223,7 @@ func defaultConfig() (*Config, error) {
 			EnableLabeling:      selinux.GetEnabled(),
 			Env:                 configfile.NewSlice(defaultContainerEnv),
 			EnvHost:             false,
+			EnvMerge:            configfile.Slice{},
 			HTTPProxy:           true,
 			IPCNS:               "shareable",
 			Init:                false,

common/pkg/config/modules_test.go

@@ -57,6 +57,11 @@ var _ = Describe("Config Modules", func() {
 		gomega.Expect(err).ToNot(gomega.HaveOccurred())
 		gomega.Expect(c.Containers.InitPath).To(gomega.Equal("etc four"))
 		gomega.Expect(c.Containers.Env.Get()).To(gomega.Equal([]string{"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin", "usr share only"}))
+		gomega.Expect(c.Containers.EnvMerge.Get()).To(gomega.Equal([]string{
+			"PATH=/base/bin:${PATH}",
+			"PATH=/usr/local/share/bin:${PATH}",
+			"etc only env_merge conf",
+		}))
 		gomega.Expect(c.Network.DefaultNetwork).To(gomega.Equal("etc only conf"))
 		gomega.Expect(c.LoadedModules()).To(gomega.HaveLen(3)) // 3 modules are getting loaded!
 

common/pkg/config/testdata/containers_default.conf

@@ -65,6 +65,8 @@ env = [
     "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
 ]
 
+env_merge = ["FOO=bar"]
+
 # Run an init inside the container that forwards signals and reaps processes.
 init = false
 

common/pkg/config/testdata/modules/etc/containers/containers.conf.modules/sub/etc-only.conf

@@ -1,2 +1,5 @@
 [network]
 default_network="etc only conf"
+
+[containers]
+env_merge=["PATH=/usr/local/share/bin:${PATH}", "etc only env_merge conf", {append=true}]

common/pkg/config/testdata/modules/usr/share/containers/containers.conf.modules/sub/share-only.conf

@@ -1,2 +1,3 @@
 [containers]
 env=["usr share only", {append=true}]
+env_merge=["PATH=/base/bin:${PATH}"]