run,create: add support for --env-merge for preprocessing vars

Allow end users to preprocess default environment variables before
injecting them into container using `--env-merge`

Usage
```
podman run -it --rm --env-merge some=${some}-edit --env-merge
some2=${some2}-edit2 myimage sh
```

Closes: https://github.com/containers/podman/issues/15288

Signed-off-by: Aditya R <arajan@redhat.com>

cmd/podman/common/create.go

@@ -124,6 +124,14 @@ func DefineCreateFlags(cmd *cobra.Command, cf *entities.ContainerCreateOptions,
 			"This is a Docker specific option and is a NOOP",
 		)
 
+		envMergeFlagName := "env-merge"
+		createFlags.StringArrayVar(
+			&cf.EnvMerge,
+			envMergeFlagName, []string{},
+			"Preprocess environment variables from image before injecting them into the container",
+		)
+		_ = cmd.RegisterFlagCompletionFunc(envMergeFlagName, completion.AutocompleteNone)
+
 		envFlagName := "env"
 		createFlags.StringArrayP(
 			envFlagName, "e", Env(),

docs/source/markdown/options/env-merge.md

@@ -0,0 +1,5 @@
+#### **--env-merge**=*env*
+
+Preprocess default environment variables for the containers. For example
+if image contains environment variable `hello=world` user can preprocess
+it using `--env-merge hello=${hello}-some` so new value will be `hello=world-some`.

docs/source/markdown/podman-create.1.md.in

@@ -208,6 +208,8 @@ Read in a line delimited file of environment variables. See **Environment** note
 
 @@option env-host
 
+@@option env-merge
+
 @@option expose
 
 #### **--gidmap**=*container_gid:host_gid:amount*

docs/source/markdown/podman-run.1.md.in

@@ -243,6 +243,8 @@ Read in a line delimited file of environment variables. See **Environment** note
 
 @@option env-host
 
+@@option env-merge
+
 @@option expose
 
 #### **--gidmap**=*container_gid:host_gid:amount*

go.mod

@@ -49,6 +49,7 @@ require (
 	github.com/opencontainers/runtime-spec v1.0.3-0.20211214071223-8958f93039ab
 	github.com/opencontainers/runtime-tools v0.9.1-0.20220714195903-17b3287fafb7
 	github.com/opencontainers/selinux v1.10.1
+	github.com/openshift/imagebuilder v1.2.4-0.20220711175835-4151e43600df
 	github.com/rootless-containers/rootlesskit v1.0.1
 	github.com/sirupsen/logrus v1.9.0
 	github.com/spf13/cobra v1.5.0

pkg/api/handlers/compat/containers_create.go

@@ -408,6 +408,7 @@ func cliOpts(cc handlers.CreateContainerConfig, rtc *config.Config) (*entities.C
 		Systemd:           "true", // podman default
 		TmpFS:             parsedTmp,
 		TTY:               cc.Config.Tty,
+		EnvMerge:          cc.EnvMerge,
 		UnsetEnv:          cc.UnsetEnv,
 		UnsetEnvAll:       cc.UnsetEnvAll,
 		User:              cc.Config.User,

pkg/api/handlers/types.go

@@ -127,6 +127,7 @@ type CreateContainerConfig struct {
 	dockerContainer.Config                                // desired container configuration
 	HostConfig             dockerContainer.HostConfig     // host dependent configuration for container
 	NetworkingConfig       dockerNetwork.NetworkingConfig // network configuration for container
+	EnvMerge               []string                       // preprocess env variables from image before injecting into containers
 	UnsetEnv               []string                       // unset specified default environment variables
 	UnsetEnvAll            bool                           // unset all default environment variables
 }

pkg/domain/entities/pods.go

@@ -263,6 +263,7 @@ type ContainerCreateOptions struct {
 	TTY               bool
 	Timezone          string
 	Umask             string
+	EnvMerge          []string
 	UnsetEnv          []string
 	UnsetEnvAll       bool
 	UIDMap            []string

pkg/specgen/generate/container.go

@@ -19,6 +19,7 @@ import (
 	"github.com/containers/podman/v4/pkg/signal"
 	"github.com/containers/podman/v4/pkg/specgen"
 	spec "github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/openshift/imagebuilder"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
 )
@@ -131,6 +132,17 @@ func CompleteSpec(ctx context.Context, r *libpod.Runtime, s *specgen.SpecGenerat
 		defaultEnvs = envLib.Join(envLib.DefaultEnvVariables(), envLib.Join(defaultEnvs, envs))
 	}
 
+	for _, e := range s.EnvMerge {
+		processedWord, err := imagebuilder.ProcessWord(e, envLib.Slice(defaultEnvs))
+		if err != nil {
+			return nil, fmt.Errorf("unable to process variables for --env-merge %s: %w", e, err)
+		}
+		splitWord := strings.Split(processedWord, "=")
+		if _, ok := defaultEnvs[splitWord[0]]; ok {
+			defaultEnvs[splitWord[0]] = splitWord[1]
+		}
+	}
+
 	for _, e := range s.UnsetEnv {
 		delete(defaultEnvs, e)
 	}

pkg/specgen/specgen.go

@@ -204,6 +204,9 @@ type ContainerBasicConfig struct {
 	// The execution domain system allows Linux to provide limited support
 	// for binaries compiled under other UNIX-like operating systems.
 	Personality *spec.LinuxPersonality `json:"personality,omitempty"`
+	// EnvMerge takes the specified environment variables from image and preprocess them before injecting them into the
+	// container.
+	EnvMerge []string `json:"envmerge,omitempty"`
 	// UnsetEnv unsets the specified default environment variables from the image or from buildin or containers.conf
 	// Optional.
 	UnsetEnv []string `json:"unsetenv,omitempty"`

pkg/specgenutil/specgen.go

@@ -839,6 +839,9 @@ func FillOutSpecGen(s *specgen.SpecGenerator, c *entities.ContainerCreateOptions
 	if !s.Volatile {
 		s.Volatile = c.Rm
 	}
+	if len(s.EnvMerge) == 0 || len(c.EnvMerge) != 0 {
+		s.EnvMerge = c.EnvMerge
+	}
 	if len(s.UnsetEnv) == 0 || len(c.UnsetEnv) != 0 {
 		s.UnsetEnv = c.UnsetEnv
 	}

test/e2e/run_env_test.go

@@ -82,6 +82,17 @@ var _ = Describe("Podman run", func() {
 		Expect(session.OutputToString()).To(ContainSubstring("HOSTNAME"))
 	})
 
+	It("podman run with --env-merge", func() {
+		dockerfile := `FROM quay.io/libpod/alpine:latest
+ENV hello=world
+`
+		podmanTest.BuildImage(dockerfile, "test", "false")
+		session := podmanTest.Podman([]string{"run", "--rm", "--env-merge", "hello=${hello}-earth", "test", "env"})
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(Exit(0))
+		Expect(session.OutputToString()).To(ContainSubstring("world-earth"))
+	})
+
 	It("podman run --env-host environment test", func() {
 		env := append(os.Environ(), "FOO=BAR")
 		session := podmanTest.PodmanAsUser([]string{"run", "--rm", "--env-host", ALPINE, "/bin/printenv", "FOO"}, 0, 0, "", env)

vendor/modules.txt

@@ -620,6 +620,7 @@ github.com/opencontainers/selinux/go-selinux/label
 github.com/opencontainers/selinux/pkg/pwalk
 github.com/opencontainers/selinux/pkg/pwalkdir
 # github.com/openshift/imagebuilder v1.2.4-0.20220711175835-4151e43600df
+## explicit
 github.com/openshift/imagebuilder
 github.com/openshift/imagebuilder/dockerfile/command
 github.com/openshift/imagebuilder/dockerfile/parser