fix: pebble exec inherits environment from daemon

Currently, the environment variables from the pebble daemon
are not inherited while executing ``pebble exec`` commands.

Change this behavior and inherit all enviroment variables
available to the pebble daemon, in pebble exec.

Addresses ROCKS-684 on Jira.

Author: rebornplusplus

internals/daemon/api_exec.go

@@ -18,7 +18,9 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"os"
 	"os/exec"
+	"strings"
 	"time"
 
 	"github.com/canonical/pebble/internals/osutil"
@@ -73,13 +75,30 @@ func v1PostExec(c *Command, req *http.Request, _ *userState) Response {
 		return statusBadRequest("%v", err)
 	}
 
+	// Inherit the pebble daemon environment.
+	environment := make(map[string]string)
+	for key, val := range payload.Environment {
+		environment[key] = val
+	}
+	for _, kv := range os.Environ() {
+		parts := strings.SplitN(kv, "=", 2)
+		key := parts[0]
+		val := ""
+		if len(parts) == 2 {
+			val = parts[1]
+		}
+		if _, ok := environment[key]; !ok {
+			environment[key] = val
+		}
+	}
+
 	st := c.d.overlord.State()
 	st.Lock()
 	defer st.Unlock()
 
 	args := &cmdstate.ExecArgs{
 		Command:     payload.Command,
-		Environment: payload.Environment,
+		Environment: environment,
 		WorkingDir:  payload.WorkingDir,
 		Timeout:     timeout,
 		UserID:      uid,

internals/daemon/api_exec_test.go

@@ -108,6 +108,28 @@ func (s *execSuite) TestEnvironment(c *C) {
 	c.Check(stderr, Equals, "")
 }
 
+func (s *execSuite) TestEnvironmentInheritedFromDaemon(c *C) {
+	oldEnv, envWasSet := os.LookupEnv("FOO")
+	err := os.Setenv("FOO", "bar")
+	c.Check(err, IsNil)
+	defer func() {
+		var err error
+		if envWasSet {
+			err = os.Setenv("FOO", oldEnv)
+		} else {
+			err = os.Unsetenv("FOO")
+		}
+		c.Check(err, IsNil)
+	}()
+
+	stdout, stderr, waitErr := s.exec(c, "", &client.ExecOptions{
+		Command: []string{"/bin/sh", "-c", "echo FOO=$FOO"},
+	})
+	c.Check(waitErr, IsNil)
+	c.Check(stdout, Equals, "FOO=bar\n")
+	c.Check(stderr, Equals, "")
+}
+
 func (s *execSuite) TestWorkingDir(c *C) {
 	workingDir := c.MkDir()
 	stdout, stderr, waitErr := s.exec(c, "", &client.ExecOptions{