dnf-json: Change dnf-json to be a daemon

The service is started via systemd activation sockets.
The service serves http POST requests, the same json as before is
expected as the body of the request, and the same json as before is sent
as the response of the request.

internal/distro/distro_test_common/distro_test_common.go

@@ -132,7 +132,7 @@ func TestDistro_Manifest(t *testing.T, pipelinePath string, prefix string, regis
 func getImageTypePkgSpecSets(imageType distro.ImageType, bp blueprint.Blueprint, repos []rpmmd.RepoConfig, cacheDir, dnfJsonPath string) map[string][]rpmmd.PackageSpec {
 	imgPackageSets := imageType.PackageSets(bp)
 
-	rpm_md := rpmmd.NewRPMMD(cacheDir, dnfJsonPath)
+	rpm_md := rpmmd.NewRPMMD(cacheDir)
 
 	imgPackageSpecSets := make(map[string][]rpmmd.PackageSpec)
 	for name, packages := range imgPackageSets {

internal/rpmmd/repository.go

@@ -1,12 +1,15 @@
 package rpmmd
 
 import (
+	"bytes"
+	"context"
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
 	"log"
+	"net"
+	"net/http"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"sort"
 	"strconv"
@@ -313,7 +316,7 @@ func LoadRepositories(confPaths []string, distro string) (map[string][]RepoConfi
 	return repoConfigs, nil
 }
 
-func runDNF(dnfJsonPath string, command string, arguments interface{}, result interface{}) error {
+func runDNF(command string, arguments interface{}, result interface{}) error {
 	var call = struct {
 		Command   string      `json:"command"`
 		Arguments interface{} `json:"arguments,omitempty"`
@@ -322,39 +325,31 @@ func runDNF(dnfJsonPath string, command string, arguments interface{}, result in
 		arguments,
 	}
 
-	cmd := exec.Command(dnfJsonPath)
+	httpc := http.Client{
+		Transport: &http.Transport{
+			DialContext: func(_ context.Context, _, _ string) (net.Conn, error) {
+				return net.Dial("unix", "/run/osbuild-dnf-json/api.sock")
+			},
+		},
+	}
 
-	stdin, err := cmd.StdinPipe()
+	bpost, err := json.Marshal(call)
 	if err != nil {
 		return err
 	}
 
-	cmd.Stderr = os.Stderr
-	stdout, err := cmd.StdoutPipe()
+	response, err := httpc.Post("http://unix", "application/json", bytes.NewReader(bpost))
+	if err != nil {
+		return err
+	}
+	defer response.Body.Close()
+
+	output, err := ioutil.ReadAll(response.Body)
 	if err != nil {
 		return err
 	}
 
-	err = cmd.Start()
-	if err != nil {
-		return err
-	}
-
-	err = json.NewEncoder(stdin).Encode(call)
-	if err != nil {
-		return err
-	}
-	stdin.Close()
-
-	output, err := ioutil.ReadAll(stdout)
-	if err != nil {
-		return err
-	}
-
-	err = cmd.Wait()
-
-	const DnfErrorExitCode = 10
-	if runError, ok := err.(*exec.ExitError); ok && runError.ExitCode() == DnfErrorExitCode {
+	if response.StatusCode != http.StatusOK {
 		var dnfError DNFError
 		err = json.Unmarshal(output, &dnfError)
 		if err != nil {
@@ -376,10 +371,9 @@ func runDNF(dnfJsonPath string, command string, arguments interface{}, result in
 type rpmmdImpl struct {
 	CacheDir      string
 	subscriptions *rhsm.Subscriptions
-	dnfJsonPath   string
 }
 
-func NewRPMMD(cacheDir, dnfJsonPath string) RPMMD {
+func NewRPMMD(cacheDir string) RPMMD {
 	subscriptions, err := rhsm.LoadSystemSubscriptions()
 	if err != nil {
 		log.Println("Failed to load subscriptions. osbuild-composer will fail to build images if the "+
@@ -391,7 +385,6 @@ func NewRPMMD(cacheDir, dnfJsonPath string) RPMMD {
 	return &rpmmdImpl{
 		CacheDir:      cacheDir,
 		subscriptions: subscriptions,
-		dnfJsonPath:   dnfJsonPath,
 	}
 }
 
@@ -442,7 +435,7 @@ func (r *rpmmdImpl) FetchMetadata(repos []RepoConfig, modulePlatformID, arch, re
 		Packages  PackageList       `json:"packages"`
 	}
 
-	err := runDNF(r.dnfJsonPath, "dump", arguments, &reply)
+	err := runDNF("dump", arguments, &reply)
 
 	sort.Slice(reply.Packages, func(i, j int) bool {
 		return reply.Packages[i].Name < reply.Packages[j].Name
@@ -477,7 +470,7 @@ func (r *rpmmdImpl) Depsolve(packageSet PackageSet, repos []RepoConfig, modulePl
 		Checksums    map[string]string `json:"checksums"`
 		Dependencies []dnfPackageSpec  `json:"dependencies"`
 	}
-	err := runDNF(r.dnfJsonPath, "depsolve", arguments, &reply)
+	err := runDNF("depsolve", arguments, &reply)
 
 	dependencies := make([]PackageSpec, len(reply.Dependencies))
 	for i, pack := range reply.Dependencies {