rpmmd: Add error reporting support to dnf-json

Previously dnf-json hasn't been able to report any reports. This commit
tries to fix it with introduction of somewhat flexible error format.

dnf-json

@@ -5,6 +5,8 @@ import dnf
 import json
 import sys
 
+DNF_ERROR_EXIT_CODE = 10
+
 
 def timestamp_to_rfc3339(timestamp):
     d = datetime.datetime.utcfromtimestamp(package.buildtime)
@@ -39,6 +41,11 @@ def create_base(repos):
     return base
 
 
+def exit_with_dnf_error(kind: str, reason: str):
+    json.dump({"kind": kind, "reason": reason}, sys.stdout)
+    sys.exit(DNF_ERROR_EXIT_CODE)
+
+
 call = json.load(sys.stdin)
 command = call["command"]
 arguments = call.get("arguments", {})
@@ -63,8 +70,21 @@ if command == "dump":
 
 elif command == "depsolve":
     base = create_base(arguments.get("repos", {}))
-    base.install_specs(arguments["package-specs"])
-    base.resolve()
+    errors = []
+    for pkgspec in arguments["package-specs"]:
+        try:
+            base.install_specs([pkgspec])
+        except dnf.exceptions.MarkingError as e:
+            errors.append((pkgspec, str(e)))
+    if errors:
+        formatted_errors = ", ".join((f"{package} ({err})" for package, err in errors))
+        exit_with_dnf_error("MarkingError", f"The following package(s) had problems: {formatted_errors}")
+
+    try:
+        base.resolve()
+    except dnf.exceptions.DepsolveError as e:
+        exit_with_dnf_error("DepsolveError", f"There was a problem depsolving {arguments['package-specs']}: {e}")
+
     packages = []
     for package in base.transaction.install_set:
         packages.append({

internal/rpmmd/repository.go

@@ -2,6 +2,8 @@ package rpmmd
 
 import (
 	"encoding/json"
+	"fmt"
+	"io/ioutil"
 	"os"
 	"os/exec"
 	"sort"
@@ -44,6 +46,15 @@ type RPMMD interface {
 	Depsolve(specs []string, repos []RepoConfig) ([]PackageSpec, error)
 }
 
+type DNFError struct {
+	Kind   string `json:"kind"`
+	Reason string `json:"reason"`
+}
+
+func (err *DNFError) Error() string {
+	return fmt.Sprintf("DNF error occured: %s: %s", err.Kind, err.Reason)
+}
+
 func runDNF(command string, arguments interface{}, result interface{}) error {
 	var call = struct {
 		Command   string      `json:"command"`
@@ -77,12 +88,31 @@ func runDNF(command string, arguments interface{}, result interface{}) error {
 	}
 	stdin.Close()
 
-	err = json.NewDecoder(stdout).Decode(result)
+	output, err := ioutil.ReadAll(stdout)
 	if err != nil {
 		return err
 	}
 
-	return cmd.Wait()
+	err = cmd.Wait()
+
+	const DnfErrorExitCode = 10
+	if runError, ok := err.(*exec.ExitError); ok && runError.ExitCode() == DnfErrorExitCode {
+		var dnfError DNFError
+		err = json.Unmarshal(output, &dnfError)
+		if err != nil {
+			return err
+		}
+
+		return &dnfError
+	}
+
+	err = json.Unmarshal(output, result)
+
+	if err != nil {
+		return err
+	}
+
+	return nil
 }
 
 type rpmmdImpl struct{}