Backport removal of non- stdlib errors from lxd/response (stable-5.…

…21) (#14411)

This backports #14408.

lxd/db/errors.go

@@ -2,9 +2,19 @@ package db
 
 import (
 	"fmt"
+	"net/http"
+
+	"github.com/canonical/go-dqlite/v2/driver"
+	"github.com/mattn/go-sqlite3"
 )
 
 var (
 	// ErrNoClusterMember is used to indicate no cluster member has been found for a resource.
 	ErrNoClusterMember = fmt.Errorf("No cluster member found")
 )
+
+// SmartErrors are used to return more appropriate errors to the caller.
+var SmartErrors = map[int][]error{
+	http.StatusConflict:           {sqlite3.ErrConstraintUnique},
+	http.StatusServiceUnavailable: {driver.ErrNoAvailableLeader},
+}

lxd/main.go

@@ -9,6 +9,7 @@ import (
 	"github.com/spf13/cobra"
 
 	"github.com/canonical/lxd/lxd/daemon"
+	"github.com/canonical/lxd/lxd/db"
 	"github.com/canonical/lxd/lxd/events"
 	"github.com/canonical/lxd/lxd/operations"
 	"github.com/canonical/lxd/lxd/response"
@@ -54,7 +55,7 @@ func (c *cmdGlobal) Run(cmd *cobra.Command, args []string) error {
 	operations.Init(daemon.Debug)
 
 	// Set debug for the response package
-	response.Init(daemon.Debug)
+	response.Init(daemon.Debug, db.SmartErrors)
 
 	// Setup logger
 	syslog := ""

lxd/response/response.go

@@ -21,9 +21,19 @@ import (
 
 var debug bool
 
-// Init sets the debug variable to the provided value.
-func Init(d bool) {
+// Init sets the debug variable to the provided value and registers any additional smart error mappings.
+func Init(d bool, smartErrors map[int][]error) {
 	debug = d
+
+	for code, additionalErrors := range smartErrors {
+		existingErrs, ok := httpResponseErrors[code]
+		if ok {
+			httpResponseErrors[code] = append(existingErrs, additionalErrors...)
+			continue
+		}
+
+		httpResponseErrors[code] = additionalErrors
+	}
 }
 
 // Response represents an API response.