fix(pdfengines): selection of PDF engines and add a new module interface for modules that want to print system message on startup

pkg/modules/pdfengines/pdfengines.go

@@ -3,6 +3,7 @@ package pdfengines
 import (
 	"errors"
 	"fmt"
+	"strings"
 
 	"github.com/gotenberg/gotenberg/v7/pkg/gotenberg"
 	"github.com/gotenberg/gotenberg/v7/pkg/modules/api"
@@ -118,14 +119,25 @@ func (mod PDFEngines) Validate() error {
 	return fmt.Errorf("non-existing PDF engine(s): %s - available PDF engine(s): %s", nonExistingEngines, availableEngines)
 }
 
+// SystemMessages returns one message with the selected gotenberg.PDFEngine
+// modules.
+func (mod PDFEngines) SystemMessages() []string {
+	return []string{
+		strings.Join(mod.names[:], " "),
+	}
+}
+
 // PDFEngine returns a gotenberg.PDFEngine.
 func (mod PDFEngines) PDFEngine() (gotenberg.PDFEngine, error) {
-	engines := make([]gotenberg.PDFEngine, len(mod.engines))
+	engines := make([]gotenberg.PDFEngine, len(mod.names))
 
-	i := 0
-	for _, engine := range mod.engines {
-		engines[i] = engine
-		i++
+	for i, name := range mod.names {
+		for _, engine := range mod.engines {
+			if name == engine.(gotenberg.Module).Descriptor().ID {
+				engines[i] = engine
+				break
+			}
+		}
 	}
 
 	return newMultiPDFEngines(engines...), nil
@@ -155,6 +167,7 @@ var (
 	_ gotenberg.Module            = (*PDFEngines)(nil)
 	_ gotenberg.Provisioner       = (*PDFEngines)(nil)
 	_ gotenberg.Validator         = (*PDFEngines)(nil)
+	_ gotenberg.SystemLogger      = (*PDFEngines)(nil)
 	_ gotenberg.PDFEngineProvider = (*PDFEngines)(nil)
 	_ api.Router                  = (*PDFEngines)(nil)
 )

pkg/modules/pdfengines/pdfengines_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/gotenberg/gotenberg/v7/pkg/gotenberg"
@@ -252,11 +253,40 @@ func TestPDFEngine_Validate(t *testing.T) {
 	}
 }
 
+func TestPDFEngines_SystemMessages(t *testing.T) {
+	mod := new(PDFEngines)
+	mod.names = []string{"foo", "bar"}
+
+	messages := mod.SystemMessages()
+	if len(messages) != 1 {
+		t.Errorf("expected one and only one message but got %d", len(messages))
+	}
+
+	expect := strings.Join(mod.names[:], " ")
+	if messages[0] != expect {
+		t.Errorf("expected message '%s' but got '%s'", expect, messages[0])
+	}
+}
+
 func TestPDFEngine_PDFEngine(t *testing.T) {
 	mod := new(PDFEngines)
-	mod.engines = []gotenberg.PDFEngine{
-		struct{ ProtoPDFEngine }{},
-	}
+	mod.names = []string{"foo", "bar"}
+	mod.engines = func() []gotenberg.PDFEngine {
+		engine1 := struct{ ProtoPDFEngine }{}
+		engine1.descriptor = func() gotenberg.ModuleDescriptor {
+			return gotenberg.ModuleDescriptor{ID: "foo", New: func() gotenberg.Module { return engine1 }}
+		}
+
+		engine2 := struct{ ProtoPDFEngine }{}
+		engine2.descriptor = func() gotenberg.ModuleDescriptor {
+			return gotenberg.ModuleDescriptor{ID: "bar", New: func() gotenberg.Module { return engine2 }}
+		}
+
+		return []gotenberg.PDFEngine{
+			engine1,
+			engine2,
+		}
+	}()
 
 	_, err := mod.PDFEngine()
 	if err != nil {