fix: use gcf runtime specific builder instead of unified builder (#120)

client/buildpacks.go

@@ -23,6 +23,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"regexp"
 	"time"
 
 	pack "github.com/buildpacks/pack/pkg/client"
@@ -31,7 +32,7 @@ import (
 
 const (
 	image             = "conformance-test-func"
-	builderURL        = "gcr.io/buildpacks/builder:%s"
+	builderURL        = "gcr.io/gae-runtimes/buildpacks/%s/builder:%s"
 	gcfTargetPlatform = "gcf"
 )
 
@@ -82,7 +83,10 @@ func (b *buildpacksFunctionServer) OutputFile() ([]byte, error) {
 }
 
 func (b *buildpacksFunctionServer) build(ctx context.Context) error {
-	builder := fmt.Sprintf(builderURL, b.tag)
+	builder, err := b.buildpackBuilderImage()
+	if err != nil {
+		return err
+	}
 
 	cmd := exec.Command("docker", "pull", builder)
 	output, err := cmd.CombinedOutput()
@@ -114,6 +118,16 @@ func (b *buildpacksFunctionServer) build(ctx context.Context) error {
 	return nil
 }
 
+var runtimeLanguageRegexp = regexp.MustCompile(`^[a-zA-Z]+`)
+
+func (b *buildpacksFunctionServer) buildpackBuilderImage() (string, error) {
+	runtimeLanguage := runtimeLanguageRegexp.FindString(b.runtime)
+	if runtimeLanguage == "" {
+		return "", fmt.Errorf("Invalid runtime format. Runtime should start with language followed by version. Example: go119, python311. Got %q", b.runtime)
+	}
+	return fmt.Sprintf(builderURL, runtimeLanguage, b.tag), nil
+}
+
 func (b *buildpacksFunctionServer) run() (func(), error) {
 	// Create logs output files.
 	var err error

client/buildpacks_test.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestBuildpackBuilderImage(t *testing.T) {
+	testCases := []struct {
+		name           string
+		runtime        string
+		tag            string
+		wantError      bool
+		wantBuilderURL string
+	}{
+		{
+			name:           "Extracts go from go119",
+			runtime:        "go119",
+			tag:            "1.2.3",
+			wantBuilderURL: fmt.Sprintf(builderURL, "go", "1.2.3"),
+		},
+		{
+			name:      "Fails with incorrect runtime format",
+			runtime:   "11go",
+			tag:       "latest",
+			wantError: true,
+		},
+		{
+			name:           "Extracts php from php82",
+			runtime:        "php82",
+			tag:            "latest",
+			wantBuilderURL: fmt.Sprintf(builderURL, "php", "latest"),
+		},
+		{
+			name:           "Extracts nodejs from nodejs18",
+			runtime:        "nodejs18",
+			tag:            "18",
+			wantBuilderURL: fmt.Sprintf(builderURL, "nodejs", "18"),
+		},
+		{
+			name:           "Extracts dotnet from dotnet6",
+			runtime:        "dotnet6",
+			tag:            "123",
+			wantBuilderURL: fmt.Sprintf(builderURL, "dotnet", "123"),
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			b := &buildpacksFunctionServer{
+				runtime: tc.runtime,
+				tag:     tc.tag,
+			}
+
+			builderImage, err := b.buildpackBuilderImage()
+
+			if err != nil && !tc.wantError {
+				t.Fatalf("Got unexpected error: %v", err)
+			}
+
+			if builderImage != tc.wantBuilderURL {
+				t.Errorf("buildpackBuilderImage() = %q, want %q", builderImage, tc.wantBuilderURL)
+			}
+		})
+	}
+}