feat(scanner): implement file-based target passing for large target lists

Signed-off-by: Deluan <deluan@navidrome.org>

scanner/external_test.go

@@ -0,0 +1,160 @@
+package scanner
+
+import (
+	"context"
+	"os"
+	"strings"
+
+	"github.com/navidrome/navidrome/model"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("targetArguments", func() {
+	var ctx context.Context
+
+	BeforeEach(func() {
+		ctx = GinkgoT().Context()
+	})
+
+	Context("with small target list", func() {
+		It("returns command-line arguments for single target", func() {
+			targets := []model.ScanTarget{
+				{LibraryID: 1, FolderPath: "Music/Rock"},
+			}
+
+			args, cleanup, err := targetArguments(ctx, targets, argLengthThreshold)
+			Expect(err).ToNot(HaveOccurred())
+			defer cleanup()
+			Expect(args).To(Equal([]string{"-t", "1:Music/Rock"}))
+		})
+
+		It("returns command-line arguments for multiple targets", func() {
+			targets := []model.ScanTarget{
+				{LibraryID: 1, FolderPath: "Music/Rock"},
+				{LibraryID: 2, FolderPath: "Music/Jazz"},
+				{LibraryID: 3, FolderPath: "Classical"},
+			}
+
+			args, cleanup, err := targetArguments(ctx, targets, argLengthThreshold)
+			Expect(err).ToNot(HaveOccurred())
+			defer cleanup()
+			Expect(args).To(Equal([]string{
+				"-t", "1:Music/Rock",
+				"-t", "2:Music/Jazz",
+				"-t", "3:Classical",
+			}))
+		})
+
+		It("handles targets with special characters", func() {
+			targets := []model.ScanTarget{
+				{LibraryID: 1, FolderPath: "Music/Rock & Roll"},
+				{LibraryID: 2, FolderPath: "Music/Jazz (Modern)"},
+			}
+
+			args, cleanup, err := targetArguments(ctx, targets, argLengthThreshold)
+			Expect(err).ToNot(HaveOccurred())
+			defer cleanup()
+			Expect(args).To(Equal([]string{
+				"-t", "1:Music/Rock & Roll",
+				"-t", "2:Music/Jazz (Modern)",
+			}))
+		})
+	})
+
+	Context("with large target list exceeding threshold", func() {
+		It("returns --target-file argument when exceeding threshold", func() {
+			// Create enough targets to exceed the threshold
+			var targets []model.ScanTarget
+			for i := 1; i <= 600; i++ {
+				targets = append(targets, model.ScanTarget{
+					LibraryID:  1,
+					FolderPath: "Music/VeryLongFolderPathToSimulateRealScenario/SubFolder",
+				})
+			}
+
+			args, cleanup, err := targetArguments(ctx, targets, argLengthThreshold)
+			Expect(err).ToNot(HaveOccurred())
+			defer cleanup()
+			Expect(args).To(HaveLen(2))
+			Expect(args[0]).To(Equal("--target-file"))
+
+			// Verify the file exists and has correct format
+			filePath := args[1]
+			Expect(filePath).To(ContainSubstring("navidrome-scan-targets-"))
+			Expect(filePath).To(HaveSuffix(".txt"))
+
+			// Verify file actually exists
+			_, err = os.Stat(filePath)
+			Expect(err).ToNot(HaveOccurred())
+		})
+
+		It("creates temp file with correct format", func() {
+			// Use custom threshold to easily exceed it
+			targets := []model.ScanTarget{
+				{LibraryID: 1, FolderPath: "Music/Rock"},
+				{LibraryID: 2, FolderPath: "Music/Jazz"},
+				{LibraryID: 3, FolderPath: "Classical"},
+			}
+
+			// Set threshold very low to force file usage
+			args, cleanup, err := targetArguments(ctx, targets, 10)
+			Expect(err).ToNot(HaveOccurred())
+			defer cleanup()
+			Expect(args[0]).To(Equal("--target-file"))
+
+			// Verify file exists with correct format
+			filePath := args[1]
+			Expect(filePath).To(ContainSubstring("navidrome-scan-targets-"))
+			Expect(filePath).To(HaveSuffix(".txt"))
+
+			// Verify file content
+			content, err := os.ReadFile(filePath)
+			Expect(err).ToNot(HaveOccurred())
+			lines := strings.Split(strings.TrimSpace(string(content)), "\n")
+			Expect(lines).To(HaveLen(3))
+			Expect(lines[0]).To(Equal("1:Music/Rock"))
+			Expect(lines[1]).To(Equal("2:Music/Jazz"))
+			Expect(lines[2]).To(Equal("3:Classical"))
+		})
+	})
+
+	Context("edge cases", func() {
+		It("handles empty target list", func() {
+			var targets []model.ScanTarget
+
+			args, cleanup, err := targetArguments(ctx, targets, argLengthThreshold)
+			Expect(err).ToNot(HaveOccurred())
+			defer cleanup()
+			Expect(args).To(BeEmpty())
+		})
+
+		It("uses command-line args when exactly at threshold", func() {
+			// Create targets that are exactly at threshold
+			targets := []model.ScanTarget{
+				{LibraryID: 1, FolderPath: "Music"},
+			}
+
+			// Estimate length should be 11 bytes
+			estimatedLength := estimateArgLength(targets)
+
+			args, cleanup, err := targetArguments(ctx, targets, estimatedLength)
+			Expect(err).ToNot(HaveOccurred())
+			defer cleanup()
+			Expect(args).To(Equal([]string{"-t", "1:Music"}))
+		})
+
+		It("uses file when one byte over threshold", func() {
+			targets := []model.ScanTarget{
+				{LibraryID: 1, FolderPath: "Music"},
+			}
+
+			// Set threshold just below the estimated length
+			estimatedLength := estimateArgLength(targets)
+			args, cleanup, err := targetArguments(ctx, targets, estimatedLength-1)
+			Expect(err).ToNot(HaveOccurred())
+			defer cleanup()
+			Expect(args[0]).To(Equal("--target-file"))
+		})
+	})
+})