internal/pkg: implement caching for files

This change contains primitives for validating and caching single-file artifacts.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/dir_test.go

@@ -0,0 +1,47 @@
+package pkg_test
+
+import (
+	"io/fs"
+	"testing"
+	"testing/fstest"
+
+	"hakurei.app/internal/pkg"
+)
+
+func TestFlatten(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		fsys fs.FS
+		want pkg.Checksum
+	}{
+		{"sample cache file", fstest.MapFS{
+			".": {Mode: 020000000700},
+
+			"checksum": {Mode: 020000000700},
+			"checksum/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX": {Mode: 0400, Data: []byte{0x0}},
+			"checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq": {Mode: 0400, Data: []byte{0x0, 0x0, 0x0, 0x0, 0xad, 0xb, 0x0, 0x4, 0xfe, 0xfe, 0x0, 0x0, 0xfe, 0xca, 0x0, 0x0}},
+
+			"identifier": {Mode: 020000000700},
+			"identifier/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX": {Mode: 0400, Data: []byte{0x0}},
+			"identifier/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq": {Mode: 0400, Data: []byte{0x0, 0x0, 0x0, 0x0, 0xad, 0xb, 0x0, 0x4, 0xfe, 0xfe, 0x0, 0x0, 0xfe, 0xca, 0x0, 0x0}},
+			"identifier/cafebabecafebabecafebabecafebabecafebabecafebabecafebabecafebabe": {Mode: 0400, Data: []byte{0x0, 0x0, 0x0, 0x0, 0xad, 0xb, 0x0, 0x4, 0xfe, 0xfe, 0x0, 0x0, 0xfe, 0xca, 0x0, 0x0}},
+			"identifier/deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef": {Mode: 0400, Data: []byte{0x0, 0x0, 0x0, 0x0, 0xad, 0xb, 0x0, 0x4, 0xfe, 0xfe, 0x0, 0x0, 0xfe, 0xca, 0x0, 0x0}},
+		}, pkg.MustDecode("lvK4lY9bQUFscHpxqHmiPvptjUwOgn3BFhzCXZMeupkY1n22WUPSuh7pswEvVZrx")},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got, err := pkg.HashFS(tc.fsys, "."); err != nil {
+				t.Fatalf("HashFS: error = %v", err)
+			} else if got != tc.want {
+				t.Fatalf("HashFS: %v", &pkg.ChecksumMismatchError{
+					Got:  got,
+					Want: tc.want,
+				})
+			}
+		})
+	}
+}