fix(fs): fix mergefs bug where files were opened too many times (#2287)

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

2 files changed, 114 insertions, 123 deletions

diff --git a/internal/datafs/mergefs.go b/internal/datafs/mergefs.go
index b056aff7..dd74eb67 100644
--- a/internal/datafs/mergefs.go
+++ b/internal/datafs/mergefs.go
@@ -122,8 +122,8 @@ func (f *mergeFS) Open(name string) (fs.File, error) {
 		// unescaped '+' characters to make it simpler to provide types like
 		// "application/array+json"
 		overrideType := typeOverrideParam()
-		mimeType := u.Query().Get(overrideType)
-		mimeType = strings.ReplaceAll(mimeType, " ", "+")
+		mimeTypeHint := u.Query().Get(overrideType)
+		mimeTypeHint = strings.ReplaceAll(mimeTypeHint, " ", "+")
 
 		// now that we have the hint, remove it from the URL - we can't have it
 		// leaking into the filesystem layer
@@ -151,23 +151,6 @@ func (f *mergeFS) Open(name string) (fs.File, error) {
 
 		fsys = fsimpl.WithHTTPClientFS(f.httpClient, fsys)
 
-		// find the content type
-		fi, err := fs.Stat(fsys, base)
-		if err != nil {
-			return nil, &fs.PathError{
-				Op: "open", Path: name,
-				Err: fmt.Errorf("stat merge part %q: %w", part, err),
-			}
-		}
-
-		if fi.ModTime().After(modTime) {
-			modTime = fi.ModTime()
-		}
-
-		if mimeType == "" {
-			mimeType = fsimpl.ContentType(fi)
-		}
-
 		f, err := fsys.Open(base)
 		if err != nil {
 			return nil, &fs.PathError{
@@ -176,7 +159,7 @@ func (f *mergeFS) Open(name string) (fs.File, error) {
 			}
 		}
 
-		subFiles[i] = subFile{f, mimeType}
+		subFiles[i] = subFile{f, mimeTypeHint}
 	}
 
 	return &mergeFile{
@@ -226,18 +209,16 @@ func (f *mergeFile) Read(p []byte) (int, error) {
 	if f.merged == nil {
 		f.readMux.Lock()
 		defer f.readMux.Unlock()
+
 		// read from all and merge
-		data := make([]map[string]interface{}, len(f.subFiles))
+		data := make([]map[string]any, len(f.subFiles))
 		for i, sf := range f.subFiles {
-			b, err := io.ReadAll(sf)
-			if err != nil && !errors.Is(err, io.EOF) {
-				return 0, fmt.Errorf("readAll: %w", err)
-			}
-
-			data[i], err = parseMap(sf.contentType, string(b))
+			d, err := f.readSubFile(sf)
 			if err != nil {
-				return 0, fmt.Errorf("parsing map with content type %s: %w", sf.contentType, err)
+				return 0, fmt.Errorf("readSubFile: %w", err)
 			}
+
+			data[i] = d
 		}
 
 		md, err := mergeData(data)
@@ -253,6 +234,36 @@ func (f *mergeFile) Read(p []byte) (int, error) {
 	return f.merged.Read(p)
 }
 
+func (f *mergeFile) readSubFile(sf subFile) (map[string]any, error) {
+	// stat for content type and modTime
+	fi, err := sf.Stat()
+	if err != nil {
+		return nil, fmt.Errorf("stat merge part %q: %w", f.name, err)
+	}
+
+	// the merged file's modTime is the most recent of all the sub-files
+	if fi.ModTime().After(f.modTime) {
+		f.modTime = fi.ModTime()
+	}
+
+	// if we haven't been given a content type hint, guess the normal way
+	if sf.contentType == "" {
+		sf.contentType = fsimpl.ContentType(fi)
+	}
+
+	b, err := io.ReadAll(sf)
+	if err != nil && !errors.Is(err, io.EOF) {
+		return nil, fmt.Errorf("readAll: %w", err)
+	}
+
+	sfData, err := parseMap(sf.contentType, string(b))
+	if err != nil {
+		return nil, fmt.Errorf("parsing map with content type %s: %w", sf.contentType, err)
+	}
+
+	return sfData, nil
+}
+
 func mergeData(data []map[string]interface{}) ([]byte, error) {
 	dst := data[0]
 	data = data[1:]
@@ -269,17 +280,19 @@ func mergeData(data []map[string]interface{}) ([]byte, error) {
 	return []byte(s), nil
 }
 
-func parseMap(mimeType, data string) (map[string]interface{}, error) {
+func parseMap(mimeType, data string) (map[string]any, error) {
 	datum, err := parsers.ParseData(mimeType, data)
 	if err != nil {
 		return nil, fmt.Errorf("parseData: %w", err)
 	}
-	var m map[string]interface{}
+
+	var m map[string]any
 	switch datum := datum.(type) {
-	case map[string]interface{}:
+	case map[string]any:
 		m = datum
 	default:
 		return nil, fmt.Errorf("unexpected data type '%T' for datasource (type %s); merge: can only merge maps", datum, mimeType)
 	}
+
 	return m, nil
 }
diff --git a/internal/datafs/mergefs_test.go b/internal/datafs/mergefs_test.go
index 17ffa716..b332722b 100644
--- a/internal/datafs/mergefs_test.go
+++ b/internal/datafs/mergefs_test.go
@@ -2,6 +2,7 @@ package datafs
 
 import (
 	"context"
+	"fmt"
 	"io"
 	"io/fs"
 	"mime"
@@ -31,19 +32,7 @@ func setupMergeFsys(ctx context.Context, t *testing.T) fs.FS {
 	yamlContent := "hello: earth\ngoodnight: moon\n"
 	arrayContent := `["hello", "world"]`
 
-	wd, _ := os.Getwd()
-
-	// MapFS doesn't support windows path separators, so we use / exclusively
-	// in this test
-	vol := filepath.VolumeName(wd)
-	if vol != "" && wd != vol {
-		wd = wd[len(vol)+1:]
-	} else if wd[0] == '/' {
-		wd = wd[1:]
-	}
-	wd = filepath.ToSlash(wd)
-
-	t.Logf("wd: %s", wd)
+	wd := wdForTest(t)
 
 	fsys := WrapWdFS(fstest.MapFS{
 		"tmp":                              {Mode: fs.ModeDir | 0o777},
@@ -90,84 +79,22 @@ func setupMergeFsys(ctx context.Context, t *testing.T) fs.FS {
 	return fsys
 }
 
-// func TestReadMerge(t *testing.T) {
-// 	ctx := context.Background()
-
-// 	jsonContent := `{"hello": "world"}`
-// 	yamlContent := "hello: earth\ngoodnight: moon\n"
-// 	arrayContent := `["hello", "world"]`
-
-// 	mergedContent := "goodnight: moon\nhello: world\n"
-
-// 	fsys := fstest.MapFS{}
-// 	fsys["tmp"] = &fstest.MapFile{Mode: fs.ModeDir | 0777}
-// 	fsys["tmp/jsonfile.json"] = &fstest.MapFile{Data: []byte(jsonContent)}
-// 	fsys["tmp/array.json"] = &fstest.MapFile{Data: []byte(arrayContent)}
-// 	fsys["tmp/yamlfile.yaml"] = &fstest.MapFile{Data: []byte(yamlContent)}
-// 	fsys["tmp/textfile.txt"] = &fstest.MapFile{Data: []byte(`plain text...`)}
-
-// 	// workding dir with volume name trimmed
-// 	wd, _ := os.Getwd()
-// 	vol := filepath.VolumeName(wd)
-// 	wd = wd[len(vol)+1:]
-
-// 	fsys[path.Join(wd, "jsonfile.json")] = &fstest.MapFile{Data: []byte(jsonContent)}
-// 	fsys[path.Join(wd, "array.json")] = &fstest.MapFile{Data: []byte(arrayContent)}
-// 	fsys[path.Join(wd, "yamlfile.yaml")] = &fstest.MapFile{Data: []byte(yamlContent)}
-// 	fsys[path.Join(wd, "textfile.txt")] = &fstest.MapFile{Data: []byte(`plain text...`)}
-
-// 	fsmux := fsimpl.NewMux()
-// 	fsmux.Add(fsimpl.WrappedFSProvider(&fsys, "file"))
-// 	ctx = datafs.ContextWithFSProvider(ctx, fsmux)
-
-// 	source := &Source{Alias: "foo", URL: mustParseURL("merge:file:///tmp/jsonfile.json|file:///tmp/yamlfile.yaml")}
-// 	d := &Data{
-// 		Sources: map[string]*Source{
-// 			"foo":       source,
-// 			"bar":       {Alias: "bar", URL: mustParseURL("file:///tmp/jsonfile.json")},
-// 			"baz":       {Alias: "baz", URL: mustParseURL("file:///tmp/yamlfile.yaml")},
-// 			"text":      {Alias: "text", URL: mustParseURL("file:///tmp/textfile.txt")},
-// 			"badscheme": {Alias: "badscheme", URL: mustParseURL("bad:///scheme.json")},
-// 			"badtype":   {Alias: "badtype", URL: mustParseURL("file:///tmp/textfile.txt?type=foo/bar")},
-// 			"array":     {Alias: "array", URL: mustParseURL("file:///tmp/array.json?type=" + url.QueryEscape(jsonArrayMimetype))},
-// 		},
-// 		Ctx: ctx,
-// 	}
-
-// 	actual, err := d.readMerge(ctx, source)
-// 	require.NoError(t, err)
-// 	assert.Equal(t, mergedContent, string(actual))
-
-// 	source.URL = mustParseURL("merge:bar|baz")
-// 	actual, err = d.readMerge(ctx, source)
-// 	require.NoError(t, err)
-// 	assert.Equal(t, mergedContent, string(actual))
-
-// 	source.URL = mustParseURL("merge:./jsonfile.json|baz")
-// 	actual, err = d.readMerge(ctx, source)
-// 	require.NoError(t, err)
-// 	assert.Equal(t, mergedContent, string(actual))
-
-// 	source.URL = mustParseURL("merge:file:///tmp/jsonfile.json")
-// 	_, err = d.readMerge(ctx, source)
-// 	require.Error(t, err)
-
-// 	source.URL = mustParseURL("merge:bogusalias|file:///tmp/jsonfile.json")
-// 	_, err = d.readMerge(ctx, source)
-// 	require.Error(t, err)
-
-// 	source.URL = mustParseURL("merge:file:///tmp/jsonfile.json|badscheme")
-// 	_, err = d.readMerge(ctx, source)
-// 	require.Error(t, err)
-
-// 	source.URL = mustParseURL("merge:file:///tmp/jsonfile.json|badtype")
-// 	_, err = d.readMerge(ctx, source)
-// 	require.Error(t, err)
-
-// 	source.URL = mustParseURL("merge:file:///tmp/jsonfile.json|array")
-// 	_, err = d.readMerge(ctx, source)
-// 	require.Error(t, err)
-// }
+func wdForTest(t *testing.T) string {
+	t.Helper()
+
+	wd, _ := os.Getwd()
+
+	// MapFS doesn't support windows path separators, so we use / exclusively
+	vol := filepath.VolumeName(wd)
+	if vol != "" && wd != vol {
+		wd = wd[len(vol)+1:]
+	} else if wd[0] == '/' {
+		wd = wd[1:]
+	}
+	wd = filepath.ToSlash(wd)
+
+	return wd
+}
 
 func TestMergeData(t *testing.T) {
 	def := map[string]interface{}{
@@ -228,7 +155,6 @@ func TestMergeData(t *testing.T) {
 }
 
 func TestMergeFS_Open(t *testing.T) {
-	// u, _ := url.Parse("merge:")
 	fsys := setupMergeFsys(context.Background(), t)
 	assert.IsType(t, &mergeFS{}, fsys)
 
@@ -354,3 +280,55 @@ func TestMergeFS_ReadFile(t *testing.T) {
 		})
 	}
 }
+
+func TestMergeFS_ReadsSubFilesOnce(t *testing.T) {
+	mergedContent := "goodnight: moon\nhello: world\n"
+
+	wd := wdForTest(t)
+
+	fsys := WrapWdFS(
+		openOnce(&fstest.MapFS{
+			path.Join(wd, "tmp/jsonfile.json"): {Data: []byte(`{"hello": "world"}`)},
+			path.Join(wd, "tmp/yamlfile.yaml"): {Data: []byte("hello: earth\ngoodnight: moon\n")},
+		}))
+
+	mux := fsimpl.NewMux()
+	mux.Add(MergeFS)
+	mux.Add(WrappedFSProvider(fsys, "file", ""))
+
+	ctx := ContextWithFSProvider(context.Background(), mux)
+
+	reg := NewRegistry()
+	reg.Register("jsonfile", config.DataSource{URL: mustParseURL("tmp/jsonfile.json")})
+	reg.Register("yamlfile", config.DataSource{URL: mustParseURL("tmp/yamlfile.yaml")})
+
+	fsys, err := NewMergeFS(mustParseURL("merge:///"))
+	require.NoError(t, err)
+
+	fsys = WithDataSourceRegistryFS(reg, fsys)
+	fsys = fsimpl.WithContextFS(ctx, fsys)
+
+	b, err := fs.ReadFile(fsys, "jsonfile|yamlfile")
+	require.NoError(t, err)
+	assert.Equal(t, mergedContent, string(b))
+}
+
+type openOnceFS struct {
+	fs     *fstest.MapFS
+	opened map[string]struct{}
+}
+
+// a filesystem that only allows opening or stating a file once
+func openOnce(fsys *fstest.MapFS) fs.FS {
+	return &openOnceFS{fs: fsys, opened: map[string]struct{}{}}
+}
+
+func (f *openOnceFS) Open(name string) (fs.File, error) {
+	if _, ok := f.opened[name]; ok {
+		return nil, fmt.Errorf("open: %q already opened", name)
+	}
+
+	f.opened[name] = struct{}{}
+
+	return f.fs.Open(name)
+}