Open absolute paths as files, limited Windows support (#1159)

Ref #994, #1000

Alternate approach to #999, this approach brings absolute path support
to Windows.
It does so by checking for absolute paths and handling them using the
file factory directly.

To test different paths without trying to actually open them (UNC paths
hit the network), this change also
prefactors the sink registry into a separate type that allows stubbing
of the `os.OpenFile` call.

Note: This change does not bring full Windows support -- many tests
still fail, and Windows file URIs don't work.

Author: prashantv

sink.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2016 Uber Technologies, Inc.
+// Copyright (c) 2016-2022 Uber Technologies, Inc.
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy
 // of this software and associated documentation files (the "Software"), to deal
@@ -26,6 +26,7 @@ import (
 	"io"
 	"net/url"
 	"os"
+	"path/filepath"
 	"strings"
 	"sync"
 
@@ -34,34 +35,14 @@ import (
 
 const schemeFile = "file"
 
-var (
-	_sinkMutex     sync.RWMutex
-	_sinkFactories map[string]func(*url.URL) (Sink, error) // keyed by scheme
-)
-
-func init() {
-	resetSinkRegistry()
-}
-
-func resetSinkRegistry() {
-	_sinkMutex.Lock()
-	defer _sinkMutex.Unlock()
-
-	_sinkFactories = map[string]func(*url.URL) (Sink, error){
-		schemeFile: newFileSink,
-	}
-}
+var _sinkRegistry = newSinkRegistry()
 
 // Sink defines the interface to write to and close logger destinations.
 type Sink interface {
 	zapcore.WriteSyncer
 	io.Closer
 }
 
-type nopCloserSink struct{ zapcore.WriteSyncer }
-
-func (nopCloserSink) Close() error { return nil }
-
 type errSinkNotFound struct {
 	scheme string
 }
@@ -70,16 +51,29 @@ func (e *errSinkNotFound) Error() string {
 	return fmt.Sprintf("no sink found for scheme %q", e.scheme)
 }
 
-// RegisterSink registers a user-supplied factory for all sinks with a
-// particular scheme.
-//
-// All schemes must be ASCII, valid under section 3.1 of RFC 3986
-// (https://tools.ietf.org/html/rfc3986#section-3.1), and must not already
-// have a factory registered. Zap automatically registers a factory for the
-// "file" scheme.
-func RegisterSink(scheme string, factory func(*url.URL) (Sink, error)) error {
-	_sinkMutex.Lock()
-	defer _sinkMutex.Unlock()
+type nopCloserSink struct{ zapcore.WriteSyncer }
+
+func (nopCloserSink) Close() error { return nil }
+
+type sinkRegistry struct {
+	mu        sync.Mutex
+	factories map[string]func(*url.URL) (Sink, error)          // keyed by scheme
+	openFile  func(string, int, os.FileMode) (*os.File, error) // type matches os.OpenFile
+}
+
+func newSinkRegistry() *sinkRegistry {
+	sr := &sinkRegistry{
+		factories: make(map[string]func(*url.URL) (Sink, error)),
+		openFile:  os.OpenFile,
+	}
+	sr.RegisterSink(schemeFile, sr.newFileSinkFromURL)
+	return sr
+}
+
+// RegisterScheme registers the given factory for the specific scheme.
+func (sr *sinkRegistry) RegisterSink(scheme string, factory func(*url.URL) (Sink, error)) error {
+	sr.mu.Lock()
+	defer sr.mu.Unlock()
 
 	if scheme == "" {
 		return errors.New("can't register a sink factory for empty string")
@@ -88,14 +82,22 @@ func RegisterSink(scheme string, factory func(*url.URL) (Sink, error)) error {
 	if err != nil {
 		return fmt.Errorf("%q is not a valid scheme: %v", scheme, err)
 	}
-	if _, ok := _sinkFactories[normalized]; ok {
+	if _, ok := sr.factories[normalized]; ok {
 		return fmt.Errorf("sink factory already registered for scheme %q", normalized)
 	}
-	_sinkFactories[normalized] = factory
+	sr.factories[normalized] = factory
 	return nil
 }
 
-func newSink(rawURL string) (Sink, error) {
+func (sr *sinkRegistry) newSink(rawURL string) (Sink, error) {
+	// URL parsing doesn't work well for Windows paths such as `c:\log.txt`, as scheme is set to
+	// the drive, and path is unset unless `c:/log.txt` is used.
+	// To avoid Windows-specific URL handling, we instead check IsAbs to open as a file.
+	// filepath.IsAbs is OS-specific, so IsAbs('c:/log.txt') is false outside of Windows.
+	if filepath.IsAbs(rawURL) {
+		return sr.newFileSinkFromPath(rawURL)
+	}
+
 	u, err := url.Parse(rawURL)
 	if err != nil {
 		return nil, fmt.Errorf("can't parse %q as a URL: %v", rawURL, err)
@@ -104,16 +106,27 @@ func newSink(rawURL string) (Sink, error) {
 		u.Scheme = schemeFile
 	}
 
-	_sinkMutex.RLock()
-	factory, ok := _sinkFactories[u.Scheme]
-	_sinkMutex.RUnlock()
+	sr.mu.Lock()
+	factory, ok := sr.factories[u.Scheme]
+	sr.mu.Unlock()
 	if !ok {
 		return nil, &errSinkNotFound{u.Scheme}
 	}
 	return factory(u)
 }
 
-func newFileSink(u *url.URL) (Sink, error) {
+// RegisterSink registers a user-supplied factory for all sinks with a
+// particular scheme.
+//
+// All schemes must be ASCII, valid under section 0.1 of RFC 3986
+// (https://tools.ietf.org/html/rfc3983#section-3.1), and must not already
+// have a factory registered. Zap automatically registers a factory for the
+// "file" scheme.
+func RegisterSink(scheme string, factory func(*url.URL) (Sink, error)) error {
+	return _sinkRegistry.RegisterSink(scheme, factory)
+}
+
+func (sr *sinkRegistry) newFileSinkFromURL(u *url.URL) (Sink, error) {
 	if u.User != nil {
 		return nil, fmt.Errorf("user and password not allowed with file URLs: got %v", u)
 	}
@@ -130,13 +143,18 @@ func newFileSink(u *url.URL) (Sink, error) {
 	if hn := u.Hostname(); hn != "" && hn != "localhost" {
 		return nil, fmt.Errorf("file URLs must leave host empty or use localhost: got %v", u)
 	}
-	switch u.Path {
+
+	return sr.newFileSinkFromPath(u.Path)
+}
+
+func (sr *sinkRegistry) newFileSinkFromPath(path string) (Sink, error) {
+	switch path {
 	case "stdout":
 		return nopCloserSink{os.Stdout}, nil
 	case "stderr":
 		return nopCloserSink{os.Stderr}, nil
 	}
-	return os.OpenFile(u.Path, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0666)
+	return sr.openFile(path, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0666)
 }
 
 func normalizeScheme(s string) (string, error) {

sink_test.go

@@ -33,9 +33,22 @@ import (
 	"go.uber.org/zap/zapcore"
 )
 
+func stubSinkRegistry(t testing.TB) *sinkRegistry {
+	origSinkRegistry := _sinkRegistry
+	t.Cleanup(func() {
+		_sinkRegistry = origSinkRegistry
+	})
+
+	r := newSinkRegistry()
+	_sinkRegistry = r
+	return r
+}
+
 func TestRegisterSink(t *testing.T) {
+	stubSinkRegistry(t)
+
 	const (
-		memScheme = "m"
+		memScheme = "mem"
 		nopScheme = "no-op.1234"
 	)
 	var memCalls, nopCalls int
@@ -52,16 +65,14 @@ func TestRegisterSink(t *testing.T) {
 		return nopCloserSink{zapcore.AddSync(io.Discard)}, nil
 	}
 
-	defer resetSinkRegistry()
-
 	require.NoError(t, RegisterSink(strings.ToUpper(memScheme), memFactory), "Failed to register scheme %q.", memScheme)
-	require.NoError(t, RegisterSink(nopScheme, nopFactory), "Failed to register scheme %q.", memScheme)
+	require.NoError(t, RegisterSink(nopScheme, nopFactory), "Failed to register scheme %q.", nopScheme)
 
 	sink, close, err := Open(
 		memScheme+"://somewhere",
 		nopScheme+"://somewhere-else",
 	)
-	assert.NoError(t, err, "Unexpected error opening URLs with registered schemes.")
+	require.NoError(t, err, "Unexpected error opening URLs with registered schemes.")
 
 	defer close()
 
@@ -89,9 +100,8 @@ func TestRegisterSinkErrors(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run("scheme-"+tt.scheme, func(t *testing.T) {
-			defer resetSinkRegistry()
-
-			err := RegisterSink(tt.scheme, nopFactory)
+			r := newSinkRegistry()
+			err := r.RegisterSink(tt.scheme, nopFactory)
 			assert.ErrorContains(t, err, tt.err)
 		})
 	}

sink_windows_test.go

@@ -0,0 +1,71 @@
+// Copyright (c) 2022 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+//go:build windows
+
+package zap
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestWindowsPaths(t *testing.T) {
+	// See https://docs.microsoft.com/en-us/dotnet/standard/io/file-path-formats
+	tests := []struct {
+		msg  string
+		path string
+	}{
+		{
+			msg:  "local path with drive",
+			path: `c:\log.json`,
+		},
+		{
+			msg:  "local path with drive using forward slash",
+			path: `c:/log.json`,
+		},
+		{
+			msg:  "local path without drive",
+			path: `\Temp\log.json`,
+		},
+		{
+			msg:  "unc path",
+			path: `\\Server2\Logs\log.json`,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.msg, func(t *testing.T) {
+			sr := newSinkRegistry()
+
+			openFilename := "<not called>"
+			sr.openFile = func(filename string, _ int, _ os.FileMode) (*os.File, error) {
+				openFilename = filename
+				return nil, assert.AnError
+			}
+
+			_, err := sr.newSink(tt.path)
+			assert.Equal(t, assert.AnError, err, "expect stub error from OpenFile")
+			assert.Equal(t, tt.path, openFilename, "unexpected path opened")
+		})
+	}
+}

writer.go

@@ -68,7 +68,7 @@ func open(paths []string) ([]zapcore.WriteSyncer, func(), error) {
 
 	var openErr error
 	for _, path := range paths {
-		sink, err := newSink(path)
+		sink, err := _sinkRegistry.newSink(path)
 		if err != nil {
 			openErr = multierr.Append(openErr, fmt.Errorf("open sink %q: %w", path, err))
 			continue

writer_test.go

@@ -240,7 +240,7 @@ func (w *testWriter) Sync() error {
 }
 
 func TestOpenWithErroringSinkFactory(t *testing.T) {
-	defer resetSinkRegistry()
+	stubSinkRegistry(t)
 
 	msg := "expected factory error"
 	factory := func(_ *url.URL) (Sink, error) {