errors: Fix low risk race condition at server close

See issue #1371 for more information.

caddyhttp/errors/errors.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"runtime"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/mholt/caddy"
@@ -32,6 +33,7 @@ type ErrorHandler struct {
 	LogRoller        *httpserver.LogRoller
 	Debug            bool          // if true, errors are written out to client rather than to a log
 	file             *os.File      // a log file to close when done
+	fileMu           *sync.RWMutex // like with log middleware, os.File can't "safely" be closed in a different goroutine
 }
 
 func (h ErrorHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
@@ -48,7 +50,9 @@ func (h ErrorHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, er
 			fmt.Fprintln(w, errMsg)
 			return 0, err // returning 0 signals that a response has been written
 		}
+		h.fileMu.RLock()
 		h.Log.Println(errMsg)
+		h.fileMu.RUnlock()
 	}
 
 	if status >= 400 {
@@ -69,8 +73,10 @@ func (h ErrorHandler) errorPage(w http.ResponseWriter, r *http.Request, code int
 		errorPage, err := os.Open(pagePath)
 		if err != nil {
 			// An additional error handling an error... <insert grumpy cat here>
+			h.fileMu.RLock()
 			h.Log.Printf("%s [NOTICE %d %s] could not load error page: %v",
 				time.Now().Format(timeFormat), code, r.URL.String(), err)
+			h.fileMu.RUnlock()
 			httpserver.DefaultErrorFunc(w, r, code)
 			return
 		}
@@ -83,8 +89,10 @@ func (h ErrorHandler) errorPage(w http.ResponseWriter, r *http.Request, code int
 
 		if err != nil {
 			// Epic fail... sigh.
+			h.fileMu.RLock()
 			h.Log.Printf("%s [NOTICE %d %s] could not respond with %s: %v",
 				time.Now().Format(timeFormat), code, r.URL.String(), pagePath, err)
+			h.fileMu.RUnlock()
 			httpserver.DefaultErrorFunc(w, r, code)
 		}
 
@@ -146,7 +154,9 @@ func (h ErrorHandler) recovery(w http.ResponseWriter, r *http.Request) {
 		httpserver.WriteTextResponse(w, http.StatusInternalServerError, fmt.Sprintf("%s\n\n%s", panicMsg, stack))
 	} else {
 		// Currently we don't use the function name, since file:line is more conventional
+		h.fileMu.RLock()
 		h.Log.Printf(panicMsg)
+		h.fileMu.RUnlock()
 		h.errorPage(w, r, http.StatusInternalServerError)
 	}
 }

caddyhttp/errors/errors_test.go

@@ -11,6 +11,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"sync"
 	"testing"
 
 	"github.com/mholt/caddy/caddyhttp/httpserver"
@@ -33,6 +34,7 @@ func TestErrors(t *testing.T) {
 			http.StatusForbidden: "not_exist_file",
 		},
 		Log:    log.New(&buf, "", 0),
+		fileMu: new(sync.RWMutex),
 	}
 	_, notExistErr := os.Open("not_exist_file")
 
@@ -121,6 +123,7 @@ func TestVisibleErrorWithPanic(t *testing.T) {
 		Next: httpserver.HandlerFunc(func(w http.ResponseWriter, r *http.Request) (int, error) {
 			panic(panicMsg)
 		}),
+		fileMu: new(sync.RWMutex),
 	}
 
 	req, err := http.NewRequest("GET", "/", nil)
@@ -177,6 +180,7 @@ func TestGenericErrorPage(t *testing.T) {
 			http.StatusNotFound: notFoundErrorPagePath,
 		},
 		Log:    log.New(&buf, "", 0),
+		fileMu: new(sync.RWMutex),
 	}
 
 	tests := []struct {

caddyhttp/errors/setup.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"path/filepath"
 	"strconv"
+	"sync"
 
 	"github.com/hashicorp/go-syslog"
 	"github.com/mholt/caddy"
@@ -64,7 +65,9 @@ func setup(c *caddy.Controller) error {
 	// When server stops, close any open log file
 	c.OnShutdown(func() error {
 		if handler.file != nil {
+			handler.fileMu.Lock()
 			handler.file.Close()
+			handler.fileMu.Unlock()
 		}
 		return nil
 	})
@@ -81,7 +84,7 @@ func errorsParse(c *caddy.Controller) (*ErrorHandler, error) {
 	// Very important that we make a pointer because the startup
 	// function that opens the log file must have access to the
 	// same instance of the handler, not a copy.
-	handler := &ErrorHandler{ErrorPages: make(map[int]string)}
+	handler := &ErrorHandler{ErrorPages: make(map[int]string), fileMu: new(sync.RWMutex)}
 
 	cfg := httpserver.GetConfig(c)
 

caddyhttp/errors/setup_test.go

@@ -3,6 +3,7 @@ package errors
 import (
 	"path/filepath"
 	"reflect"
+	"sync"
 	"testing"
 
 	"github.com/mholt/caddy"
@@ -58,18 +59,22 @@ func TestErrorsParse(t *testing.T) {
 	}{
 		{`errors`, false, ErrorHandler{
 			ErrorPages: map[int]string{},
+			fileMu:     new(sync.RWMutex),
 		}},
 		{`errors errors.txt`, false, ErrorHandler{
 			ErrorPages: map[int]string{},
 			LogFile:    "errors.txt",
+			fileMu:     new(sync.RWMutex),
 		}},
 		{`errors visible`, false, ErrorHandler{
 			ErrorPages: map[int]string{},
 			Debug:      true,
+			fileMu:     new(sync.RWMutex),
 		}},
 		{`errors { log visible }`, false, ErrorHandler{
 			ErrorPages: map[int]string{},
 			Debug:      true,
+			fileMu:     new(sync.RWMutex),
 		}},
 		{`errors { log errors.txt
         404 404.html
@@ -80,6 +85,7 @@ func TestErrorsParse(t *testing.T) {
 				404: "404.html",
 				500: "500.html",
 			},
+			fileMu: new(sync.RWMutex),
 		}},
 		{`errors { log errors.txt { size 2 age 10 keep 3 } }`, false, ErrorHandler{
 			LogFile: "errors.txt",
@@ -90,6 +96,7 @@ func TestErrorsParse(t *testing.T) {
 				LocalTime:  true,
 			},
 			ErrorPages: map[int]string{},
+			fileMu:     new(sync.RWMutex),
 		}},
 		{`errors { log errors.txt {
             size 3
@@ -110,6 +117,7 @@ func TestErrorsParse(t *testing.T) {
 				MaxBackups: 5,
 				LocalTime:  true,
 			},
+			fileMu: new(sync.RWMutex),
 		}},
 		{`errors { log errors.txt
         * generic_error.html
@@ -122,6 +130,7 @@ func TestErrorsParse(t *testing.T) {
 				404: "404.html",
 				503: "503.html",
 			},
+			fileMu: new(sync.RWMutex),
 		}},
 		// test absolute file path
 		{`errors {
@@ -131,16 +140,17 @@ func TestErrorsParse(t *testing.T) {
 				ErrorPages: map[int]string{
 					404: testAbs,
 				},
+				fileMu: new(sync.RWMutex),
 			}},
 		// Next two test cases is the detection of duplicate status codes
 		{`errors {
         503 503.html
         503 503.html
-}`, true, ErrorHandler{ErrorPages: map[int]string{}}},
+}`, true, ErrorHandler{ErrorPages: map[int]string{}, fileMu: new(sync.RWMutex)}},
 		{`errors {
         * generic_error.html
         * generic_error.html
-}`, true, ErrorHandler{ErrorPages: map[int]string{}}},
+}`, true, ErrorHandler{ErrorPages: map[int]string{}, fileMu: new(sync.RWMutex)}},
 	}
 	for i, test := range tests {
 		actualErrorsRule, err := errorsParse(caddy.NewTestController("http", test.inputErrorsRules))