Provide better panic handling (#5902)

This PR gitea'ises the macaron.Recovery() handler meaning that in
the event of panic we get proper gitea 500 pages and the stacktrace
is logged with the gitea logger.

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/context/context.go

@@ -136,7 +136,7 @@ func (ctx *Context) ServerError(title string, err error) {
 	}
 
 	ctx.Data["Title"] = "Internal Server Error"
-	ctx.HTML(404, base.TplName("status/500"))
+	ctx.HTML(http.StatusInternalServerError, base.TplName("status/500"))
 }
 
 // NotFoundOrServerError use error check function to determine if the error

modules/context/panic.go

@@ -0,0 +1,112 @@
+// Copyright 2013 Martini Authors
+// Copyright 2014 The Macaron Authors
+// Copyright 2019 The Gitea Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"): you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations
+// under the License.
+
+package context
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"runtime"
+
+	macaron "gopkg.in/macaron.v1"
+)
+
+// Recovery returns a middleware that recovers from any panics and writes a 500 and a log if so.
+// Although similar to macaron.Recovery() the main difference is that this error will be created
+// with the gitea 500 page.
+func Recovery() macaron.Handler {
+	return func(ctx *Context) {
+		defer func() {
+			if err := recover(); err != nil {
+				combinedErr := fmt.Errorf("%s\n%s", err, string(stack(3)))
+				ctx.ServerError("PANIC:", combinedErr)
+			}
+		}()
+
+		ctx.Next()
+	}
+}
+
+var (
+	unknown = []byte("???")
+)
+
+// Although we could just use debug.Stack(), this routine will return the source code
+// skip the provided number of frames - i.e. allowing us to ignore this function call
+// and the preceding function call.
+// If the problem is a lack of memory of course all this is not going to work...
+func stack(skip int) []byte {
+	buf := new(bytes.Buffer)
+
+	// Store the last file we opened as its probable that the preceding stack frame
+	// will be in the same file
+	var lines [][]byte
+	var lastFilename string
+	for i := skip; ; i++ { // Skip over frames
+		programCounter, filename, lineNumber, ok := runtime.Caller(i)
+		// If we can't retrieve the information break - basically we're into go internals at this point.
+		if !ok {
+			break
+		}
+
+		// Print equivalent of debug.Stack()
+		fmt.Fprintf(buf, "%s:%d (0x%x)\n", filename, lineNumber, programCounter)
+		// Now try to print the offending line
+		if filename != lastFilename {
+			data, err := ioutil.ReadFile(filename)
+			if err != nil {
+				// can't read this sourcefile
+				// likely we don't have the sourcecode available
+				continue
+			}
+			lines = bytes.Split(data, []byte{'\n'})
+			lastFilename = filename
+		}
+		fmt.Fprintf(buf, "\t%s: %s\n", functionName(programCounter), source(lines, lineNumber))
+	}
+	return buf.Bytes()
+}
+
+// functionName converts the provided programCounter into a function name
+func functionName(programCounter uintptr) []byte {
+	function := runtime.FuncForPC(programCounter)
+	if function == nil {
+		return unknown
+	}
+	name := []byte(function.Name())
+
+	// Because we provide the filename we can drop the preceding package name.
+	if lastslash := bytes.LastIndex(name, []byte("/")); lastslash >= 0 {
+		name = name[lastslash+1:]
+	}
+	// And the current package name.
+	if period := bytes.Index(name, []byte(".")); period >= 0 {
+		name = name[period+1:]
+	}
+	// And we should just replace the interpunct with a dot
+	name = bytes.Replace(name, []byte("·"), []byte("."), -1)
+	return name
+}
+
+// source returns a space-trimmed slice of the n'th line.
+func source(lines [][]byte, n int) []byte {
+	n-- // in stack trace, lines are 1-indexed but our array is 0-indexed
+	if n < 0 || n >= len(lines) {
+		return unknown
+	}
+	return bytes.TrimSpace(lines[n])
+}

routers/routes/routes.go

@@ -136,6 +136,9 @@ func NewMacaron() *macaron.Macaron {
 		DisableDebug: !setting.EnablePprof,
 	}))
 	m.Use(context.Contexter())
+	// OK we are now set-up enough to allow us to create a nicer recovery than
+	// the default macaron recovery
+	m.Use(context.Recovery())
 	m.SetAutoHead(true)
 	return m
 }

templates/status/500.tmpl

@@ -3,7 +3,8 @@
 	<p style="margin-top: 100px"><img src="{{AppSubUrl}}/img/500.png" alt="500"/></p>
 	<div class="ui divider"></div>
 	<br>
-	{{if .ErrorMsg}}<p>An error has occurred : {{.ErrorMsg}}</p>{{end}}
+	{{if .ErrorMsg}}<p>An error has occurred :</p>
+	<pre style="text-align: left">{{.ErrorMsg}}</pre>{{end}}
 	{{if .ShowFooterVersion}}<p>Application Version: {{AppVer}}</p>{{end}}
 	{{if .IsAdmin}}<p>If you are sure this is Gitea bug, please search for issue on <a href="https://github.com/go-gitea/gitea/issues">GitHub</a> and open new issue if necessary.</p>{{end}}
 </div>