logging: Print stack trace in case of errors.

fixes #1827

cmd/errors.go

@@ -0,0 +1,122 @@
+/*
+ * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ *
+ * 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 cmd
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+)
+
+// Holds the current directory path. Used for trimming path in traceError()
+var rootPath string
+
+// Figure out the rootPath
+func initError() {
+	// Root path is automatically determined from the calling function's source file location.
+	// Catch the calling function's source file path.
+	_, file, _, _ := runtime.Caller(1)
+	// Save the directory alone.
+	rootPath = filepath.Dir(file)
+}
+
+// Represents a stack frame in the stack trace.
+type traceInfo struct {
+	file string // File where error occurred
+	line int    // Line where error occurred
+	name string // Name of the function where error occurred
+}
+
+// Error - error type containing cause and the stack trace.
+type Error struct {
+	e     error       // Holds the cause error
+	trace []traceInfo // stack trace
+	errs  []error     // Useful for XL to hold errors from all disks
+}
+
+// Implement error interface.
+func (e Error) Error() string {
+	return e.e.Error()
+}
+
+// Trace - returns stack trace.
+func (e Error) Trace() []string {
+	var traceArr []string
+	for _, info := range e.trace {
+		traceArr = append(traceArr, fmt.Sprintf("%s:%d:%s",
+			info.file, info.line, info.name))
+	}
+	return traceArr
+}
+
+// NewStorageError - return new Error type.
+func traceError(e error, errs ...error) error {
+	if e == nil {
+		return nil
+	}
+	err := &Error{}
+	err.e = e
+	err.errs = errs
+
+	stack := make([]uintptr, 40)
+	length := runtime.Callers(2, stack)
+	if length > len(stack) {
+		length = len(stack)
+	}
+	stack = stack[:length]
+
+	for _, pc := range stack {
+		pc = pc - 1
+		fn := runtime.FuncForPC(pc)
+		file, line := fn.FileLine(pc)
+		name := fn.Name()
+		if strings.HasSuffix(name, "ServeHTTP") {
+			break
+		}
+		if strings.HasSuffix(name, "runtime.") {
+			break
+		}
+
+		file = strings.TrimPrefix(file, rootPath+string(os.PathSeparator))
+		name = strings.TrimPrefix(name, "github.com/minio/minio/cmd.")
+		err.trace = append(err.trace, traceInfo{file, line, name})
+	}
+
+	return err
+}
+
+// Returns the underlying cause error.
+func errorCause(err error) error {
+	if e, ok := err.(*Error); ok {
+		err = e.e
+	}
+	return err
+}
+
+// Returns slice of underlying cause error.
+func errorsCause(errs []error) []error {
+	Errs := make([]error, len(errs))
+	for i, err := range errs {
+		if err == nil {
+			continue
+		}
+		Errs[i] = errorCause(err)
+	}
+	return Errs
+}