integrate error codes with pkg/errors to provide error tracing

pkg/error_code/codes.go

@@ -39,14 +39,16 @@ func NewInvalidInputErr(err error) ErrorCode {
 
 var _ ErrorCode = (*invalidInputErr)(nil)     // assert implements interface
 var _ HasClientData = (*invalidInputErr)(nil) // assert implements interface
+var _ Causer = (*invalidInputErr)(nil)        // assert implements interface
 
-// internalError gives the code InvalidInputCode
-type internalErr struct{ CodedError }
+// internalError gives the code InternalCode
+type internalErr struct{ StackCode }
 
 // NewInternalErr creates an internalError from an err
 // If the given err is an ErrorCode that is a descendant of InternalCode,
 // its code will be used.
 // This ensures the intention of sending an HTTP 50x.
+// This function also records a stack trace.
 func NewInternalErr(err error) ErrorCode {
 	code := InternalCode
 	if errcode, ok := err.(ErrorCode); ok {
@@ -55,11 +57,12 @@ func NewInternalErr(err error) ErrorCode {
 			code = errCode
 		}
 	}
-	return internalErr{CodedError{GetCode: code, Err: err}}
+	return internalErr{NewStackCode(CodedError{GetCode: code, Err: err}, 2)}
 }
 
 var _ ErrorCode = (*internalErr)(nil)     // assert implements interface
 var _ HasClientData = (*internalErr)(nil) // assert implements interface
+var _ Causer = (*internalErr)(nil)        // assert implements interface
 
 // notFound gives the code NotFoundCode
 type notFoundErr struct{ CodedError }
@@ -73,6 +76,7 @@ func NewNotFoundErr(err error) ErrorCode {
 
 var _ ErrorCode = (*notFoundErr)(nil)     // assert implements interface
 var _ HasClientData = (*notFoundErr)(nil) // assert implements interface
+var _ Causer = (*notFoundErr)(nil)        // assert implements interface
 
 // CodedError is a convenience to attach a code to an error and already satisfy the ErrorCode interface.
 // If the error is a struct, that struct will get preseneted as data to the client.
@@ -101,11 +105,17 @@ func NewCodedError(err error, code Code) CodedError {
 
 var _ ErrorCode = (*CodedError)(nil)     // assert implements interface
 var _ HasClientData = (*CodedError)(nil) // assert implements interface
+var _ Causer = (*CodedError)(nil)        // assert implements interface
 
 func (e CodedError) Error() string {
 	return e.Err.Error()
 }
 
+// Cause satisfies the Causer interface.
+func (e CodedError) Cause() error {
+	return e.Err
+}
+
 // Code returns the GetCode field
 func (e CodedError) Code() Code {
 	return e.GetCode

pkg/error_code/error_code.go

@@ -21,7 +21,7 @@
 // This package is designed to have few opinions and be a starting point for how you want to do errors in your project.
 // The main requirement is to satisfy the ErrorCode interface by attaching a Code to an Error.
 // See the documentation of ErrorCode.
-// Additional optional interfaces HasClientData and HasOperation are provided for extensibility
+// Additional optional interfaces HasClientData, HasOperation, Causer, and StackTracer are provided for extensibility
 // in creating structured error data representations.
 //
 // Hierarchies are supported: a Code can point to a parent.
@@ -31,16 +31,20 @@
 // A few generic top-level error codes are provided here.
 // You are encouraged to create your own application customized error codes rather than just using generic errors.
 //
-// See JSONFormat for an opinion on how to send back meta data about errors with the error data to a client.
+// See NewJSONFormat for an opinion on how to send back meta data about errors with the error data to a client.
 // JSONFormat includes a body of response data (the "data field") that is by default the data from the Error
 // serialized to JSON.
-// This package provides no help on versioning error data.
+//
+// Errors are traced via PreviousErrorCode() which shows up as the Previous field in JSONFormat.
+// Stack traces are automatically added by NewInternalErr and show up as the Stack field in JSONFormat.
 package errcode
 
 import (
 	"fmt"
 	"net/http"
 	"strings"
+
+	"github.com/pkg/errors"
 )
 
 // CodeStr is a representation of the type of a particular error.
@@ -163,7 +167,7 @@ func (code Code) HTTPCode() int {
 // For an application specific error with a 1:1 mapping between a go error structure and a RegisteredCode,
 // You probably want to use this interface directly. Example:
 //
-//	// First define a normal error type
+// 	// First define a normal error type
 //	type PathBlocked struct {
 //		start     uint64 `json:"start"`
 //		end       uint64 `json:"end"`
@@ -177,7 +181,7 @@ func (code Code) HTTPCode() int {
 //	// Now define the code
 //	var PathBlockedCode = errcode.StateCode.Child("state.blocked")
 //
-//	// Now attach the code to the error type
+// 	// Now attach the code to the error type
 //	func (e PathBlocked) Code() Code {
 //		return PathBlockedCode
 //	}
@@ -206,13 +210,22 @@ func ClientData(errCode ErrorCode) interface{} {
 }
 
 // JSONFormat is an opinion on how to serialize an ErrorCode to JSON.
-// Msg is the string from Error().
-// The Data field is filled in by GetClientData
+// * Code is the error code string (CodeStr)
+// * Msg is the string from Error() and should be friendly to end users.
+// * Data is the ad-hoc data filled in by GetClientData and should be consumable by clients.
+// * Operation is the high-level operation that was happening at the time of the error.
+// The Operation field may be missing, and the Data field may be empty.
+//
+// The rest of the fields may be populated sparsely depending on the application:
+// * Previous gives JSONFormat data for an ErrorCode that was wrapped by this one. It relies on the PreviousErrorCode function.
+// * Stack is a stack trace. Usually only internal errors populate this.
 type JSONFormat struct {
-	Data      interface{} `json:"data"`
-	Msg       string      `json:"msg"`
-	Code      CodeStr     `json:"code"`
-	Operation string      `json:"operation,omitempty"`
+	Code      CodeStr           `json:"code"`
+	Msg       string            `json:"msg"`
+	Data      interface{}       `json:"data"`
+	Operation string            `json:"operation,omitempty"`
+	Previous  *JSONFormat       `json:"previous,omitempty"`
+	Stack     errors.StackTrace `json:"stack,omitempty"`
 }
 
 // OperationClientData gives the results of both the ClientData and Operation functions.
@@ -231,11 +244,20 @@ func OperationClientData(errCode ErrorCode) (string, interface{}) {
 // NewJSONFormat turns an ErrorCode into a JSONFormat
 func NewJSONFormat(errCode ErrorCode) JSONFormat {
 	op, data := OperationClientData(errCode)
+
+	var previous *JSONFormat
+	if prevCode := PreviousErrorCode(errCode); prevCode != nil {
+		ptrVar := NewJSONFormat(prevCode)
+		previous = &ptrVar
+	}
+
 	return JSONFormat{
 		Data:      data,
 		Msg:       errCode.Error(),
 		Code:      errCode.Code().CodeStr(),
 		Operation: op,
+		Stack:     StackTrace(errCode),
+		Previous:  previous,
 	}
 }
 

pkg/error_code/error_code_test.go

@@ -14,12 +14,13 @@
 package errcode_test
 
 import (
-	"errors"
+	"encoding/json"
 	"fmt"
 	"reflect"
 	"testing"
 
 	"github.com/pingcap/pd/pkg/error_code"
+	"github.com/pkg/errors"
 )
 
 // Test setting the HTTP code
@@ -202,13 +203,33 @@ func TestNewInvalidInputErr(t *testing.T) {
 	ErrorEquals(t, err, "error")
 	ClientDataEquals(t, err, MinimalError{}, internalCodeStr)
 
+	wrappedInternalErr := errcode.NewInternalErr(internalErr)
+	AssertCode(t, err, internalCodeStr)
+	AssertHTTPCode(t, err, 500)
+	ErrorEquals(t, err, "error")
+	ClientDataEquals(t, wrappedInternalErr, MinimalError{}, internalCodeStr)
+	// It should use the original stack trace, not the wrapped
+	AssertStackEquals(t, wrappedInternalErr, errcode.StackTrace(internalErr))
+
 	err = errcode.NewInvalidInputErr(InternalChild{})
 	AssertCode(t, err, internalChildCodeStr)
 	AssertHTTPCode(t, err, 503)
 	ErrorEquals(t, err, "internal child error")
 	ClientDataEquals(t, err, InternalChild{}, internalChildCodeStr)
 }
 
+func TestStackTrace(t *testing.T) {
+	internalCodeStr := errcode.CodeStr("internal")
+	err := errors.New("errors stack")
+	wrappedInternalErr := errcode.NewInternalErr(err)
+	AssertCode(t, wrappedInternalErr, internalCodeStr)
+	AssertHTTPCode(t, wrappedInternalErr, 500)
+	ErrorEquals(t, err, "errors stack")
+	ClientDataEquals(t, wrappedInternalErr, err, internalCodeStr)
+	// It should use the original stack trace, not the wrapped
+	AssertStackEquals(t, wrappedInternalErr, errcode.StackTrace(err))
+}
+
 func TestNewInternalErr(t *testing.T) {
 	internalCodeStr := errcode.CodeStr("internal")
 	err := errcode.NewInternalErr(errors.New("new error"))
@@ -314,17 +335,30 @@ func ClientDataEquals(t *testing.T, code errcode.ErrorCode, data interface{}, co
 		codeStr = codeStrs[0]
 	}
 	t.Helper()
-	if !reflect.DeepEqual(errcode.ClientData(code), data) {
-		t.Errorf("\nClientData expected: %#v\n ClientData but got: %#v", data, errcode.ClientData(code))
-	}
+
+	jsonEquals(t, "ClientData", data, errcode.ClientData(code))
+
 	jsonExpected := errcode.JSONFormat{
 		Data:      data,
 		Msg:       code.Error(),
 		Code:      codeStr,
 		Operation: errcode.Operation(data),
+		Stack:     errcode.StackTrace(code),
+	}
+	newJSON := errcode.NewJSONFormat(code)
+	newJSON.Previous = nil
+	jsonEquals(t, "JSONFormat", jsonExpected, newJSON)
+}
+
+func jsonEquals(t *testing.T, errPrefix string, expectedIn interface{}, gotIn interface{}) {
+	t.Helper()
+	got, err1 := json.Marshal(gotIn)
+	expected, err2 := json.Marshal(expectedIn)
+	if err1 != nil || err2 != nil {
+		t.Errorf("%v could not serialize to json", errPrefix)
 	}
-	if !reflect.DeepEqual(errcode.NewJSONFormat(code), jsonExpected) {
-		t.Errorf("\nJSON expected: %+v\n JSON but got: %+v", jsonExpected, errcode.NewJSONFormat(code))
+	if !reflect.DeepEqual(expected, got) {
+		t.Errorf("%v\nClientData expected: %#v\n ClientData but got: %#v", errPrefix, expected, got)
 	}
 }
 
@@ -343,3 +377,11 @@ func AssertOperation(t *testing.T, v interface{}, op string) {
 		t.Errorf("\nOp expected: %#v\n Op but got: %#v", op, opGot)
 	}
 }
+
+func AssertStackEquals(t *testing.T, given errcode.ErrorCode, stExpected errors.StackTrace) {
+	t.Helper()
+	stGiven := errcode.StackTrace(given)
+	if stGiven == nil || stExpected == nil || stGiven[0] != stExpected[0] {
+		t.Errorf("\nStack expected: %#v\n Stack but got: %#v", stExpected[0], stGiven[0])
+	}
+}

pkg/error_code/operation.go

@@ -56,6 +56,11 @@ type OpErrCode struct {
 	Err       ErrorCode
 }
 
+// Cause satisfies the Causer interface
+func (e OpErrCode) Cause() error {
+	return e.Err
+}
+
 // Error prefixes the operation to the underlying Err Error.
 func (e OpErrCode) Error() string {
 	return e.Operation + ": " + e.Err.Error()
@@ -79,6 +84,7 @@ func (e OpErrCode) GetClientData() interface{} {
 var _ ErrorCode = (*OpErrCode)(nil)     // assert implements interface
 var _ HasClientData = (*OpErrCode)(nil) // assert implements interface
 var _ HasOperation = (*OpErrCode)(nil)  // assert implements interface
+var _ Causer = (*OpErrCode)(nil)        // assert implements interface
 
 // AddOp is constructed by Op. It allows method chaining with AddTo.
 type AddOp func(ErrorCode) OpErrCode
@@ -94,7 +100,7 @@ func (addOp AddOp) AddTo(err ErrorCode) OpErrCode {
 //	op := errcode.Op("path.move.x")
 //	if start < obstable && obstacle < end  {
 //		return op.AddTo(PathBlocked{start, end, obstacle})
-// 	}
+//	}
 //
 func Op(operation string) AddOp {
 	return func(err ErrorCode) OpErrCode {