Move ErrorCode logic to new errcode package

Make HTTP status codes match the ErrorCode by looking it up in the Descriptors

Signed-off-by: Doug Davis <dug@us.ibm.com>

docs/api/errcode/errors.go

@@ -0,0 +1,206 @@
+package errcode
+
+import (
+	"fmt"
+	"net/http"
+	"strings"
+)
+
+// ErrorCode represents the error type. The errors are serialized via strings
+// and the integer format may change and should *never* be exported.
+type ErrorCode int
+
+// ErrorDescriptor provides relevant information about a given error code.
+type ErrorDescriptor struct {
+	// Code is the error code that this descriptor describes.
+	Code ErrorCode
+
+	// Value provides a unique, string key, often captilized with
+	// underscores, to identify the error code. This value is used as the
+	// keyed value when serializing api errors.
+	Value string
+
+	// Message is a short, human readable decription of the error condition
+	// included in API responses.
+	Message string
+
+	// Description provides a complete account of the errors purpose, suitable
+	// for use in documentation.
+	Description string
+
+	// HTTPStatusCode provides the http status code that is associated with
+	// this error condition.
+	HTTPStatusCode int
+}
+
+var (
+	errorCodeToDescriptors = map[ErrorCode]ErrorDescriptor{}
+	idToDescriptors        = map[string]ErrorDescriptor{}
+)
+
+const (
+	// ErrorCodeUnknown is a catch-all for errors not defined below.
+	ErrorCodeUnknown ErrorCode = 10000 + iota
+)
+
+var errorDescriptors = []ErrorDescriptor{
+	{
+		Code:    ErrorCodeUnknown,
+		Value:   "UNKNOWN",
+		Message: "unknown error",
+		Description: `Generic error returned when the error does not have an
+									        API classification.`,
+		HTTPStatusCode: http.StatusInternalServerError,
+	},
+}
+
+// LoadErrors will register a new set of Errors into the system
+func LoadErrors(errs *[]ErrorDescriptor) {
+	for _, descriptor := range *errs {
+		if _, ok := idToDescriptors[descriptor.Value]; ok {
+			panic(fmt.Sprintf("ErrorValue %s is already registered", descriptor.Value))
+		}
+		if _, ok := errorCodeToDescriptors[descriptor.Code]; ok {
+			panic(fmt.Sprintf("ErrorCode %d is already registered", descriptor.Code))
+		}
+
+		errorCodeToDescriptors[descriptor.Code] = descriptor
+		idToDescriptors[descriptor.Value] = descriptor
+	}
+}
+
+// ParseErrorCode attempts to parse the error code string, returning
+// ErrorCodeUnknown if the error is not known.
+func ParseErrorCode(s string) ErrorCode {
+	desc, ok := idToDescriptors[s]
+
+	if !ok {
+		return ErrorCodeUnknown
+	}
+
+	return desc.Code
+}
+
+// Descriptor returns the descriptor for the error code.
+func (ec ErrorCode) Descriptor() ErrorDescriptor {
+	d, ok := errorCodeToDescriptors[ec]
+
+	if !ok {
+		return ErrorCodeUnknown.Descriptor()
+	}
+
+	return d
+}
+
+// String returns the canonical identifier for this error code.
+func (ec ErrorCode) String() string {
+	return ec.Descriptor().Value
+}
+
+// Message returned the human-readable error message for this error code.
+func (ec ErrorCode) Message() string {
+	return ec.Descriptor().Message
+}
+
+// MarshalText encodes the receiver into UTF-8-encoded text and returns the
+// result.
+func (ec ErrorCode) MarshalText() (text []byte, err error) {
+	return []byte(ec.String()), nil
+}
+
+// UnmarshalText decodes the form generated by MarshalText.
+func (ec *ErrorCode) UnmarshalText(text []byte) error {
+	desc, ok := idToDescriptors[string(text)]
+
+	if !ok {
+		desc = ErrorCodeUnknown.Descriptor()
+	}
+
+	*ec = desc.Code
+
+	return nil
+}
+
+// Error provides a wrapper around ErrorCode with extra Details provided.
+type Error struct {
+	Code    ErrorCode   `json:"code"`
+	Message string      `json:"message,omitempty"`
+	Detail  interface{} `json:"detail,omitempty"`
+}
+
+// Error returns a human readable representation of the error.
+func (e Error) Error() string {
+	return fmt.Sprintf("%s: %s",
+		strings.ToLower(strings.Replace(e.Code.String(), "_", " ", -1)),
+		e.Message)
+}
+
+// Errors provides the envelope for multiple errors and a few sugar methods
+// for use within the application.
+type Errors struct {
+	Errors []Error `json:"errors,omitempty"`
+}
+
+// Push pushes an error on to the error stack, with the optional detail
+// argument. It is a programming error (ie panic) to push more than one
+// detail at a time.
+func (errs *Errors) Push(code ErrorCode, details ...interface{}) {
+	if len(details) > 1 {
+		panic("please specify zero or one detail items for this error")
+	}
+
+	var detail interface{}
+	if len(details) > 0 {
+		detail = details[0]
+	}
+
+	if err, ok := detail.(error); ok {
+		detail = err.Error()
+	}
+
+	errs.PushErr(Error{
+		Code:    code,
+		Message: code.Message(),
+		Detail:  detail,
+	})
+}
+
+// PushErr pushes an error interface onto the error stack.
+func (errs *Errors) PushErr(err error) {
+	switch err.(type) {
+	case Error:
+		errs.Errors = append(errs.Errors, err.(Error))
+	default:
+		errs.Errors = append(errs.Errors, Error{Message: err.Error()})
+	}
+}
+
+func (errs *Errors) Error() string {
+	switch errs.Len() {
+	case 0:
+		return "<nil>"
+	case 1:
+		return errs.Errors[0].Error()
+	default:
+		msg := "errors:\n"
+		for _, err := range errs.Errors {
+			msg += err.Error() + "\n"
+		}
+		return msg
+	}
+}
+
+// Clear clears the errors.
+func (errs *Errors) Clear() {
+	errs.Errors = nil
+}
+
+// Len returns the current number of errors.
+func (errs *Errors) Len() int {
+	return len(errs.Errors)
+}
+
+// init loads the default errors that are part of the errcode package
+func init() {
+	LoadErrors(&errorDescriptors)
+}