Errors (#2290)

* add errors.As

convert target err to *Error, return false if err don't match *Error

* update errors.As to (*Error, bool)

* fixing FromError panic issue when err is nil

errors/errors.go

@@ -4,6 +4,7 @@ package errors
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
 )
@@ -138,9 +139,24 @@ func Equal(err1 error, err2 error) bool {
 
 // FromError try to convert go error to *Error
 func FromError(err error) *Error {
+	if err == nil {
+		return nil
+	}
 	if verr, ok := err.(*Error); ok && verr != nil {
 		return verr
 	}
 
 	return Parse(err.Error())
 }
+
+// As finds the first error in err's chain that matches *Error
+func As(err error) (*Error, bool) {
+	if err == nil {
+		return nil, false
+	}
+	var merr *Error
+	if errors.As(err, &merr) {
+		return merr, true
+	}
+	return nil, false
+}

errors/errors_test.go

@@ -17,7 +17,10 @@ func TestFromError(t *testing.T) {
 	if merr.Id != "go.micro.test" || merr.Code != 404 {
 		t.Fatalf("invalid conversation %v != %v", err, merr)
 	}
-
+	merr = FromError(nil)
+	if merr != nil {
+		t.Fatalf("%v should be nil", merr)
+	}
 }
 
 func TestEqual(t *testing.T) {
@@ -75,3 +78,23 @@ func TestErrors(t *testing.T) {
 		}
 	}
 }
+
+func TestAs(t *testing.T) {
+	err := NotFound("go.micro.test", "%s", "example")
+	merr, match := As(err)
+	if !match {
+		t.Fatalf("%v should convert to *Error", err)
+	}
+	if merr.Id != "go.micro.test" || merr.Code != 404 || merr.Detail != "example" {
+		t.Fatalf("invalid conversation %v != %v", err, merr)
+	}
+	err = er.New(err.Error())
+	merr, match = As(err)
+	if match || merr != nil {
+		t.Fatalf("%v should not convert to *Error", err)
+	}
+	merr, match = As(nil)
+	if match || merr != nil {
+		t.Fatalf("nil should not convert to *Error")
+	}
+}