How to write MeshKit compatible errors

Meshery pervasively uses MeshKit as a golang and infrastructure management-specific library in all of its components. MeshKit helps populate error messages with a uniform and useful set of informative attributes.

To help with creating error codes, MeshKit contains a tool that analyzes, verifies and updates error codes in Meshery source code trees. It extracts error details into a file that can be used for publishing all error code references on the Meshery error codes reference page. The objective to create this was to avoid centralized handling of error codes and automating everything

In order to create a Meshery error object, you will need to create a custom wrapper object for the native golang error. This can be done from the MeshKit Error package.

This tool will create a couple of files, one of them is designed to be used to generate the error reference on the Meshery Documentation website. The file errorutil_analyze_summary.json contains a summary of the analysis, notably lists of duplicates etc.

Conventions to follow while creating errors

  1. Errors names and codes are namespaced to components, i.e. they need to be unique within a component, which is verified by this tool.
  2. Errors are not to be reused across components and modules.
  3. Error codes are not to be set as integer. CI will take care of updating Error codes from a string to an integer.
  4. Running make error analyzes your code and returns any warnings to be aware of.
  5. Capitalize the first letter of the every error description.
  6. Using errors.NewDefault(…) is deprecated. This tool emits a warning if its use is detected.
  7. Use errors.New(…) from MeshKit to create actual errors with all the details. This is often done in a factory function. It is important that the error code variable is used here, not a literal. Specify detailed descriptions, probable causes, and remedies. They need to be string literals, call expressions are ignored. This tool extracts this information from the code and exports it. For the Code argument in the errors.New use the same Error name and append a β€œCode” after it. e.g error name : ErrApplyManifest then the error code is ErrApplyManifestCode
  8. Set the value to any string, like β€œreplace_me” (no convention here), e.g. ErrApplyManifestCode = β€œreplace_me”.
  9. By convention, error codes and the factory functions live in files called error.go. The tool checks all files, but updates only error.go files.

Use the errors.New() function to create a new instance of the error object and pass situation-specific attributes as function arguments. These attributes are:

  • Code
  • Short Description
  • Long Description
  • Probable Cause
  • Suggested Remediation


errors.New(ErrExampleCode, errors.Alert, []string{"<short-description>"}, []string{"<long-description>"}, []string{"<probable-cause>"}, []string{"<suggested remediation>"})


In this example we are creating an Error for being unable to marshal JSON

var ( // Error code ErrMarshalCode= "replace_me" //Static errors (for example) ErrExample = errors.New(ErrExampleCode, errors.Alert, []string{"<short-description>"}, []string{"<long-description>"}, []string{"<probable-cause>"}, []string{"<suggested remediation>"}) ) // Dynamic errors //Error Name func ErrMarshal(err error, obj string) error { return errors.New(ErrMarshalCode, errors.Alert, []string{"Unable to marshal the : ", obj}, []string{err.Error()}, []string{}, []string{}) }

Replacing old Error Codes


bd, err := json.Marshal(providers) if err != nil { http.Error(w, "unable to marshal the providers", http.StatusInternalServerError) return }


bd, err := json.Marshal(providers) if err != nil { obj := "provider" http.Error(w, ErrMarshal(err, obj).Error(), http.StatusInternalServerError) return }

Replacing logrus

There already exists an interface for logger in MeshKit.


To enforce the use of meshkit errors, meshkit logger was designed such that it only works with meshkit errors. If a non-meshkit error is logged through the logger, it would panic and kill the process. See: meshkit#119 for more insight.

Defining a Logger

type Logger struct { log logger.Handler }


logrus.Debugf("meshLocationURL: %s", meshLocationURL)
l.log.Debug("meshLocationURL: ", meshLocationURL)


logrus.Errorf("error marshaling data: %v.", err)
l.log.Error(ErrMarshal(err, obj))

A small program using meshkit errors and logger

package main import ( "fmt" "os" meshkitErrors "" "" ) var ( // CI will replace `test_code` with new error code ErrOpeningFileCode = "test_code" ) func main() { log, err := logger.New("test", logger.Options{ Format: logger.SyslogLogFormat, DebugLevel: true, }) if err != nil { fmt.Println(err) os.Exit(1) } // logging meshkit error err = openFileWithMeshkitError("some.txt") if err != nil { log.Error(err) } // OUTPUT // ERRO[2021-11-10T17:31:28+05:30] open some.txt: no such file or directory app=test code=1001 probable-cause="empty string passed as argument .file with this name doesn't exist" severity=2 short-description="unable to open file" suggested-remediation="pass a non-empty string as filename .create file before opening it" // logging non meshkit error err = openFile("some.txt") if err != nil { log.Error(err) } // OUTPUT // panic: interface conversion: error is *fs.PathError, not *errors.Error // goroutine 1 [running]: //{0x50dfc0, 0xc000068450}) // /home/rudraksh/go/pkg/mod/ +0x90 //*Logger).Error(0xc00000e040, {0x50dfc0, 0xc000068450}) // /home/rudraksh/go/pkg/mod/ +0xbb // main.main() // /home/rudraksh/trash/meshkitplay/main.go:32 +0xe2 // exit status 2 } // this returns a non meshkit error func openFile(name string) error { _, err := os.Open(name) return err } // this returns a meshkit error func openFileWithMeshkitError(name string) error { _, err := os.Open(name) return ErrOpeningFile(err) } func ErrOpeningFile(err error) error { return meshkitErrors.New(ErrOpeningFileCode, meshkitErrors.Alert, []string{"unable to open file"}, []string{err.Error()}, []string{"empty string passed as argument ", "file with this name doesn't exist"}, []string{"pass a non-empty string as filename ", "create file before opening it"}) }

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