{"record":{"id":"3cae69155b9d55eb","repo":"kubernetes/kops","slug":"error-writing-to-stdout-v-3cae69","errorCode":null,"errorMessage":"error writing to stdout: %v","messagePattern":"error writing to stdout: (.+?)","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"pkg/commands/helpers/kubectl_auth.go","lineNumber":142,"sourceCode":"\tisCached := false\n\tif cached != nil {\n\t\texecCredential = cached\n\t\tisCached = true\n\t} else {\n\t\tstatus, err := buildCredentials(ctx, f, options)\n\t\tif err != nil {\n\t\t\treturn err\n\t\t}\n\t\texecCredential.Status = *status\n\t}\n\n\tb, err := json.MarshalIndent(execCredential, \"\", \"  \")\n\tif err != nil {\n\t\treturn fmt.Errorf(\"error marshaling json: %v\", err)\n\t}\n\t_, err = out.Write(b)\n\tif err != nil {\n\t\treturn fmt.Errorf(\"error writing to stdout: %v\", err)\n\t}\n\n\tif !isCached {\n\t\tif err := os.MkdirAll(filepath.Dir(cacheFilePath), 0o755); err != nil {\n\t\t\tklog.Warningf(\"failed to make cache directory for %q: %v\", cacheFilePath, err)\n\t\t}\n\t\tif err := os.WriteFile(cacheFilePath, b, 0o600); err != nil {\n\t\t\tklog.Warningf(\"failed to write cache file %q: %v\", cacheFilePath, err)\n\t\t}\n\t}\n\n\treturn nil\n}\n\n// ExecCredential specifies the client.authentication.k8s.io ExecCredential object\ntype ExecCredential struct {\n\tAPIVersion string               `json:\"apiVersion,omitempty\"`\n\tKind       string               `json:\"kind,omitempty\"`","sourceCodeStart":124,"sourceCodeEnd":160,"githubUrl":"https://github.com/kubernetes/kops/blob/4c8573c808a73d578c5eadc86d410646ea0b0d73/pkg/commands/helpers/kubectl_auth.go#L124-L160","documentation":"The helper writes the marshaled ExecCredential JSON to the provided io.Writer (normally stdout, consumed by kubectl). If the Write call fails — a broken pipe or closed stdout — it returns this wrapped error. kubectl then sees the credential plugin fail and authentication for the cluster fails.","triggerScenarios":"out.Write(b) errors: stdout is a closed pipe (e.g. `kops helpers kubectl-auth ... | head -c0`), the process was invoked with an unusable stdout, or a custom io.Writer passed to RunKubectlAuthHelper returns an error.","commonSituations":"Running the command manually without piping to kubectl and closing the pipe; using it in a pipeline that exits early; embedding the helper where stdout handling is incorrect.","solutions":["Run the helper only via kubectl's exec credential plugin mechanism so stdout is consumed.","If piping manually, ensure the downstream command reads all output before exiting.","When calling in Go, pass a valid, open io.Writer and check its error behavior."],"exampleFix":"// before\n$ kops helpers kubectl-auth --cluster c | head -c0\n// after\n$ kubectl get nodes   # let kubectl invoke the plugin itself","handlingStrategy":"try-catch","validationCode":null,"typeGuard":null,"tryCatchPattern":"err := helpers.RunKubectlAuthHelper(ctx, f, out, options)\nif err != nil && strings.Contains(err.Error(), \"error writing to stdout\") {\n    // stdout closed/unusable; rerun the helper letting kubectl consume output\n    return retryViaKubectl()\n}","preventionTips":["Invoke the helper via kubectl's exec credential plugin, not ad-hoc pipes.","Avoid pipelines that close stdout early (e.g. `| head`).","When calling in Go, pass a reliable writer such as os.Stdout or bytes.Buffer."],"tags":["io","stdout","broken-pipe"],"backgroundTag":"broken-pipe","analyzedSha":"4c8573c808a73d578c5eadc86d410646ea0b0d73","analyzedAt":"2026-09-05T04:13:19.212Z","contentChangedAt":"2026-09-05T04:13:19.212Z","schemaVersion":2},"datasetVersion":"2026-09-12T07:17:12.445Z"}