{"id":"f9ef8138c599df7f","repo":"gofiber/fiber","slug":"failed-to-read-client-ca-file-q-w","errorCode":null,"errorMessage":"failed to read client CA file %q: %w","messagePattern":"failed to read client CA file %q: %w","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"critical","filePath":"listen.go","lineNumber":309,"sourceCode":"\t// Serve\n\tif cfg.BeforeServeFunc != nil {\n\t\tif err := cfg.BeforeServeFunc(app); err != nil {\n\t\t\treturn err\n\t\t}\n\t}\n\n\tserved = true\n\treturn app.server.Serve(ln)\n}\n\nfunc applyClientCert(tlsConfig *tls.Config, certClientFile string) error {\n\tif certClientFile == \"\" {\n\t\treturn nil\n\t}\n\n\tclientCACert, err := os.ReadFile(filepath.Clean(certClientFile))\n\tif err != nil {\n\t\treturn fmt.Errorf(\"failed to read client CA file %q: %w\", certClientFile, err)\n\t}\n\n\tclientCertPool := x509.NewCertPool()\n\tif ok := clientCertPool.AppendCertsFromPEM(clientCACert); !ok {\n\t\treturn fmt.Errorf(\"failed to parse client CA certificate from %q\", certClientFile)\n\t}\n\n\ttlsConfig.ClientAuth = tls.RequireAndVerifyClientCert\n\ttlsConfig.ClientCAs = clientCertPool\n\n\treturn nil\n}\n\n// Listener serves HTTP requests from the given listener.\n// You should enter custom ListenConfig to customize startup. (prefork, startup message, graceful shutdown...)\nfunc (app *App) Listener(ln net.Listener, config ...ListenConfig) error {\n\tcfg := listenConfigDefault(config...)\n","sourceCodeStart":291,"sourceCodeEnd":327,"githubUrl":"https://github.com/gofiber/fiber/blob/9a4c7e57fe0b080a04235d28a4b0d2b4b353d58c/listen.go#L291-L327","documentation":"Returned during App.Listen startup when Config.CertClientFile (the client CA certificate for mutual TLS) is set but os.ReadFile cannot read it. applyClientCert reads the PEM file to populate the ClientCAs pool and enable RequireAndVerifyClientCert. The error wraps the file path and the underlying os error.","triggerScenarios":"Calling app.Listen(\":443\", fiber.ListenConfig{CertClientFile: \"/etc/ca/client-ca.pem\"}) where the file is missing, unreadable, or the path is wrong. mTLS is being configured but the CA bundle cannot be loaded.","commonSituations":"Client CA bundle not included in the deployment, wrong path, permission issues, or the file is empty/corrupt. Since ClientAuth is set to RequireAndVerifyClientCert right after, clients will be rejected until this is resolved.","solutions":["Verify the client CA file exists and is readable: ls -l on the path.","Use an absolute path for the CA bundle.","Confirm the file is PEM-encoded (BEGIN CERTIFICATE).","Include the CA bundle in the container image / secret mount.","If mTLS is not intended, remove the CertClientFile setting."],"exampleFix":"// before\napp.Listen(\":443\", fiber.ListenConfig{\n    CertFile:     \"/tls/cert.pem\",\n    CertKeyFile:  \"/tls/key.pem\",\n    CertClientFile: \"ca.pem\", // wrong relative path\n})\n\n// after\napp.Listen(\":443\", fiber.ListenConfig{\n    CertFile:       \"/tls/cert.pem\",\n    CertKeyFile:    \"/tls/key.pem\",\n    CertClientFile: \"/tls/client-ca.pem\",\n})","handlingStrategy":"validation","validationCode":"// Validate the client CA file before Listen\nif certClientFile != \"\" {\n    if _, err := os.ReadFile(filepath.Clean(certClientFile)); err != nil {\n        log.Fatalf(\"cannot read client CA file: %v\", err)\n    }\n}","typeGuard":null,"tryCatchPattern":"if err := app.Listen(\":443\", fiber.ListenConfig{\n    CertFile: certFile, CertKeyFile: keyFile, CertClientFile: caFile,\n}); err != nil {\n    log.Fatalf(\"startup failed: %v\", err)\n}","preventionTips":["Use absolute paths for the client CA bundle.","Verify the file exists and is PEM-encoded at deploy time.","Mount the CA bundle as a secret/config in the container.","Remove CertClientFile if mTLS is not required."],"tags":["mtls","tls","certificate","startup","security","go"],"analyzedSha":"9a4c7e57fe0b080a04235d28a4b0d2b4b353d58c","analyzedAt":"2026-08-04T21:44:03.395Z","schemaVersion":2}