{"record":{"id":"b9778f4e6389ed8c","repo":"gofiber/fiber","slug":"failed-to-bind-to-response-headers-w","errorCode":null,"errorMessage":"failed to bind to response headers: %w","messagePattern":"failed to bind to response headers: %w","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"middleware/idempotency/idempotency.go","lineNumber":155,"sourceCode":"\t\t} else if ok {\n\t\t\treturn nil\n\t\t}\n\n\t\t// Execute the request handler\n\t\tif err := c.Next(); err != nil {\n\t\t\t// If the request handler returned an error, return it and skip idempotency\n\t\t\treturn err\n\t\t}\n\n\t\t// Construct response\n\t\tres := &response{\n\t\t\tStatusCode: c.Response().StatusCode(),\n\t\t\tBody:       c.Response().Body(),\n\t\t}\n\t\t{\n\t\t\theaders := make(map[string][]string)\n\t\t\tif err := c.Bind().RespHeader(headers); err != nil {\n\t\t\t\treturn fmt.Errorf(\"failed to bind to response headers: %w\", err)\n\t\t\t}\n\n\t\t\tif keepResponseHeaders == nil {\n\t\t\t\t// Keep all\n\t\t\t\tres.Headers = headers\n\t\t\t} else {\n\t\t\t\t// Filter\n\t\t\t\tres.Headers = make(map[string][]string)\n\t\t\t\tfor h, vals := range headers {\n\t\t\t\t\tif shouldKeepHeader(h) {\n\t\t\t\t\t\tres.Headers[h] = vals\n\t\t\t\t\t}\n\t\t\t\t}\n\t\t\t}\n\t\t}\n\n\t\t// Marshal response\n\t\tbs, err := res.MarshalMsg(nil)","sourceCodeStart":137,"sourceCodeEnd":173,"githubUrl":"https://github.com/gofiber/fiber/blob/a105acad6c1e4576a77f01e02973f67e962bb58d/middleware/idempotency/idempotency.go#L137-L173","documentation":"Returned when c.Bind().RespHeader(headers) fails while collecting response headers to cache. Binding response headers into a map[string][]string fails if the binder encounters malformed header bytes or a header map type it cannot populate. It is rare — Fiber's binder is generally robust — but surfaces bad header content set by upstream handlers.","triggerScenarios":"After the request handler runs, the idempotency middleware binds the response headers into a map; if any header contains invalid bytes (control chars, non-ASCII without encoding) or the target type is wrong, Bind returns an error wrapped here.","commonSituations":"An upstream handler sets a header with raw binary/control characters, a Content-Type with bad encoding metadata, or a custom binder configuration that rejects certain headers; also possible after a Fiber version upgrade that tightened header validation.","solutions":["Audit headers set by your handlers and any middleware upstream of idempotency.","Sanitize header values (strip control bytes) before setting them.","Use KeepResponseHeaders to restrict caching to a known-good header subset.","Update Fiber and check the bind release notes for stricter validation."],"exampleFix":"// before\napp.Use(idempotency.New()) // caches all headers\n// after — only cache safe headers\napp.Use(idempotency.New(idempotency.Config{\n    KeepResponseHeaders: []string{\"Content-Type\", \"X-Request-Id\"},\n}))","handlingStrategy":"validation","validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":["Sanitize header values before setting them (strip control bytes).","Use KeepResponseHeaders to cache only known-safe headers.","Audit upstream middleware that mutates response headers."],"tags":["idempotency","binder","http-headers","validation"],"backgroundTag":null,"analyzedSha":"a105acad6c1e4576a77f01e02973f67e962bb58d","analyzedAt":"2026-08-11T17:33:26.942Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}