{"record":{"id":"dfc48efc19c234b6","repo":"gofiber/fiber","slug":"failed-to-write-string-w","errorCode":null,"errorMessage":"failed to write string: %w","messagePattern":"failed to write string: %w","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"warning","filePath":"router.go","lineNumber":263,"sourceCode":"\t// \"/internal \" — reachable through \"/internal%20\" under UnescapePath — reads\n\t// as \"/internal\", a different route. No URL names either.\n\tnormalized := urlnorm.AsBrowserReads(route.Path)\n\tif normalized != route.Path || urlnorm.LeadingSlashes(normalized) > 1 {\n\t\treturn \"\", ErrRouteNotRepresentable\n\t}\n\n\tif len(route.routeParser.segs) == 0 {\n\t\treturn urlnorm.RootedPath(route.Path), nil\n\t}\n\n\tbuf := bytebufferpool.Get()\n\tdefer bytebufferpool.Put(buf)\n\n\tfor _, segment := range route.routeParser.segs {\n\t\tif !segment.IsParam {\n\t\t\t_, err := buf.WriteString(segment.Const)\n\t\t\tif err != nil {\n\t\t\t\treturn \"\", fmt.Errorf(\"failed to write string: %w\", err)\n\t\t\t}\n\t\t\tcontinue\n\t\t}\n\n\t\tvar (\n\t\t\tval   any\n\t\t\tfound bool\n\t\t)\n\n\t\t// Prefer an exact parameter name match\n\t\tif val, found = params[segment.ParamName]; !found && !route.caseSensitive {\n\t\t\t// Fall back to a case-insensitive match using a deterministic winner\n\t\t\tvar matchedKey string\n\t\t\tfoundMatch := false\n\t\t\tfor key := range params {\n\t\t\t\tif utils.EqualFold(key, segment.ParamName) && (!foundMatch || key < matchedKey) {\n\t\t\t\t\tmatchedKey = key\n\t\t\t\t\tfoundMatch = true","sourceCodeStart":245,"sourceCodeEnd":281,"githubUrl":"https://github.com/gofiber/fiber/blob/a105acad6c1e4576a77f01e02973f67e962bb58d/router.go#L245-L281","documentation":"Returned by buildRouteURL() (Route.URL / GetRouteURL) when writing a constant route segment to a bytebufferpool.Buffer fails. bytebufferpool.Buffer.WriteString only errors if the underlying write exceeds MaxInt32 bytes — functionally unreachable for URL construction. Encountering this error indicates memory corruption or an absurdly large constant route path.","triggerScenarios":"Calling route.URL(params) or res.GetRouteURL(name, params) where the route has constant segments (not parameters), and buf.WriteString(segment.Const) returns an error. Realistically never fires under normal operation.","commonSituations":"This is a defensive guard. If it appears, suspect a corrupted bytebufferpool state from unsafe concurrent reuse of a pooled buffer, or a route registered with a multi-gigabyte constant path (misconfiguration).","solutions":["Treat as a fatal/panic condition — if WriteString on a pooled buffer errors, memory integrity is suspect; restart the process.","Audit route registrations for pathological constant paths (e.g., a path built from an unbounded external string).","Ensure no code retains bytebufferpool.Buffers past their Put() (double-use)."],"exampleFix":null,"handlingStrategy":"try-catch","validationCode":"// Bound constant route paths at registration time.\nfunc registerRoute(app *fiber.App, path string) {\n    if len(path) > 4096 { panic(\"route path too long: \" + path) }\n    app.Get(path, /* ... */)\n}","typeGuard":null,"tryCatchPattern":"if url, err := route.URL(params); err != nil {\n    // Practically unreachable; treat as fatal.\n    log.Panicf(\"route.URL constant write failed: %v\", err)\n} else {\n    _ = url\n}","preventionTips":["Do not build route paths from unbounded external strings.","Never reuse bytebufferpool.Buffers past Put()."],"tags":["routing","url-generation","bytebufferpool","defensive"],"backgroundTag":null,"analyzedSha":"a105acad6c1e4576a77f01e02973f67e962bb58d","analyzedAt":"2026-08-11T17:33:26.942Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}