{"record":{"id":"722e68131af101cc","repo":"hyperledger/fabric","slug":"cannot-open-file-part-s-from-request-body","errorCode":null,"errorMessage":"cannot open file part %s from request body","messagePattern":"cannot open file part (.+?) from request body","errorType":"http","errorClass":null,"httpStatus":400,"severity":"error","filePath":"orderer/common/channelparticipation/restapi.go","lineNumber":449,"sourceCode":"\tif err != nil {\n\t\th.sendResponseJsonError(resp, http.StatusBadRequest, errors.Wrap(err, \"cannot read form from request body\"))\n\t\treturn nil\n\t}\n\n\tif _, exist := form.File[FormDataConfigBlockKey]; !exist {\n\t\th.sendResponseJsonError(resp, http.StatusBadRequest, errors.Errorf(\"form does not contains part key: %s\", FormDataConfigBlockKey))\n\t\treturn nil\n\t}\n\n\tif len(form.File) != 1 || len(form.Value) != 0 {\n\t\th.sendResponseJsonError(resp, http.StatusBadRequest, errors.New(\"form contains too many parts\"))\n\t\treturn nil\n\t}\n\n\tfileHeader := form.File[FormDataConfigBlockKey][0]\n\tfile, err := fileHeader.Open()\n\tif err != nil {\n\t\th.sendResponseJsonError(resp, http.StatusBadRequest, errors.Wrapf(err, \"cannot open file part %s from request body\", FormDataConfigBlockKey))\n\t\treturn nil\n\t}\n\n\tblockBytes, err := io.ReadAll(file)\n\tif err != nil {\n\t\th.sendResponseJsonError(resp, http.StatusBadRequest, errors.Wrapf(err, \"cannot read file part %s from request body\", FormDataConfigBlockKey))\n\t\treturn nil\n\t}\n\n\tblock := &cb.Block{}\n\terr = proto.Unmarshal(blockBytes, block)\n\tif err != nil {\n\t\th.logger.Debugf(\"Failed to unmarshal blockBytes: %s\", err)\n\t\th.sendResponseJsonError(resp, http.StatusBadRequest, errors.Wrapf(err, \"cannot unmarshal file part %s into a block\", FormDataConfigBlockKey))\n\t\treturn nil\n\t}\n\n\treturn block","sourceCodeStart":431,"sourceCodeEnd":467,"githubUrl":"https://github.com/hyperledger/fabric/blob/2736b63f8fd5932511d56fe68b7039d15977f7f6/orderer/common/channelparticipation/restapi.go#L431-L467","documentation":"This error wraps the OS/multipart error returned when the server cannot open the uploaded file part from the request body. After locating the 'config-block' file part, the handler calls fileHeader.Open(); if that fails the error is wrapped and returned with HTTP 400. It indicates a malformed multipart stream or an I/O problem reading the uploaded part, not a problem with the block content itself.","triggerScenarios":"POSTing to the join endpoint where the multipart file part for 'config-block' exists but its embedded file cannot be opened — typically a truncated or malformed multipart body, or the connection dropping mid-read.","commonSituations":"Proxy/load-balancer truncating large uploads; client timing out mid-upload and closing the stream; malformed multipart boundary produced by a hand-rolled HTTP client; body exceeding MaxBytesReader limits causing read failures.","solutions":["Retry the upload ensuring the client fully writes the multipart body before awaiting the response","Verify the HTTP client generates a valid multipart/form-data body (use a standard library like curl, requests, or Go's mime/multipart)","Check proxy/gateway timeout and body-size settings so the upload is not truncated","Capture the wrapped cause in the response to identify the underlying open error"],"exampleFix":"// before: hand-built multipart body with wrong boundary headers\nhttp.Post(url, \"multipart/form-data\", body)\n// after\nvar b bytes.Buffer\nw := multipart.NewWriter(&b)\nf, _ := w.CreateFormFile(\"config-block\", \"genesis.block\")\nf.Write(blockBytes)\nw.Close()\nhttp.Post(url, w.FormDataContentType(), &b)","handlingStrategy":"try-catch","validationCode":"// pre-flight: ensure the block file exists and is readable client-side\nst, err := os.Stat(blockPath)\nif err != nil || st.Size() == 0 {\n    return fmt.Errorf(\"block file %s missing or empty: %w\", blockPath, err)\n}","typeGuard":null,"tryCatchPattern":"resp, err := client.Post(url, w.FormDataContentType(), &buf)\nif err != nil {\n    return fmt.Errorf(\"upload interrupted, retry with full body write: %w\", err)\n}\nif resp.StatusCode == http.StatusBadRequest {\n    var e map[string]string\n    json.NewDecoder(resp.Body).Decode(&e)\n    return fmt.Errorf(\"server rejected multipart body: %v\", e)\n}","preventionTips":["Use a standard multipart library to build the body","Ensure the client writes the full body before reading the response","Check proxy timeouts and buffering for large uploads"],"tags":["http","fabric","multipart-form","io"],"backgroundTag":"multipart-part-open-failed","analyzedSha":"2736b63f8fd5932511d56fe68b7039d15977f7f6","analyzedAt":"2026-09-04T08:52:36.465Z","contentChangedAt":"2026-09-04T08:52:36.465Z","schemaVersion":2},"datasetVersion":"2026-09-08T15:18:49.778Z"}