{"record":{"id":"1cfb1762d04a43c8","repo":"XTLS/Xray-core","slug":"failed-to-write-addons-protobuf-length","errorCode":null,"errorMessage":"failed to write addons protobuf length","messagePattern":"failed to write addons protobuf length","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"warning","filePath":"proxy/vless/encoding/addons.go","lineNumber":25,"sourceCode":"\n\t\"github.com/xtls/xray-core/common/buf\"\n\t\"github.com/xtls/xray-core/common/errors\"\n\t\"github.com/xtls/xray-core/common/protocol\"\n\t\"github.com/xtls/xray-core/common/session\"\n\t\"github.com/xtls/xray-core/proxy\"\n\t\"github.com/xtls/xray-core/proxy/vless\"\n\t\"google.golang.org/protobuf/proto\"\n)\n\nfunc EncodeHeaderAddons(buffer *buf.Buffer, addons *Addons) error {\n\tswitch addons.Flow {\n\tcase vless.XRV:\n\t\tbytes, err := proto.Marshal(addons)\n\t\tif err != nil {\n\t\t\treturn errors.New(\"failed to marshal addons protobuf value\").Base(err)\n\t\t}\n\t\tif err := buffer.WriteByte(byte(len(bytes))); err != nil {\n\t\t\treturn errors.New(\"failed to write addons protobuf length\").Base(err)\n\t\t}\n\t\tif _, err := buffer.Write(bytes); err != nil {\n\t\t\treturn errors.New(\"failed to write addons protobuf value\").Base(err)\n\t\t}\n\tdefault:\n\t\tif err := buffer.WriteByte(0); err != nil {\n\t\t\treturn errors.New(\"failed to write addons protobuf length\").Base(err)\n\t\t}\n\t}\n\n\treturn nil\n}\n\nfunc DecodeHeaderAddons(buffer *buf.Buffer, reader io.Reader) (*Addons, error) {\n\taddons := new(Addons)\n\tbuffer.Clear()\n\tif _, err := buffer.ReadFullFrom(reader, 1); err != nil {\n\t\treturn nil, errors.New(\"failed to read addons protobuf length\").Base(err)","sourceCodeStart":7,"sourceCodeEnd":43,"githubUrl":"https://github.com/XTLS/Xray-core/blob/7d214f8b094f75322fa3990f8aadad1c912f24f5/proxy/vless/encoding/addons.go#L7-L43","documentation":"While writing the XTLS Vision addons block, Xray writes the marshaled length as one byte into a preallocated buf.Buffer. WriteByte on an internal buffer fails only if the buffer is full (2048 bytes by default) — not reachable here since the buffer is fresh. Effectively an internal invariant check, not an expected runtime error.","triggerScenarios":"Would require the header buffer to already be at capacity before encoding addons, which the call sequence prevents. Not user-triggerable through configuration.","commonSituations":"Should not occur; if it does, suspect a modified/forked xray build with changed buffer handling.","solutions":["Upgrade to an official xray-core release","Collect logs and report upstream if reproducible"],"exampleFix":null,"handlingStrategy":"try-catch","validationCode":null,"typeGuard":null,"tryCatchPattern":"if err := encoding.EncodeHeaderAddons(buffer, addons); err != nil {\n\t// any addons encode failure is per-connection: log and close\n\tlog.Warnf(\"addons encode: %v\", err)\n\treturn conn.Close()\n}","preventionTips":["Treat encode-stage addons errors as internal bugs: upgrade builds","Avoid heavily modified forks that alter buffer sizing"],"tags":["vless","xtls","encoding","buffer","internal"],"backgroundTag":null,"analyzedSha":"7d214f8b094f75322fa3990f8aadad1c912f24f5","analyzedAt":"2026-08-15T14:26:24.325Z","schemaVersion":2},"datasetVersion":"2026-08-15T22:17:37.221Z"}