Module protobuf 

The AG-UI binary transport — not implemented.

This module exists so that a build with the protobuf feature can still negotiate and name the media type, and so the reason it does nothing is written down next to the code rather than discovered at runtime.

Why there is no encoder here

The binary transport is defined by events.proto in the upstream @ag-ui/proto package. Its Event message is a oneof over 21 of the protocol’s 36 event types:

TEXT_MESSAGE_START, TEXT_MESSAGE_CONTENT, TEXT_MESSAGE_END, TEXT_MESSAGE_CHUNK, TOOL_CALL_START, TOOL_CALL_ARGS, TOOL_CALL_END, TOOL_CALL_CHUNK, STATE_SNAPSHOT, STATE_DELTA, MESSAGES_SNAPSHOT, RAW, CUSTOM, RUN_STARTED, RUN_FINISHED, RUN_ERROR, STEP_STARTED, STEP_FINISHED, SUBAGENT_STARTED, SUBAGENT_FINISHED, SUBAGENT_ERROR.

(Upstream’s own documentation says 19: the two *_CHUNK events have a oneof arm but no EventType enum value to select it with, so they cannot be encoded in practice either.)

The other 15 have no wire representation at all: every REASONING_* event, both ACTIVITY_* events, all five deprecated THINKING_* events, and TOOL_CALL_RESULT. An agent that reasons, reports activities, or returns a tool result — which is most of them — cannot express its stream in this format. Encoding such a run would mean silently dropping events, so this crate declines to encode any.

Generating the Rust types would also mean either a build.rs that requires protoc on every consumer’s machine or checked-in generated code that drifts from upstream. Neither is worth it for a format that cannot carry the protocol.

What to do instead

Use sse, which carries all 36 event types. Revisit this module when upstream events.proto covers the full set.

Structs

ProtobufFormatter

Placeholder for the binary formatter.

Constants

COVERED_EVENT_TYPES

The event types upstream events.proto can represent.

Functions

is_covered

Whether the binary transport can represent event_type.