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designcraft/docs/control-protocol.md
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Brandon ThomasandClaude Opus 5.5 48dfbcfd19 Merge origin/main into data-merge
Resolve conflicts keeping both sides: doc gains both `cjk` and
`datamerge` modules; file.open resolves data-merge sources and loads the
document's fonts; DocState keeps preview_stash/preview_record and fonts.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
2026-10-07 22:28:15 -04:00

3.7 KiB

Control protocol

Start the app with --control <port> (or DESIGNCRAFT_CONTROL_PORT). The server listens on 127.0.0.1 only and speaks JSON lines: one request object per line, one reply per line.

Only requests are read. Every line must be a JSON object with a string method (id and params are optional; blank lines are skipped). Anything else gets one error reply ({"ok": false, "error": "… closing the connection"}) and the server closes the connection, so nothing sent after it on that connection runs. That covers text that isn't JSON, a JSON array or number, an object without method, invalid UTF-8, and a line longer than 4 MiB. An HTTP request (for example a web page's cross-origin fetch to 127.0.0.1:<port>) therefore can't smuggle a command in its body: its request line is rejected first. At most 16 connections are served at once; further ones get an error line and are closed. Clients that get an error reply should reconnect. The port has no authentication, so only enable it while you use it. Transport: apps/designcraft/src/control_server.rs.

{"id": 1, "method": "engine.execute", "params": {"command": "frame.create", "params": {"rect": [36, 36, 300, 200], "content": "text"}}}
{"id": 1, "ok": true, "result": {"id": 10, "story": 11}}
Method Params What it does
engine.execute / ui.menu.invoke {command, params} Run any engine or UI command (see engine.commands). ui.menu.invoke without params acts like choosing the menu item: a command labelled "…" that takes parameters opens its dialog
engine.commands — Every command: id, label, menu path, shortcut, params doc, enabled
document.inspect — Pages, spreads, items, stories (overset), styles, swatches, selection
ui.inspect — Tool, UI state, view (zoom/origin), canvas rect, perf
ui.menu.list / ui.tool.list — Menu tree / Tools panel groups
ui.tool.select {tool} Select a tool (selection, type, rectangleFrame, …)
ui.pointer {events:[{kind: down|drag|up|move|doubleclick, x, y, space?: "screen"|"canvas"}], mods?} Drive the active tool through the same code path as the mouse
ui.key / ui.text {key, shift?, alt?, cmd?} / {text} Synthetic keyboard input (typing into a text frame)
ui.move / ui.click / ui.drag screen points, button?: left|right|middle Real egui pointer input — reaches every widget, menu and panel
ui.set {brightness?, panel?, rulers?, guides?, frameEdges?, baselineGrid?, textThreads?, screenMode?, zoom?, page?, fit?} UI state
ui.dialog.open {id, fields?} Open a dialog by id (e.g. paragraphStyleOptions with {name, section})
ui.dialog.set / ui.dialog.confirm / ui.dialog.cancel {field, value} Fill and confirm the open dialog
ui.resize, ui.focus Window control
ui.screenshot {path?} PNG of the whole window
ui.render {path?, page?, scale?, bleed?} Render a page headlessly (PNG; base64 if no path)
app.open / app.save / app.export / app.quit Files

Data merge runs through engine.execute like any command: data.source.select, data.fields, data.placeholder.add / .remove, data.options, data.preview / data.preview.stop, data.merge. data.merge creates and activates a new merged document; the template stays as it was (agents.md).

Headless window screenshots (locked screen, hidden window): cargo run -p designcraft-ui-egui --example ui_shot -- script.jsonl, where each line is one of the requests above, {"shot": "/abs/out.png"} or {"steps": n} (renders the whole UI offscreen with wgpu).

The MCP server (designcraft-cli mcp) wraps the same methods for Claude and other agents.