DocsThe plugin protocol

The plugin protocol

Synced from the app repository (docs/plugins/protocol.md).

What Skwir and a plugin from outside say to each other (ADR-045, ADR-046, ADR-047). The types are in skwir_plugin_api::protocol (crates/plugin-api/src/protocol.rs); a Rust plugin uses them, a plugin in another language writes the same JSON. How to write a plugin: README.md.

Versions

The protocol is experimental (ADR-047, point 6). Until it is declared stable, a new version may change what an older one said, and Skwir then stops speaking the older one; the release notes say so. Once stable, a plugin written for an older version runs unchanged and is never asked what its version did not have.

A manifest states the version its plugin speaks (api, default 1). Skwir speaks versions OLDEST to VERSION, both 1 today.

Transports

Program: JSON-RPC 2.0, one message per line on its standard input (Skwir's messages) and standard output (the plugin's). A line is at most 64 MiB, newline included (MESSAGE_LIMIT). Standard error goes to Skwir's log. Skwir closes standard input when it no longer needs the program.
Module: the WIT world skwir:plugin@0.1.0 (crates/plugin-api/wit/plugin.wit). Skwir calls the export call(method, params) with the method's name and its parameters as JSON text, and reads the answer as JSON text, or an error message. The plugin calls the imports read(file, offset, length) and log(level, message).

One call at a time per plugin: Skwir sends the next once one is answered. While answering, the plugin may send read requests and log notifications.

Files

A call about files names each as a File:

{ "handle": 1, "name": "note.txt", "path": "/home/a/note.txt",

"mime": "text/plain", "size": 42 }

Field	Type
`handle`	u32	Reads its bytes (`read`); valid while the call is answered.
`name`	string	A name that is not UTF-8 is shown lossily.
`path`	string	For display only.
`mime`	string, optional	When known.
`size`	u64, optional	Bytes, when known.

Skwir asks

`initialize` (program only, first)

{ "api": 1, "capabilities": ["read"] }

api is the newest version Skwir speaks; capabilities what the plugin was granted. Answer { "api": 1 } with the version the plugin speaks; a version Skwir does not speak is refused.

`field`

{ "key": "word-count.words", "file": { … } }

key is one of the manifest's field keys. Answer { "value": 7 }: a string, a number, a boolean or a list of them, or null (or no value) when the file says nothing.

`thumbnail`

{ "file": { … }, "size": 256 }

size is the side, in pixels, of the square the picture must fit. Answer { "png": "<base64>" }, or { "png": null } for no thumbnail.

`inspect`

{ "file": { … }, "offset": 4096, "query": "needle", "source": false, "target": null }

Field	Default
`offset`	0	Where the page asked starts: a byte, a row, a section, as the plugin numbers them (its `previous` and `next`).
`query`	null	What to find from `offset` on; the answer's `position` says where.
`source`	false	The file's source asked rather than its presentation.
`target`	null	A row's own `target`, asked for.

Answer null (nothing to show), or an inspection:

{ "kind": "hex",
  "title": "Hex · 9.8 KB",
  "text": [],
  "columns": ["Offset", "…", "ASCII"],
  "rows": [ { "cells": ["0000000000000000", "…", "…"],
              "bytes": null, "depth": 0, "branch": false, "target": null } ],
  "previous": null, "next": 4096, "position": 0,
  "notice": "Match at 0x64",
  "details": [ { "label": "Version", "value": "1.2" } ] }

Field	Default
`kind`	`text`	`text` (paragraphs), `code` (lines, monospaced), `hex` (offset, bytes, characters), `table` (rows and columns).
`title`	required
`text`	`[]`	Paragraphs, or lines of code.
`columns`	`[]`
`rows`	`[]`	Each: `cells`; `bytes` (a container member's size, optional); `depth` (0); `branch` (false); `target` (what `target` asks for this row, optional).
`previous`, `next`	null	Where the page before and after starts, if any.
`position`	0	Where what was asked (found) is.
`notice`	`""`	A line over the page: what a search found, what was left out.
`details`	`[]`	`{ label, value }` facts the format knows, for Details.

A preview that converts or shows pages is not asked inspect.

`convert`

For a preview declared with converts = true:

{ "file": { "handle": 1, "name": "sunset.ppm", … } }

Answer null (nothing to show for this file), or a file in a format Skwir shows, which it previews as it would that file (a PDF in the reader, a picture zoomed and fitted, audio or video in the player, Markdown, a table, a track on the map):

{ "name": "sunset.png", "data": "<base64>" }

Skwir types it by its name (the extension) and bytes, as any file.
It must fit one message: about 48 MB once in base64.
Skwir caches it in the plugin's cache folder under the file's version and the plugin's, and asks again only when either changes.
The file's own views stay its own: View as hex shows the original's bytes, not the converted file's.
A link in it is followed only when the plugin has network; otherwise a click could carry away what it read.

`page`

For a preview declared with pages = true: the file shown a page at a time, each page a picture the plugin draws when shown, with its text where it lies (a document format Skwir does not read, a file of several pictures). Skwir reads it in its own reader, as a PDF: pages scrolled or turned, zoomed, text selected, copied and searched, links followed, outline listed.

{ "file": { … }, "page": 2, "side": 2048, "text": true }

Field	Default
`page`	required	From 1.
`side`	required	Longest side to draw at, in pixels. 0 asks no picture: only the page count, or a page's text (a search reads text without drawing).
`text`	false	Asks the page's text and links too.

Answer null (nothing to show for this file), or:

{ "pages": 12,
  "png": "<base64>",
  "width": 612, "height": 792,
  "text": [ { "text": "Chapter one", "x": 0.1, "y": 0.08, "width": 0.4, "height": 0.03,
              "edges": [0.1, 0.13, 0.16, …] } ],
  "links": [ { "x": 0.1, "y": 0.9, "width": 0.2, "height": 0.03, "page": 3 },
             { "x": 0.5, "y": 0.9, "width": 0.3, "height": 0.03, "uri": "https://example.com/" } ],
  "outline": [ { "title": "Chapter one", "depth": 0, "page": 1 } ] }

Every field but pages may be left out.

Field
`pages`	How many pages the file has.
`png`	The page drawn; null past the last page, or when `side` is 0.
`width`, `height`	The page's own size in CSS pixels (1/96 inch): what 100% shows. Default: the picture's size.
`text`	Runs (a word, a line) in reading order. `x`, `y`, `width`, `height` are the run's box as fractions of the page's width and height, from its top left. Optional `edges`: where each character starts, as a fraction of the page's width, one per character, so a selection follows each glyph; without them each character is an equal part of its run.
`links`	A box (as for runs) and where it leads: `page` (from 1) of this file, or `uri`.
`outline`	The file's headings: `title`, `depth` (0 at the top, default 0), `page` it starts on (optional).

Skwir joins two runs on one line with a space and lines with a line break, and searches the text case-insensitively.
An address link is followed only when the plugin has network; otherwise the panel says why.
The outline is the file's, the same for any page: Skwir reads it once, with the page count.
Skwir caches what it is answered in the plugin's cache folder, under the file's version and the plugin's: the page count and outline, each page's picture by side, and its text and links separately. Nothing is asked twice.
With converts too, Skwir asks convert first and reads in pages a file convert answers null for. The Netpbm plugin converts a single picture to PNG and shows a file of several one picture a page.

`command`

{ "command": "word-count.count", "args": { }, "entries": [ { "handle": 1, … } ] }

command is one of the manifest's command names; args follows its schema (default null); entries are the files it acts on, those its caller named, else a pane's selection (default []). Answer one of:

{ "answer": "done" }
{ "answer": "value", "value": { "total": 9 } }
{ "answer": "text", "text": "…", "said": "Copied 3 paths" }
{ "answer": "plan", "title": "Rename by date", "note": null,
  "steps": [ { "op": "rename", "file": 1, "name": "2026-10-07.txt" },
             { "op": "trash", "file": 2 },
             { "op": "move", "file": 3, "to": "/home/a/Archive" },
             { "op": "copy", "file": 4, "to": "/home/a/Archive" },
             { "op": "mkdir", "path": "/home/a/Archive" } ] }

Answer	Meaning
`done`	Nothing to report.
`value`	A value for the caller (a script, an agent).
`text`	Text for the clipboard; `said` is what Skwir says once it is there.
`plan`	A plan the caller applies or proposes. Needs the `write` capability. `note` is optional.

A step's file is a handle of the call's files: rename gives it name in its folder, trash trashes it, move and copy put it into the folder to. mkdir makes the folder path. to and path are absolute.

`$/cancel` (program only, notification)

{ "id": 7 }

Skwir stopped waiting for call 7; its read requests are refused from then on.

The plugin asks

`read`

{ "file": 1, "offset": 0, "length": 65536 }

Answered { "data": "<base64>" }: at most 4 MiB (READ_LIMIT; a longer length is cut to it), fewer at the file's end. Refused for a handle that is not a file of the call being answered, after $/cancel, and for a plugin without the read capability.

`log` (notification)

{ "level": "warn", "message": "…" }

level is error, warn, info or debug.

Errors

A JSON-RPC error's message (for a module, the error call returns) is what Skwir reports: a preview shows it where the page would be; a command's caller receives it. Skwir does not read the code; its own errors and the Rust guest's use -32000. A request to Skwir for a method other than read is answered with an error.

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