Binary Protocol Quick Reference

Simple Explanation

Presto templates are not a bunch of files -- they are executable programs. You feed Markdown text in, and they produce typesetting code (Typst). It's that simple.

Imagine a black box: Markdown goes in on the left, Typst comes out on the right. This black box can also answer a few questions -- "Who are you?" (--manifest), "Got an example?" (--example), "What version?" (--version). The Presto application interacts with templates through these four methods and no others.

Template binaries run in a strict sandbox: 30-second timeout, no network access, no file writing, minimal environment variables. This means template code cannot steal data or cause damage.

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Protocol Quick Reference

Four Invocation Methods

Method	Command	stdin	stdout	Purpose
Convert	./binary	Markdown text	Typst code	Core function: turn Markdown into typesetting code
Metadata	./binary --manifest	None	manifest JSON	Extract template info during installation
Example	./binary --example	None	Markdown text	Showcase template output
Version	./binary --version	None	Version string	Version check and update detection

Security Constraints

Constraint	Value	Description
Execution timeout	30 seconds	Maximum time per invocation
Build timeout	300 seconds (5 minutes)	Maximum time for template build
Manifest size limit	1 MB	--manifest output limit
Example size limit	1 MB	--example output limit
Typst output limit	10 MB	Conversion output limit
Build artifact limit	50 MB	Compiled binary size limit
Environment variables	Only PATH=/usr/local/bin:/usr/bin:/bin	Minimal environment, no other variables
Network access	Prohibited	macOS sandbox-exec / Linux unshare --net
File writing	Prohibited	Output only via stdout
CLI flags	Only the four above	No additional flags beyond the protocol

Three Layers of Security

Layer	Mechanism	Purpose
Static analysis	Import blocklist	Block dangerous dependencies pre-build
Runtime sandbox	macOS sandbox-exec / Linux unshare --net	Isolate network and filesystem
Output validation	Format checking	Ensure stdout contains only valid content

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Interaction Sequence Diagram

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Detailed Explanation

1. Convert: Core Function

This is the reason templates exist. Presto passes the user's Markdown to the template binary via stdin, and the binary processes it and returns Typst source code via stdout.

Internal processing flow:

1. splitFrontmatter() -- Separate the YAML header (page configuration) from the body
2. writePageSetup() -- Generate Typst page setup code based on frontmatter fields
3. renderBody() -- Parse Markdown AST with goldmark, converting each node to Typst syntax

Key constraints:

• stdin accepts only Markdown text
• stdout must output only valid Typst source code
• Cannot read or write any files, cannot access the network
• Automatically terminated after 30 seconds

2. Metadata: --manifest

When installing a template, the first thing Presto does is call --manifest to get the template's self-description. This JSON tells Presto:

• The template's name, author, and version
• Which fonts are required
• Which frontmatter fields are supported (types, defaults, formats)

Manifest data is embedded in the binary at compile time via Go's //go:embed -- it's not generated at runtime.

3. Example: --example

Returns a sample Markdown document, used for:

• Preview display in the template store
• A starter template when users first use it
• Input data for automated testing

Also embedded via //go:embed.

4. Version: --version

Returns the version string, read from the version field of the embedded manifest.json. Used for:

• Checking if the template has updates
• Compatibility checks (in conjunction with minPrestoVersion)

5. Embedding Mechanism

Templates follow a "binary embedding model," not a "file copying model." All resources are packaged into the executable at compile time:

//go:embed manifest.json
var manifestData []byte

//go:embed example.md
var exampleData []byte

This means:

• Distribution involves only a single file, with no additional resource directories needed
• No external file dependencies at runtime, eliminating "config not found" issues
• Sandbox restrictions are easier to enforce -- the binary doesn't need to read any external files

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Complete manifest.json Example

{
  "name": "academic-paper",
  "displayName": "Academic Paper",
  "description": "A typesetting template for Chinese academic papers, supporting common structures such as abstract, keywords, and references",
  "version": "1.2.0",
  "author": "Zhang San <zhangsan@example.com>",
  "license": "MIT",
  "minPrestoVersion": "0.5.0",
  "keywords": ["academic", "paper", "Chinese", "LaTeX alternative"],
  "requiredFonts": [
    {
      "name": "NotoSerifCJKsc",
      "displayName": "Noto Serif CJK SC",
      "url": "https://github.com/notofonts/noto-cjk/releases"
    },
    {
      "name": "NotoSansCJKsc",
      "displayName": "Noto Sans CJK SC",
      "url": "https://github.com/notofonts/noto-cjk/releases"
    }
  ],
  "frontmatterSchema": {
    "title": {
      "type": "string",
      "default": "Untitled Paper"
    },
    "author": {
      "type": "string",
      "default": "Anonymous"
    },
    "date": {
      "type": "string",
      "format": "date"
    },
    "abstract": {
      "type": "string",
      "default": ""
    },
    "keywords": {
      "type": "string",
      "default": ""
    },
    "twocolumn": {
      "type": "boolean",
      "default": false
    },
    "fontsize": {
      "type": "string",
      "default": "12pt"
    },
    "papersize": {
      "type": "string",
      "default": "a4"
    },
    "margin": {
      "type": "string",
      "default": "2.5cm"
    },
    "linestretch": {
      "type": "number",
      "default": 1.5
    }
  }
}

Field descriptions:

Field	Required	Description
name	Yes	Template unique identifier, lowercase + hyphens
displayName	Yes	User-visible template name
description	Yes	Template purpose description
version	Yes	Semantic version number (semver)
author	Yes	Author information
license	Yes	Open source license
minPrestoVersion	Yes	Minimum compatible Presto version
keywords	No	Search keywords
requiredFonts	No	List of required fonts
frontmatterSchema	Yes	User-configurable frontmatter field definitions

Supported type values in frontmatterSchema:

type	Description	Example default
"string"	Text	"Untitled Paper"
"number"	Number	1.5
"boolean"	Boolean	false

The optional format field hints at UI rendering (e.g., "date" will display a date picker).