formatitko/katex-server/index.mjs

// KaTeX rendering server
// Listens on unix socket, path is provided as first argument
// Expects JSON lines, each line is a query with the following schema:
// {
//   formulas: [
//     {
//       tex: string,
//       options?: object
//     }
//   ],
//   options?: object
// }

// see https://katex.org/docs/options.html for list of available options
// If options formulas[].options field is used, the global options field is ignored.

// For each line, returns one JSON line with the following schema:
// {
//   results: [
//     { html?: string } | { error?: string }
//   ]
// } | { error?: string }


// If one formula is invalid, the error in results is used
// If the entire query is invalid (couldn't parse JSON, for example), the outer error field is used


import katex from 'katex'
import net from 'net'
import * as readline from 'readline'

const myArgs = process.argv.slice(2)

const unixSocketPath = myArgs[0]
if (!unixSocketPath) {
    console.error('you must specify socket path')
    process.exit(1)
}

// This server listens on a Unix socket at /var/run/mysocket
var unixServer = net.createServer(handleClient);
unixServer.listen(unixSocketPath);

function handleExit(signal) {
    // unixServer.emit('close')
    unixServer.close(function () {

    });
    process.exit(0); // put this into the callback to avoid closing open connections
}
process.on('SIGINT', handleExit);
process.on('SIGQUIT', handleExit);
process.on('SIGTERM', handleExit);
process.on('exit', handleExit);

const defaultOptions = {}

/**
 * @param {net.Socket} socket
 * @returns {Promise<void>}
 * */
function socketWrite(socket, data) {
    return new Promise((resolve, reject) => {
        socket.write(data, (err) => {
            if (err) {
                reject(err)
            } else {
                resolve()
            }
        })
    })
}

/**
 * @param {net.Socket} client
 * */
async function handleClient(client) {
    const rl = readline.createInterface({ input: client })
    
    /* Added by GS: A stack of katex's `macros` objects, each group inherits
     * the one from the parent group and can add its own stuff without
     * affecting the parent.
     */
    const macroStack = [{}]
    for await (const line of rl) {
        try {
            // The custom commands for pushing and popping the macro stack.
            if (line === "begingroup") {
                // Copy the current state of macros and push it onto the stack.
                macroStack.push({...macroStack.slice(-1)[0]})
                continue
            } else if (line === "endgroup") {
                macroStack.pop()
                continue
            }
            const query = JSON.parse(line)
            const results = []
            for (const input of query.formulas) {
                const options = input.options ?? query.options ?? defaultOptions
                // Add macros from the macros option
                if (options.macros) {
                    for (const macro of Object.keys(options.macros)) {
                        macroStack.slice(-1)[macro] = options.macros[macro]
                    }
                }
                options.macros = macroStack.slice(-1)[0]
                // Enforce globalGroup option, katex then saves created macros
                // into the options.macros object.
                options.globalGroup = true
                try {
                    const html = katex.renderToString(input.tex, options)
                    results.push({ html })
                } catch (e) {
                    results.push({ error: String(e) })
                }
            }
            await socketWrite(client, JSON.stringify({ results }, null, query.debug ? '  ' : undefined))
            await socketWrite(client, '\n')
        } catch (e) {
            console.error(e)
            await socketWrite(client, JSON.stringify({ error: String(e) }))
            await socketWrite(client, '\n')
        }
    }
}