Using ST_AsMVT() and ST_AsMVTGeom() in express to build a vector tile endpoint

gistfile1.txt

/* GET /tiles/:z/:x/:y.mvt */
/* Retreive a vector tile by tileid */
router.get('/tiles/:z/:x/:y.mvt', async (req, res) => {
  const { z, x, y } = req.params;

  // calculate the bounding polygon for this tile 
  const bbox = mercator.bbox(x, y, z, false);

  // Query the database, using ST_AsMVTGeom() to clip the geometries
  // Wrap the whole query with ST_AsMVT(), which will create a protocol buffer
  const SQL = `
    SELECT ST_AsMVT(q, 'internal-layer-name', 4096, 'geom')
    FROM (
      SELECT
          somecolumn,
          ST_AsMVTGeom(
              geom,
              ST_MakeEnvelope(${bbox[0]}, ${bbox[1]}, ${bbox[2]}, ${bbox[3]}, 4326),
              4096,
              256,
              false
          ) geom
      FROM sometable c
    ) q
  `;

  try {
    const tile = await db.one(SQL);

    // set the response header content type
    res.setHeader('Content-Type', 'application/x-protobuf');

    // trigger catch if the vector tile has no data, (return a 204)
    if (tile.st_asmvt.length === 0) {
      res.status(204);
    }    
    
    // send the tile!
    res.send(tile.st_asmvt);
  } catch (e) {
    res.status(404).send({
      error: e.toString(),
    });
  }
});