feat: Fetch style from url (#1462)

* made the serve_style.add and addStyle functions async and return promises

* added fetching to addStyle() function and parsed it into serve_style and serve_rendered

* fixed linting issues

* removed async from synchronous functions

* added fetch example to docs

docs/config.rst

@@ -57,6 +57,9 @@ Example:
         "tilejson": {
           "format": "webp"
         }
+      },
+      "remote": {
+        "style": "https://demotiles.maplibre.org/style.json"
       }
     },
     "data": {
@@ -209,7 +212,7 @@ Not used by default.
 
 Each item in this object defines one style (map). It can have the following options:
 
-* ``style`` -- name of the style json file [required]
+* ``style`` -- name of the style json file or url of a remote hosted style [required]
 * ``serve_rendered`` -- whether to render the raster tiles for this style or not
 * ``serve_data`` -- whether to allow access to the original tiles, sprites and required glyphs
 * ``tilejson`` -- properties to add to the TileJSON created for the raster data

src/serve_rendered.js

@@ -1027,10 +1027,19 @@ export const serve_rendered = {
    * @param {object} params Parameters object.
    * @param {string} id ID of the item.
    * @param {object} programOpts - An object containing the program options
+   * @param {object} style pre-fetched/read StyleJSON object.
    * @param {Function} dataResolver Function to resolve data.
    * @returns {Promise<void>}
    */
-  add: async function (options, repo, params, id, programOpts, dataResolver) {
+  add: async function (
+    options,
+    repo,
+    params,
+    id,
+    programOpts,
+    style,
+    dataResolver,
+  ) {
     const map = {
       renderers: [],
       renderersStatic: [],
@@ -1040,7 +1049,7 @@ export const serve_rendered = {
 
     const { publicUrl, verbose } = programOpts;
 
-    let styleJSON;
+    const styleJSON = clone(style);
     /**
      * Creates a pool of renderers.
      * @param {number} ratio Pixel ratio
@@ -1229,12 +1238,6 @@ export const serve_rendered = {
 
     const styleFile = params.style;
     const styleJSONPath = path.resolve(options.paths.styles, styleFile);
-    try {
-      styleJSON = JSON.parse(await fsp.readFile(styleJSONPath));
-    } catch (e) {
-      console.log('Error parsing style file');
-      return false;
-    }
 
     if (styleJSON.sprite) {
       if (!Array.isArray(styleJSON.sprite)) {

src/serve_style.js

@@ -196,9 +196,10 @@ export const serve_style = {
    * @param {object} params Parameters object containing style path
    * @param {string} id ID of the style.
    * @param {object} programOpts - An object containing the program options
+   * @param {object} style pre-fetched/read StyleJSON object.
    * @param {Function} reportTiles Function for reporting tile sources.
    * @param {Function} reportFont Function for reporting font usage
-   * @returns {boolean} true if add is succesful
+   * @returns {boolean} true if add is successful
    */
   add: function (
     options,
@@ -206,21 +207,14 @@ export const serve_style = {
     params,
     id,
     programOpts,
+    style,
     reportTiles,
     reportFont,
   ) {
     const { publicUrl } = programOpts;
     const styleFile = path.resolve(options.paths.styles, params.style);
+    const styleJSON = clone(style);
 
-    let styleFileData;
-    try {
-      styleFileData = fs.readFileSync(styleFile); // TODO: could be made async if this function was
-    } catch (e) {
-      console.log(`Error reading style file "${params.style}"`);
-      return false;
-    }
-
-    const styleJSON = JSON.parse(styleFileData);
     const validationErrors = validateStyleMin(styleJSON);
     if (validationErrors.length > 0) {
       console.log(`The file "${params.style}" is not a valid style file:`);

src/server.js

@@ -178,10 +178,29 @@ async function start(opts) {
    * @param {object} item - The style configuration object.
    * @param {boolean} allowMoreData - Whether to allow adding more data sources.
    * @param {boolean} reportFonts - Whether to report fonts.
-   * @returns {void}
+   * @returns {Promise<void>}
    */
-  function addStyle(id, item, allowMoreData, reportFonts) {
+  async function addStyle(id, item, allowMoreData, reportFonts) {
     let success = true;
+
+    let styleJSON;
+    try {
+      if (isValidHttpUrl(item.style)) {
+        const res = await fetch(item.style);
+        if (!res.ok) {
+          throw new Error(`fetch error ${res.status}`);
+        }
+        styleJSON = await res.json();
+      } else {
+        const styleFile = path.resolve(options.paths.styles, item.style);
+        const styleFileData = await fs.promises.readFile(styleFile);
+        styleJSON = JSON.parse(styleFileData);
+      }
+    } catch (e) {
+      console.log(`Error getting style file "${item.style}"`);
+      return false;
+    }
+
     if (item.serve_data !== false) {
       success = serve_style.add(
         options,
@@ -189,6 +208,7 @@ async function start(opts) {
         item,
         id,
         opts,
+        styleJSON,
         (styleSourceId, protocol) => {
           let dataItemId;
           for (const id of Object.keys(data)) {
@@ -246,6 +266,7 @@ async function start(opts) {
             item,
             id,
             opts,
+            styleJSON,
             function dataResolver(styleSourceId) {
               let fileType;
               let inputFile;
@@ -271,6 +292,7 @@ async function start(opts) {
         item.serve_rendered = false;
       }
     }
+    return success;
   }
 
   for (const id of Object.keys(config.styles || {})) {
@@ -279,8 +301,7 @@ async function start(opts) {
       console.log(`Missing "style" property for ${id}`);
       continue;
     }
-
-    addStyle(id, item, true, true);
+    startupPromises.push(addStyle(id, item, true, true));
   }
   startupPromises.push(
     serve_font(options, serving.fonts, opts).then((sub) => {