previews exported files, adds preview tests

src/preview.ts

@@ -4,7 +4,7 @@ import type {FSWatcher, WatchEventType} from "node:fs";
 import {access, constants} from "node:fs/promises";
 import {createServer} from "node:http";
 import type {IncomingMessage, RequestListener, Server, ServerResponse} from "node:http";
-import {basename, dirname, join, normalize} from "node:path/posix";
+import {basename, dirname, extname, join, normalize} from "node:path/posix";
 import {difference} from "d3-array";
 import type {PatchItem} from "fast-array-diff";
 import {getPatch} from "fast-array-diff";
@@ -184,6 +184,8 @@ export class PreviewServer {
       } else {
         if ((pathname = normalize(pathname)).startsWith("..")) throw new Error("Invalid path: " + pathname);
 
+        const ext = extname(pathname).replace(/^\.html$/, "");
+
         // Normalize the pathname (e.g., adding ".html" or removing ".html"
         // based on preserveExtension) and redirect if necessary.
         const normalizedPathname = encodeURI(config.normalizePath(pathname));
@@ -197,7 +199,7 @@ export class PreviewServer {
         // request represents a JavaScript embed (such as /chart.js), and takes
         // precedence over any page (such as /chart.js.md). Generate a wrapper
         // module that allows this JavaScript module to be embedded remotely.
-        if (pathname.endsWith(".js")) {
+        if (ext === ".js") {
           try {
             end(req, res, await renderModule(root, pathname), "text/javascript");
             return;
@@ -206,6 +208,20 @@ export class PreviewServer {
           }
         }
 
+        // If an export asset (such as /robots.txt or /embed/[param].svg) exists
+        // for this path, send it. It takes priority over a page robots.txt.md.
+        if (ext && ext !== ".md") {
+          const file = loaders.find(pathname);
+          if (file) {
+            try {
+              send(req, join(root, await file.load())).pipe(res);
+              return;
+            } catch (error) {
+              if (!isEnoent(error)) throw error;
+            }
+          }
+        }
+
         // If this path ends with a slash, then add an implicit /index to the
         // end of the path. Otherwise, remove the .html extension (we use clean
         // paths as the internal canonical representation; see normalizePage).

test/preview/dashboard/asset.txt.ts

@@ -0,0 +1 @@
+process.stdout.write(`Built by ${import.meta.url}`);

test/preview/dashboard/robots.txt

@@ -0,0 +1,2 @@
+User-agent: *
+Disallow: /

test/preview/preview-test.ts

@@ -48,7 +48,11 @@ describe("preview server", () => {
     expect(res.text).to.have.string("This text is not visible by default.");
   });
 
-  // TODO - tests for /_observablehq and data loader requests
+  it("serves scripts from _observablehq/", async () => {
+    const res = await chai.request(testServerUrl).get("/_observablehq/stdlib.js");
+    expect(res).to.have.status(200);
+    expect(res.text).to.have.string("function FileAttachment");
+  });
 
   it("serves local imports", async () => {
     const res = await chai.request(testServerUrl).get("/_import/format.js");
@@ -68,9 +72,27 @@ describe("preview server", () => {
     assert.ok(res.text);
   });
 
+  it("serves files built with a data loader", async () => {
+    const res = await chai.request(testServerUrl).get("/_file/asset.txt");
+    expect(res).to.have.status(200);
+    expect(res.text).to.have.string("Built by");
+  });
+
   it("handles missing files", async () => {
     const res = await chai.request(testServerUrl).get("/_file/idontexist.csv");
     expect(res).to.have.status(404);
     expect(res.text).to.have.string("File not found");
   });
+
+  it("serves exported files", async () => {
+    const res = await chai.request(testServerUrl).get("/robots.txt");
+    expect(res).to.have.status(200);
+    expect(res.text).to.have.string("User-agent:");
+  });
+
+  it("serves exported files built with a data loader", async () => {
+    const res = await chai.request(testServerUrl).get("/asset.txt");
+    expect(res).to.have.status(200);
+    expect(res.text).to.have.string("Built by");
+  });
 });