Export table schema (#459)

* add endpoint
* Add table-schema transformation data

test/server/lib/DocApi.ts

@@ -2138,6 +2138,62 @@ function testDocApi() {
     assert.deepEqual(resp.data, { error: 'tableId parameter should be a string: undefined' });
   });
 
+  it("GET /docs/{did}/download/table-schema serves table-schema-encoded document", async function() {
+    const resp = await axios.get(`${serverUrl}/api/docs/${docIds.TestDoc}/download/table-schema?tableId=Foo`, chimpy);
+    assert.equal(resp.status, 200);
+    const expected = {
+      format: "csv",
+      mediatype: "text/csv",
+      encoding: "utf-8",
+      dialect: {
+        delimiter: ",",
+        doubleQuote: true,
+      },
+      name: 'foo',
+      title: 'Foo',
+      schema: {
+        fields: [{
+          name: 'A',
+          type: 'string',
+          format: 'default',
+        }, {
+          name: 'B',
+          type: 'string',
+          format: 'default',
+        }]
+      }
+    };
+    assert.deepInclude(resp.data, expected);
+
+    const resp2 = await axios.get(resp.data.path, chimpy);
+    assert.equal(resp2.status, 200);
+    assert.equal(resp2.data, 'A,B\nSanta,1\nBob,11\nAlice,2\nFelix,22\n');
+  });
+
+  it("GET /docs/{did}/download/table-schema respects permissions", async function() {
+    // kiwi has no access to TestDoc
+    const resp = await axios.get(`${serverUrl}/api/docs/${docIds.TestDoc}/download/table-schema?tableId=Table1`, kiwi);
+    assert.equal(resp.status, 403);
+    assert.deepEqual(resp.data, {"error":"No view access"});
+  });
+
+  it("GET /docs/{did}/download/table-schema returns 404 if tableId is invalid", async function() {
+    const resp = await axios.get(
+      `${serverUrl}/api/docs/${docIds.TestDoc}/download/table-schema?tableId=MissingTableId`,
+      chimpy,
+    );
+    assert.equal(resp.status, 404);
+    assert.deepEqual(resp.data, { error: 'Table MissingTableId not found.' });
+  });
+
+  it("GET /docs/{did}/download/table-schema returns 400 if tableId is missing", async function() {
+    const resp = await axios.get(
+      `${serverUrl}/api/docs/${docIds.TestDoc}/download/table-schema`, chimpy);
+    assert.equal(resp.status, 400);
+    assert.deepEqual(resp.data, { error: 'tableId parameter should be a string: undefined' });
+  });
+
+
   it("GET /docs/{did}/download/xlsx serves XLSX-encoded document", async function() {
     const resp = await axios.get(`${serverUrl}/api/docs/${docIds.Timesheets}/download/xlsx?tableId=Table1`, chimpy);
     assert.equal(resp.status, 200);