Upload max of 5 active requests at a time

Closes #9

datasette_paste/templates/paste_create_table.html

@@ -245,37 +245,23 @@ <h1>Paste data to create a table</h1>
 contentTa.addEventListener('keyup', limited);
 limited();
 
-form.onsubmit = function(event) {
-  event.preventDefault();
-  const table = document.getElementById('id_table_name').value.trim();
-  if (!table) {
-    alert('Please enter a table name');
-    return;
-  }
-  const content = document.getElementById('id_content').value.trim();
-  if (!content) {
-    alert('Please paste some content');
-    return;
-  }
-  if (!currentRows.length) {
-    alert('No rows found in content');
-    return;
-  }
-  progressBar.style.display = 'block';
-  progressBar.value = 0;
-  progressBar.max = currentRows.length;
-  // Submit to API in batches of 100
-  const url = window.location.pathname.replace('/-/paste', '/-/create');
-  const headers = new Headers();
-  headers.append('Content-Type', 'application/json');
-  const batchSize = 100;
-  for (let i = 0; i < currentRows.length; i += batchSize) {
-    const batch = currentRows.slice(i, i + batchSize);
+const batchSize = 100;
+const numParallel = 5;
+
+async function uploadRows(rows, url, headers, table, progressBar) {
+  let activeRequests = 0;
+  for (let i = 0; i < rows.length; i += batchSize) {
+    const batch = rows.slice(i, i + batchSize);
+    while (activeRequests >= numParallel) {
+      await new Promise(resolve => setTimeout(resolve, 25));
+    }
+    activeRequests++;
     fetch(url, {
       method: 'POST',
       headers: headers,
       body: JSON.stringify({table: table, rows: batch})
     }).then(response => {
+      activeRequests--;
       if (!response.ok) {
         throw new Error('Failed to upload rows: ' + response.statusText);
       }
@@ -290,9 +276,36 @@ <h1>Paste data to create a table</h1>
         alert('Error uploading rows: ' + json.error);
       }
     }).catch(error => {
+      activeRequests--;
       alert('Error uploading rows: ' + error);
     });
   }
+}
+
+form.onsubmit = function(event) {
+  event.preventDefault();
+  const table = document.getElementById('id_table_name').value.trim();
+  if (!table) {
+    alert('Please enter a table name');
+    return;
+  }
+  const content = document.getElementById('id_content').value.trim();
+  if (!content) {
+    alert('Please paste some content');
+    return;
+  }
+  if (!currentRows.length) {
+    alert('No rows found in content');
+    return;
+  }
+  progressBar.style.display = 'block';
+  progressBar.value = 0;
+  progressBar.max = currentRows.length;
+  // Submit to API in batches
+  const url = window.location.pathname.replace('/-/paste', '/-/create');
+  const headers = new Headers();
+  headers.append('Content-Type', 'application/json');
+  uploadRows(currentRows, url, headers, table, progressBar);
 };
 
 function parseJsonArray(string) {