P2P Download

What is P2P Download?

P2P downloads let you receive a real-time notification the moment a file is downloaded in your browser session, then fetch the file directly from the active session — no polling, no waiting for Anchor to process the file, no storage APIs required.

How It Works

Traditional downloads:

Browser downloads file → Anchor stores the file → You poll GET /downloads → Fetch from Anchor storage

P2P downloads:

Browser downloads file → Anchor.downloadReady CDP event fires → You fetch directly from the browser

When a file is downloaded, the browser emits a custom CDP event (Anchor.downloadReady) over your existing WebSocket connection. The event includes a pre-built fetch URL that streams the file bytes directly from the browser’s disk.

Implementation

Connect to the session and listen for the CDP event

Connect Playwright over CDP as usual, then open a CDPSession on the page to listen for the Anchor.downloadReady event.

import { chromium } from "playwright";
import AnchorBrowser from "anchorbrowser";
import fs from "fs";

const { ANCHOR_API_KEY } = process.env;
const client = new AnchorBrowser({ apiKey: ANCHOR_API_KEY });

const session = await client.sessions.create();
const { cdp_url, id: sessionId } = session.data;

const browser = await chromium.connectOverCDP(cdp_url);
const page = browser.contexts()[0].pages()[0];

const cdpSession = await page.context().newCDPSession(page);

const downloadReady = new Promise((resolve) => {
  cdpSession.on("Anchor.downloadReady", (params) => resolve(params));
});

import os
from playwright.sync_api import sync_playwright
from anchorbrowser import Anchorbrowser

ANCHOR_API_KEY = os.getenv("ANCHOR_API_KEY")
client = Anchorbrowser(api_key=ANCHOR_API_KEY)

session = client.sessions.create()
cdp_url = session.data["cdp_url"]

with sync_playwright() as p:
    browser = p.chromium.connect_over_cdp(cdp_url)
    page = browser.contexts[0].pages[0]
    cdp_session = page.context.new_cdp_session(page)

    download_params = {}

    def on_download_ready(params):
        download_params.update(params)

    cdp_session.on("Anchor.downloadReady", on_download_ready)

Trigger the download

Use Playwright as normal to navigate and click the download link.

await page.goto("https://example.com/reports");
await page.click("#download-report");

with sync_playwright() as p:
    browser = p.chromium.connect_over_cdp(cdp_url)
    page = browser.contexts[0].pages[0]
    page.goto("https://example.com/reports")
    page.click("#download-report")

Receive the event and fetch the file

Wait for the Anchor.downloadReady event, then use the p2pDownloadUrl from the event params to fetch the file.

// Wait for the download event
const event = await downloadReady;

console.log(`Download ready: ${event.suggestedFilename} (${event.size} bytes)`);

// Fetch the file directly from the session
const response = await fetch(
  `https://api.anchorbrowser.io${event.p2pDownloadUrl}`,
  { headers: { "anchor-api-key": ANCHOR_API_KEY } }
);

fs.writeFileSync(
  event.suggestedFilename,
  Buffer.from(await response.arrayBuffer())
);

console.log(`Saved ${event.suggestedFilename}`);
await browser.close();

import requests, time

# Wait for the download event (up to 15 seconds)
timeout = 15
start = time.time()
while not download_params and time.time() - start < timeout:
    time.sleep(0.1)

params = download_params
print(f"Download ready: {params['suggestedFilename']} ({params['size']} bytes)")

# Fetch the file directly from the session
response = requests.get(
    f"https://api.anchorbrowser.io{params['p2pDownloadUrl']}",
    headers={"anchor-api-key": ANCHOR_API_KEY},
    stream=True,
)

with open(params["suggestedFilename"], "wb") as f:
    for chunk in response.iter_content(chunk_size=8192):
        f.write(chunk)

print(f"Saved {params['suggestedFilename']}")

The `Anchor.downloadReady` Event

The event is emitted on the CDP WebSocket connection as soon as the file lands on disk.

{
  "method": "Anchor.downloadReady",
  "params": {
    "localDownloadId": "4e901615-5f83-4773-a1af-773e15a19be8",
    "suggestedFilename": "report.pdf",
    "url": "https://example.com/report.pdf",
    "originUrl": "https://example.com/reports",
    "size": 1048576,
    "duration": 2300,
    "p2pDownloadUrl": "/v1/sessions/{sessionId}/downloads/{localDownloadId}/p2p"
  }
}

Field	Description
`localDownloadId`	Unique ID for this download, valid for the lifetime of the session
`suggestedFilename`	The filename as suggested by the browser
`url`	The URL the file was downloaded from
`originUrl`	The page URL where the download was triggered
`size`	File size in bytes
`duration`	Time to complete the download in milliseconds
`p2pDownloadUrl`	Relative URL to fetch the file — prepend your API base URL

Fetch Endpoint

GET /v1/sessions/:session_id/downloads/:local_download_id/p2p

This endpoint streams the file directly from the active session. It is only available while the session is active. Once the session ends, use the standard session downloads API to retrieve files from Anchor storage.

Status	Meaning
`200`	File streamed successfully
`404`	`local_download_id` not found (may have expired with the session)
`410`	Session is no longer active — use the standard `/downloads/:id/fetch` instead

Limitations

The P2P fetch URL is only valid while the session is running. After the session ends, the file is no longer accessible via this endpoint.
Files are still stored by Anchor in the background as a fallback. Once the session completes, they are accessible via the standard list session downloads API.
Blob and data URL downloads (files generated client-side in JavaScript) are supported.

Introduction

Platform

Integrations

Account

What is P2P Download?

How It Works

Implementation

The `Anchor.downloadReady` Event

Fetch Endpoint

Limitations

​What is P2P Download?

​How It Works

​Implementation

​The Anchor.downloadReady Event

​Fetch Endpoint

​Limitations

What is P2P Download?

How It Works

Implementation

The `Anchor.downloadReady` Event

Fetch Endpoint

Limitations