# Handling HTTP/3 Requests with Scrapling's Fetcher Class: A Complete Guide

> Learn to handle HTTP/3 requests with Scrapling's Fetcher class. This guide shows you how to easily enable HTTP/3 for faster web scraping.

- Repository: [Karim shoair/Scrapling](https://github.com/D4Vinci/Scrapling)
- Tags: how-to-guide
- Published: 2026-03-08

---

**Scrapling enables HTTP/3 requests through the optional `http3` parameter in the `Fetcher` and `AsyncFetcher` classes, which internally configures curl-cffi to use `CurlHttpVersion.V3ONLY`.**

Scrapling is a Python web scraping library built on top of **curl-cffi**, providing high-level abstractions through its `Fetcher` and `AsyncFetcher` classes. When handling HTTP/3 requests with Scrapling's Fetcher class, developers can leverage the optional `http3` flag to force HTTP/3-only connections, though this requires understanding the internal configuration flow from session initialization through to the actual curl execution.

## How HTTP/3 Support Works in Scrapling

Scrapling's HTTP client architecture delegates protocol handling to curl-cffi, with HTTP/3 support controlled through a cascading configuration system.

### The http3 Configuration Flag

The `http3` parameter is defined as an optional boolean throughout the codebase. In [`scrapling/engines/_browsers/_types.py`](https://github.com/D4Vinci/Scrapling/blob/main/scrapling/engines/_browsers/_types.py) (line 32), the `RequestsSession` TypedDict declares `http3: Optional[bool]`, making the flag part of the type-checked API. This parameter propagates from high-level fetcher classes down to the static engine that interfaces with curl-cffi.

### Internal Implementation Details

The actual HTTP/3 activation occurs in [`scrapling/engines/static.py`](https://github.com/D4Vinci/Scrapling/blob/main/scrapling/engines/static.py) through three key phases:

1. **Session Initialization** (lines 71-84): The `__init__` method stores `self._default_http3` from the `http3` kwarg, establishing the session-wide default.

2. **Argument Merging** (lines 104-108): The `_merge_request_args` method reads a request-level `http3` flag, falling back to the session default if not provided.

3. **Curl Version Switch** (lines 156-162): When `http3` is truthy, the code injects `http_version = CurlHttpVersion.V3ONLY` into the arguments passed to curl-cffi. This section also emits a warning if `impersonate` is active, as some sites reject HTTP/3 when custom browser headers are generated.

## Enabling HTTP/3 in Your Code

Scrapling provides multiple patterns for activating HTTP/3 depending on your architecture needs.

### Session-Level Configuration

For applications requiring HTTP/3 across multiple requests, configure the session once using `FetcherSession`:

```python
from scrapling.fetchers.requests import FetcherSession

# All requests inside this context will use HTTP/3

with FetcherSession(http3=True) as sess:
    resp = sess.get("https://http3.tech")
    print(resp.status_code, resp.http_version)   # → 200, "HTTP/3"

```

This approach stores the `http3=True` default in [`scrapling/engines/static.py`](https://github.com/D4Vinci/Scrapling/blob/main/scrapling/engines/static.py) and applies it to every request made through that session instance.

### Per-Request Overrides

When you need HTTP/3 only for specific calls while maintaining standard HTTP/1.1 or HTTP/2 for others:

```python
from scrapling.fetchers.requests import FetcherSession

with FetcherSession() as sess:                     # default: HTTP/1.1/2

    # Normal request – no HTTP/3

    r1 = sess.get("https://example.com")
    print(r1.http_version)                       # e.g. "HTTP/2"

    # Force HTTP/3 just for this call

    r2 = sess.get("https://http3.tech", http3=True)
    print(r2.http_version)                       # "HTTP/3"

```

The `_merge_request_args` method in [`scrapling/engines/static.py`](https://github.com/D4Vinci/Scrapling/blob/main/scrapling/engines/static.py) handles this fallback logic, checking for a request-level `http3` parameter before defaulting to the session configuration.

### Using the Fetcher Facade

For quick scripts or single requests, use the low-level `Fetcher` class directly:

```python
from scrapling.fetchers.requests import Fetcher

# Fetcher is a thin wrapper around a global SyncSession instance

resp = Fetcher.get("https://http3.tech", http3=True)
print(resp.http_version)      # "HTTP/3"

```

This approach bypasses explicit session management while still supporting the `http3` parameter through the same underlying mechanism in [`scrapling/engines/static.py`](https://github.com/D4Vinci/Scrapling/blob/main/scrapling/engines/static.py).

## Important Considerations and Warnings

### HTTP/3 and Browser Impersonation Conflicts

When combining `http3=True` with the `impersonate` parameter (which generates browser-like headers), Scrapling emits a warning from [`scrapling/engines/static.py`](https://github.com/D4Vinci/Scrapling/blob/main/scrapling/engines/static.py) (lines 156-162). Some servers reject HTTP/3 connections when they detect mismatched or custom browser headers, potentially causing connection errors.

```python
import logging
logging.basicConfig(level=logging.WARNING)

from scrapling.fetchers.requests import FetcherSession

with FetcherSession(http3=True, impersonate="chrome") as sess:
    sess.get("https://http3.tech")

# → WARNING: The argument `http3` might cause errors if used with `impersonate` argument...

```

**Recommendation:** Disable impersonation (`impersonate=False`) when you need reliable HTTP/3 connectivity, or test thoroughly against your target site to verify compatibility.

## Summary

- Scrapling supports HTTP/3 through the optional `http3` boolean parameter in `Fetcher`, `AsyncFetcher`, and `FetcherSession` classes.
- The flag propagates through [`scrapling/engines/static.py`](https://github.com/D4Vinci/Scrapling/blob/main/scrapling/engines/static.py), where `_merge_request_args` injects `CurlHttpVersion.V3ONLY` when HTTP/3 is enabled.
- Configure HTTP/3 at the session level for consistency across requests, or override per-request for selective usage.
- Avoid combining `http3=True` with `impersonate` unless you have verified server compatibility, as this triggers warnings and potential connection failures.

## Frequently Asked Questions

### Does Scrapling support HTTP/3 by default?

No, HTTP/3 is disabled by default in Scrapling. You must explicitly set `http3=True` either when creating a `FetcherSession` or on individual request methods. The default behavior uses HTTP/1.1 or HTTP/2 depending on server support and curl-cffi's negotiation.

### Can I use HTTP/3 with browser impersonation?

While technically possible, combining `http3=True` with the `impersonate` parameter is not recommended. According to the implementation in [`scrapling/engines/static.py`](https://github.com/D4Vinci/Scrapling/blob/main/scrapling/engines/static.py), this combination triggers a warning because some servers reject HTTP/3 connections when they detect custom browser headers. For reliable HTTP/3 requests, disable impersonation by setting `impersonate=False`.

### How do I check if a response used HTTP/3?

The response object returned by Scrapling's fetcher methods includes an `http_version` attribute. After making a request with `http3=True`, inspect `response.http_version` to verify the protocol. A successful HTTP/3 connection will return the string `"HTTP/3"` or similar, depending on how curl-cffi reports the version.

### Is HTTP/3 available in AsyncFetcher?

Yes, the `AsyncFetcher` class supports the same `http3` parameter as the synchronous `Fetcher`. The underlying `FetcherSession` and `AsyncFetcherSession` classes in [`scrapling/fetchers/requests.py`](https://github.com/D4Vinci/Scrapling/blob/main/scrapling/fetchers/requests.py) both expose the `http3` argument, which propagates to the same `_merge_request_args` logic in [`scrapling/engines/static.py`](https://github.com/D4Vinci/Scrapling/blob/main/scrapling/engines/static.py) for protocol negotiation.