rex-tls

rex-tls is a Python HTTP client with a native Rust TLS and HTTP core. It offers a familiar Requests-style API and transport profiles for Android Chrome, WebView, Cronet, OkHttp, and Flutter dart:io, including persistent connections, cookies, HTTP and SOCKS5 proxies, streaming I/O, asyncio support, and bounded session pools.

The native core owns TLS handshakes, ALPN, HTTP/1.1 serialization, HTTP/2 framing, HTTP/3 over QUIC, request-header ordering, response framing, and connection reuse. Python code provides the public API and Requests-compatible objects.

Highlights

• Versioned Android Chrome 149 and 150 profiles with HTTP/1.1, HTTP/2, and HTTP/3 support.
• A versioned Android Cronet 151 profile with HTTP/1.1, HTTP/2, and HTTP/3 support.
• Versioned Android WebView 140 through 150 profiles with HTTP/1.1 and HTTP/2 support.
• Versioned OkHttp 4.12 and 5.4 profiles with HTTP/1.1 and HTTP/2 support.
• A versioned Flutter 3.47.1 / Dart 3.13.1 Android profile for the default HTTP/1.1-only dart:io HttpClient transport and Dio IO adapter.
• Five versioned Flutter iOS profiles from 3.35.7 through 3.47.1, each built, signed, captured, and validated on a physical iOS device.
• Requests-style Session.request(), method helpers, CookieJar operations, redirects, timeouts, proxies, streaming, and Response properties.
• Native connection reuse and HTTP/2 or HTTP/3 multiplexing.
• Synchronous, asynchronous, shared-state pool, and isolated-state pool APIs.
• Incremental uploads and downloads with bounded memory use.

What's new in 2.13.0

• Added five physical-device-verified Flutter iOS profiles covering Flutter 3.35.7, 3.38.10, 3.41.9, 3.44.9, and 3.47.1.
• Pinned each profile to its exact Dart runtime and verified six cold ClientHello samples per version across dart:io and Dio.
• Verified iOS AES-first cipher preference, TLS 1.2, TLS 1.3 HelloRetryRequest, certificate rejection, HTTP/1.1 Header order, connection reuse, the 15-second idle boundary, and four-way concurrency.
• Added bounded Mac automation for SDK validation, Release app signing, RVI packet capture, TLS lifecycle capture, and behavior collection.

What's new in 2.12.0

• Completed packet-level audits for Flutter Android 3.47.1 and every WebView profile from 140 through 150. WebView coverage includes main documents, same-origin and cross-origin frames, scripts, styles, images, fetch, XHR, CORS preflight, and request bodies over HTTP/1.1 and HTTP/2.
• Added separate Android Chromium ordering policies for navigation, ordinary subresources, same-site and cross-site fetch, preflight, and HTTP/3 fetch.
• Confirmed with three cold device and three native runs per Chrome version that ordinary HTTP/3 fetch does not contain Pragma or Cache-Control. Chrome and WebView profile defaults never synthesize either field.
• Corrected WebView H2 priority behavior, IP-host SNI handling, HTTP/1.1 content-type casing, Chrome caller-only Header ordering, and OkHttp's generated HTTP/1.1 Content-Type casing.
• Hardened incremental response decoding, streaming uploads and downloads, H2 reader fairness, GOAWAY handling, cancellation, and Windows pending-socket handling.
• Revalidated Chrome 149/150 H3 wire shape and six connection lifecycle scenarios, plus the complete OkHttp 4.12 and 5.4 behavior matrices.
• Expanded the Requests-style surface, including Session.request(), response cookies, mutable session cookies, streaming readers, async sessions, and HTTP/SOCKS5 proxy routing.

Custom TLS/H1/H2 configurations remain isolated from built-in profiles. Custom HTTP/3 is not supported.

Installation

python -m pip install rex-tls==2.13.0

Requirements:

The package is distributed as binary wheels. Installation on an unsupported platform fails instead of silently building a different native core from a source distribution.

Transport profiles

Aliases are explicit mappings:

Use a versioned name when an application must remain pinned to one profile. The profiles cover application-layer TLS and HTTP behavior. Operating-system IP and TCP packet fields are produced by the machine running rex-tls.

Choose the profile that matches the networking component used by the original client:

• Use chrome_android_149 or chrome_android_150 for Android Chrome browser traffic.
• Use cronet_android_151 for an Android app that sends requests through the packaged Cronet engine.
• Use webview_android_140 through webview_android_150 for the matching WebView provider. The request policies cover main documents, frames, subresources, fetch/XHR, CORS, and request bodies.
• Use okhttp_4.12 or okhttp_5.4 for an Android app that sends requests through that OkHttp version.
• Use flutter_android_3.47.1 for a Flutter Android app that uses the default dart:io HttpClient, including Dio with its default IO adapter.
• Use flutter_ios_3.35.7, flutter_ios_3.38.10, flutter_ios_3.41.9, flutter_ios_3.44.9, or flutter_ios_3.47.1 for the matching Flutter iOS transport. These are not aliases of the Android profile.
• Use profile="custom" only when the caller owns and validates a separate TLS/H1/H2 definition. It does not identify itself as a built-in profile.

Flutter Android 3.47.1

import rex_tls

with rex_tls.Session("flutter_android_3.47.1", timeout=20) as session:
    response = session.get("https://example.com/api")

print(response)
print(response.http_version)

This profile is pinned to Flutter 3.47.1 and Dart 3.13.1. The Android release probe used dart:io HttpClient; Dio 5.11.0 with its default IOHttpClientAdapter produced the same stable TLS and Header behavior.

The real client sends no ALPN and therefore uses HTTP/1.1. The profile does not claim H2 or H3, so http2=True and http3="only" are rejected. Its process-cold, warm-process, forced-new-connection, and same-connection-reuse paths were collected separately. New TLS connections remain cold and do not add a PSK extension; an open HTTP/1.1 connection is reused by sequential requests.

With no caller Headers, the lowercase wire order is user-agent, accept-encoding, then host. Dart's defaults remain present when application Headers are supplied. Ordering uses the complete Dart 3.13 Android AOT HashMap mutation history rather than Python dictionary order, including hidden framing fields and resize boundaries. HTTP CONNECT uses the same Android AOT HashMap behavior, and the TLS ClientHello inside the tunnel is identical to the direct path.

Only one case-sensitive Content-Encoding value exactly equal to gzip is decoded automatically. Uppercase, comma-list, Brotli, deflate, zstd, and unknown values remain encoded; repeated field lines fail. Flutter keeps the original Content-Encoding and Content-Length fields visible after decoding. Buffered and streaming paths also match Dart's truncated-gzip and checksum behavior. Detailed verified behavior and the evidence definition are in the Flutter Android profile document.

The profile uses Dart's 15-second idle lifetime. When max_connections_per_route is omitted, it also follows Dart's default uncapped per-host policy; pass an integer to apply an explicit bound.

Flutter iOS 3.35.7 through 3.47.1

import rex_tls

with rex_tls.Session("flutter_ios_3.47.1", timeout=20) as session:
    response = session.get("https://example.com/api")

print(response)
print(response.http_version)

The versioned iOS profiles cover Flutter 3.35.7 / Dart 3.9.2, Flutter 3.38.10 / Dart 3.10.9, Flutter 3.41.9 / Dart 3.11.5, Flutter 3.44.9 / Dart 3.12.2, and Flutter 3.47.1 / Dart 3.13.1. All use the default dart:io HttpClient. Dio 5.11.0 with IOHttpClientAdapter produces the same ClientHello and HTTP/1.1 transport behavior in every captured version.

The iOS and Android profiles share the Dart extension order, supported groups, signature algorithms, lack of ALPN, HTTP/1.1 Header rules, 15-second idle boundary, and response decoding. They are still separate because iOS prefers AES-GCM cipher suites before ChaCha20 and therefore has a different JA3.

Each version passed three cold-process dart:io samples. It also passed three cold-process Dio samples, four concurrent connections, TLS 1.2, TLS 1.3 HelloRetryRequest, certificate rejection, direct reuse, the 14/16-second idle boundary, and a service-side HTTP/1.1 Header check. The full contracts are in the Flutter iOS profile document and the five-version matrix.

The generic aliases flutter and flutter_latest continue to select the Android profile for backward compatibility. Select flutter_ios_3.47.1 explicitly for iOS.

Cronet 151

Use the exact versioned name when HTTP/3 must be required:

import rex_tls

with rex_tls.Session(
    profile="cronet_android_151",
    http3="only",
) as session:
    response = session.get(
        "https://example.com/api",
        headers={
            "X-Application-Id": "example",
            "User-Agent": "ExampleApp/1.0 Cronet/151.0.7922.83",
        },
    )

print(response.http_version)
print(response.connection_reused)

Connection reuse is exposed through Response.connection_reused.

Cronet is an application networking library, not the Android Chrome browser or Android WebView. Its profile therefore has its own default Headers and priority behavior. H1, H2, and H3 share the same Session cookie jar and connection lifecycle, while each protocol retains its audited wire order.

Android WebView 140 through 150

import rex_tls

with rex_tls.Session(profile="webview_android_144") as session:
    response = session.get("https://example.com/")

print(response.http_version)

WebView 140 through 149 have independently collected baselines with the same stable TLS fields. WebView 150 has its own signature-algorithm change. None of the profiles uses the Android Chrome or Cronet Header table. Their default navigation omits Chrome Client Hints and uses the WebView navigation order. The exact User-Agent, Accept-Language, and X-Requested-With values depend on the embedding app and runtime.

When headers is empty, rex-tls supplies the stable WebView navigation defaults but does not invent an application package for X-Requested-With. When headers is non-empty, the existing exact-header contract applies: rex-tls sorts only the fields supplied by the caller and does not add profile defaults. Pass the complete app Header set when an application-specific X-Requested-With value is required.

Controlled navigation for every supported WebView version did not attempt QUIC after authenticated Alt-Svc across three- and four-navigation sequences, so these profiles do not claim HTTP/3 support. http3="only" is rejected. The per-version evidence definition and usage notes are in the Android WebView profile document.

Caller-defined TLS and HTTP/2 profiles

Use profile="custom" when the wire configuration comes from your own tls-client or requests-go definition. A custom configuration is separate from all built-in profiles and does not claim to represent any particular browser, application, or device.

Import a tls-client configuration

import rex_tls

tls_client_config = {
    "ja3String": (
        "771,4865-4866-4867-49195-49199,"
        "0-10-11-13-16-18-27-43-45-51-17613-65037,"
        "4588-29-23-24,0"
    ),
    "supportedSignatureAlgorithms": [
        "ecdsa_secp256r1_sha256",
        "rsa_pss_rsae_sha256",
        "rsa_pkcs1_sha256",
        "ecdsa_secp384r1_sha384",
        "rsa_pss_rsae_sha384",
        "rsa_pkcs1_sha384",
        "rsa_pss_rsae_sha512",
        "rsa_pkcs1_sha512",
    ],
    "supportedVersions": ["GREASE", "1.3", "1.2"],
    "keyShareCurves": ["GREASE", "X25519MLKEM768", "X25519"],
    "alpnProtocols": ["h2", "http/1.1"],
    "alpsProtocols": ["h2"],
    "certCompressionAlgos": ["brotli"],
    "h2Settings": {
        "HEADER_TABLE_SIZE": 65536,
        "ENABLE_PUSH": 0,
        "INITIAL_WINDOW_SIZE": 6291456,
    },
    "h2SettingsOrder": [
        "HEADER_TABLE_SIZE",
        "ENABLE_PUSH",
        "INITIAL_WINDOW_SIZE",
    ],
    "connectionFlow": 15663105,
    "streamId": 1,
    "pseudoHeaderOrder": [":method", ":authority", ":scheme", ":path"],
    "headerPriority": {
        "streamDep": 0,
        "exclusive": True,
        "weight": 255,
    },
}

config = rex_tls.CustomTLSConfig.from_tls_client(
    tls_client_config,
    header_order=["accept", "host", "user-agent", "x-request-id"],
)

with rex_tls.Session(
    profile="custom",
    tls_config=config,
    http2=True,
) as session:
    response = session.get(
        "https://example.com/",
        headers={
            "X-Request-Id": "example",
            "User-Agent": "caller-owned-agent",
            "Accept": "*/*",
        },
    )
    print(response.http_version)

tls-client stores an HTTP/2 priority weight as its encoded byte. The value 255 in headerPriority therefore represents the displayed HTTP/2 weight 256. CustomTLSConfig performs that conversion automatically.

Import a requests-go configuration

import rex_tls

config = rex_tls.CustomTLSConfig.from_requests_go(requests_go_config)

with rex_tls.Session(profile="custom", tls_config=config) as session:
    response = session.request("GET", "https://example.com/")

from_requests_go() accepts a requests-go TLSConfig mapping or a stored capture document containing tls and http2 sections. It converts the requests-go HTTP/2 weight representation and preserves its extension, SETTINGS, pseudo-header, and ordinary Header order.

Custom-profile rules

• profile="custom" requires a CustomTLSConfig. Passing tls_config to a built-in profile raises an error.
• Custom profile v1 accepts HTTPS URLs only; allowHttp=True is rejected.
• Accepted custom fields are emitted by the project-owned TLS, HTTP/1.1, and HTTP/2 paths. Unknown or unsupported fields are rejected.
• The configuration is immutable. config.identifier is derived from the normalized wire configuration, and Session.profile reports a short custom: identifier.
• http2=True requires h2 in ALPN and extension 16 in the ClientHello extension list. It means that successful HTTP/2 negotiation is mandatory.
• A custom profile supplies no browser or OkHttp default Headers. The request contains the Headers provided by the caller plus protocol-required fields such as Host, Content-Length, or HTTP/2 pseudo-headers.
• header_order sorts only fields that are present; it does not add or remove caller Headers. Unlisted fields keep their relative order after listed fields. Include host when its HTTP/1.1 position matters.
• Extension 41 may be specified only as the final extension. BoringSSL emits it only when a resumable TLS session supplies a pre-shared key.
• Custom HTTP/3, delegated credentials, record-size-limit configuration, caller-provided ECH payloads, and explicit padding extension placement are not supported by custom profile v1.
• profiles() and profile_info() describe only the built-in profiles. The caller is responsible for validating a custom configuration against its intended source.

Custom profiles work with AsyncSession, HTTP and SOCKS5 proxies, shared or isolated pools, streaming requests, and streaming responses. Each pool member uses the same immutable configuration while retaining its own connection and cookie state according to the selected pool mode.

Quick start

import rex_tls

response = rex_tls.get(
    "https://example.com/",
    profile="chrome_android_150",
    params={"page": 1},
    timeout=20,
)

response.raise_for_status()
print(response.status_code)
print(response.http_version)
print(response.text)

Top-level request(), get(), post(), put(), patch(), delete(), head(), and options() create a temporary session. Reuse a Session when making more than one request to the same service.

import rex_tls

response = rex_tls.request(
    "POST",
    "https://api.example.com/items",
    profile="okhttp_5.4",
    json={"name": "example", "enabled": True},
)

Persistent sessions

A Session retains cookies, connections, protocol state, and TLS session tickets across requests.

Session.request(method, url, ...) is the generic request entry point. get(), post(), put(), patch(), delete(), head(), and options() are convenience wrappers around it.

import rex_tls

with rex_tls.Session(profile="chrome_android_150") as session:
    response = session.request(
        method="POST",
        url="https://example.com/api/items",
        params={"source": "python"},
        headers={"accept": "application/json"},
        cookies={"request-only": "value"},
        json={"name": "example"},
        timeout=20,
    )
    response.raise_for_status()

The example explicitly uses method="POST", url="https://example.com/api/items", and timeout=20.

The same Session can carry subsequent requests and expose connection reuse:

from rex_tls import Session

with Session("okhttp_5.4", timeout=20) as session:
    session.headers.update({"accept": "application/json"})
    session.cookies.set("locale", "en-US")

    first = session.get("https://example.com/api/profile")
    second = session.get("https://example.com/api/settings")

    print(second.connection_reused)
    print(session.cookies.get_dict())

connection_reused is False when a new connection was required and True when the request used an existing connection. A server close, a different origin or proxy route, incompatible protocol state, an unread streaming body, or a connection limit can prevent reuse.

Session options

session = Session(
    profile="chrome_android_150",
    timeout=30,
    verify=True,
    proxy=None,
    proxies=None,
    follow_redirects=True,
    max_redirects=10,
    trust_env=False,
    http3="off",
    http2=False,
    max_connections_per_route=None,
    tls_config=None,
)

Request arguments

Session.request() and every method helper accept the following request options:

content, data, and json are mutually exclusive. files may be combined with form fields in data, but not with content or json.

Timeouts and redirects

A single timeout value applies one absolute request deadline and the same value to each TCP socket phase:

response = session.get("https://example.com/", timeout=20)

A pair separates TCP connect and socket read/write limits. Its sum is the absolute deadline for the complete redirect chain:

response = session.get("https://example.com/", timeout=(3, 10))

The split form is timeout=(3, 10).

HTTP/3 uses the combined absolute deadline because QUIC connection progress is managed by one protocol driver.

Disable redirects per request when the caller wants to inspect the next hop:

response = session.get(
    "https://example.com/redirect",
    allow_redirects=False,
)

print(response.is_redirect)
print(response.next)

response.history contains followed redirect responses from oldest to newest. For 307 and 308 redirects, seekable upload sources are rewound to their original position. A one-shot source raises UnrewindableBodyError when replay is required.

Request headers and wire order

Headers can be a mapping or an ordered list of pairs:

headers = [
    ("Accept", "application/json"),
    ("X-Trace", "one"),
    ("X-Trace", "two"),
]

response = session.get("https://example.com/api", headers=headers)

The native core prepares headers using the selected profile and negotiated protocol:

• When both Session.headers and request headers are empty, the selected profile supplies its default headers.
• When the caller supplies headers, rex-tls does not add unrelated profile defaults. It can still generate fields required by the URL, cookies, body, or wire protocol.
• Chrome and WebView defaults never add Pragma or Cache-Control. If a caller explicitly supplies either field, rex-tls preserves it and only places it in the selected request-class order.
• Cronet always retains its transport-managed User-Agent, Accept-Encoding, and H2/H3 priority fields when application Headers are present, matching the pinned Cronet engine. Supplying one of those names replaces its value.
• Chrome profiles sort known fields with protocol-specific navigation and fetch order tables. Unknown fields keep their caller-relative order after known fields.
• The WebView profile uses its independent navigation table. It never adds an application-specific X-Requested-With value on the caller's behalf.
• OkHttp profiles preserve caller field order and apply only the casing required by the selected wire protocol.
• HTTP/1.1 uses profile casing for recognized fields. Unknown HTTP/1.1 names keep the caller's spelling.
• HTTP/2 and HTTP/3 send ordinary field names in lowercase. Pseudo headers are generated by the native core and are not supplied in headers.

PC Chrome Header order with Android TLS

The versioned Android Chrome profiles can intentionally combine their Android TLS/HTTP transport profile with PC Chrome ordinary Header order. The switch is automatic when the caller explicitly supplies a desktop Chromium User-Agent:

import rex_tls

pc_headers = {
    "User-Agent": (
        "Mozilla/5.0 (Windows NT 10.0; Win64; x64) "
        "AppleWebKit/537.36 (KHTML, like Gecko) "
        "Chrome/151.0.0.0 Safari/537.36"
    ),
    "sec-ch-ua-platform": '"Windows"',
    "sec-ch-ua": '"Google Chrome";v="151", "Chromium";v="151"',
    "sec-ch-ua-mobile": "?0",
    "Content-Type": "application/json",
    "Accept": "*/*",
    "Sec-Fetch-Site": "cross-site",
    "Sec-Fetch-Mode": "cors",
    "Sec-Fetch-Dest": "empty",
}

with rex_tls.Session("chrome_android_150", http2=True) as session:
    response = session.post(
        "https://example.com/api",
        headers=pc_headers,
        json={"enabled": True},
    )

print(response.request.headers.raw)

Selection rules:

• The User-Agent must contain Chrome/, Chromium/, or Edg/ and a desktop platform marker such as Windows NT, Macintosh, X11;, or CrOS .
• Android, iPhone, iPad, Mobile, or Tablet keeps the Android order.
• An empty Header set still uses the Android profile defaults.
• Only fields already present are sorted. The mode does not add PC browser defaults or remove caller fields.
• TLS ClientHello, ALPN, H2/H3 SETTINGS, priorities, connection pools, and Session.profile remain the selected Android Chrome profile.
• The branch applies only to chrome_android_149 and chrome_android_150; Cronet, OkHttp, and custom profiles are unchanged.

PC Chrome 150 and 151 produced the same observed fetch order over H1 and H2. The selected Android TLS, ALPN, H2/H3 settings, and connection behavior remain unchanged when desktop Header ordering is selected.

Navigation versus fetch requests

Chrome H2 selects its legacy HEADERS priority from the prepared request:

• Empty Session and request headers use the complete navigation defaults and weight 256.
• Sec-Fetch-Mode: navigate, Sec-Fetch-Dest: document, or Upgrade-Insecure-Requests: 1 marks an explicit navigation request and uses weight 256.
• Other explicit header sets are treated as fetch/API requests and use weight 220. Typical signals are Sec-Fetch-Mode: cors and Sec-Fetch-Dest: empty.

# Top-level document navigation.
navigation_headers = {
    "Sec-Fetch-Mode": "navigate",
    "Sec-Fetch-Dest": "document",
    "Upgrade-Insecure-Requests": "1",
    "Accept": "text/html,application/xhtml+xml",
}

# JSON API request made with fetch semantics.
fetch_headers = {
    "Sec-Fetch-Mode": "cors",
    "Sec-Fetch-Dest": "empty",
    "Content-Type": "application/json",
    "Accept": "*/*",
}

Supplying only ordinary fields such as User-Agent and Accept, without a navigation signal, selects fetch behavior. navigation_site changes the Sec-Fetch-Site value in generated Chrome navigation defaults; it does not convert an explicit fetch header set into navigation headers.

Do not copy an HTTP/1.1 header block unchanged into HTTP/2 or HTTP/3. Connection, Proxy-Connection, Keep-Alive, Transfer-Encoding, and Upgrade are connection-specific and are rejected. TE is valid only with the value trailers. For HTTP/3, omit Host; authority comes from the request URL.

For example, this is valid for HTTP/1.1:

h1_headers = {
    "Host": "www.example.com",
    "Connection": "keep-alive",
    "Accept": "application/json",
    "User-Agent": "my-client/1.0",
}

For a forced HTTP/2 request, use ordinary end-to-end headers only:

h2_headers = {
    "accept": "application/json",
    "user-agent": "my-client/1.0",
}

with Session("chrome_android_150", http2=True) as session:
    response = session.get("https://www.example.com/", headers=h2_headers)

The complete H1, H2, and H3 header contract is documented in the header guide.

Cookies

Session.cookies is a mutable Requests-style CookieJar view backed by the native session:

from rex_tls import Session

with Session("okhttp_5.4") as session:
    session.cookies.update({"theme": "dark"})
    session.cookies.set(
        "api-token",
        "value",
        domain="api.example.com",
        path="/v1",
        secure=True,
    )

    print(session.cookies.get("theme"))
    print(session.cookies.get_dict())
    print(session.cookies.items())

    session.cookies.clear(
        domain="api.example.com",
        path="/v1",
        name="api-token",
    )

Available CookieJar operations:

A valid response cookie with Domain=example.com is accepted when the response host is example.com or a subdomain such as api.example.com. A cookie is rejected when its Domain does not match the response host or is a public suffix such as com.

Response and Session cookie containers have different scopes:

with Session("okhttp_5.4") as session:
    response = session.get("https://example.com/login")

    # Cookies accepted from this response only.
    print(response.cookies.get_dict())

    # All cookies retained for later requests.
    print(session.cookies.get_dict())

Both containers expose the common methods above. Mutating response.cookies does not mutate session.cookies. Cookie storage evaluates Domain, Path, Secure, expiry, deletion, prefix rules, IP-address rules, HttpOnly, SameSite, and the built-in public-suffix list.

An unscoped get(name) raises CookieConflictError when multiple stored domain/path identities have the same name. Supply domain and path to make the lookup unambiguous.

HTTP and SOCKS5 proxies

Use proxy when one proxy handles every route:

proxy_url = "http://username:password@proxy.example:8080"

with Session("okhttp_5.4", proxy=proxy_url) as session:
    response = session.get("https://example.com/")

Use proxies for per-scheme routing and bypass rules:

proxies = {
    "http": "http://proxy.example:8080",
    "https": "http://proxy.example:8080",
    "all": "http://fallback.example:8080",
    "no_proxy": ".internal.example,localhost,127.0.0.1",
}

with Session("chrome_android_149", proxies=proxies) as session:
    response = session.get("https://example.com/")

Proxy selection uses this order:

1. A per-request proxies entry updates the Session.proxies mapping for that request.
2. The target scheme key, http or https, takes priority over all.
3. no_proxy bypasses the selected proxy.
4. When trust_env=True, unset routes may use HTTP_PROXY, HTTPS_PROXY, ALL_PROXY, and NO_PROXY.

Set an explicit route value to None to disable that route. proxy and proxies cannot be passed together to the Session constructor.

HTTP proxy URLs use the http:// scheme. HTTP destinations use absolute-form requests; HTTPS destinations use HTTP CONNECT. Basic proxy credentials are supported. Percent-encode reserved characters in usernames and passwords.

SOCKS5 uses the same arguments:

# Local destination DNS resolution.
with Session("okhttp_5.4", proxy="socks5://127.0.0.1:1080") as session:
    response = session.get("https://example.com/")

# Proxy-side destination DNS resolution and username/password authentication.
with Session(
    "chrome_android_150",
    proxy="socks5h://username:password@proxy.example:1080",
) as session:
    response = session.get("https://example.com/")

IPv4 and IPv6 literals are always sent as literal addresses. SOCKS5 itself does not encrypt proxy credentials, so use it over a trusted network path.

HTTP CONNECT and SOCKS5 establish a tunnel first. The selected rex-tls TLS ClientHello, ALPN, and H1/H2 behavior are then generated inside that tunnel; the proxy type does not replace the selected TLS profile.

Supported proxy schemes are http://, socks5://, and socks5h://. HTTPS proxy URLs, SOCKS4, PAC, NTLM/Digest proxy authentication, and MASQUE are not implemented.

HTTP version selection

The negotiated protocol is available as response.http_version.

Require HTTP/2

with Session("chrome_android_150", http2=True) as session:
    response = session.get("https://example.com/")
    assert response.http_version == "HTTP/2"

http2=True requires HTTPS and an actual HTTP/2 ALPN result. The request fails if the server selects HTTP/1.1. It cannot be combined with an HTTP/3 mode.

Select HTTP/3

HTTP/3 is available for the exact versioned Chrome and Cronet profiles:

with Session("chrome_android_150", http3="auto") as session:
    first = session.get("https://example.com/")
    second = session.get("https://example.com/")
    print(first.http_version, second.http_version)

with Session("chrome_android_149", http3="only") as session:
    response = session.get("https://example.com/")
    assert response.http_version == "HTTP/3"

with Session("cronet_android_151", http3="only") as session:
    response = session.get("https://example.com/")
    assert response.http_version == "HTTP/3"

In auto mode, the first request to an origin normally uses H2 or H1 so rex-tls can authenticate and learn the origin's Alt-Svc advertisement. A later request may use H3. Auto mode does not mean the first request is forced onto QUIC.

HTTP/3 requires HTTPS. OkHttp and WebView profiles do not offer H3. HTTP CONNECT and SOCKS5 are TCP proxy mechanisms, so http3="only" is rejected when a proxy is selected. Auto mode uses the proxied H2/H1 path.

Streaming downloads and content decoding

Set stream=True and close the response after use. A context manager releases the connection when the body reaches EOF or the response is closed:

from rex_tls import Session

with Session("chrome_android_150") as session:
    with session.get("https://example.com/large.bin", stream=True) as response:
        response.raise_for_status()
        with open("large.bin", "wb") as output:
            for chunk in response.iter_content(chunk_size=64 * 1024):
                output.write(chunk)

Streaming readers:

• iter_content(chunk_size=..., decode_unicode=False) yields body chunks.
• iter_lines(chunk_size=..., decode_unicode=False, delimiter=None) yields complete lines.
• raw.read(size) and raw.readinto(buffer) provide file-like byte access.
• Accessing content consumes and caches an unread streaming body.
• close() releases the response without reading the remaining body.

Automatic decoding depends on the profile:

• Chrome, WebView, and Cronet profiles decode identity, gzip, deflate, Brotli, zstd, and stacked codings in reverse application order.
• OkHttp profiles automatically decode only a single gzip coding.
• The Flutter profile decodes only one exact lowercase gzip value, preserves representation Headers, and otherwise follows Dart's pass-through and error behavior.
• decode_content=False preserves the compressed wire body.
• Truncated, corrupt, or oversized decoded bodies raise ContentDecodingError.

The decoder is incremental and does not buffer the entire decoded body before yielding chunks.

Streaming uploads and multipart files

File objects and byte iterables are uploaded incrementally:

with Session("okhttp_5.4") as session:
    with open("large.bin", "rb") as source:
        response = session.post(
            "https://example.com/upload",
            content=source,
        )

Multipart form uploads use files:

with Session("okhttp_5.4") as session:
    with open("image.png", "rb") as source:
        response = session.post(
            "https://example.com/form",
            data={"title": "example"},
            files={"file": ("image.png", source, "image/png")},
        )

Known-length H1 bodies use Content-Length; unknown-length H1 bodies use chunked transfer. H2 and H3 bodies are streamed through their native flow-control paths. Seekable sources can be replayed across 307 or 308 redirects.

Async API

AsyncSession provides an asyncio interface while the native work runs outside the event-loop thread:

import asyncio
from rex_tls import AsyncSession

async def main() -> None:
    async with AsyncSession(
        "okhttp_5.4",
        max_concurrency=8,
        http2=True,
    ) as session:
        urls = [f"https://example.com/items/{item}" for item in range(10)]
        responses = await asyncio.gather(*(session.get(url) for url in urls))
        print([response.status_code for response in responses])

asyncio.run(main())

AsyncSession accepts the same transport and request options as Session, plus max_concurrency, which bounds active operations. It exposes request(), all method helpers, cancel(), acancel(), close_origin(), aclose_origin(), close(), and async context management. Its close() method is awaited.

Async streaming uses aiter_content(), aiter_lines(), and aclose():

from rex_tls import AsyncSession

async def stream_events(session: AsyncSession) -> None:
    response = await session.get("https://example.com/events", stream=True)
    async with response:
        async for line in response.aiter_lines():
            print(line)

Bounded session pools

SessionPool and AsyncSessionPool provide a fixed number of independent native sessions. Waiting callers are served in FIFO order.

from concurrent.futures import ThreadPoolExecutor
from rex_tls import SessionPool

urls = [f"https://example.com/items/{item}" for item in range(20)]

with SessionPool(
    "okhttp_4.12",
    max_connections=8,
    session_mode="shared",
) as pool:
    pool.headers["accept"] = "application/json"
    with ThreadPoolExecutor(max_workers=16) as executor:
        responses = list(executor.map(pool.get, urls))

Pool state modes:

In isolated mode, pool.headers, pool.proxies, and pool.cookies raise an error because no pool-wide value exists. Lease one member when several requests must retain the same isolated state:

with SessionPool(
    "okhttp_5.4",
    max_connections=4,
    session_mode="isolated",
) as pool:
    with pool.acquire(timeout=1) as account:
        account.headers["authorization"] = "Bearer example-token"
        account.cookies.set("account", "one")
        account.get("https://example.com/step-1")
        account.get("https://example.com/step-2")

Pool requests accept pool_timeout for the time spent waiting for a member. The ordinary timeout continues to control network work. A streaming response holds its pool member until the body is consumed or the response is closed.

AsyncSessionPool provides the same modes and uses async with pool.acquire() for an isolated lease.

Response API

Response implements the commonly used public Requests response surface and adds native transport information.

Requests-style attributes

Requests-style methods

Response supports boolean conversion and synchronous or asynchronous context management. HTTPError and JSONDecodeError retain both response and request context.

Printing or inspecting a response keeps the transport version visible:

print(response)  # <Response [200 HTTP/2]>

Response.headers combines duplicate values for ordinary mapping access. response.headers.get_all(name) returns every value, while response.headers.raw preserves the received name/value order.

Prepared request metadata includes:

For H1, prepared headers include Host. For H2 and H3, names are lowercase and pseudo headers are represented by method, URL, path, and authority metadata rather than inserted into the ordinary header mapping.

rex-tls transport attributes

response = session.get("https://example.com/account")

print(response.status_code, response.elapsed)
print(response.request.method, response.request.path_url)
print(response.cookies.get_dict())
print(response.http_version, response.connection_reused)

Cancellation and connection control

Session, AsyncSession, and both pool types expose:

• cancel() to cancel active native work.
• close_origin(url) to remove and close the cached route for one origin.
• close() to permanently close the client.

AsyncSession and AsyncSessionPool also provide acancel() and aclose_origin(); their close() methods are awaited. Response provides aclose() for asynchronous stream cleanup. Cancelling one queued pool lease or one HTTP/2 stream does not cancel unrelated callers.

Error handling

import rex_tls

try:
    response = rex_tls.get(
        "https://example.com/",
        profile="chrome_android_150",
        timeout=10,
    )
    response.raise_for_status()
except rex_tls.HTTPError as exc:
    print(f"HTTP error: {exc}")
except rex_tls.RequestError as exc:
    print(f"Request failed: {exc}")
    print(exc.protocol, exc.phase, exc.code, exc.retryable)
except rex_tls.MobileTLSError as exc:
    print(f"Native client error: {exc}")
except (TypeError, ValueError) as exc:
    print(f"Invalid configuration: {exc}")

Public exception types:

InvalidJSONError and JSONDecodeError both describe invalid response JSON and retain response/request context.

Every RequestError exposes bounded diagnostic fields:

rex-tls does not automatically replay a request body merely because retryable is true. The application remains responsible for deciding whether its operation is safe to retry.

Requests compatibility

Supported Requests-style behavior includes:

• Top-level request and method helpers.
• Persistent Session state and generic Session.request().
• Query parameters, mappings, ordered duplicate headers, form data, JSON, multipart files, request cookies, and streamed bodies.
• Mutable Session.headers, Session.proxies, and Session.cookies.
• Numeric and split timeouts, redirects, certificate verification, HTTP and SOCKS5 proxies, and environment proxy discovery.
• Buffered and streaming Response content, text, JSON, headers, cookies, elapsed time, history, prepared request metadata, links, and status helpers.

The following Requests extension points are not implemented:

• Authentication handler objects passed through auth=.
• Response hooks.
• Transport adapters, adapter mounting, and custom adapter routing.
• Custom RequestsCookieJar policy objects.
• PreparedRequest mutation followed by Session.send().

Applications that depend on one of these extension points must keep Requests or adapt that integration before switching clients.

TLS verification

Certificate verification is enabled by default and uses the installed certifi CA bundle:

# Default CA bundle.
Session("chrome_android_150", verify=True)

# Custom CA file.
Session("chrome_android_150", verify="/path/to/private-ca.pem")

# Disable verification explicitly.
Session("chrome_android_150", verify=False)

Disabling verification removes server identity protection and should be limited to controlled test endpoints.

Performance

Practical summary

Reuse one Session for repeated calls. It avoids repeated Python setup, reuses TCP/TLS connections, retains TLS session tickets, and allows H2 or H3 multiplexing. AsyncSession is the normal choice for asyncio. Use a pool when the application needs independent state or several H1 connections; adding a pool does not automatically improve an already multiplexed H2 connection.

Controlled localhost measurements show that no client is fastest in every scenario:

• rex-tls has low warm-request overhead and scales strongly in the measured H1 concurrency cases.
• never_primp was slightly faster than rex-tls for the measured single H1 request and remained competitive under concurrency.
• curl_cffi was faster in the measured medium-concurrency H2 case, while the rex-tls pool was faster at the measured high-concurrency H2 point.
• httpcloak was slower than rex-tls in the measured H1 points.
• H2 and H3 stability, connection count, memory use, and protocol behavior should be considered together with raw throughput.

Same-host comparison

The H1 table used a warm client, a 4 KiB response, 100 samples, and the same Windows 11 / CPython 3.14 host. RPS means completed requests per second; higher is better.

The controlled H2 table used a 1 ms server delay and 100 samples:

These are implementation-overhead tests, not a promise for public websites. DNS, TLS handshakes, proxies, server latency, security software, response size, and network quality can change the ranking. Compare clients on the actual workload before choosing one solely for speed.

A 256 MiB streaming upload and download remained incremental in the local regression suite rather than buffering the whole body in Python.

Benchmark definitions, limitations, and reproducible commands are in the performance guide.

Runtime information

import rex_tls

print(rex_tls.__version__)
print(rex_tls.profiles())
print(dict(rex_tls.native_versions()))
print(rex_tls.profile_info("chrome_android_150"))

License

MIT