Add makefile() to session

[geosone]

The following patch simplifies creating a Python webserver. It is currently used for the https://gitea.disconnected-by-peer.at/geos_one/bongo webmail part.

python3-gnutls-3.1.13-add-session-makefile-support.patch

[geosone]

Some more context on this patch, in case it's useful for review:

Why it's needed: Session/ServerSession implement send()/recv()/sendall() directly against GnuTLS, but the class never overrides makefile(). Since Session.__getattr__ falls through anything the class doesn't define to self.socket (the raw, unencrypted socket underneath), calling .makefile() on an unpatched session silently returns a file object backed by the plaintext socket instead of the TLS session — confirmed by hand before writing this patch: reading from it yields the literal ClientHello bytes, not decrypted application data. That's a real footgun for anyone using this library with socketserver/http.server-based code (or anything else that relies on socket.makefile()), since neither side raises an error — it just silently talks plaintext.

What the patch does: adds Session.makefile(mode="rb", buffering=-1), mirroring socket.makefile()'s own real implementation shape — a small io.RawIOBase subclass (_SessionIO) routed through send()/recv(), feeding io.BufferedReader/BufferedWriter/BufferedRWPair, the same way socket.SocketIO backs socket.makefile() itself. Text mode isn't supported (only "rb"/"wb"/"rwb"), since a TLS session has no natural encoding to assume at the ciphertext boundary and every consumer this is meant to help (http.server/socketserver) only ever requests binary mode anyway.

It's intentionally minimal and additive — one new class, one new method, no changes to any existing method's behavior — to keep it low-risk for other consumers of this library that never touch makefile() (including your own gnutls.interfaces.twisted integration).

Verified before and after (not assumed): a real local GnuTLS handshake between a ClientSession and ServerSession over a socketpair(), then a full HTTP-shaped request/response exchanged purely through Session.makefile('rb')/makefile('wb') on the server side, correctly encrypts/decrypts on both ends. Before the patch, the same call sequence silently exposed the plaintext ClientHello instead.

In production use (the Bongo webmail server linked above), this backs a real http.server.BaseHTTPRequestHandler-based service — BongoWebServer.get_request() handshakes each connection and wraps it in a small adapter exposing exactly the socket-like surface socketserver touches (makefile(), close(), getpeername(), etc.), with makefile() delegating straight to this patch's Session.makefile().

Happy to adjust the patch (naming, buffering defaults, etc.) if you'd like it shaped differently before merging.