fix: recv selector

flake.nix

@@ -24,7 +24,7 @@
           stdenv = pkgs.overrideCC pkgs.stdenv llvmPackages.clang;
         } ({
           buildInputs = with pkgs; [
-            cmake gmp libuv ccache pkg-config
+            cmake gmp libuv ccache pkg-config openssl
             llvmPackages.bintools  # wrapped lld
             llvmPackages.llvm  # llvm-symbolizer for asan/lsan
             gdb

src/CMakeLists.txt

@@ -347,6 +347,35 @@ if(NOT LEAN_STANDALONE)
   string(APPEND LEAN_EXTRA_LINKER_FLAGS " ${LIBUV_LDFLAGS}")
 endif()
 
+# OpenSSL
+if("${CMAKE_SYSTEM_NAME}" MATCHES "Emscripten")
+  # Only on WebAssembly we compile OpenSSL ourselves
+  set(OPENSSL_EMSCRIPTEN_FLAGS "${EMSCRIPTEN_SETTINGS}")
+
+  # OpenSSL needs to be configured for Emscripten using their configuration system
+  ExternalProject_add(openssl
+    PREFIX openssl
+    GIT_REPOSITORY https://github.com/openssl/openssl
+    # Sync version with flake.nix if applicable
+    GIT_TAG openssl-3.0.15
+    CONFIGURE_COMMAND <SOURCE_DIR>/Configure linux-generic32 no-shared no-dso no-engine no-tests --prefix=<INSTALL_DIR> CC=${CMAKE_C_COMPILER} CXX=${CMAKE_CXX_COMPILER} AR=${CMAKE_AR} CFLAGS=${OPENSSL_EMSCRIPTEN_FLAGS}
+    BUILD_COMMAND emmake make -j
+    INSTALL_COMMAND emmake make install_sw
+    BUILD_IN_SOURCE ON)
+  set(OPENSSL_INCLUDE_DIR "${CMAKE_BINARY_DIR}/openssl/include")
+  set(OPENSSL_CRYPTO_LIBRARY "${CMAKE_BINARY_DIR}/openssl/lib/libcrypto.a")
+  set(OPENSSL_SSL_LIBRARY "${CMAKE_BINARY_DIR}/openssl/lib/libssl.a")
+  set(OPENSSL_LIBRARIES "${OPENSSL_SSL_LIBRARY} ${OPENSSL_CRYPTO_LIBRARY}")
+else()
+  find_package(OpenSSL REQUIRED)
+  set(OPENSSL_LIBRARIES ${OPENSSL_SSL_LIBRARY} ${OPENSSL_CRYPTO_LIBRARY})
+endif()
+include_directories(${OPENSSL_INCLUDE_DIR})
+if(NOT LEAN_STANDALONE)
+  string(JOIN " " OPENSSL_LIBRARIES ${OPENSSL_LIBRARIES})
+  string(APPEND LEAN_EXTRA_LINKER_FLAGS " ${OPENSSL_LIBRARIES}")
+endif()
+
 # Windows SDK (for ICU)
 if(CMAKE_SYSTEM_NAME MATCHES "Windows")
   # Pass 'tools' to skip MSVC version check (as MSVC/Visual Studio is not necessarily installed)
@@ -721,9 +750,9 @@ if(STAGE GREATER 1)
   endif()
 else()
   add_subdirectory(runtime)
-  if(CMAKE_SYSTEM_NAME MATCHES "Emscripten")
-    add_dependencies(leanrt libuv)
-    add_dependencies(leanrt_initial-exec libuv)
+  if("${CMAKE_SYSTEM_NAME}" MATCHES "Emscripten")
+    add_dependencies(leanrt libuv openssl)
+    add_dependencies(leanrt_initial-exec libuv openssl)
   endif()
 
   add_subdirectory(util)

src/Lean/Runtime.lean

@@ -21,6 +21,9 @@ opaque maxSmallNatFn : Unit → Nat
 @[extern "lean_libuv_version"]
 opaque libUVVersionFn : Unit → Nat
 
+@[extern "lean_openssl_version"]
+opaque openSSLVersionFn : Unit → Nat
+
 def closureMaxArgs : Nat :=
   closureMaxArgsFn ()
 
@@ -30,4 +33,7 @@ def maxSmallNat : Nat :=
 def libUVVersion : Nat :=
   libUVVersionFn ()
 
+def openSSLVersion : Nat :=
+  openSSLVersionFn ()
+
 end Lean

src/Std/Internal.lean

@@ -9,6 +9,7 @@ prelude
 public import Std.Internal.Async
 public import Std.Internal.Parsec
 public import Std.Internal.UV
+public import Std.Internal.SSL
 
 @[expose] public section
 

src/Std/Internal/Async.lean

@@ -10,6 +10,7 @@ public import Std.Internal.Async.Basic
 public import Std.Internal.Async.ContextAsync
 public import Std.Internal.Async.Timer
 public import Std.Internal.Async.TCP
+public import Std.Internal.Async.TCP.SSL
 public import Std.Internal.Async.UDP
 public import Std.Internal.Async.DNS
 public import Std.Internal.Async.Select
@@ -17,3 +18,4 @@ public import Std.Internal.Async.Process
 public import Std.Internal.Async.System
 public import Std.Internal.Async.Signal
 public import Std.Internal.Async.IO
+public import Std.Internal.SSL

src/Std/Internal/Async/TCP/SSL.lean

@@ -0,0 +1,417 @@
+/-
+Copyright (c) 2026 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Sofia Rodrigues
+-/
+module
+
+prelude
+public import Std.Time
+public import Std.Internal.UV.TCP
+public import Std.Internal.Async.Timer
+public import Std.Internal.Async.Select
+public import Std.Internal.SSL
+
+public section
+
+namespace Std
+namespace Internal
+namespace IO
+namespace Async
+namespace TCP
+namespace SSL
+
+open Std.Net
+
+/--
+Default chunk size used by TLS I/O loops.
+-/
+def ioChunkSize : UInt64 := 16 * 1024
+
+/--
+Represents a TLS-enabled TCP server socket.
+-/
+structure Server where
+  private ofNative ::
+    native : Internal.UV.TCP.Socket
+
+/--
+Represents a TLS-enabled TCP client socket.
+-/
+structure Client where
+  private ofNative ::
+    native : Internal.UV.TCP.Socket
+    ssl : Std.Internal.SSL.Session
+
+@[inline]
+private def feedEncryptedChunk (ssl : Std.Internal.SSL.Session) (encrypted : ByteArray) : Async Unit := do
+  if encrypted.size == 0 then
+    return ()
+  let consumed ← ssl.feedEncrypted encrypted
+  if consumed.toNat != encrypted.size then
+    throw <| IO.userError s!"TLS input short write: consumed {consumed} / {encrypted.size} bytes"
+
+@[inline]
+private partial def flushEncrypted (native : Internal.UV.TCP.Socket) (ssl : Std.Internal.SSL.Session) : Async Unit := do
+  let out ← ssl.drainEncrypted
+  if out.size == 0 then
+    return ()
+  Async.ofPromise <| native.send #[out]
+  flushEncrypted native ssl
+
+/--
+Runs the TLS handshake loop until the handshake is established.
+-/
+private partial def handshake (native : Internal.UV.TCP.Socket) (ssl : Std.Internal.SSL.Session) (chunkSize : UInt64 := ioChunkSize) : Async Unit := do
+  let done ← ssl.handshake
+  flushEncrypted native ssl
+  if done then
+    return ()
+  let encrypted? ← Async.ofPromise <| native.recv? chunkSize
+  match encrypted? with
+  | none =>
+    throw <| IO.userError "peer closed connection before TLS handshake completed"
+  | some encrypted =>
+    feedEncryptedChunk ssl encrypted
+    handshake native ssl chunkSize
+
+namespace Server
+
+/--
+Configures the shared TLS server context with PEM certificate and private key files.
+-/
+@[inline]
+def configureContext (certFile keyFile : String) : IO Unit :=
+  Std.Internal.SSL.configureServerContext certFile keyFile
+
+/--
+Creates a new TLS-enabled TCP server socket.
+-/
+@[inline]
+def mk : IO Server := do
+  let native ← Internal.UV.TCP.Socket.new
+  return Server.ofNative native
+
+/--
+Binds the server socket to the specified address.
+-/
+@[inline]
+def bind (s : Server) (addr : SocketAddress) : IO Unit :=
+  s.native.bind addr
+
+/--
+Listens for incoming connections with the given backlog.
+-/
+@[inline]
+def listen (s : Server) (backlog : UInt32) : IO Unit :=
+  s.native.listen backlog
+
+@[inline] private def mkServerClient (native : Internal.UV.TCP.Socket) : IO Client := do
+  let ssl ← Std.Internal.SSL.Session.mkServer
+  return Client.ofNative native ssl
+
+/--
+Accepts an incoming TLS client connection and performs the TLS handshake.
+-/
+@[inline]
+def accept (s : Server) (chunkSize : UInt64 := ioChunkSize) : Async Client := do
+  let native ← Async.ofPromise <| s.native.accept
+  let client ← mkServerClient native
+  SSL.handshake client.native client.ssl chunkSize
+  return client
+
+/--
+Tries to accept an incoming TLS client connection.
+-/
+@[inline]
+def tryAccept (s : Server) : IO (Option Client) := do
+  let res ← s.native.tryAccept
+  let socket ← IO.ofExcept res
+  match socket with
+  | none => return none
+  | some native => return some (← mkServerClient native)
+
+/--
+Creates a `Selector` that resolves once `s` has a connection available.
+-/
+def acceptSelector (s : TCP.SSL.Server) : Selector Client :=
+  {
+    tryFn :=
+      s.tryAccept
+
+    registerFn waiter := do
+      let task ← s.native.accept
+
+      -- If we get cancelled the promise will be dropped so prepare for that
+      IO.chainTask (t := task.result?) fun res => do
+        match res with
+        | none => return ()
+        | some res =>
+          let lose := return ()
+          let win promise := do
+            try
+              let native ← IO.ofExcept res
+              let ssl ← Std.Internal.SSL.Session.mkServer
+              promise.resolve (.ok (Client.ofNative native ssl))
+            catch e =>
+              promise.resolve (.error e)
+          waiter.race lose win
+
+    unregisterFn := s.native.cancelAccept
+  }
+
+/--
+Gets the local address of the server socket.
+-/
+@[inline]
+def getSockName (s : Server) : IO SocketAddress :=
+  s.native.getSockName
+
+/--
+Enables the Nagle algorithm for all client sockets accepted by this server socket.
+-/
+@[inline]
+def noDelay (s : Server) : IO Unit :=
+  s.native.noDelay
+
+/--
+Enables TCP keep-alive for all client sockets accepted by this server socket.
+-/
+@[inline]
+def keepAlive (s : Server) (enable : Bool) (delay : Std.Time.Second.Offset) (_ : delay.val ≥ 1 := by decide) : IO Unit :=
+  s.native.keepAlive enable.toInt8 delay.val.toNat.toUInt32
+
+end Server
+
+namespace Client
+
+/--
+Configures the shared TLS client context.
+`caFile` may be empty to use default trust settings.
+-/
+@[inline]
+def configureContext (caFile := "") (verifyPeer := true) : IO Unit :=
+  Std.Internal.SSL.configureClientContext caFile verifyPeer
+
+/--
+Creates a new TLS-enabled TCP client socket with a client-side TLS session.
+-/
+@[inline]
+def mk : IO Client := do
+  let native ← Internal.UV.TCP.Socket.new
+  let ssl ← Std.Internal.SSL.Session.mkClient
+  return Client.ofNative native ssl
+
+/--
+Binds the client socket to the specified address.
+-/
+@[inline]
+def bind (s : Client) (addr : SocketAddress) : IO Unit :=
+  s.native.bind addr
+
+/--
+Sets SNI server name used during the TLS handshake.
+-/
+@[inline]
+def setServerName (s : Client) (host : String) : IO Unit :=
+  s.ssl.setServerName host
+
+/--
+Performs the TLS handshake on an established TCP connection.
+-/
+@[inline]
+def handshake (s : Client) (chunkSize : UInt64 := ioChunkSize) : Async Unit :=
+  SSL.handshake s.native s.ssl chunkSize
+
+/--
+Connects the client socket to the given address and performs the TLS handshake.
+-/
+@[inline]
+def connect (s : Client) (addr : SocketAddress) (chunkSize : UInt64 := ioChunkSize) : Async Unit := do
+  Async.ofPromise <| s.native.connect addr
+  s.handshake chunkSize
+
+/--
+Attempts to write plaintext data into TLS. Returns true when accepted.
+Any encrypted TLS output generated is flushed to the socket.
+-/
+@[inline]
+def write (s : Client) (data : ByteArray) : Async Bool := do
+  let accepted ← s.ssl.write data
+  flushEncrypted s.native s.ssl
+  return accepted
+
+/--
+Sends data through a TLS-enabled socket.
+Fails if OpenSSL reports the write as pending additional I/O.
+-/
+@[inline]
+def send (s : Client) (data : ByteArray) : Async Unit := do
+  if ← s.write data then
+    return ()
+  else
+    throw <| IO.userError "TLS write is pending additional I/O; call `recv?` or retry later"
+
+/--
+Sends multiple data buffers through the TLS-enabled socket.
+-/
+@[inline]
+def sendAll (s : Client) (data : Array ByteArray) : Async Unit :=
+  data.forM (s.send ·)
+
+/--
+Receives decrypted plaintext data from TLS.
+If no plaintext is immediately available, this function pulls encrypted data from TCP first.
+-/
+partial def recv? (s : Client) (size : UInt64) (chunkSize : UInt64 := ioChunkSize) : Async (Option ByteArray) := do
+  match ← s.ssl.read? size with
+  | some plain =>
+    flushEncrypted s.native s.ssl
+    return some plain
+  | none =>
+    flushEncrypted s.native s.ssl
+    let encrypted? ← Async.ofPromise <| s.native.recv? chunkSize
+    match encrypted? with
+    | none =>
+      return none
+    | some encrypted =>
+      feedEncryptedChunk s.ssl encrypted
+      recv? s size chunkSize
+
+/--
+Tries to receive decrypted plaintext data without blocking.
+Returns `some (some data)` if plaintext is available, `some none` if the peer closed,
+or `none` if no data is ready yet.
+-/
+partial def tryRecv (s : Client) (size : UInt64) (chunkSize : UInt64 := ioChunkSize) : Async (Option (Option ByteArray)) := do
+  let pending ← s.ssl.pendingPlaintext
+
+  if pending > 0 then
+    let res ← s.recv? size
+    return some res
+  else
+    let readableWaiter ← s.native.waitReadable
+
+    flushEncrypted s.native s.ssl
+
+    if ← readableWaiter.isResolved then
+      let encrypted? ← Async.ofPromise <| s.native.recv? ioChunkSize
+      match encrypted? with
+      | none =>
+        return none
+      | some encrypted =>
+        feedEncryptedChunk s.ssl encrypted
+        tryRecv s size chunkSize
+    else
+      s.native.cancelRecv
+      return none
+
+/--
+Feeds encrypted socket data into SSL until plaintext is pending.
+Resolves the returned promise once plaintext is available. If no more socket data
+is available (or the promise gets dropped), it exits without resolving.
+-/
+partial def waitReadable (s : Client) (chunkSize : UInt64 := ioChunkSize) : Async Unit := do
+  if (← s.ssl.pendingPlaintext) > 0 then
+    return ()
+
+  let rec go : Async Unit := do
+    let readable ← Async.ofPromise <| s.native.waitReadable
+
+    if !readable then
+      return ()
+
+    let encrypted? ← Async.ofPromise <| s.native.recv? chunkSize
+
+    match encrypted? with
+    | none =>
+      return ()
+    | some encrypted =>
+      feedEncryptedChunk s.ssl encrypted
+      flushEncrypted s.native s.ssl
+
+      if (← s.ssl.pendingPlaintext) > 0 then
+        return ()
+      else
+        go
+
+  go
+
+/--
+Creates a `Selector` that resolves once `s` has plaintext data available.
+-/
+def recvSelector (s : TCP.SSL.Client) (size : UInt64) : Selector (Option ByteArray) :=
+  {
+    tryFn := s.tryRecv size
+
+    registerFn waiter := do
+      let readableWaiter ← s.waitReadable.asTask
+
+      -- If we get cancelled the promise will be dropped so prepare for that
+      discard <| IO.mapTask (t := readableWaiter) fun res => do
+        match res with
+        | .error _ => return ()
+        | .ok _ =>
+          let lose := return ()
+          let win promise := do
+            try
+              -- We know that this read should not block.
+              let result ← (s.recv? size).block
+              promise.resolve (.ok result)
+            catch e =>
+              promise.resolve (.error e)
+          waiter.race lose win
+
+    unregisterFn := s.native.cancelRecv
+  }
+
+/--
+Shuts down the write side of the client socket.
+-/
+@[inline]
+def shutdown (s : Client) : Async Unit :=
+  Async.ofPromise <| s.native.shutdown
+
+/--
+Gets the remote address of the client socket.
+-/
+@[inline]
+def getPeerName (s : Client) : IO SocketAddress :=
+  s.native.getPeerName
+
+/--
+Gets the local address of the client socket.
+-/
+@[inline]
+def getSockName (s : Client) : IO SocketAddress :=
+  s.native.getSockName
+
+/--
+Returns the X.509 verification result code for this TLS session.
+-/
+@[inline]
+def verifyResult (s : Client) : IO UInt64 :=
+  s.ssl.verifyResult
+
+/--
+Enables the Nagle algorithm for the client socket.
+-/
+@[inline]
+def noDelay (s : Client) : IO Unit :=
+  s.native.noDelay
+
+/--
+Enables TCP keep-alive with a specified delay for the client socket.
+-/
+@[inline]
+def keepAlive (s : Client) (enable : Bool) (delay : Std.Time.Second.Offset) (_ : delay.val ≥ 0 := by decide) : IO Unit :=
+  s.native.keepAlive enable.toInt8 delay.val.toNat.toUInt32
+
+end Client
+
+end SSL
+end TCP
+end Async
+end IO
+end Internal
+end Std

src/Std/Internal/SSL.lean

@@ -0,0 +1,117 @@
+/-
+Copyright (c) 2026 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Sofia Rodrigues
+-/
+module
+
+prelude
+public import Init.System.Promise
+
+public section
+
+namespace Std
+namespace Internal
+namespace SSL
+
+private opaque SessionImpl : NonemptyType.{0}
+
+/--
+Represents an OpenSSL session backed by memory BIOs.
+-/
+def Session : Type := SessionImpl.type
+
+instance : Nonempty Session := by exact SessionImpl.property
+
+/--
+Configures the shared server context with a certificate and key in PEM format.
+-/
+@[extern "lean_uv_ssl_configure_server_ctx"]
+opaque configureServerContext (certFile : @& String) (keyFile : @& String) : IO Unit
+
+/--
+Configures the shared client context.
+`caFile` may be empty to keep default trust configuration.
+-/
+@[extern "lean_uv_ssl_configure_client_ctx"]
+opaque configureClientContext (caFile : @& String) (verifyPeer : Bool) : IO Unit
+
+namespace Session
+
+/--
+Creates a new SSL session. Set `isServer := true` for server-side handshakes.
+-/
+@[extern "lean_uv_ssl_mk"]
+opaque mk (isServer : Bool) : IO Session
+
+/--
+Creates a server-side SSL session.
+-/
+@[extern "lean_uv_ssl_mk_server"]
+opaque mkServer : IO Session
+
+/--
+Creates a client-side SSL session.
+-/
+@[extern "lean_uv_ssl_mk_client"]
+opaque mkClient : IO Session
+
+/--
+Sets SNI host name for client-side handshakes.
+-/
+@[extern "lean_uv_ssl_set_server_name"]
+opaque setServerName (ssl : @& Session) (host : @& String) : IO Unit
+
+/--
+Gets the X.509 verify result code after handshake.
+-/
+@[extern "lean_uv_ssl_verify_result"]
+opaque verifyResult (ssl : @& Session) : IO UInt64
+
+/--
+Runs one handshake step. Returns true when handshake is complete.
+-/
+@[extern "lean_uv_ssl_handshake"]
+opaque handshake (ssl : @& Session) : IO Bool
+
+/--
+Attempts to write plaintext application data into SSL.
+Returns true when accepted, false when OpenSSL needs more I/O first.
+-/
+@[extern "lean_uv_ssl_write"]
+opaque write (ssl : @& Session) (data : @& ByteArray) : IO Bool
+
+/--
+Attempts to read decrypted plaintext data. Returns none when OpenSSL needs more I/O.
+-/
+@[extern "lean_uv_ssl_read"]
+opaque read? (ssl : @& Session) (maxBytes : UInt64) : IO (Option ByteArray)
+
+/--
+Feeds encrypted TLS bytes into the SSL input BIO.
+-/
+@[extern "lean_uv_ssl_feed_encrypted"]
+opaque feedEncrypted (ssl : @& Session) (data : @& ByteArray) : IO UInt64
+
+/--
+Drains encrypted TLS bytes from the SSL output BIO.
+-/
+@[extern "lean_uv_ssl_drain_encrypted"]
+opaque drainEncrypted (ssl : @& Session) : IO ByteArray
+
+/--
+Returns the amount of encrypted TLS bytes currently pending in the output BIO.
+-/
+@[extern "lean_uv_ssl_pending_encrypted"]
+opaque pendingEncrypted (ssl : @& Session) : IO UInt64
+
+/--
+Returns the amount of decrypted plaintext bytes currently buffered inside the SSL object.
+-/
+@[extern "lean_uv_ssl_pending_plaintext"]
+opaque pendingPlaintext (ssl : @& Session) : IO UInt64
+
+end Session
+end SSL
+end Internal
+end Std

src/runtime/CMakeLists.txt

@@ -33,6 +33,8 @@ set(
   uv/dns.cpp
   uv/system.cpp
   uv/signal.cpp
+  openssl.cpp
+  openssl/session.cpp
 )
 if(USE_MIMALLOC)
   list(APPEND RUNTIME_OBJS ${LEAN_BINARY_DIR}/../mimalloc/src/mimalloc/src/static.c)

src/runtime/init_module.cpp

@@ -14,6 +14,8 @@ Author: Leonardo de Moura
 #include "runtime/mutex.h"
 #include "runtime/init_module.h"
 #include "runtime/libuv.h"
+#include "runtime/openssl.h"
+#include "runtime/openssl/session.h"
 
 namespace lean {
 extern "C" LEAN_EXPORT void lean_initialize_runtime_module() {
@@ -25,6 +27,8 @@ extern "C" LEAN_EXPORT void lean_initialize_runtime_module() {
     initialize_mutex();
     initialize_process();
     initialize_stack_overflow();
+    initialize_openssl();
+    initialize_openssl_session();
     initialize_libuv();
 }
 void initialize_runtime_module() {
@@ -32,6 +36,7 @@ void initialize_runtime_module() {
 }
 void finalize_runtime_module() {
     finalize_stack_overflow();
+    finalize_openssl();
     finalize_process();
     finalize_mutex();
     finalize_thread();

src/runtime/openssl.cpp

@@ -0,0 +1,96 @@
+/*
+Copyright (c) 2026 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Author: Sofia Rodrigues
+*/
+#include "runtime/openssl.h"
+#include "runtime/io.h"
+
+#include <mutex>
+
+#ifndef LEAN_EMSCRIPTEN
+#include <openssl/opensslv.h>
+#include <openssl/err.h>
+
+namespace lean {
+
+static std::once_flag g_openssl_init_once;
+static SSL_CTX * g_ssl_server_ctx = nullptr;
+static SSL_CTX * g_ssl_client_ctx = nullptr;
+
+static void configure_ctx_common(SSL_CTX * ctx) {
+    SSL_CTX_set_mode(ctx, SSL_MODE_AUTO_RETRY);
+
+    #ifdef SSL_OP_NO_RENEGOTIATION
+    SSL_CTX_clear_options(ctx, SSL_OP_NO_RENEGOTIATION);
+    #endif
+    #ifdef SSL_OP_ALLOW_CLIENT_RENEGOTIATION
+    SSL_CTX_set_options(ctx, SSL_OP_ALLOW_CLIENT_RENEGOTIATION);
+    #endif
+}
+
+static void initialize_openssl_once() {
+    if (OPENSSL_init_ssl(0, nullptr) != 1) {
+        lean_internal_panic("failed to initialize OpenSSL");
+    }
+
+    g_ssl_server_ctx = SSL_CTX_new(TLS_server_method());
+    g_ssl_client_ctx = SSL_CTX_new(TLS_client_method());
+
+    if (g_ssl_server_ctx == nullptr || g_ssl_client_ctx == nullptr) {
+        if (g_ssl_server_ctx != nullptr) SSL_CTX_free(g_ssl_server_ctx);
+        if (g_ssl_client_ctx != nullptr) SSL_CTX_free(g_ssl_client_ctx);
+        g_ssl_server_ctx = nullptr;
+        g_ssl_client_ctx = nullptr;
+        lean_internal_panic("failed to create OpenSSL SSL_CTX pair");
+    }
+
+    configure_ctx_common(g_ssl_server_ctx);
+    configure_ctx_common(g_ssl_client_ctx);
+}
+
+void initialize_openssl() {
+    std::call_once(g_openssl_init_once, initialize_openssl_once);
+}
+
+void finalize_openssl() {
+    if (g_ssl_server_ctx != nullptr) {
+        SSL_CTX_free(g_ssl_server_ctx);
+        g_ssl_server_ctx = nullptr;
+    }
+    if (g_ssl_client_ctx != nullptr) {
+        SSL_CTX_free(g_ssl_client_ctx);
+        g_ssl_client_ctx = nullptr;
+    }
+}
+
+SSL_CTX * get_openssl_server_ctx() {
+    initialize_openssl();
+    return g_ssl_server_ctx;
+}
+
+SSL_CTX * get_openssl_client_ctx() {
+    initialize_openssl();
+    return g_ssl_client_ctx;
+}
+
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_openssl_version(lean_obj_arg o) {
+    return lean_unsigned_to_nat(OPENSSL_VERSION_NUMBER);
+}
+
+#else
+
+namespace lean {
+
+void initialize_openssl() {}
+void finalize_openssl() {}
+
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_openssl_version(lean_obj_arg o) {
+    return lean_box(0);
+}
+
+#endif

src/runtime/openssl.h

@@ -0,0 +1,25 @@
+/*
+Copyright (c) 2026 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Author: Sofia Rodrigues
+*/
+#pragma once
+#include <lean/lean.h>
+
+#ifndef LEAN_EMSCRIPTEN
+#include <openssl/ssl.h>
+#endif
+
+namespace lean {
+
+void initialize_openssl();
+void finalize_openssl();
+
+#ifndef LEAN_EMSCRIPTEN
+SSL_CTX * get_openssl_server_ctx();
+SSL_CTX * get_openssl_client_ctx();
+#endif
+
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_openssl_version(lean_obj_arg);

src/runtime/openssl/session.cpp

@@ -0,0 +1,561 @@
+/*
+Copyright (c) 2026 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Author: Sofia Rodrigues
+*/
+
+#include "runtime/openssl/session.h"
+
+#include <climits>
+#include <cstdlib>
+#include <cstring>
+#include <string>
+
+#ifndef LEAN_EMSCRIPTEN
+#include <openssl/err.h>
+#endif
+
+namespace lean {
+
+#ifndef LEAN_EMSCRIPTEN
+
+static inline lean_object * mk_ssl_error(char const * where, int ssl_err = 0) {
+    unsigned long err = ERR_get_error();
+    char err_buf[256];
+    err_buf[0] = '\0';
+
+    if (err != 0) {
+        ERR_error_string_n(err, err_buf, sizeof(err_buf));
+    }
+
+    // Drain remaining errors so they don't pollute future calls.
+    ERR_clear_error();
+
+    std::string msg(where);
+    
+    if (ssl_err != 0) {
+        msg += " (ssl_error=" + std::to_string(ssl_err) + ")";
+    }
+    if (err_buf[0] != '\0') {
+        msg += ": ";
+        msg += err_buf;
+    }
+
+    return lean_mk_io_user_error(mk_string(msg.c_str()));
+}
+
+static inline lean_obj_res mk_ssl_io_error(char const * where, int ssl_err = 0) {
+    return lean_io_result_mk_error(mk_ssl_error(where, ssl_err));
+}
+
+static inline lean_object * mk_empty_byte_array() {
+    lean_object * arr = lean_alloc_sarray(1, 0, 0);
+    lean_sarray_set_size(arr, 0);
+    return arr;
+}
+
+static void free_pending_writes(lean_ssl_session_object * obj) {
+    if (obj->pending_writes != nullptr) {
+        for (size_t i = 0; i < obj->pending_writes_count; i++) {
+            free(obj->pending_writes[i].data);
+        }
+        free(obj->pending_writes);
+        obj->pending_writes = nullptr;
+    }
+    obj->pending_writes_count = 0;
+}
+
+static bool append_pending_write(lean_ssl_session_object * obj, char const * data, size_t size) {
+    char * copy = (char*)malloc(size);
+    if (copy == nullptr) return false;
+
+    std::memcpy(copy, data, size);
+
+    size_t new_count = obj->pending_writes_count + 1;
+    lean_ssl_pending_write * new_arr = (lean_ssl_pending_write*)realloc(
+        obj->pending_writes, sizeof(lean_ssl_pending_write) * new_count
+    );
+
+    if (new_arr == nullptr) {
+        free(copy);
+        return false;
+    }
+
+    obj->pending_writes = new_arr;
+    obj->pending_writes[obj->pending_writes_count].data = copy;
+    obj->pending_writes[obj->pending_writes_count].size = size;
+    obj->pending_writes_count = new_count;
+    return true;
+}
+
+/*
+Return values:
+  1 -> write completed
+  0 -> write blocked (WANT_READ / WANT_WRITE / ZERO_RETURN)
+ -1 -> fatal error
+*/
+static int ssl_write_step(lean_ssl_session_object * obj, char const * data, size_t size, int * out_err) {
+    if (size > INT_MAX) {
+        *out_err = SSL_ERROR_SSL;
+        return -1;
+    }
+
+    int rc = SSL_write(obj->ssl, data, (int)size);
+    if (rc > 0) {
+        return 1;
+    }
+
+    int err = SSL_get_error(obj->ssl, rc);
+    *out_err = err;
+    if (err == SSL_ERROR_WANT_READ || err == SSL_ERROR_WANT_WRITE || err == SSL_ERROR_ZERO_RETURN) {
+        return 0;
+    }
+    return -1;
+}
+
+/*
+Return values:
+  1 -> all pending writes flushed
+  0 -> still blocked by renegotiation
+ -1 -> fatal error, *out_err filled
+*/
+static int try_flush_pending_writes(lean_ssl_session_object * obj, int * out_err) {
+    if (obj->pending_writes_count == 0) return 1;
+
+    size_t completed = 0;
+
+    for (size_t i = 0; i < obj->pending_writes_count; i++) {
+        lean_ssl_pending_write * pw = &obj->pending_writes[i];
+
+        while (pw->size > 0) {
+            int err = 0;
+            int step = ssl_write_step(obj, pw->data, pw->size, &err);
+
+            if (step == 1) {
+                // We do not enable partial writes, so a successful SSL_write consumes the full buffer.
+                pw->size = 0;
+                continue;
+            }
+
+            if (step == 0) {
+                goto done;
+            }
+
+            *out_err = err;
+            return -1;
+        }
+
+        free(pw->data);
+        pw->data = nullptr;
+        completed++;
+    }
+
+done:
+    if (completed > 0) {
+        obj->pending_writes_count -= completed;
+        if (obj->pending_writes_count == 0) {
+            free(obj->pending_writes);
+            obj->pending_writes = nullptr;
+        } else {
+            std::memmove(
+                obj->pending_writes,
+                obj->pending_writes + completed,
+                sizeof(lean_ssl_pending_write) * obj->pending_writes_count
+            );
+            // Keep memory usage proportional to currently queued writes.
+            lean_ssl_pending_write * shrunk = (lean_ssl_pending_write*)realloc(
+                obj->pending_writes,
+                sizeof(lean_ssl_pending_write) * obj->pending_writes_count
+            );
+            if (shrunk != nullptr) {
+                obj->pending_writes = shrunk;
+            }
+        }
+    }
+
+    return obj->pending_writes_count == 0 ? 1 : 0;
+}
+
+void lean_ssl_session_finalizer(void * ptr) {
+    lean_ssl_session_object * obj = (lean_ssl_session_object*)ptr;
+
+    if (obj->ssl != nullptr) {
+        SSL_free(obj->ssl);
+    }
+
+    free_pending_writes(obj);
+    free(obj);
+}
+
+void initialize_openssl_session() {
+    g_ssl_session_external_class = lean_register_external_class(lean_ssl_session_finalizer, [](void * obj, lean_object * f) {
+        (void)obj;
+        (void)f;
+    });
+}
+
+static lean_obj_res mk_ssl_session(uint8_t is_server) {
+    SSL_CTX * ctx = is_server ? get_openssl_server_ctx() : get_openssl_client_ctx();
+    if (ctx == nullptr) {
+        return mk_ssl_io_error("failed to initialize OpenSSL context");
+    }
+
+    SSL * ssl = SSL_new(ctx);
+    if (ssl == nullptr) {
+        return mk_ssl_io_error("SSL_new failed");
+    }
+
+    BIO * read_bio = BIO_new(BIO_s_mem());
+    BIO * write_bio = BIO_new(BIO_s_mem());
+
+    if (read_bio == nullptr || write_bio == nullptr) {
+        if (read_bio != nullptr) BIO_free(read_bio);
+        if (write_bio != nullptr) BIO_free(write_bio);
+        SSL_free(ssl);
+        return mk_ssl_io_error("BIO_new failed");
+    }
+
+    BIO_set_nbio(read_bio, 1);
+    BIO_set_nbio(write_bio, 1);
+
+    SSL_set_bio(ssl, read_bio, write_bio);
+    SSL_set_mode(ssl, SSL_MODE_AUTO_RETRY);
+
+    if (is_server) {
+        SSL_set_accept_state(ssl);
+    } else {
+        SSL_set_connect_state(ssl);
+    }
+
+    lean_ssl_session_object * ssl_obj = (lean_ssl_session_object*)malloc(sizeof(lean_ssl_session_object));
+    if (ssl_obj == nullptr) {
+        SSL_free(ssl);
+        return mk_ssl_io_error("failed to allocate SSL session object");
+    }
+
+    ssl_obj->ssl = ssl;
+    ssl_obj->read_bio = read_bio;
+    ssl_obj->write_bio = write_bio;
+    ssl_obj->pending_writes_count = 0;
+    ssl_obj->pending_writes = nullptr;
+
+    lean_object * obj = lean_ssl_session_object_new(ssl_obj);
+    lean_mark_mt(obj);
+    return lean_io_result_mk_ok(obj);
+}
+
+/* Std.Internal.SSL.Session.mk (isServer : Bool) : IO Session */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_mk(uint8_t is_server) {
+    return mk_ssl_session(is_server);
+}
+
+/* Std.Internal.SSL.Session.mkServer : IO Session */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_mk_server() {
+    return mk_ssl_session(1);
+}
+
+/* Std.Internal.SSL.Session.mkClient : IO Session */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_mk_client() {
+    return mk_ssl_session(0);
+}
+
+/* Std.Internal.SSL.configureServerContext (certFile keyFile : @& String) : IO Unit */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_configure_server_ctx(b_obj_arg cert_file, b_obj_arg key_file) {
+    SSL_CTX * ctx = get_openssl_server_ctx();
+    if (ctx == nullptr) {
+        return mk_ssl_io_error("failed to initialize OpenSSL context");
+    }
+
+    const char * cert = lean_string_cstr(cert_file);
+    const char * key = lean_string_cstr(key_file);
+
+    if (SSL_CTX_use_certificate_file(ctx, cert, SSL_FILETYPE_PEM) <= 0) {
+        return mk_ssl_io_error("SSL_CTX_use_certificate_file failed");
+    }
+
+    if (SSL_CTX_use_PrivateKey_file(ctx, key, SSL_FILETYPE_PEM) <= 0) {
+        return mk_ssl_io_error("SSL_CTX_use_PrivateKey_file failed");
+    }
+
+    if (SSL_CTX_check_private_key(ctx) != 1) {
+        return mk_ssl_io_error("SSL_CTX_check_private_key failed");
+    }
+
+    return lean_io_result_mk_ok(lean_box(0));
+}
+
+/* Std.Internal.SSL.configureClientContext (caFile : @& String) (verifyPeer : Bool) : IO Unit */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_configure_client_ctx(b_obj_arg ca_file, uint8_t verify_peer) {
+    SSL_CTX * ctx = get_openssl_client_ctx();
+    if (ctx == nullptr) {
+        return mk_ssl_io_error("failed to initialize OpenSSL client context");
+    }
+
+    const char * ca = lean_string_cstr(ca_file);
+    if (ca != nullptr && ca[0] != '\0') {
+        if (SSL_CTX_load_verify_locations(ctx, ca, nullptr) != 1) {
+            return mk_ssl_io_error("SSL_CTX_load_verify_locations failed");
+        }
+    } else if (verify_peer) {
+        // Fall back to platform trust anchors when no custom CA file is provided.
+        if (SSL_CTX_set_default_verify_paths(ctx) != 1) {
+            return mk_ssl_io_error("SSL_CTX_set_default_verify_paths failed");
+        }
+    }
+
+    SSL_CTX_set_verify(ctx, verify_peer ? SSL_VERIFY_PEER : SSL_VERIFY_NONE, nullptr);
+    return lean_io_result_mk_ok(lean_box(0));
+}
+
+/* Std.Internal.SSL.Session.setServerName (ssl : @& Session) (host : @& String) : IO Unit */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_set_server_name(b_obj_arg ssl, b_obj_arg host) {
+    lean_ssl_session_object * ssl_obj = lean_to_ssl_session_object(ssl);
+    const char * server_name = lean_string_cstr(host);
+    if (SSL_set_tlsext_host_name(ssl_obj->ssl, server_name) != 1) {
+        return mk_ssl_io_error("SSL_set_tlsext_host_name failed");
+    }
+    return lean_io_result_mk_ok(lean_box(0));
+}
+
+/* Std.Internal.SSL.Session.verifyResult (ssl : @& Session) : IO UInt64 */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_verify_result(b_obj_arg ssl) {
+    lean_ssl_session_object * ssl_obj = lean_to_ssl_session_object(ssl);
+    long result = SSL_get_verify_result(ssl_obj->ssl);
+    return lean_io_result_mk_ok(lean_box_uint64((uint64_t)result));
+}
+
+/* Std.Internal.SSL.Session.handshake (ssl : @& Session) : IO Bool */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_handshake(b_obj_arg ssl) {
+    lean_ssl_session_object * ssl_obj = lean_to_ssl_session_object(ssl);
+    int rc = SSL_do_handshake(ssl_obj->ssl);
+
+    if (rc == 1) {
+        return lean_io_result_mk_ok(lean_box(1));
+    }
+
+    int err = SSL_get_error(ssl_obj->ssl, rc);
+    if (err == SSL_ERROR_WANT_READ || err == SSL_ERROR_WANT_WRITE || err == SSL_ERROR_ZERO_RETURN) {
+        return lean_io_result_mk_ok(lean_box(0));
+    }
+
+    return mk_ssl_io_error("SSL_do_handshake failed", err);
+}
+
+/* Std.Internal.SSL.Session.write (ssl : @& Session) (data : @& ByteArray) : IO Bool */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_write(b_obj_arg ssl, b_obj_arg data) {
+    lean_ssl_session_object * ssl_obj = lean_to_ssl_session_object(ssl);
+    size_t data_len = lean_sarray_size(data);
+    char const * payload = (char const*)lean_sarray_cptr(data);
+
+    if (data_len == 0) {
+        return lean_io_result_mk_ok(lean_box(1));
+    }
+
+    int err = 0;
+    int step = ssl_write_step(ssl_obj, payload, data_len, &err);
+    if (step == 1) {
+        return lean_io_result_mk_ok(lean_box(1));
+    }
+
+    // If renegotiation blocks writes, queue plaintext and retry after subsequent reads.
+    if (step == 0 && err == SSL_ERROR_WANT_READ) {
+        if (!append_pending_write(ssl_obj, payload, data_len)) {
+            return mk_ssl_io_error("failed to append pending SSL write");
+        }
+        return lean_io_result_mk_ok(lean_box(0));
+    }
+
+    if (step == 0 && (err == SSL_ERROR_WANT_WRITE || err == SSL_ERROR_ZERO_RETURN)) {
+        return lean_io_result_mk_ok(lean_box(0));
+    }
+
+    return mk_ssl_io_error("SSL_write failed", err);
+}
+
+/* Std.Internal.SSL.Session.read? (ssl : @& Session) (maxBytes : UInt64) : IO (Option ByteArray) */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_read(b_obj_arg ssl, uint64_t max_bytes) {
+    lean_ssl_session_object * ssl_obj = lean_to_ssl_session_object(ssl);
+
+    if (max_bytes == 0) {
+        return lean_io_result_mk_ok(mk_option_some(mk_empty_byte_array()));
+    }
+
+    if (max_bytes > INT_MAX) {
+        max_bytes = INT_MAX;
+    }
+
+    lean_object * out = lean_alloc_sarray(1, 0, max_bytes);
+    int rc = SSL_read(ssl_obj->ssl, (void*)lean_sarray_cptr(out), (int)max_bytes);
+
+    if (rc > 0) {
+        int flush_err = 0;
+        if (try_flush_pending_writes(ssl_obj, &flush_err) < 0) {
+            lean_dec(out);
+            return mk_ssl_io_error("pending SSL write flush failed", flush_err);
+        }
+        lean_sarray_set_size(out, (size_t)rc);
+        return lean_io_result_mk_ok(mk_option_some(out));
+    }
+
+    lean_dec(out);
+
+    int err = SSL_get_error(ssl_obj->ssl, rc);
+    if (err == SSL_ERROR_WANT_READ || err == SSL_ERROR_WANT_WRITE || err == SSL_ERROR_ZERO_RETURN) {
+        int flush_err = 0;
+        if (try_flush_pending_writes(ssl_obj, &flush_err) < 0) {
+            return mk_ssl_io_error("pending SSL write flush failed", flush_err);
+        }
+        return lean_io_result_mk_ok(mk_option_none());
+    }
+
+    return mk_ssl_io_error("SSL_read failed", err);
+}
+
+/* Std.Internal.SSL.Session.feedEncrypted (ssl : @& Session) (data : @& ByteArray) : IO UInt64 */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_feed_encrypted(b_obj_arg ssl, b_obj_arg data) {
+    lean_ssl_session_object * ssl_obj = lean_to_ssl_session_object(ssl);
+    size_t data_len = lean_sarray_size(data);
+
+    if (data_len == 0) {
+        return lean_io_result_mk_ok(lean_box_uint64(0));
+    }
+
+    if (data_len > INT_MAX) {
+        return mk_ssl_io_error("BIO_write input too large");
+    }
+
+    int rc = BIO_write(ssl_obj->read_bio, lean_sarray_cptr(data), (int)data_len);
+    if (rc >= 0) {
+        return lean_io_result_mk_ok(lean_box_uint64((uint64_t)rc));
+    }
+
+    if (BIO_should_retry(ssl_obj->read_bio)) {
+        return lean_io_result_mk_ok(lean_box_uint64(0));
+    }
+
+    return mk_ssl_io_error("BIO_write failed");
+}
+
+/* Std.Internal.SSL.Session.drainEncrypted (ssl : @& Session) : IO ByteArray */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_drain_encrypted(b_obj_arg ssl) {
+    lean_ssl_session_object * ssl_obj = lean_to_ssl_session_object(ssl);
+    size_t pending = BIO_ctrl_pending(ssl_obj->write_bio);
+
+    if (pending == 0) {
+        return lean_io_result_mk_ok(mk_empty_byte_array());
+    }
+
+    if (pending > INT_MAX) {
+        return mk_ssl_io_error("BIO_pending output too large");
+    }
+
+    lean_object * out = lean_alloc_sarray(1, 0, pending);
+    int rc = BIO_read(ssl_obj->write_bio, (void*)lean_sarray_cptr(out), (int)pending);
+
+    if (rc >= 0) {
+        lean_sarray_set_size(out, (size_t)rc);
+        return lean_io_result_mk_ok(out);
+    }
+
+    lean_dec(out);
+
+    if (BIO_should_retry(ssl_obj->write_bio)) {
+        return lean_io_result_mk_ok(mk_empty_byte_array());
+    }
+
+    return mk_ssl_io_error("BIO_read failed");
+}
+
+/* Std.Internal.SSL.Session.pendingEncrypted (ssl : @& Session) : IO UInt64 */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_pending_encrypted(b_obj_arg ssl) {
+    lean_ssl_session_object * ssl_obj = lean_to_ssl_session_object(ssl);
+    return lean_io_result_mk_ok(lean_box_uint64((uint64_t)BIO_ctrl_pending(ssl_obj->write_bio)));
+}
+
+/* Std.Internal.SSL.Session.pendingPlaintext (ssl : @& Session) : IO UInt64 */
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_pending_plaintext(b_obj_arg ssl) {
+    lean_ssl_session_object * ssl_obj = lean_to_ssl_session_object(ssl);
+    return lean_io_result_mk_ok(lean_box_uint64((uint64_t)SSL_pending(ssl_obj->ssl)));
+}
+
+#else
+
+void initialize_openssl_session() {}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_mk(uint8_t is_server) {
+    (void)is_server;
+    return io_result_mk_error("lean_uv_ssl_mk is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_configure_server_ctx(b_obj_arg cert_file, b_obj_arg key_file) {
+    (void)cert_file;
+    (void)key_file;
+    return io_result_mk_error("lean_uv_ssl_configure_server_ctx is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_configure_client_ctx(b_obj_arg ca_file, uint8_t verify_peer) {
+    (void)ca_file;
+    (void)verify_peer;
+    return io_result_mk_error("lean_uv_ssl_configure_client_ctx is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_set_server_name(b_obj_arg ssl, b_obj_arg host) {
+    (void)ssl;
+    (void)host;
+    return io_result_mk_error("lean_uv_ssl_set_server_name is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_verify_result(b_obj_arg ssl) {
+    (void)ssl;
+    return io_result_mk_error("lean_uv_ssl_verify_result is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_mk_server() {
+    return io_result_mk_error("lean_uv_ssl_mk_server is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_mk_client() {
+    return io_result_mk_error("lean_uv_ssl_mk_client is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_handshake(b_obj_arg ssl) {
+    (void)ssl;
+    return io_result_mk_error("lean_uv_ssl_handshake is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_write(b_obj_arg ssl, b_obj_arg data) {
+    (void)ssl;
+    (void)data;
+    return io_result_mk_error("lean_uv_ssl_write is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_read(b_obj_arg ssl, uint64_t max_bytes) {
+    (void)ssl;
+    (void)max_bytes;
+    return io_result_mk_error("lean_uv_ssl_read is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_feed_encrypted(b_obj_arg ssl, b_obj_arg data) {
+    (void)ssl;
+    (void)data;
+    return io_result_mk_error("lean_uv_ssl_feed_encrypted is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_drain_encrypted(b_obj_arg ssl) {
+    (void)ssl;
+    return io_result_mk_error("lean_uv_ssl_drain_encrypted is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_pending_encrypted(b_obj_arg ssl) {
+    (void)ssl;
+    return io_result_mk_error("lean_uv_ssl_pending_encrypted is not supported");
+}
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_pending_plaintext(b_obj_arg ssl) {
+    (void)ssl;
+    return io_result_mk_error("lean_uv_ssl_pending_plaintext is not supported");
+}
+
+#endif
+
+}

src/runtime/openssl/session.h

@@ -0,0 +1,55 @@
+/*
+Copyright (c) 2026 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Author: Sofia Rodrigues
+*/
+#pragma once
+
+#include <lean/lean.h>
+#include "runtime/io.h"
+#include "runtime/object.h"
+#include "runtime/openssl.h"
+
+#ifndef LEAN_EMSCRIPTEN
+#include <openssl/ssl.h>
+#include <openssl/bio.h>
+#endif
+
+namespace lean {
+
+static lean_external_class * g_ssl_session_external_class = nullptr;
+void initialize_openssl_session();
+
+#ifndef LEAN_EMSCRIPTEN
+typedef struct {
+    char * data;
+    size_t size;
+} lean_ssl_pending_write;
+
+typedef struct {
+    SSL * ssl;
+    BIO * read_bio;
+    BIO * write_bio;
+    size_t pending_writes_count;
+    lean_ssl_pending_write * pending_writes;
+} lean_ssl_session_object;
+
+static inline lean_object * lean_ssl_session_object_new(lean_ssl_session_object * s) { return lean_alloc_external(g_ssl_session_external_class, s); }
+static inline lean_ssl_session_object * lean_to_ssl_session_object(lean_object * o) { return (lean_ssl_session_object*)(lean_get_external_data(o)); }
+#endif
+
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_mk(uint8_t is_server);
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_mk_server();
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_mk_client();
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_configure_server_ctx(b_obj_arg cert_file, b_obj_arg key_file);
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_configure_client_ctx(b_obj_arg ca_file, uint8_t verify_peer);
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_set_server_name(b_obj_arg ssl, b_obj_arg host);
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_verify_result(b_obj_arg ssl);
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_handshake(b_obj_arg ssl);
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_write(b_obj_arg ssl, b_obj_arg data);
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_read(b_obj_arg ssl, uint64_t max_bytes);
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_feed_encrypted(b_obj_arg ssl, b_obj_arg data);
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_drain_encrypted(b_obj_arg ssl);
+extern "C" LEAN_EXPORT lean_obj_res lean_uv_ssl_pending_encrypted(b_obj_arg ssl);
+
+}