avformat: implement SChannel SSP TLS protocol

This implementation does not support TLS listen sockets and loading
CA/Certs from files.

The Windows API does not support loading PEM certs, and would either
require a manual loader or instead be limited to loading Windows PFX
certificates

TLS listen sockets would have to be implemented quite separately, as many
of the APIs are different for server-mode (as opposed to client mode).

configure

@@ -281,6 +281,8 @@ External library support:
   --enable-opengl          enable OpenGL rendering [no]
   --enable-openssl         enable openssl, needed for https support
                            if gnutls is not used [no]
+  --disable-schannel       disable SChannel SSP, needed for TLS support on
+                           Windows if openssl and gnutls are not used [autodetect]
   --disable-sdl            disable sdl [autodetect]
   --disable-securetransport disable Secure Transport, needed for TLS support
                            on OSX if openssl and gnutls are not used [autodetect]
@@ -1468,6 +1470,7 @@ EXTERNAL_LIBRARY_LIST="
     opencl
     opengl
     openssl
+    schannel
     sdl
     securetransport
     x11grab
@@ -2763,13 +2766,15 @@ sctp_protocol_deps="struct_sctp_event_subscribe"
 sctp_protocol_select="network"
 srtp_protocol_select="rtp_protocol"
 tcp_protocol_select="network"
-tls_gnutls_protocol_deps="gnutls !tls_securetransport_protocol"
+tls_gnutls_protocol_deps="gnutls !tls_schannel_protocol !tls_securetransport_protocol"
 tls_gnutls_protocol_select="tcp_protocol"
-tls_openssl_protocol_deps="openssl !tls_securetransport_protocol !tls_gnutls_protocol"
+tls_openssl_protocol_deps="openssl !tls_schannel_protocol !tls_securetransport_protocol !tls_gnutls_protocol"
 tls_openssl_protocol_select="tcp_protocol"
+tls_schannel_protocol_deps="schannel"
+tls_schannel_protocol_select="tcp_protocol"
 tls_securetransport_protocol_deps="securetransport"
 tls_securetransport_protocol_select="tcp_protocol"
-tls_protocol_deps_any="tls_securetransport_protocol tls_gnutls_protocol tls_openssl_protocol"
+tls_protocol_deps_any="tls_schannel_protocol tls_securetransport_protocol tls_gnutls_protocol tls_openssl_protocol"
 udp_protocol_select="network"
 udplite_protocol_select="network"
 unix_protocol_deps="sys_un_h"
@@ -5511,6 +5516,9 @@ disabled securetransport || { check_func SecIdentityCreate "-Wl,-framework,CoreF
     check_lib2 "Security/SecureTransport.h Security/Security.h" "SSLCreateContext SecItemImport" "-Wl,-framework,CoreFoundation -Wl,-framework,Security" &&
     enable securetransport; }
 
+disabled schannel || { check_func_headers "windows.h Security.h" InitializeSecurityContext -DSECURITY_WIN32 -lSecur32 &&
+                       enable schannel && add_extralibs -lSecur32; }
+
 makeinfo --version > /dev/null 2>&1 && enable makeinfo  || disable makeinfo
 enabled makeinfo \
     && [ 0$(makeinfo --version | grep "texinfo" | sed 's/.*texinfo[^0-9]*\([0-9]*\)\..*/\1/') -ge 5 ] \

libavformat/Makefile

@@ -544,6 +544,7 @@ OBJS-$(CONFIG_SUBFILE_PROTOCOL)          += subfile.o
 OBJS-$(CONFIG_TCP_PROTOCOL)              += tcp.o
 OBJS-$(CONFIG_TLS_GNUTLS_PROTOCOL)       += tls_gnutls.o tls.o
 OBJS-$(CONFIG_TLS_OPENSSL_PROTOCOL)      += tls_openssl.o tls.o
+OBJS-$(CONFIG_TLS_SCHANNEL_PROTOCOL)     += tls_schannel.o tls.o
 OBJS-$(CONFIG_TLS_SECURETRANSPORT_PROTOCOL) += tls_securetransport.o tls.o
 OBJS-$(CONFIG_UDP_PROTOCOL)              += udp.o
 OBJS-$(CONFIG_UDPLITE_PROTOCOL)          += udp.o

libavformat/allformats.c

@@ -395,6 +395,7 @@ void av_register_all(void)
     REGISTER_PROTOCOL(SRTP,             srtp);
     REGISTER_PROTOCOL(SUBFILE,          subfile);
     REGISTER_PROTOCOL(TCP,              tcp);
+    REGISTER_PROTOCOL(TLS_SCHANNEL,     tls_schannel);
     REGISTER_PROTOCOL(TLS_SECURETRANSPORT, tls_securetransport);
     REGISTER_PROTOCOL(TLS_GNUTLS,       tls_gnutls);
     REGISTER_PROTOCOL(TLS_OPENSSL,      tls_openssl);

libavformat/tls.h

@@ -26,7 +26,7 @@
 #include "url.h"
 #include "libavutil/opt.h"
 
-#define CONFIG_TLS_PROTOCOL (CONFIG_TLS_GNUTLS_PROTOCOL | CONFIG_TLS_OPENSSL_PROTOCOL | CONFIG_TLS_SECURETRANSPORT_PROTOCOL)
+#define CONFIG_TLS_PROTOCOL (CONFIG_TLS_GNUTLS_PROTOCOL | CONFIG_TLS_OPENSSL_PROTOCOL | CONFIG_TLS_SECURETRANSPORT_PROTOCOL | CONFIG_TLS_SCHANNEL_PROTOCOL)
 
 typedef struct TLSShared {
     char *ca_file;

libavformat/tls_schannel.c

+/*
+ * Copyright (c) 2015 Hendrik Leppkes
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/** Based on the CURL SChannel module */
+
+#include "avformat.h"
+#include "internal.h"
+#include "network.h"
+#include "os_support.h"
+#include "url.h"
+#include "tls.h"
+
+#define SECURITY_WIN32
+#include <security.h>
+#include <schnlsp.h>
+
+#define SCHANNEL_INITIAL_BUFFER_SIZE   4096
+#define SCHANNEL_FREE_BUFFER_SIZE      1024
+
+/* mingw does not define this symbol */
+#ifndef SECBUFFER_ALERT
+#define SECBUFFER_ALERT                17
+#endif
+
+typedef struct TLSContext {
+    const AVClass *class;
+    TLSShared tls_shared;
+
+    CredHandle cred_handle;
+    TimeStamp cred_timestamp;
+
+    CtxtHandle ctxt_handle;
+    TimeStamp ctxt_timestamp;
+
+    ULONG request_flags;
+    ULONG context_flags;
+
+    uint8_t *enc_buf;
+    int enc_buf_size;
+    int enc_buf_offset;
+
+    uint8_t *dec_buf;
+    int dec_buf_size;
+    int dec_buf_offset;
+
+    SecPkgContext_StreamSizes sizes;
+
+    int connected;
+    int connection_closed;
+    int sspi_close_notify;
+} TLSContext;
+
+static void init_sec_buffer(SecBuffer *buffer, unsigned long type,
+                            void *data, unsigned long size)
+{
+    buffer->cbBuffer   = size;
+    buffer->BufferType = type;
+    buffer->pvBuffer   = data;
+}
+
+static void init_sec_buffer_desc(SecBufferDesc *desc, SecBuffer *buffers,
+                                 unsigned long buffer_count)
+{
+    desc->ulVersion = SECBUFFER_VERSION;
+    desc->pBuffers = buffers;
+    desc->cBuffers = buffer_count;
+}
+
+static int tls_shutdown_client(URLContext *h)
+{
+    TLSContext *c = h->priv_data;
+    TLSShared *s = &c->tls_shared;
+    int ret;
+
+    if (c->connected) {
+        SecBufferDesc BuffDesc;
+        SecBuffer Buffer;
+        SECURITY_STATUS sspi_ret;
+        SecBuffer outbuf;
+        SecBufferDesc outbuf_desc;
+
+        DWORD dwshut = SCHANNEL_SHUTDOWN;
+        init_sec_buffer(&Buffer, SECBUFFER_TOKEN, &dwshut, sizeof(dwshut));
+        init_sec_buffer_desc(&BuffDesc, &Buffer, 1);
+
+        sspi_ret = ApplyControlToken(&c->ctxt_handle, &BuffDesc);
+        if (sspi_ret != SEC_E_OK)
+            av_log(h, AV_LOG_ERROR, "ApplyControlToken failed\n");
+
+        init_sec_buffer(&outbuf, SECBUFFER_EMPTY, NULL, 0);
+        init_sec_buffer_desc(&outbuf_desc, &outbuf, 1);
+
+        sspi_ret = InitializeSecurityContext(&c->cred_handle, &c->ctxt_handle, s->host,
+                                             c->request_flags, 0, 0, NULL, 0, &c->ctxt_handle,
+                                             &outbuf_desc, &c->context_flags, &c->ctxt_timestamp);
+        if (sspi_ret == SEC_E_OK || sspi_ret == SEC_I_CONTEXT_EXPIRED) {
+            ret = ffurl_write(s->tcp, outbuf.pvBuffer, outbuf.cbBuffer);
+            FreeContextBuffer(outbuf.pvBuffer);
+            if (ret < 0 || ret != outbuf.cbBuffer)
+                av_log(h, AV_LOG_ERROR, "Failed to send close message\n");
+        }
+
+        c->connected = 0;
+    }
+    return 0;
+}
+
+static int tls_close(URLContext *h)
+{
+    TLSContext *c = h->priv_data;
+
+    tls_shutdown_client(h);
+
+    DeleteSecurityContext(&c->ctxt_handle);
+    FreeCredentialsHandle(&c->cred_handle);
+
+    av_freep(&c->enc_buf);
+    c->enc_buf_size = c->enc_buf_offset = 0;
+
+    av_freep(&c->dec_buf);
+    c->dec_buf_size = c->dec_buf_offset = 0;
+
+    if (c->tls_shared.tcp)
+        ffurl_close(c->tls_shared.tcp);
+    return 0;
+}
+
+static int tls_client_handshake_loop(URLContext *h, int initial)
+{
+    TLSContext *c = h->priv_data;
+    TLSShared *s = &c->tls_shared;
+    SECURITY_STATUS sspi_ret;
+    SecBuffer outbuf[3];
+    SecBufferDesc outbuf_desc;
+    SecBuffer inbuf[2];
+    SecBufferDesc inbuf_desc;
+    int i, ret = 0, read_data = initial;
+
+    if (c->enc_buf == NULL) {
+        c->enc_buf_offset = 0;
+        ret = av_reallocp(&c->enc_buf, SCHANNEL_INITIAL_BUFFER_SIZE);
+        if (ret < 0)
+            goto fail;
+        c->enc_buf_size = SCHANNEL_INITIAL_BUFFER_SIZE;
+    }
+
+    if (c->dec_buf == NULL) {
+        c->dec_buf_offset = 0;
+        ret = av_reallocp(&c->dec_buf, SCHANNEL_INITIAL_BUFFER_SIZE);
+        if (ret < 0)
+            goto fail;
+        c->dec_buf_size = SCHANNEL_INITIAL_BUFFER_SIZE;
+    }
+
+    while (1) {
+        if (c->enc_buf_size - c->enc_buf_offset < SCHANNEL_FREE_BUFFER_SIZE) {
+            c->enc_buf_size = c->enc_buf_offset + SCHANNEL_FREE_BUFFER_SIZE;
+            ret = av_reallocp(&c->enc_buf, c->enc_buf_size);
+            if (ret < 0) {
+                c->enc_buf_size = c->enc_buf_offset = 0;
+                goto fail;
+            }
+        }
+
+        if (read_data) {
+            ret = ffurl_read(c->tls_shared.tcp, c->enc_buf + c->enc_buf_offset,
+                             c->enc_buf_size - c->enc_buf_offset);
+            if (ret < 0) {
+                av_log(h, AV_LOG_ERROR, "Failed to read handshake response\n");
+                goto fail;
+            }
+            c->enc_buf_offset += ret;
+        }
+
+        /* input buffers */
+        init_sec_buffer(&inbuf[0], SECBUFFER_TOKEN, av_malloc(c->enc_buf_offset), c->enc_buf_offset);
+        init_sec_buffer(&inbuf[1], SECBUFFER_EMPTY, NULL, 0);
+        init_sec_buffer_desc(&inbuf_desc, inbuf, 2);
+
+        if (inbuf[0].pvBuffer == NULL) {
+            av_log(h, AV_LOG_ERROR, "Failed to allocate input buffer\n");
+            ret = AVERROR(ENOMEM);
+            goto fail;
+        }
+
+        memcpy(inbuf[0].pvBuffer, c->enc_buf, c->enc_buf_offset);
+
+        /* output buffers */
+        init_sec_buffer(&outbuf[0], SECBUFFER_TOKEN, NULL, 0);
+        init_sec_buffer(&outbuf[1], SECBUFFER_ALERT, NULL, 0);
+        init_sec_buffer(&outbuf[2], SECBUFFER_EMPTY, NULL, 0);
+        init_sec_buffer_desc(&outbuf_desc, outbuf, 3);
+
+        sspi_ret = InitializeSecurityContext(&c->cred_handle, &c->ctxt_handle, s->host, c->request_flags,
+                                             0, 0, &inbuf_desc, 0, NULL, &outbuf_desc, &c->context_flags,
+                                             &c->ctxt_timestamp);
+        av_freep(&inbuf[0].pvBuffer);
+
+        if (sspi_ret == SEC_E_INCOMPLETE_MESSAGE) {
+            av_log(h, AV_LOG_DEBUG, "Received incomplete handshake, need more data\n");
+            read_data = 1;
+            continue;
+        }
+
+        /* remote requests a client certificate - attempt to continue without one anyway */
+        if (sspi_ret == SEC_I_INCOMPLETE_CREDENTIALS &&
+            !(c->request_flags & ISC_REQ_USE_SUPPLIED_CREDS)) {
+            av_log(h, AV_LOG_VERBOSE, "Client certificate has been requested, ignoring\n");
+            c->request_flags |= ISC_REQ_USE_SUPPLIED_CREDS;
+            read_data = 0;
+            continue;
+        }
+
+        /* continue handshake */
+        if (sspi_ret == SEC_I_CONTINUE_NEEDED || sspi_ret == SEC_E_OK) {
+            for (i = 0; i < 3; i++) {
+                if (outbuf[i].BufferType == SECBUFFER_TOKEN && outbuf[i].cbBuffer > 0) {
+                    ret = ffurl_write(c->tls_shared.tcp, outbuf[i].pvBuffer, outbuf[i].cbBuffer);
+                    if (ret < 0 || ret != outbuf[i].cbBuffer) {
+                        av_log(h, AV_LOG_VERBOSE, "Failed to send handshake data\n");
+                        ret = AVERROR(EIO);
+                        goto fail;
+                    }
+                }
+
+                if (outbuf[i].pvBuffer != NULL) {
+                    FreeContextBuffer(outbuf[i].pvBuffer);
+                    outbuf[i].pvBuffer = NULL;
+                }
+            }
+        } else {
+            if (sspi_ret == SEC_E_WRONG_PRINCIPAL)
+                av_log(h, AV_LOG_ERROR, "SNI or certificate check failed\n");
+            else
+                av_log(h, AV_LOG_ERROR, "Creating security context failed (0x%lx)\n", sspi_ret);
+            ret = AVERROR_UNKNOWN;
+            goto fail;
+        }
+
+        if (inbuf[1].BufferType == SECBUFFER_EXTRA && inbuf[1].cbBuffer > 0) {
+            if (c->enc_buf_offset > inbuf[1].cbBuffer) {
+                memmove(c->enc_buf, (c->enc_buf + c->enc_buf_offset) - inbuf[1].cbBuffer,
+                        inbuf[1].cbBuffer);
+                c->enc_buf_offset = inbuf[1].cbBuffer;
+                if (sspi_ret == SEC_I_CONTINUE_NEEDED) {
+                    read_data = 0;
+                    continue;
+                }
+            }
+        } else {
+            c->enc_buf_offset  = 0;
+        }
+
+        if (sspi_ret == SEC_I_CONTINUE_NEEDED) {
+            read_data = 1;
+            continue;
+        }
+
+        break;
+    }
+
+    return 0;
+
+fail:
+    /* free any remaining output data */
+    for (i = 0; i < 3; i++) {
+        if (outbuf[i].pvBuffer != NULL) {
+            FreeContextBuffer(outbuf[i].pvBuffer);
+            outbuf[i].pvBuffer = NULL;
+        }
+    }
+
+    return ret;
+}
+
+static int tls_client_handshake(URLContext *h)
+{
+    TLSContext *c = h->priv_data;
+    TLSShared *s = &c->tls_shared;
+    SecBuffer outbuf;
+    SecBufferDesc outbuf_desc;
+    SECURITY_STATUS sspi_ret;
+    int ret;
+
+    init_sec_buffer(&outbuf, SECBUFFER_EMPTY, NULL, 0);
+    init_sec_buffer_desc(&outbuf_desc, &outbuf, 1);
+
+    c->request_flags = ISC_REQ_SEQUENCE_DETECT | ISC_REQ_REPLAY_DETECT |
+                       ISC_REQ_CONFIDENTIALITY | ISC_REQ_ALLOCATE_MEMORY |
+                       ISC_REQ_STREAM;
+
+    sspi_ret = InitializeSecurityContext(&c->cred_handle, NULL, s->host, c->request_flags, 0, 0,
+                                         NULL, 0, &c->ctxt_handle, &outbuf_desc, &c->context_flags,
+                                         &c->ctxt_timestamp);
+    if (sspi_ret != SEC_I_CONTINUE_NEEDED) {
+        av_log(h, AV_LOG_ERROR, "Unable to create initial security context (0x%lx)\n", sspi_ret);
+        ret = AVERROR_UNKNOWN;
+        goto fail;
+    }
+
+    ret = ffurl_write(s->tcp, outbuf.pvBuffer, outbuf.cbBuffer);
+    FreeContextBuffer(outbuf.pvBuffer);
+    if (ret < 0 || ret != outbuf.cbBuffer) {
+        av_log(h, AV_LOG_ERROR, "Failed to send initial handshake data\n");
+        ret = AVERROR(EIO);
+        goto fail;
+    }
+
+    return tls_client_handshake_loop(h, 1);
+
+fail:
+    DeleteSecurityContext(&c->ctxt_handle);
+    return ret;
+}
+
+static int tls_open(URLContext *h, const char *uri, int flags, AVDictionary **options)
+{
+    TLSContext *c = h->priv_data;
+    TLSShared *s = &c->tls_shared;
+    SECURITY_STATUS sspi_ret;
+    SCHANNEL_CRED schannel_cred = { 0 };
+    int ret;
+
+    if ((ret = ff_tls_open_underlying(s, h, uri, options)) < 0)
+        goto fail;
+
+    if (s->listen) {
+        av_log(h, AV_LOG_ERROR, "TLS Listen Sockets with SChannel is not implemented.\n");
+        ret = AVERROR(EINVAL);
+        goto fail;
+    }
+
+    /* SChannel Options */
+    schannel_cred.dwVersion = SCHANNEL_CRED_VERSION;
+
+    if (s->verify)
+        schannel_cred.dwFlags = SCH_CRED_AUTO_CRED_VALIDATION |
+                                SCH_CRED_REVOCATION_CHECK_CHAIN;
+    else
+        schannel_cred.dwFlags = SCH_CRED_MANUAL_CRED_VALIDATION |
+                                SCH_CRED_IGNORE_NO_REVOCATION_CHECK |
+                                SCH_CRED_IGNORE_REVOCATION_OFFLINE;
+
+    /* Get credential handle */
+    sspi_ret = AcquireCredentialsHandle(NULL, (TCHAR *)UNISP_NAME, SECPKG_CRED_OUTBOUND,
+                                        NULL,  &schannel_cred, NULL, NULL, &c->cred_handle,
+                                        &c->cred_timestamp);
+    if (sspi_ret != SEC_E_OK) {
+        av_log(h, AV_LOG_ERROR, "Unable to acquire security credentials (0x%lx)\n", sspi_ret);
+        ret = AVERROR_UNKNOWN;
+        goto fail;
+    }
+
+    ret = tls_client_handshake(h);
+    if (ret < 0)
+        goto fail;
+
+    c->connected = 1;
+
+    return 0;
+
+fail:
+    tls_close(h);
+    return ret;
+}
+
+static int tls_read(URLContext *h, uint8_t *buf, int len)
+{
+    TLSContext *c = h->priv_data;
+    TLSShared *s = &c->tls_shared;
+    SECURITY_STATUS sspi_ret = SEC_E_OK;
+    SecBuffer inbuf[4];
+    SecBufferDesc inbuf_desc;
+    int size, ret;
+    int min_enc_buf_size = len + SCHANNEL_FREE_BUFFER_SIZE;
+
+    if (len <= c->dec_buf_offset)
+        goto cleanup;
+
+    if (c->sspi_close_notify)
+        goto cleanup;
+
+    if (!c->connection_closed) {
+        size = c->enc_buf_size - c->enc_buf_offset;
+        if (size < SCHANNEL_FREE_BUFFER_SIZE || c->enc_buf_size < min_enc_buf_size) {
+            c->enc_buf_size = c->enc_buf_offset + SCHANNEL_FREE_BUFFER_SIZE;
+            if (c->enc_buf_size < min_enc_buf_size)
+                c->enc_buf_size = min_enc_buf_size;
+            ret = av_reallocp(&c->enc_buf, c->enc_buf_size);
+            if (ret < 0) {
+                c->enc_buf_size = c->enc_buf_offset = 0;
+                return ret;
+            }
+        }
+
+        ret = ffurl_read(s->tcp, c->enc_buf + c->enc_buf_offset,
+                         c->enc_buf_size - c->enc_buf_offset);
+        if (ret < 0) {
+            av_log(h, AV_LOG_ERROR, "Unable to read from socket\n");
+            return ret;
+        } else if (ret == 0)
+            c->connection_closed = 1;
+
+        c->enc_buf_offset += ret;
+    }
+
+    while (c->enc_buf_offset > 0 && sspi_ret == SEC_E_OK && c->dec_buf_offset < len) {
+        /*  input buffer */
+        init_sec_buffer(&inbuf[0], SECBUFFER_DATA, c->enc_buf, c->enc_buf_offset);
+
+        /* additional buffers for possible output */
+        init_sec_buffer(&inbuf[1], SECBUFFER_EMPTY, NULL, 0);
+        init_sec_buffer(&inbuf[2], SECBUFFER_EMPTY, NULL, 0);
+        init_sec_buffer(&inbuf[3], SECBUFFER_EMPTY, NULL, 0);
+        init_sec_buffer_desc(&inbuf_desc, inbuf, 4);
+
+        sspi_ret = DecryptMessage(&c->ctxt_handle, &inbuf_desc, 0, NULL);
+        if (sspi_ret == SEC_E_OK || sspi_ret == SEC_I_RENEGOTIATE ||
+            sspi_ret == SEC_I_CONTEXT_EXPIRED) {
+            /* handle decrypted data */
+            if (inbuf[1].BufferType == SECBUFFER_DATA) {
+                /* grow buffer if needed */
+                size = inbuf[1].cbBuffer > SCHANNEL_FREE_BUFFER_SIZE ?
+                       inbuf[1].cbBuffer : SCHANNEL_FREE_BUFFER_SIZE;
+                if (c->dec_buf_size - c->dec_buf_offset < size || c->dec_buf_size < len)  {
+                    c->dec_buf_size = c->dec_buf_offset + size;
+                    if (c->dec_buf_size < len)
+                        c->dec_buf_size = len;
+                    ret = av_reallocp(&c->dec_buf, c->dec_buf_size);
+                    if (ret < 0) {
+                        c->dec_buf_size = c->dec_buf_offset = 0;
+                        return ret;
+                    }
+                }
+
+                /* copy decrypted data to buffer */
+                size = inbuf[1].cbBuffer;
+                if (size) {
+                    memcpy(c->dec_buf + c->dec_buf_offset, inbuf[1].pvBuffer, size);
+                    c->dec_buf_offset += size;
+                }
+            }
+            if (inbuf[3].BufferType == SECBUFFER_EXTRA && inbuf[3].cbBuffer > 0) {
+                if (c->enc_buf_offset > inbuf[3].cbBuffer) {
+                    memmove(c->enc_buf, (c->enc_buf + c->enc_buf_offset) - inbuf[3].cbBuffer,
+                    inbuf[3].cbBuffer);
+                    c->enc_buf_offset = inbuf[3].cbBuffer;
+                }
+            } else
+                c->enc_buf_offset = 0;
+
+            if (sspi_ret == SEC_I_RENEGOTIATE) {
+                if (c->enc_buf_offset) {
+                    av_log(h, AV_LOG_ERROR, "Cannot renegotiate, encrypted data buffer not empty\n");
+                    ret = AVERROR_UNKNOWN;
+                    goto cleanup;
+                }
+
+                av_log(h, AV_LOG_VERBOSE, "Re-negotiating security context\n");
+                ret = tls_client_handshake_loop(h, 0);
+                if (ret < 0) {
+                    goto cleanup;
+                }
+                sspi_ret = SEC_E_OK;
+                continue;
+            } else if (sspi_ret == SEC_I_CONTEXT_EXPIRED) {
+                c->sspi_close_notify = 1;
+                if (!c->connection_closed) {
+                    c->connection_closed = 1;
+                    av_log(h, AV_LOG_VERBOSE, "Server closed the connection\n");
+                }
+                ret = 0;
+                goto cleanup;
+            }
+        } else if (sspi_ret == SEC_E_INCOMPLETE_MESSAGE) {
+            ret = AVERROR(EAGAIN);
+            goto cleanup;
+        } else {
+            av_log(h, AV_LOG_ERROR, "Unable to decrypt message\n");
+            ret = AVERROR(EIO);
+            goto cleanup;
+        }
+    }
+
+    ret = 0;
+
+cleanup:
+    size = FFMIN(len, c->dec_buf_offset);
+    if (size) {
+        memcpy(buf, c->dec_buf, size);
+        memmove(c->dec_buf, c->dec_buf + size, c->dec_buf_offset - size);
+        c->dec_buf_offset -= size;
+
+        return size;
+    }
+
+    if (ret == 0 && !c->connection_closed)
+        ret = AVERROR(EAGAIN);
+
+    return ret < 0 ? ret : 0;
+}
+
+static int tls_write(URLContext *h, const uint8_t *buf, int len)
+{
+    TLSContext *c = h->priv_data;
+    TLSShared *s = &c->tls_shared;
+    SECURITY_STATUS sspi_ret;
+    int ret = 0, data_size;
+    uint8_t *data = NULL;
+    SecBuffer outbuf[4];
+    SecBufferDesc outbuf_desc;
+
+    if (c->sizes.cbMaximumMessage == 0) {
+        sspi_ret = QueryContextAttributes(&c->ctxt_handle, SECPKG_ATTR_STREAM_SIZES, &c->sizes);
+        if (sspi_ret != SEC_E_OK)
+            return AVERROR_UNKNOWN;
+    }
+
+    /* limit how much data we can consume */
+    len = FFMIN(len, c->sizes.cbMaximumMessage);
+
+    data_size = c->sizes.cbHeader + len + c->sizes.cbTrailer;
+    data = av_malloc(data_size);
+    if (data == NULL)
+        return AVERROR(ENOMEM);
+
+    init_sec_buffer(&outbuf[0], SECBUFFER_STREAM_HEADER,
+                  data, c->sizes.cbHeader);
+    init_sec_buffer(&outbuf[1], SECBUFFER_DATA,
+                  data + c->sizes.cbHeader, len);
+    init_sec_buffer(&outbuf[2], SECBUFFER_STREAM_TRAILER,
+                  data + c->sizes.cbHeader + len,
+                  c->sizes.cbTrailer);
+    init_sec_buffer(&outbuf[3], SECBUFFER_EMPTY, NULL, 0);
+    init_sec_buffer_desc(&outbuf_desc, outbuf, 4);
+
+    memcpy(outbuf[1].pvBuffer, buf, len);
+
+    sspi_ret = EncryptMessage(&c->ctxt_handle, 0, &outbuf_desc, 0);
+    if (sspi_ret == SEC_E_OK)  {
+        len = outbuf[0].cbBuffer + outbuf[1].cbBuffer + outbuf[2].cbBuffer;
+        ret = ffurl_write(s->tcp, data, len);
+        if (ret < 0 || ret != len) {
+            ret = AVERROR(EIO);
+            av_log(h, AV_LOG_ERROR, "Writing encrypted data to socket failed\n");
+            goto done;
+        }
+    } else {
+        av_log(h, AV_LOG_ERROR, "Encrypting data failed\n");
+        if (sspi_ret == SEC_E_INSUFFICIENT_MEMORY)
+            ret = AVERROR(ENOMEM);
+        else
+            ret = AVERROR(EIO);
+        goto done;
+    }
+
+done:
+    av_freep(&data);
+    return ret < 0 ? ret : outbuf[1].cbBuffer;
+}
+
+static const AVOption options[] = {
+    TLS_COMMON_OPTIONS(TLSContext, tls_shared),
+    { NULL }
+};
+
+static const AVClass tls_class = {
+    .class_name = "tls",
+    .item_name  = av_default_item_name,
+    .option     = options,
+    .version    = LIBAVUTIL_VERSION_INT,
+};
+
+URLProtocol ff_tls_schannel_protocol = {
+    .name           = "tls",
+    .url_open2      = tls_open,
+    .url_read       = tls_read,
+    .url_write      = tls_write,
+    .url_close      = tls_close,
+    .priv_data_size = sizeof(TLSContext),
+    .flags          = URL_PROTOCOL_FLAG_NETWORK,
+    .priv_data_class = &tls_class,
+};