Imported Upstream version 3.9.4upstream/3.9.4

1 files changed, 1728 insertions, 0 deletions

diff --git a/Utilities/cmcurl/lib/vtls/schannel.c b/Utilities/cmcurl/lib/vtls/schannel.c
new file mode 100644
index 000000000..94603018b
--- /dev/null
+++ b/Utilities/cmcurl/lib/vtls/schannel.c
@@ -0,0 +1,1728 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 2012 - 2016, Marc Hoersken, <info@marc-hoersken.de>
+ * Copyright (C) 2012, Mark Salisbury, <mark.salisbury@hp.com>
+ * Copyright (C) 2012 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+
+/*
+ * Source file for all SChannel-specific code for the TLS/SSL layer. No code
+ * but vtls.c should ever call or use these functions.
+ *
+ */
+
+/*
+ * Based upon the PolarSSL implementation in polarssl.c and polarssl.h:
+ *   Copyright (C) 2010, 2011, Hoi-Ho Chan, <hoiho.chan@gmail.com>
+ *
+ * Based upon the CyaSSL implementation in cyassl.c and cyassl.h:
+ *   Copyright (C) 1998 - 2012, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * Thanks for code and inspiration!
+ */
+
+#include "curl_setup.h"
+
+#ifdef USE_SCHANNEL
+
+#ifndef USE_WINDOWS_SSPI
+#  error "Can't compile SCHANNEL support without SSPI."
+#endif
+
+#include "curl_sspi.h"
+#include "schannel.h"
+#include "vtls.h"
+#include "sendf.h"
+#include "connect.h" /* for the connect timeout */
+#include "strerror.h"
+#include "select.h" /* for the socket readyness */
+#include "inet_pton.h" /* for IP addr SNI check */
+#include "curl_multibyte.h"
+#include "warnless.h"
+#include "x509asn1.h"
+#include "curl_printf.h"
+#include "system_win32.h"
+#include "hostcheck.h"
+
+ /* The last #include file should be: */
+#include "curl_memory.h"
+#include "memdebug.h"
+
+/* ALPN requires version 8.1 of the Windows SDK, which was
+   shipped with Visual Studio 2013, aka _MSC_VER 1800:
+
+   https://technet.microsoft.com/en-us/library/hh831771%28v=ws.11%29.aspx
+*/
+#if defined(_MSC_VER) && (_MSC_VER >= 1800) && !defined(_USING_V110_SDK71_)
+#  define HAS_ALPN 1
+#endif
+
+/* Uncomment to force verbose output
+ * #define infof(x, y, ...) printf(y, __VA_ARGS__)
+ * #define failf(x, y, ...) printf(y, __VA_ARGS__)
+ */
+
+static Curl_recv schannel_recv;
+static Curl_send schannel_send;
+
+#ifdef _WIN32_WCE
+static CURLcode verify_certificate(struct connectdata *conn, int sockindex);
+#endif
+
+static void InitSecBuffer(SecBuffer *buffer, unsigned long BufType,
+                          void *BufDataPtr, unsigned long BufByteSize)
+{
+  buffer->cbBuffer = BufByteSize;
+  buffer->BufferType = BufType;
+  buffer->pvBuffer = BufDataPtr;
+}
+
+static void InitSecBufferDesc(SecBufferDesc *desc, SecBuffer *BufArr,
+                              unsigned long NumArrElem)
+{
+  desc->ulVersion = SECBUFFER_VERSION;
+  desc->pBuffers = BufArr;
+  desc->cBuffers = NumArrElem;
+}
+
+static CURLcode
+set_ssl_version_min_max(SCHANNEL_CRED *schannel_cred, struct connectdata *conn)
+{
+  struct Curl_easy *data = conn->data;
+  long ssl_version = SSL_CONN_CONFIG(version);
+  long ssl_version_max = SSL_CONN_CONFIG(version_max);
+  long i = ssl_version;
+
+  switch(ssl_version_max) {
+    case CURL_SSLVERSION_MAX_NONE:
+      ssl_version_max = ssl_version << 16;
+      break;
+    case CURL_SSLVERSION_MAX_DEFAULT:
+      ssl_version_max = CURL_SSLVERSION_MAX_TLSv1_2;
+      break;
+  }
+  for(; i <= (ssl_version_max >> 16); ++i) {
+    switch(i) {
+      case CURL_SSLVERSION_TLSv1_0:
+        schannel_cred->grbitEnabledProtocols |= SP_PROT_TLS1_0_CLIENT;
+        break;
+      case CURL_SSLVERSION_TLSv1_1:
+        schannel_cred->grbitEnabledProtocols |= SP_PROT_TLS1_1_CLIENT;
+        break;
+      case CURL_SSLVERSION_TLSv1_2:
+        schannel_cred->grbitEnabledProtocols |= SP_PROT_TLS1_2_CLIENT;
+        break;
+      case CURL_SSLVERSION_TLSv1_3:
+        failf(data, "Schannel: TLS 1.3 is not yet supported");
+        return CURLE_SSL_CONNECT_ERROR;
+    }
+  }
+  return CURLE_OK;
+}
+
+static CURLcode
+schannel_connect_step1(struct connectdata *conn, int sockindex)
+{
+  ssize_t written = -1;
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  SecBuffer outbuf;
+  SecBufferDesc outbuf_desc;
+  SecBuffer inbuf;
+  SecBufferDesc inbuf_desc;
+#ifdef HAS_ALPN
+  unsigned char alpn_buffer[128];
+#endif
+  SCHANNEL_CRED schannel_cred;
+  SECURITY_STATUS sspi_status = SEC_E_OK;
+  struct curl_schannel_cred *old_cred = NULL;
+  struct in_addr addr;
+#ifdef ENABLE_IPV6
+  struct in6_addr addr6;
+#endif
+  TCHAR *host_name;
+  CURLcode result;
+  char * const hostname = SSL_IS_PROXY() ? conn->http_proxy.host.name :
+    conn->host.name;
+
+  infof(data, "schannel: SSL/TLS connection with %s port %hu (step 1/3)\n",
+        hostname, conn->remote_port);
+
+  if(Curl_verify_windows_version(5, 1, PLATFORM_WINNT,
+                                 VERSION_LESS_THAN_EQUAL)) {
+     /* SChannel in Windows XP (OS version 5.1) uses legacy handshakes and
+        algorithms that may not be supported by all servers. */
+     infof(data, "schannel: WinSSL version is old and may not be able to "
+           "connect to some servers due to lack of SNI, algorithms, etc.\n");
+  }
+
+#ifdef HAS_ALPN
+  /* ALPN is only supported on Windows 8.1 / Server 2012 R2 and above.
+     Also it doesn't seem to be supported for Wine, see curl bug #983. */
+  connssl->use_alpn = conn->bits.tls_enable_alpn &&
+                      !GetProcAddress(GetModuleHandleA("ntdll"),
+                                      "wine_get_version") &&
+                      Curl_verify_windows_version(6, 3, PLATFORM_WINNT,
+                                                  VERSION_GREATER_THAN_EQUAL);
+#else
+  connssl->use_alpn = false;
+#endif
+
+  connssl->cred = NULL;
+
+  /* check for an existing re-usable credential handle */
+  if(SSL_SET_OPTION(primary.sessionid)) {
+    Curl_ssl_sessionid_lock(conn);
+    if(!Curl_ssl_getsessionid(conn, (void **)&old_cred, NULL, sockindex)) {
+      connssl->cred = old_cred;
+      infof(data, "schannel: re-using existing credential handle\n");
+
+      /* increment the reference counter of the credential/session handle */
+      connssl->cred->refcount++;
+      infof(data, "schannel: incremented credential handle refcount = %d\n",
+            connssl->cred->refcount);
+    }
+    Curl_ssl_sessionid_unlock(conn);
+  }
+
+  if(!connssl->cred) {
+    /* setup Schannel API options */
+    memset(&schannel_cred, 0, sizeof(schannel_cred));
+    schannel_cred.dwVersion = SCHANNEL_CRED_VERSION;
+
+    if(conn->ssl_config.verifypeer) {
+#ifdef _WIN32_WCE
+      /* certificate validation on CE doesn't seem to work right; we'll
+         do it following a more manual process. */
+      schannel_cred.dwFlags = SCH_CRED_MANUAL_CRED_VALIDATION |
+        SCH_CRED_IGNORE_NO_REVOCATION_CHECK |
+        SCH_CRED_IGNORE_REVOCATION_OFFLINE;
+#else
+      schannel_cred.dwFlags = SCH_CRED_AUTO_CRED_VALIDATION;
+      /* TODO s/data->set.ssl.no_revoke/SSL_SET_OPTION(no_revoke)/g */
+      if(data->set.ssl.no_revoke)
+        schannel_cred.dwFlags |= SCH_CRED_IGNORE_NO_REVOCATION_CHECK |
+                                 SCH_CRED_IGNORE_REVOCATION_OFFLINE;
+      else
+        schannel_cred.dwFlags |= SCH_CRED_REVOCATION_CHECK_CHAIN;
+#endif
+      if(data->set.ssl.no_revoke)
+        infof(data, "schannel: disabled server certificate revocation "
+                    "checks\n");
+      else
+        infof(data, "schannel: checking server certificate revocation\n");
+    }
+    else {
+      schannel_cred.dwFlags = SCH_CRED_MANUAL_CRED_VALIDATION |
+        SCH_CRED_IGNORE_NO_REVOCATION_CHECK |
+        SCH_CRED_IGNORE_REVOCATION_OFFLINE;
+      infof(data, "schannel: disabled server certificate revocation checks\n");
+    }
+
+    if(!conn->ssl_config.verifyhost) {
+      schannel_cred.dwFlags |= SCH_CRED_NO_SERVERNAME_CHECK;
+      infof(data, "schannel: verifyhost setting prevents Schannel from "
+            "comparing the supplied target name with the subject "
+            "names in server certificates.\n");
+    }
+
+    switch(conn->ssl_config.version) {
+    case CURL_SSLVERSION_DEFAULT:
+    case CURL_SSLVERSION_TLSv1:
+      schannel_cred.grbitEnabledProtocols = SP_PROT_TLS1_0_CLIENT |
+        SP_PROT_TLS1_1_CLIENT |
+        SP_PROT_TLS1_2_CLIENT;
+      break;
+    case CURL_SSLVERSION_TLSv1_0:
+    case CURL_SSLVERSION_TLSv1_1:
+    case CURL_SSLVERSION_TLSv1_2:
+    case CURL_SSLVERSION_TLSv1_3:
+      {
+        result = set_ssl_version_min_max(&schannel_cred, conn);
+        if(result != CURLE_OK)
+          return result;
+        break;
+      }
+    case CURL_SSLVERSION_SSLv3:
+      schannel_cred.grbitEnabledProtocols = SP_PROT_SSL3_CLIENT;
+      break;
+    case CURL_SSLVERSION_SSLv2:
+      schannel_cred.grbitEnabledProtocols = SP_PROT_SSL2_CLIENT;
+      break;
+    default:
+      failf(data, "Unrecognized parameter passed via CURLOPT_SSLVERSION");
+      return CURLE_SSL_CONNECT_ERROR;
+    }
+
+    /* allocate memory for the re-usable credential handle */
+    connssl->cred = (struct curl_schannel_cred *)
+      malloc(sizeof(struct curl_schannel_cred));
+    if(!connssl->cred) {
+      failf(data, "schannel: unable to allocate memory");
+      return CURLE_OUT_OF_MEMORY;
+    }
+    memset(connssl->cred, 0, sizeof(struct curl_schannel_cred));
+    connssl->cred->refcount = 1;
+
+    /* https://msdn.microsoft.com/en-us/library/windows/desktop/aa374716.aspx
+       */
+    sspi_status =
+      s_pSecFn->AcquireCredentialsHandle(NULL, (TCHAR *)UNISP_NAME,
+                                         SECPKG_CRED_OUTBOUND, NULL,
+                                         &schannel_cred, NULL, NULL,
+                                         &connssl->cred->cred_handle,
+                                         &connssl->cred->time_stamp);
+
+    if(sspi_status != SEC_E_OK) {
+      if(sspi_status == SEC_E_WRONG_PRINCIPAL)
+        failf(data, "schannel: SNI or certificate check failed: %s",
+              Curl_sspi_strerror(conn, sspi_status));
+      else
+        failf(data, "schannel: AcquireCredentialsHandle failed: %s",
+              Curl_sspi_strerror(conn, sspi_status));
+      Curl_safefree(connssl->cred);
+      return CURLE_SSL_CONNECT_ERROR;
+    }
+  }
+
+  /* Warn if SNI is disabled due to use of an IP address */
+  if(Curl_inet_pton(AF_INET, hostname, &addr)
+#ifdef ENABLE_IPV6
+     || Curl_inet_pton(AF_INET6, hostname, &addr6)
+#endif
+    ) {
+    infof(data, "schannel: using IP address, SNI is not supported by OS.\n");
+  }
+
+#ifdef HAS_ALPN
+  if(connssl->use_alpn) {
+    int cur = 0;
+    int list_start_index = 0;
+    unsigned int *extension_len = NULL;
+    unsigned short* list_len = NULL;
+
+    /* The first four bytes will be an unsigned int indicating number
+       of bytes of data in the rest of the the buffer. */
+    extension_len = (unsigned int *)(&alpn_buffer[cur]);
+    cur += sizeof(unsigned int);
+
+    /* The next four bytes are an indicator that this buffer will contain
+       ALPN data, as opposed to NPN, for example. */
+    *(unsigned int *)&alpn_buffer[cur] =
+      SecApplicationProtocolNegotiationExt_ALPN;
+    cur += sizeof(unsigned int);
+
+    /* The next two bytes will be an unsigned short indicating the number
+       of bytes used to list the preferred protocols. */
+    list_len = (unsigned short*)(&alpn_buffer[cur]);
+    cur += sizeof(unsigned short);
+
+    list_start_index = cur;
+
+#ifdef USE_NGHTTP2
+    if(data->set.httpversion >= CURL_HTTP_VERSION_2) {
+      memcpy(&alpn_buffer[cur], NGHTTP2_PROTO_ALPN, NGHTTP2_PROTO_ALPN_LEN);
+      cur += NGHTTP2_PROTO_ALPN_LEN;
+      infof(data, "schannel: ALPN, offering %s\n", NGHTTP2_PROTO_VERSION_ID);
+    }
+#endif
+
+    alpn_buffer[cur++] = ALPN_HTTP_1_1_LENGTH;
+    memcpy(&alpn_buffer[cur], ALPN_HTTP_1_1, ALPN_HTTP_1_1_LENGTH);
+    cur += ALPN_HTTP_1_1_LENGTH;
+    infof(data, "schannel: ALPN, offering %s\n", ALPN_HTTP_1_1);
+
+    *list_len = curlx_uitous(cur - list_start_index);
+    *extension_len = *list_len + sizeof(unsigned int) + sizeof(unsigned short);
+
+    InitSecBuffer(&inbuf, SECBUFFER_APPLICATION_PROTOCOLS, alpn_buffer, cur);
+    InitSecBufferDesc(&inbuf_desc, &inbuf, 1);
+  }
+  else
+  {
+    InitSecBuffer(&inbuf, SECBUFFER_EMPTY, NULL, 0);
+    InitSecBufferDesc(&inbuf_desc, &inbuf, 1);
+  }
+#else /* HAS_ALPN */
+  InitSecBuffer(&inbuf, SECBUFFER_EMPTY, NULL, 0);
+  InitSecBufferDesc(&inbuf_desc, &inbuf, 1);
+#endif
+
+  /* setup output buffer */
+  InitSecBuffer(&outbuf, SECBUFFER_EMPTY, NULL, 0);
+  InitSecBufferDesc(&outbuf_desc, &outbuf, 1);
+
+  /* setup request flags */
+  connssl->req_flags = ISC_REQ_SEQUENCE_DETECT | ISC_REQ_REPLAY_DETECT |
+    ISC_REQ_CONFIDENTIALITY | ISC_REQ_ALLOCATE_MEMORY |
+    ISC_REQ_STREAM;
+
+  /* allocate memory for the security context handle */
+  connssl->ctxt = (struct curl_schannel_ctxt *)
+    malloc(sizeof(struct curl_schannel_ctxt));
+  if(!connssl->ctxt) {
+    failf(data, "schannel: unable to allocate memory");
+    return CURLE_OUT_OF_MEMORY;
+  }
+  memset(connssl->ctxt, 0, sizeof(struct curl_schannel_ctxt));
+
+  host_name = Curl_convert_UTF8_to_tchar(hostname);
+  if(!host_name)
+    return CURLE_OUT_OF_MEMORY;
+
+  /* Schannel InitializeSecurityContext:
+     https://msdn.microsoft.com/en-us/library/windows/desktop/aa375924.aspx
+
+     At the moment we don't pass inbuf unless we're using ALPN since we only
+     use it for that, and Wine (for which we currently disable ALPN) is giving
+     us problems with inbuf regardless. https://github.com/curl/curl/issues/983
+  */
+  sspi_status = s_pSecFn->InitializeSecurityContext(
+    &connssl->cred->cred_handle, NULL, host_name, connssl->req_flags, 0, 0,
+    (connssl->use_alpn ? &inbuf_desc : NULL),
+    0, &connssl->ctxt->ctxt_handle,
+    &outbuf_desc, &connssl->ret_flags, &connssl->ctxt->time_stamp);
+
+  Curl_unicodefree(host_name);
+
+  if(sspi_status != SEC_I_CONTINUE_NEEDED) {
+    if(sspi_status == SEC_E_WRONG_PRINCIPAL)
+      failf(data, "schannel: SNI or certificate check failed: %s",
+            Curl_sspi_strerror(conn, sspi_status));
+    else
+      failf(data, "schannel: initial InitializeSecurityContext failed: %s",
+            Curl_sspi_strerror(conn, sspi_status));
+    Curl_safefree(connssl->ctxt);
+    return CURLE_SSL_CONNECT_ERROR;
+  }
+
+  infof(data, "schannel: sending initial handshake data: "
+        "sending %lu bytes...\n", outbuf.cbBuffer);
+
+  /* send initial handshake data which is now stored in output buffer */
+  result = Curl_write_plain(conn, conn->sock[sockindex], outbuf.pvBuffer,
+                            outbuf.cbBuffer, &written);
+  s_pSecFn->FreeContextBuffer(outbuf.pvBuffer);
+  if((result != CURLE_OK) || (outbuf.cbBuffer != (size_t) written)) {
+    failf(data, "schannel: failed to send initial handshake data: "
+          "sent %zd of %lu bytes", written, outbuf.cbBuffer);
+    return CURLE_SSL_CONNECT_ERROR;
+  }
+
+  infof(data, "schannel: sent initial handshake data: "
+        "sent %zd bytes\n", written);
+
+  connssl->recv_unrecoverable_err = CURLE_OK;
+  connssl->recv_sspi_close_notify = false;
+  connssl->recv_connection_closed = false;
+  connssl->encdata_is_incomplete = false;
+
+  /* continue to second handshake step */
+  connssl->connecting_state = ssl_connect_2;
+
+  return CURLE_OK;
+}
+
+static CURLcode
+schannel_connect_step2(struct connectdata *conn, int sockindex)
+{
+  int i;
+  ssize_t nread = -1, written = -1;
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  unsigned char *reallocated_buffer;
+  size_t reallocated_length;
+  SecBuffer outbuf[3];
+  SecBufferDesc outbuf_desc;
+  SecBuffer inbuf[2];
+  SecBufferDesc inbuf_desc;
+  SECURITY_STATUS sspi_status = SEC_E_OK;
+  TCHAR *host_name;
+  CURLcode result;
+  bool doread;
+  char * const hostname = SSL_IS_PROXY() ? conn->http_proxy.host.name :
+    conn->host.name;
+
+  doread = (connssl->connecting_state != ssl_connect_2_writing) ? TRUE : FALSE;
+
+  infof(data, "schannel: SSL/TLS connection with %s port %hu (step 2/3)\n",
+        hostname, conn->remote_port);
+
+  if(!connssl->cred || !connssl->ctxt)
+    return CURLE_SSL_CONNECT_ERROR;
+
+  /* buffer to store previously received and decrypted data */
+  if(connssl->decdata_buffer == NULL) {
+    connssl->decdata_offset = 0;
+    connssl->decdata_length = CURL_SCHANNEL_BUFFER_INIT_SIZE;
+    connssl->decdata_buffer = malloc(connssl->decdata_length);
+    if(connssl->decdata_buffer == NULL) {
+      failf(data, "schannel: unable to allocate memory");
+      return CURLE_OUT_OF_MEMORY;
+    }
+  }
+
+  /* buffer to store previously received and encrypted data */
+  if(connssl->encdata_buffer == NULL) {
+    connssl->encdata_is_incomplete = false;
+    connssl->encdata_offset = 0;
+    connssl->encdata_length = CURL_SCHANNEL_BUFFER_INIT_SIZE;
+    connssl->encdata_buffer = malloc(connssl->encdata_length);
+    if(connssl->encdata_buffer == NULL) {
+      failf(data, "schannel: unable to allocate memory");
+      return CURLE_OUT_OF_MEMORY;
+    }
+  }
+
+  /* if we need a bigger buffer to read a full message, increase buffer now */
+  if(connssl->encdata_length - connssl->encdata_offset <
+     CURL_SCHANNEL_BUFFER_FREE_SIZE) {
+    /* increase internal encrypted data buffer */
+    reallocated_length = connssl->encdata_offset +
+      CURL_SCHANNEL_BUFFER_FREE_SIZE;
+    reallocated_buffer = realloc(connssl->encdata_buffer,
+                                 reallocated_length);
+
+    if(reallocated_buffer == NULL) {
+      failf(data, "schannel: unable to re-allocate memory");
+      return CURLE_OUT_OF_MEMORY;
+    }
+    else {
+      connssl->encdata_buffer = reallocated_buffer;
+      connssl->encdata_length = reallocated_length;
+    }
+  }
+
+  for(;;) {
+    if(doread) {
+      /* read encrypted handshake data from socket */
+      result = Curl_read_plain(conn->sock[sockindex],
+                               (char *) (connssl->encdata_buffer +
+                                         connssl->encdata_offset),
+                               connssl->encdata_length -
+                               connssl->encdata_offset,
+                               &nread);
+      if(result == CURLE_AGAIN) {
+        if(connssl->connecting_state != ssl_connect_2_writing)
+          connssl->connecting_state = ssl_connect_2_reading;
+        infof(data, "schannel: failed to receive handshake, "
+              "need more data\n");
+        return CURLE_OK;
+      }
+      else if((result != CURLE_OK) || (nread == 0)) {
+        failf(data, "schannel: failed to receive handshake, "
+              "SSL/TLS connection failed");
+        return CURLE_SSL_CONNECT_ERROR;
+      }
+
+      /* increase encrypted data buffer offset */
+      connssl->encdata_offset += nread;
+      connssl->encdata_is_incomplete = false;
+      infof(data, "schannel: encrypted data got %zd\n", nread);
+    }
+
+    infof(data, "schannel: encrypted data buffer: offset %zu length %zu\n",
+          connssl->encdata_offset, connssl->encdata_length);
+
+    /* setup input buffers */
+    InitSecBuffer(&inbuf[0], SECBUFFER_TOKEN, malloc(connssl->encdata_offset),
+                  curlx_uztoul(connssl->encdata_offset));
+    InitSecBuffer(&inbuf[1], SECBUFFER_EMPTY, NULL, 0);
+    InitSecBufferDesc(&inbuf_desc, inbuf, 2);
+
+    /* setup output buffers */
+    InitSecBuffer(&outbuf[0], SECBUFFER_TOKEN, NULL, 0);
+    InitSecBuffer(&outbuf[1], SECBUFFER_ALERT, NULL, 0);
+    InitSecBuffer(&outbuf[2], SECBUFFER_EMPTY, NULL, 0);
+    InitSecBufferDesc(&outbuf_desc, outbuf, 3);
+
+    if(inbuf[0].pvBuffer == NULL) {
+      failf(data, "schannel: unable to allocate memory");
+      return CURLE_OUT_OF_MEMORY;
+    }
+
+    /* copy received handshake data into input buffer */
+    memcpy(inbuf[0].pvBuffer, connssl->encdata_buffer,
+           connssl->encdata_offset);
+
+    host_name = Curl_convert_UTF8_to_tchar(hostname);
+    if(!host_name)
+      return CURLE_OUT_OF_MEMORY;
+
+    /* https://msdn.microsoft.com/en-us/library/windows/desktop/aa375924.aspx
+       */
+    sspi_status = s_pSecFn->InitializeSecurityContext(
+      &connssl->cred->cred_handle, &connssl->ctxt->ctxt_handle,
+      host_name, connssl->req_flags, 0, 0, &inbuf_desc, 0, NULL,
+      &outbuf_desc, &connssl->ret_flags, &connssl->ctxt->time_stamp);
+
+    Curl_unicodefree(host_name);
+
+    /* free buffer for received handshake data */
+    Curl_safefree(inbuf[0].pvBuffer);
+
+    /* check if the handshake was incomplete */
+    if(sspi_status == SEC_E_INCOMPLETE_MESSAGE) {
+      connssl->encdata_is_incomplete = true;
+      connssl->connecting_state = ssl_connect_2_reading;
+      infof(data, "schannel: received incomplete message, need more data\n");
+      return CURLE_OK;
+    }
+
+    /* If the server has requested a client certificate, attempt to continue
+       the handshake without one. This will allow connections to servers which
+       request a client certificate but do not require it. */
+    if(sspi_status == SEC_I_INCOMPLETE_CREDENTIALS &&
+       !(connssl->req_flags & ISC_REQ_USE_SUPPLIED_CREDS)) {
+      connssl->req_flags |= ISC_REQ_USE_SUPPLIED_CREDS;
+      connssl->connecting_state = ssl_connect_2_writing;
+      infof(data, "schannel: a client certificate has been requested\n");
+      return CURLE_OK;
+    }
+
+    /* check if the handshake needs to be continued */
+    if(sspi_status == SEC_I_CONTINUE_NEEDED || sspi_status == SEC_E_OK) {
+      for(i = 0; i < 3; i++) {
+        /* search for handshake tokens that need to be send */
+        if(outbuf[i].BufferType == SECBUFFER_TOKEN && outbuf[i].cbBuffer > 0) {
+          infof(data, "schannel: sending next handshake data: "
+                "sending %lu bytes...\n", outbuf[i].cbBuffer);
+
+          /* send handshake token to server */
+          result = Curl_write_plain(conn, conn->sock[sockindex],
+                                    outbuf[i].pvBuffer, outbuf[i].cbBuffer,
+                                    &written);
+          if((result != CURLE_OK) ||
+             (outbuf[i].cbBuffer != (size_t) written)) {
+            failf(data, "schannel: failed to send next handshake data: "
+                  "sent %zd of %lu bytes", written, outbuf[i].cbBuffer);
+            return CURLE_SSL_CONNECT_ERROR;
+          }
+        }
+
+        /* free obsolete buffer */
+        if(outbuf[i].pvBuffer != NULL) {
+          s_pSecFn->FreeContextBuffer(outbuf[i].pvBuffer);
+        }
+      }
+    }
+    else {
+      if(sspi_status == SEC_E_WRONG_PRINCIPAL)
+        failf(data, "schannel: SNI or certificate check failed: %s",
+              Curl_sspi_strerror(conn, sspi_status));
+      else
+        failf(data, "schannel: next InitializeSecurityContext failed: %s",
+              Curl_sspi_strerror(conn, sspi_status));
+      return sspi_status == SEC_E_UNTRUSTED_ROOT ?
+          CURLE_SSL_CACERT_BADFILE : CURLE_SSL_CONNECT_ERROR;
+    }
+
+    /* check if there was additional remaining encrypted data */
+    if(inbuf[1].BufferType == SECBUFFER_EXTRA && inbuf[1].cbBuffer > 0) {
+      infof(data, "schannel: encrypted data length: %lu\n", inbuf[1].cbBuffer);
+      /*
+        There are two cases where we could be getting extra data here:
+        1) If we're renegotiating a connection and the handshake is already
+        complete (from the server perspective), it can encrypted app data
+        (not handshake data) in an extra buffer at this point.
+        2) (sspi_status == SEC_I_CONTINUE_NEEDED) We are negotiating a
+        connection and this extra data is part of the handshake.
+        We should process the data immediately; waiting for the socket to
+        be ready may fail since the server is done sending handshake data.
+      */
+      /* check if the remaining data is less than the total amount
+         and therefore begins after the already processed data */
+      if(connssl->encdata_offset > inbuf[1].cbBuffer) {
+        memmove(connssl->encdata_buffer,
+                (connssl->encdata_buffer + connssl->encdata_offset) -
+                inbuf[1].cbBuffer, inbuf[1].cbBuffer);
+        connssl->encdata_offset = inbuf[1].cbBuffer;
+        if(sspi_status == SEC_I_CONTINUE_NEEDED) {
+          doread = FALSE;
+          continue;
+        }
+      }
+    }
+    else {
+      connssl->encdata_offset = 0;
+    }
+    break;
+  }
+
+  /* check if the handshake needs to be continued */
+  if(sspi_status == SEC_I_CONTINUE_NEEDED) {
+    connssl->connecting_state = ssl_connect_2_reading;
+    return CURLE_OK;
+  }
+
+  /* check if the handshake is complete */
+  if(sspi_status == SEC_E_OK) {
+    connssl->connecting_state = ssl_connect_3;
+    infof(data, "schannel: SSL/TLS handshake complete\n");
+  }
+
+#ifdef _WIN32_WCE
+  /* Windows CE doesn't do any server certificate validation.
+     We have to do it manually. */
+  if(conn->ssl_config.verifypeer)
+    return verify_certificate(conn, sockindex);
+#endif
+
+  return CURLE_OK;
+}
+
+static CURLcode
+schannel_connect_step3(struct connectdata *conn, int sockindex)
+{
+  CURLcode result = CURLE_OK;
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  SECURITY_STATUS sspi_status = SEC_E_OK;
+  CERT_CONTEXT *ccert_context = NULL;
+#ifndef CURL_DISABLE_VERBOSE_STRINGS
+  const char * const hostname = SSL_IS_PROXY() ? conn->http_proxy.host.name :
+    conn->host.name;
+#endif
+#ifdef HAS_ALPN
+  SecPkgContext_ApplicationProtocol alpn_result;
+#endif
+
+  DEBUGASSERT(ssl_connect_3 == connssl->connecting_state);
+
+  infof(data, "schannel: SSL/TLS connection with %s port %hu (step 3/3)\n",
+        hostname, conn->remote_port);
+
+  if(!connssl->cred)
+    return CURLE_SSL_CONNECT_ERROR;
+
+  /* check if the required context attributes are met */
+  if(connssl->ret_flags != connssl->req_flags) {
+    if(!(connssl->ret_flags & ISC_RET_SEQUENCE_DETECT))
+      failf(data, "schannel: failed to setup sequence detection");
+    if(!(connssl->ret_flags & ISC_RET_REPLAY_DETECT))
+      failf(data, "schannel: failed to setup replay detection");
+    if(!(connssl->ret_flags & ISC_RET_CONFIDENTIALITY))
+      failf(data, "schannel: failed to setup confidentiality");
+    if(!(connssl->ret_flags & ISC_RET_ALLOCATED_MEMORY))
+      failf(data, "schannel: failed to setup memory allocation");
+    if(!(connssl->ret_flags & ISC_RET_STREAM))
+      failf(data, "schannel: failed to setup stream orientation");
+    return CURLE_SSL_CONNECT_ERROR;
+  }
+
+#ifdef HAS_ALPN
+  if(connssl->use_alpn) {
+    sspi_status = s_pSecFn->QueryContextAttributes(&connssl->ctxt->ctxt_handle,
+      SECPKG_ATTR_APPLICATION_PROTOCOL, &alpn_result);
+
+    if(sspi_status != SEC_E_OK) {
+      failf(data, "schannel: failed to retrieve ALPN result");
+      return CURLE_SSL_CONNECT_ERROR;
+    }
+
+    if(alpn_result.ProtoNegoStatus ==
+       SecApplicationProtocolNegotiationStatus_Success) {
+
+      infof(data, "schannel: ALPN, server accepted to use %.*s\n",
+        alpn_result.ProtocolIdSize, alpn_result.ProtocolId);
+
+#ifdef USE_NGHTTP2
+      if(alpn_result.ProtocolIdSize == NGHTTP2_PROTO_VERSION_ID_LEN &&
+         !memcmp(NGHTTP2_PROTO_VERSION_ID, alpn_result.ProtocolId,
+          NGHTTP2_PROTO_VERSION_ID_LEN)) {
+        conn->negnpn = CURL_HTTP_VERSION_2;
+      }
+      else
+#endif
+      if(alpn_result.ProtocolIdSize == ALPN_HTTP_1_1_LENGTH &&
+         !memcmp(ALPN_HTTP_1_1, alpn_result.ProtocolId,
+           ALPN_HTTP_1_1_LENGTH)) {
+        conn->negnpn = CURL_HTTP_VERSION_1_1;
+      }
+    }
+    else
+      infof(data, "ALPN, server did not agree to a protocol\n");
+  }
+#endif
+
+  /* save the current session data for possible re-use */
+  if(SSL_SET_OPTION(primary.sessionid)) {
+    bool incache;
+    struct curl_schannel_cred *old_cred = NULL;
+
+    Curl_ssl_sessionid_lock(conn);
+    incache = !(Curl_ssl_getsessionid(conn, (void **)&old_cred, NULL,
+                                      sockindex));
+    if(incache) {
+      if(old_cred != connssl->cred) {
+        infof(data, "schannel: old credential handle is stale, removing\n");
+        /* we're not taking old_cred ownership here, no refcount++ is needed */
+        Curl_ssl_delsessionid(conn, (void *)old_cred);
+        incache = FALSE;
+      }
+    }
+    if(!incache) {
+      result = Curl_ssl_addsessionid(conn, (void *)connssl->cred,
+                                     sizeof(struct curl_schannel_cred),
+                                     sockindex);
+      if(result) {
+        Curl_ssl_sessionid_unlock(conn);
+        failf(data, "schannel: failed to store credential handle");
+        return result;
+      }
+      else {
+        /* this cred session is now also referenced by sessionid cache */
+        connssl->cred->refcount++;
+        infof(data, "schannel: stored credential handle in session cache\n");
+      }
+    }
+    Curl_ssl_sessionid_unlock(conn);
+  }
+
+  if(data->set.ssl.certinfo) {
+    sspi_status = s_pSecFn->QueryContextAttributes(&connssl->ctxt->ctxt_handle,
+      SECPKG_ATTR_REMOTE_CERT_CONTEXT, &ccert_context);
+
+    if((sspi_status != SEC_E_OK) || (ccert_context == NULL)) {
+      failf(data, "schannel: failed to retrieve remote cert context");
+      return CURLE_SSL_CONNECT_ERROR;
+    }
+
+    result = Curl_ssl_init_certinfo(data, 1);
+    if(!result) {
+      if(((ccert_context->dwCertEncodingType & X509_ASN_ENCODING) != 0) &&
+         (ccert_context->cbCertEncoded > 0)) {
+
+        const char *beg = (const char *) ccert_context->pbCertEncoded;
+        const char *end = beg + ccert_context->cbCertEncoded;
+        result = Curl_extract_certinfo(conn, 0, beg, end);
+      }
+    }
+    CertFreeCertificateContext(ccert_context);
+    if(result)
+      return result;
+  }
+
+  connssl->connecting_state = ssl_connect_done;
+
+  return CURLE_OK;
+}
+
+static CURLcode
+schannel_connect_common(struct connectdata *conn, int sockindex,
+                        bool nonblocking, bool *done)
+{
+  CURLcode result;
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  curl_socket_t sockfd = conn->sock[sockindex];
+  time_t timeout_ms;
+  int what;
+
+  /* check if the connection has already been established */
+  if(ssl_connection_complete == connssl->state) {
+    *done = TRUE;
+    return CURLE_OK;
+  }
+
+  if(ssl_connect_1 == connssl->connecting_state) {
+    /* check out how much more time we're allowed */
+    timeout_ms = Curl_timeleft(data, NULL, TRUE);
+
+    if(timeout_ms < 0) {
+      /* no need to continue if time already is up */
+      failf(data, "SSL/TLS connection timeout");
+      return CURLE_OPERATION_TIMEDOUT;
+    }
+
+    result = schannel_connect_step1(conn, sockindex);
+    if(result)
+      return result;
+  }
+
+  while(ssl_connect_2 == connssl->connecting_state ||
+        ssl_connect_2_reading == connssl->connecting_state ||
+        ssl_connect_2_writing == connssl->connecting_state) {
+
+    /* check out how much more time we're allowed */
+    timeout_ms = Curl_timeleft(data, NULL, TRUE);
+
+    if(timeout_ms < 0) {
+      /* no need to continue if time already is up */
+      failf(data, "SSL/TLS connection timeout");
+      return CURLE_OPERATION_TIMEDOUT;
+    }
+
+    /* if ssl is expecting something, check if it's available. */
+    if(connssl->connecting_state == ssl_connect_2_reading
+       || connssl->connecting_state == ssl_connect_2_writing) {
+
+      curl_socket_t writefd = ssl_connect_2_writing ==
+        connssl->connecting_state ? sockfd : CURL_SOCKET_BAD;
+      curl_socket_t readfd = ssl_connect_2_reading ==
+        connssl->connecting_state ? sockfd : CURL_SOCKET_BAD;
+
+      what = Curl_socket_check(readfd, CURL_SOCKET_BAD, writefd,
+                               nonblocking ? 0 : timeout_ms);
+      if(what < 0) {
+        /* fatal error */
+        failf(data, "select/poll on SSL/TLS socket, errno: %d", SOCKERRNO);
+        return CURLE_SSL_CONNECT_ERROR;
+      }
+      else if(0 == what) {
+        if(nonblocking) {
+          *done = FALSE;
+          return CURLE_OK;
+        }
+        else {
+          /* timeout */
+          failf(data, "SSL/TLS connection timeout");
+          return CURLE_OPERATION_TIMEDOUT;
+        }
+      }
+      /* socket is readable or writable */
+    }
+
+    /* Run transaction, and return to the caller if it failed or if
+     * this connection is part of a multi handle and this loop would
+     * execute again. This permits the owner of a multi handle to
+     * abort a connection attempt before step2 has completed while
+     * ensuring that a client using select() or epoll() will always
+     * have a valid fdset to wait on.
+     */
+    result = schannel_connect_step2(conn, sockindex);
+    if(result || (nonblocking &&
+                  (ssl_connect_2 == connssl->connecting_state ||
+                   ssl_connect_2_reading == connssl->connecting_state ||
+                   ssl_connect_2_writing == connssl->connecting_state)))
+      return result;
+
+  } /* repeat step2 until all transactions are done. */
+
+  if(ssl_connect_3 == connssl->connecting_state) {
+    result = schannel_connect_step3(conn, sockindex);
+    if(result)
+      return result;
+  }
+
+  if(ssl_connect_done == connssl->connecting_state) {
+    connssl->state = ssl_connection_complete;
+    conn->recv[sockindex] = schannel_recv;
+    conn->send[sockindex] = schannel_send;
+    *done = TRUE;
+  }
+  else
+    *done = FALSE;
+
+  /* reset our connection state machine */
+  connssl->connecting_state = ssl_connect_1;
+
+  return CURLE_OK;
+}
+
+static ssize_t
+schannel_send(struct connectdata *conn, int sockindex,
+              const void *buf, size_t len, CURLcode *err)
+{
+  ssize_t written = -1;
+  size_t data_len = 0;
+  unsigned char *data = NULL;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  SecBuffer outbuf[4];
+  SecBufferDesc outbuf_desc;
+  SECURITY_STATUS sspi_status = SEC_E_OK;
+  CURLcode result;
+
+  /* check if the maximum stream sizes were queried */
+  if(connssl->stream_sizes.cbMaximumMessage == 0) {
+    sspi_status = s_pSecFn->QueryContextAttributes(
+      &connssl->ctxt->ctxt_handle,
+      SECPKG_ATTR_STREAM_SIZES,
+      &connssl->stream_sizes);
+    if(sspi_status != SEC_E_OK) {
+      *err = CURLE_SEND_ERROR;
+      return -1;
+    }
+  }
+
+  /* check if the buffer is longer than the maximum message length */
+  if(len > connssl->stream_sizes.cbMaximumMessage) {
+    *err = CURLE_SEND_ERROR;
+    return -1;
+  }
+
+  /* calculate the complete message length and allocate a buffer for it */
+  data_len = connssl->stream_sizes.cbHeader + len +
+    connssl->stream_sizes.cbTrailer;
+  data = (unsigned char *) malloc(data_len);
+  if(data == NULL) {
+    *err = CURLE_OUT_OF_MEMORY;
+    return -1;
+  }
+
+  /* setup output buffers (header, data, trailer, empty) */
+  InitSecBuffer(&outbuf[0], SECBUFFER_STREAM_HEADER,
+                data, connssl->stream_sizes.cbHeader);
+  InitSecBuffer(&outbuf[1], SECBUFFER_DATA,
+                data + connssl->stream_sizes.cbHeader, curlx_uztoul(len));
+  InitSecBuffer(&outbuf[2], SECBUFFER_STREAM_TRAILER,
+                data + connssl->stream_sizes.cbHeader + len,
+                connssl->stream_sizes.cbTrailer);
+  InitSecBuffer(&outbuf[3], SECBUFFER_EMPTY, NULL, 0);
+  InitSecBufferDesc(&outbuf_desc, outbuf, 4);
+
+  /* copy data into output buffer */
+  memcpy(outbuf[1].pvBuffer, buf, len);
+
+  /* https://msdn.microsoft.com/en-us/library/windows/desktop/aa375390.aspx */
+  sspi_status = s_pSecFn->EncryptMessage(&connssl->ctxt->ctxt_handle, 0,
+                                         &outbuf_desc, 0);
+
+  /* check if the message was encrypted */
+  if(sspi_status == SEC_E_OK) {
+    written = 0;
+
+    /* send the encrypted message including header, data and trailer */
+    len = outbuf[0].cbBuffer + outbuf[1].cbBuffer + outbuf[2].cbBuffer;
+
+    /*
+      It's important to send the full message which includes the header,
+      encrypted payload, and trailer.  Until the client receives all the
+      data a coherent message has not been delivered and the client
+      can't read any of it.
+
+      If we wanted to buffer the unwritten encrypted bytes, we would
+      tell the client that all data it has requested to be sent has been
+      sent. The unwritten encrypted bytes would be the first bytes to
+      send on the next invocation.
+      Here's the catch with this - if we tell the client that all the
+      bytes have been sent, will the client call this method again to
+      send the buffered data?  Looking at who calls this function, it
+      seems the answer is NO.
+    */
+
+    /* send entire message or fail */
+    while(len > (size_t)written) {
+      ssize_t this_write;
+      time_t timeleft;
+      int what;
+
+      this_write = 0;
+
+      timeleft = Curl_timeleft(conn->data, NULL, FALSE);
+      if(timeleft < 0) {
+        /* we already got the timeout */
+        failf(conn->data, "schannel: timed out sending data "
+              "(bytes sent: %zd)", written);
+        *err = CURLE_OPERATION_TIMEDOUT;
+        written = -1;
+        break;
+      }
+
+      what = SOCKET_WRITABLE(conn->sock[sockindex], timeleft);
+      if(what < 0) {
+        /* fatal error */
+        failf(conn->data, "select/poll on SSL socket, errno: %d", SOCKERRNO);
+        *err = CURLE_SEND_ERROR;
+        written = -1;
+        break;
+      }
+      else if(0 == what) {
+        failf(conn->data, "schannel: timed out sending data "
+              "(bytes sent: %zd)", written);
+        *err = CURLE_OPERATION_TIMEDOUT;
+        written = -1;
+        break;
+      }
+      /* socket is writable */
+
+      result = Curl_write_plain(conn, conn->sock[sockindex], data + written,
+                                len - written, &this_write);
+      if(result == CURLE_AGAIN)
+        continue;
+      else if(result != CURLE_OK) {
+        *err = result;
+        written = -1;
+        break;
+      }
+
+      written += this_write;
+    }
+  }
+  else if(sspi_status == SEC_E_INSUFFICIENT_MEMORY) {
+    *err = CURLE_OUT_OF_MEMORY;
+  }
+  else{
+    *err = CURLE_SEND_ERROR;
+  }
+
+  Curl_safefree(data);
+
+  if(len == (size_t)written)
+    /* Encrypted message including header, data and trailer entirely sent.
+       The return value is the number of unencrypted bytes that were sent. */
+    written = outbuf[1].cbBuffer;
+
+  return written;
+}
+
+static ssize_t
+schannel_recv(struct connectdata *conn, int sockindex,
+              char *buf, size_t len, CURLcode *err)
+{
+  size_t size = 0;
+  ssize_t nread = -1;
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  unsigned char *reallocated_buffer;
+  size_t reallocated_length;
+  bool done = FALSE;
+  SecBuffer inbuf[4];
+  SecBufferDesc inbuf_desc;
+  SECURITY_STATUS sspi_status = SEC_E_OK;
+  /* we want the length of the encrypted buffer to be at least large enough
+     that it can hold all the bytes requested and some TLS record overhead. */
+  size_t min_encdata_length = len + CURL_SCHANNEL_BUFFER_FREE_SIZE;
+
+  /****************************************************************************
+   * Don't return or set connssl->recv_unrecoverable_err unless in the cleanup.
+   * The pattern for return error is set *err, optional infof, goto cleanup.
+   *
+   * Our priority is to always return as much decrypted data to the caller as
+   * possible, even if an error occurs. The state of the decrypted buffer must
+   * always be valid. Transfer of decrypted data to the caller's buffer is
+   * handled in the cleanup.
+   */
+
+  infof(data, "schannel: client wants to read %zu bytes\n", len);
+  *err = CURLE_OK;
+
+  if(len && len <= connssl->decdata_offset) {
+    infof(data, "schannel: enough decrypted data is already available\n");
+    goto cleanup;
+  }
+  else if(connssl->recv_unrecoverable_err) {
+    *err = connssl->recv_unrecoverable_err;
+    infof(data, "schannel: an unrecoverable error occurred in a prior call\n");
+    goto cleanup;
+  }
+  else if(connssl->recv_sspi_close_notify) {
+    /* once a server has indicated shutdown there is no more encrypted data */
+    infof(data, "schannel: server indicated shutdown in a prior call\n");
+    goto cleanup;
+  }
+  else if(!len) {
+    /* It's debatable what to return when !len. Regardless we can't return
+    immediately because there may be data to decrypt (in the case we want to
+    decrypt all encrypted cached data) so handle !len later in cleanup.
+    */
+    ; /* do nothing */
+  }
+  else if(!connssl->recv_connection_closed) {
+    /* increase enc buffer in order to fit the requested amount of data */
+    size = connssl->encdata_length - connssl->encdata_offset;
+    if(size < CURL_SCHANNEL_BUFFER_FREE_SIZE ||
+       connssl->encdata_length < min_encdata_length) {
+      reallocated_length = connssl->encdata_offset +
+                           CURL_SCHANNEL_BUFFER_FREE_SIZE;
+      if(reallocated_length < min_encdata_length) {
+        reallocated_length = min_encdata_length;
+      }
+      reallocated_buffer = realloc(connssl->encdata_buffer,
+                                   reallocated_length);
+      if(reallocated_buffer == NULL) {
+        *err = CURLE_OUT_OF_MEMORY;
+        failf(data, "schannel: unable to re-allocate memory");
+        goto cleanup;
+      }
+
+      connssl->encdata_buffer = reallocated_buffer;
+      connssl->encdata_length = reallocated_length;
+      size = connssl->encdata_length - connssl->encdata_offset;
+      infof(data, "schannel: encdata_buffer resized %zu\n",
+            connssl->encdata_length);
+    }
+
+    infof(data, "schannel: encrypted data buffer: offset %zu length %zu\n",
+          connssl->encdata_offset, connssl->encdata_length);
+
+    /* read encrypted data from socket */
+    *err = Curl_read_plain(conn->sock[sockindex],
+                           (char *)(connssl->encdata_buffer +
+                                    connssl->encdata_offset),
+                           size, &nread);
+    if(*err) {
+      nread = -1;
+      if(*err == CURLE_AGAIN)
+        infof(data, "schannel: Curl_read_plain returned CURLE_AGAIN\n");
+      else if(*err == CURLE_RECV_ERROR)
+        infof(data, "schannel: Curl_read_plain returned CURLE_RECV_ERROR\n");
+      else
+        infof(data, "schannel: Curl_read_plain returned error %d\n", *err);
+    }
+    else if(nread == 0) {
+      connssl->recv_connection_closed = true;
+      infof(data, "schannel: server closed the connection\n");
+    }
+    else if(nread > 0) {
+      connssl->encdata_offset += (size_t)nread;
+      connssl->encdata_is_incomplete = false;
+      infof(data, "schannel: encrypted data got %zd\n", nread);
+    }
+  }
+
+  infof(data, "schannel: encrypted data buffer: offset %zu length %zu\n",
+        connssl->encdata_offset, connssl->encdata_length);
+
+  /* decrypt loop */
+  while(connssl->encdata_offset > 0 && sspi_status == SEC_E_OK &&
+        (!len || connssl->decdata_offset < len ||
+         connssl->recv_connection_closed)) {
+    /* prepare data buffer for DecryptMessage call */
+    InitSecBuffer(&inbuf[0], SECBUFFER_DATA, connssl->encdata_buffer,
+                  curlx_uztoul(connssl->encdata_offset));
+
+    /* we need 3 more empty input buffers for possible output */
+    InitSecBuffer(&inbuf[1], SECBUFFER_EMPTY, NULL, 0);
+    InitSecBuffer(&inbuf[2], SECBUFFER_EMPTY, NULL, 0);
+    InitSecBuffer(&inbuf[3], SECBUFFER_EMPTY, NULL, 0);
+    InitSecBufferDesc(&inbuf_desc, inbuf, 4);
+
+    /* https://msdn.microsoft.com/en-us/library/windows/desktop/aa375348.aspx
+       */
+    sspi_status = s_pSecFn->DecryptMessage(&connssl->ctxt->ctxt_handle,
+                                           &inbuf_desc, 0, NULL);
+
+    /* check if everything went fine (server may want to renegotiate
+       or shutdown the connection context) */
+    if(sspi_status == SEC_E_OK || sspi_status == SEC_I_RENEGOTIATE ||
+       sspi_status == SEC_I_CONTEXT_EXPIRED) {
+      /* check for successfully decrypted data, even before actual
+         renegotiation or shutdown of the connection context */
+      if(inbuf[1].BufferType == SECBUFFER_DATA) {
+        infof(data, "schannel: decrypted data length: %lu\n",
+              inbuf[1].cbBuffer);
+
+        /* increase buffer in order to fit the received amount of data */
+        size = inbuf[1].cbBuffer > CURL_SCHANNEL_BUFFER_FREE_SIZE ?
+               inbuf[1].cbBuffer : CURL_SCHANNEL_BUFFER_FREE_SIZE;
+        if(connssl->decdata_length - connssl->decdata_offset < size ||
+           connssl->decdata_length < len) {
+          /* increase internal decrypted data buffer */
+          reallocated_length = connssl->decdata_offset + size;
+          /* make sure that the requested amount of data fits */
+          if(reallocated_length < len) {
+            reallocated_length = len;
+          }
+          reallocated_buffer = realloc(connssl->decdata_buffer,
+                                       reallocated_length);
+          if(reallocated_buffer == NULL) {
+            *err = CURLE_OUT_OF_MEMORY;
+            failf(data, "schannel: unable to re-allocate memory");
+            goto cleanup;
+          }
+          connssl->decdata_buffer = reallocated_buffer;
+          connssl->decdata_length = reallocated_length;
+        }
+
+        /* copy decrypted data to internal buffer */
+        size = inbuf[1].cbBuffer;
+        if(size) {
+          memcpy(connssl->decdata_buffer + connssl->decdata_offset,
+                 inbuf[1].pvBuffer, size);
+          connssl->decdata_offset += size;
+        }
+
+        infof(data, "schannel: decrypted data added: %zu\n", size);
+        infof(data, "schannel: decrypted data cached: offset %zu length %zu\n",
+              connssl->decdata_offset, connssl->decdata_length);
+      }
+
+      /* check for remaining encrypted data */
+      if(inbuf[3].BufferType == SECBUFFER_EXTRA && inbuf[3].cbBuffer > 0) {
+        infof(data, "schannel: encrypted data length: %lu\n",
+              inbuf[3].cbBuffer);
+
+        /* check if the remaining data is less than the total amount
+         * and therefore begins after the already processed data
+         */
+        if(connssl->encdata_offset > inbuf[3].cbBuffer) {
+          /* move remaining encrypted data forward to the beginning of
+             buffer */
+          memmove(connssl->encdata_buffer,
+                  (connssl->encdata_buffer + connssl->encdata_offset) -
+                  inbuf[3].cbBuffer, inbuf[3].cbBuffer);
+          connssl->encdata_offset = inbuf[3].cbBuffer;
+        }
+
+        infof(data, "schannel: encrypted data cached: offset %zu length %zu\n",
+              connssl->encdata_offset, connssl->encdata_length);
+      }
+      else {
+        /* reset encrypted buffer offset, because there is no data remaining */
+        connssl->encdata_offset = 0;
+      }
+
+      /* check if server wants to renegotiate the connection context */
+      if(sspi_status == SEC_I_RENEGOTIATE) {
+        infof(data, "schannel: remote party requests renegotiation\n");
+        if(*err && *err != CURLE_AGAIN) {
+          infof(data, "schannel: can't renogotiate, an error is pending\n");
+          goto cleanup;
+        }
+        if(connssl->encdata_offset) {
+          *err = CURLE_RECV_ERROR;
+          infof(data, "schannel: can't renogotiate, "
+                      "encrypted data available\n");
+          goto cleanup;
+        }
+        /* begin renegotiation */
+        infof(data, "schannel: renegotiating SSL/TLS connection\n");
+        connssl->state = ssl_connection_negotiating;
+        connssl->connecting_state = ssl_connect_2_writing;
+        *err = schannel_connect_common(conn, sockindex, FALSE, &done);
+        if(*err) {
+          infof(data, "schannel: renegotiation failed\n");
+          goto cleanup;
+        }
+        /* now retry receiving data */
+        sspi_status = SEC_E_OK;
+        infof(data, "schannel: SSL/TLS connection renegotiated\n");
+        continue;
+      }
+      /* check if the server closed the connection */
+      else if(sspi_status == SEC_I_CONTEXT_EXPIRED) {
+        /* In Windows 2000 SEC_I_CONTEXT_EXPIRED (close_notify) is not
+           returned so we have to work around that in cleanup. */
+        connssl->recv_sspi_close_notify = true;
+        if(!connssl->recv_connection_closed) {
+          connssl->recv_connection_closed = true;
+          infof(data, "schannel: server closed the connection\n");
+        }
+        goto cleanup;
+      }
+    }
+    else if(sspi_status == SEC_E_INCOMPLETE_MESSAGE) {
+      connssl->encdata_is_incomplete = true;
+      if(!*err)
+        *err = CURLE_AGAIN;
+      infof(data, "schannel: failed to decrypt data, need more data\n");
+      goto cleanup;
+    }
+    else {
+      *err = CURLE_RECV_ERROR;
+      infof(data, "schannel: failed to read data from server: %s\n",
+            Curl_sspi_strerror(conn, sspi_status));
+      goto cleanup;
+    }
+  }
+
+  infof(data, "schannel: encrypted data buffer: offset %zu length %zu\n",
+        connssl->encdata_offset, connssl->encdata_length);
+
+  infof(data, "schannel: decrypted data buffer: offset %zu length %zu\n",
+        connssl->decdata_offset, connssl->decdata_length);
+
+cleanup:
+  /* Warning- there is no guarantee the encdata state is valid at this point */
+  infof(data, "schannel: schannel_recv cleanup\n");
+
+  /* Error if the connection has closed without a close_notify.
+  Behavior here is a matter of debate. We don't want to be vulnerable to a
+  truncation attack however there's some browser precedent for ignoring the
+  close_notify for compatibility reasons.
+  Additionally, Windows 2000 (v5.0) is a special case since it seems it doesn't
+  return close_notify. In that case if the connection was closed we assume it
+  was graceful (close_notify) since there doesn't seem to be a way to tell.
+  */
+  if(len && !connssl->decdata_offset && connssl->recv_connection_closed &&
+     !connssl->recv_sspi_close_notify) {
+    bool isWin2k = Curl_verify_windows_version(5, 0, PLATFORM_WINNT,
+                                               VERSION_EQUAL);
+
+    if(isWin2k && sspi_status == SEC_E_OK)
+      connssl->recv_sspi_close_notify = true;
+    else {
+      *err = CURLE_RECV_ERROR;
+      infof(data, "schannel: server closed abruptly (missing close_notify)\n");
+    }
+  }
+
+  /* Any error other than CURLE_AGAIN is an unrecoverable error. */
+  if(*err && *err != CURLE_AGAIN)
+      connssl->recv_unrecoverable_err = *err;
+
+  size = len < connssl->decdata_offset ? len : connssl->decdata_offset;
+  if(size) {
+    memcpy(buf, connssl->decdata_buffer, size);
+    memmove(connssl->decdata_buffer, connssl->decdata_buffer + size,
+            connssl->decdata_offset - size);
+    connssl->decdata_offset -= size;
+
+    infof(data, "schannel: decrypted data returned %zu\n", size);
+    infof(data, "schannel: decrypted data buffer: offset %zu length %zu\n",
+          connssl->decdata_offset, connssl->decdata_length);
+    *err = CURLE_OK;
+    return (ssize_t)size;
+  }
+
+  if(!*err && !connssl->recv_connection_closed)
+      *err = CURLE_AGAIN;
+
+  /* It's debatable what to return when !len. We could return whatever error we
+  got from decryption but instead we override here so the return is consistent.
+  */
+  if(!len)
+    *err = CURLE_OK;
+
+  return *err ? -1 : 0;
+}
+
+CURLcode
+Curl_schannel_connect_nonblocking(struct connectdata *conn, int sockindex,
+                                  bool *done)
+{
+  return schannel_connect_common(conn, sockindex, TRUE, done);
+}
+
+CURLcode
+Curl_schannel_connect(struct connectdata *conn, int sockindex)
+{
+  CURLcode result;
+  bool done = FALSE;
+
+  result = schannel_connect_common(conn, sockindex, FALSE, &done);
+  if(result)
+    return result;
+
+  DEBUGASSERT(done);
+
+  return CURLE_OK;
+}
+
+bool Curl_schannel_data_pending(const struct connectdata *conn, int sockindex)
+{
+  const struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+
+  if(connssl->use) /* SSL/TLS is in use */
+    return (connssl->decdata_offset > 0 ||
+            (connssl->encdata_offset > 0 && !connssl->encdata_is_incomplete));
+  else
+    return FALSE;
+}
+
+void Curl_schannel_close(struct connectdata *conn, int sockindex)
+{
+  if(conn->ssl[sockindex].use)
+    /* if the SSL/TLS channel hasn't been shut down yet, do that now. */
+    Curl_ssl_shutdown(conn, sockindex);
+}
+
+int Curl_schannel_shutdown(struct connectdata *conn, int sockindex)
+{
+  /* See https://msdn.microsoft.com/en-us/library/windows/desktop/aa380138.aspx
+   * Shutting Down an Schannel Connection
+   */
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  char * const hostname = SSL_IS_PROXY() ? conn->http_proxy.host.name :
+    conn->host.name;
+
+  infof(data, "schannel: shutting down SSL/TLS connection with %s port %hu\n",
+        hostname, conn->remote_port);
+
+  if(connssl->cred && connssl->ctxt) {
+    SecBufferDesc BuffDesc;
+    SecBuffer Buffer;
+    SECURITY_STATUS sspi_status;
+    SecBuffer outbuf;
+    SecBufferDesc outbuf_desc;
+    CURLcode result;
+    TCHAR *host_name;
+    DWORD dwshut = SCHANNEL_SHUTDOWN;
+
+    InitSecBuffer(&Buffer, SECBUFFER_TOKEN, &dwshut, sizeof(dwshut));
+    InitSecBufferDesc(&BuffDesc, &Buffer, 1);
+
+    sspi_status = s_pSecFn->ApplyControlToken(&connssl->ctxt->ctxt_handle,
+                                              &BuffDesc);
+
+    if(sspi_status != SEC_E_OK)
+      failf(data, "schannel: ApplyControlToken failure: %s",
+            Curl_sspi_strerror(conn, sspi_status));
+
+    host_name = Curl_convert_UTF8_to_tchar(hostname);
+    if(!host_name)
+      return CURLE_OUT_OF_MEMORY;
+
+    /* setup output buffer */
+    InitSecBuffer(&outbuf, SECBUFFER_EMPTY, NULL, 0);
+    InitSecBufferDesc(&outbuf_desc, &outbuf, 1);
+
+    sspi_status = s_pSecFn->InitializeSecurityContext(
+      &connssl->cred->cred_handle,
+      &connssl->ctxt->ctxt_handle,
+      host_name,
+      connssl->req_flags,
+      0,
+      0,
+      NULL,
+      0,
+      &connssl->ctxt->ctxt_handle,
+      &outbuf_desc,
+      &connssl->ret_flags,
+      &connssl->ctxt->time_stamp);
+
+    Curl_unicodefree(host_name);
+
+    if((sspi_status == SEC_E_OK) || (sspi_status == SEC_I_CONTEXT_EXPIRED)) {
+      /* send close message which is in output buffer */
+      ssize_t written;
+      result = Curl_write_plain(conn, conn->sock[sockindex], outbuf.pvBuffer,
+                                outbuf.cbBuffer, &written);
+
+      s_pSecFn->FreeContextBuffer(outbuf.pvBuffer);
+      if((result != CURLE_OK) || (outbuf.cbBuffer != (size_t) written)) {
+        infof(data, "schannel: failed to send close msg: %s"
+              " (bytes written: %zd)\n", curl_easy_strerror(result), written);
+      }
+    }
+  }
+
+  /* free SSPI Schannel API security context handle */
+  if(connssl->ctxt) {
+    infof(data, "schannel: clear security context handle\n");
+    s_pSecFn->DeleteSecurityContext(&connssl->ctxt->ctxt_handle);
+    Curl_safefree(connssl->ctxt);
+  }
+
+  /* free SSPI Schannel API credential handle */
+  if(connssl->cred) {
+    Curl_ssl_sessionid_lock(conn);
+    Curl_schannel_session_free(connssl->cred);
+    Curl_ssl_sessionid_unlock(conn);
+    connssl->cred = NULL;
+  }
+
+  /* free internal buffer for received encrypted data */
+  if(connssl->encdata_buffer != NULL) {
+    Curl_safefree(connssl->encdata_buffer);
+    connssl->encdata_length = 0;
+    connssl->encdata_offset = 0;
+    connssl->encdata_is_incomplete = false;
+  }
+
+  /* free internal buffer for received decrypted data */
+  if(connssl->decdata_buffer != NULL) {
+    Curl_safefree(connssl->decdata_buffer);
+    connssl->decdata_length = 0;
+    connssl->decdata_offset = 0;
+  }
+
+  return CURLE_OK;
+}
+
+void Curl_schannel_session_free(void *ptr)
+{
+  /* this is expected to be called under sessionid lock */
+  struct curl_schannel_cred *cred = ptr;
+
+  cred->refcount--;
+  if(cred->refcount == 0) {
+    s_pSecFn->FreeCredentialsHandle(&cred->cred_handle);
+    Curl_safefree(cred);
+  }
+}
+
+int Curl_schannel_init(void)
+{
+  return (Curl_sspi_global_init() == CURLE_OK ? 1 : 0);
+}
+
+void Curl_schannel_cleanup(void)
+{
+  Curl_sspi_global_cleanup();
+}
+
+size_t Curl_schannel_version(char *buffer, size_t size)
+{
+  size = snprintf(buffer, size, "WinSSL");
+
+  return size;
+}
+
+CURLcode Curl_schannel_random(unsigned char *entropy, size_t length)
+{
+  HCRYPTPROV hCryptProv = 0;
+
+  if(!CryptAcquireContext(&hCryptProv, NULL, NULL, PROV_RSA_FULL,
+                          CRYPT_VERIFYCONTEXT | CRYPT_SILENT))
+    return CURLE_FAILED_INIT;
+
+  if(!CryptGenRandom(hCryptProv, (DWORD)length, entropy)) {
+    CryptReleaseContext(hCryptProv, 0UL);
+    return CURLE_FAILED_INIT;
+  }
+
+  CryptReleaseContext(hCryptProv, 0UL);
+  return CURLE_OK;
+}
+
+#ifdef _WIN32_WCE
+static CURLcode verify_certificate(struct connectdata *conn, int sockindex)
+{
+  SECURITY_STATUS status;
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  CURLcode result = CURLE_OK;
+  CERT_CONTEXT *pCertContextServer = NULL;
+  const CERT_CHAIN_CONTEXT *pChainContext = NULL;
+  const char * const conn_hostname = SSL_IS_PROXY() ?
+    conn->http_proxy.host.name :
+    conn->host.name;
+
+  status = s_pSecFn->QueryContextAttributes(&connssl->ctxt->ctxt_handle,
+                                            SECPKG_ATTR_REMOTE_CERT_CONTEXT,
+                                            &pCertContextServer);
+
+  if((status != SEC_E_OK) || (pCertContextServer == NULL)) {
+    failf(data, "schannel: Failed to read remote certificate context: %s",
+          Curl_sspi_strerror(conn, status));
+    result = CURLE_PEER_FAILED_VERIFICATION;
+  }
+
+  if(result == CURLE_OK) {
+    CERT_CHAIN_PARA ChainPara;
+    memset(&ChainPara, 0, sizeof(ChainPara));
+    ChainPara.cbSize = sizeof(ChainPara);
+
+    if(!CertGetCertificateChain(NULL,
+                                pCertContextServer,
+                                NULL,
+                                pCertContextServer->hCertStore,
+                                &ChainPara,
+                                (data->set.ssl.no_revoke ? 0 :
+                                 CERT_CHAIN_REVOCATION_CHECK_CHAIN),
+                                NULL,
+                                &pChainContext)) {
+      failf(data, "schannel: CertGetCertificateChain failed: %s",
+            Curl_sspi_strerror(conn, GetLastError()));
+      pChainContext = NULL;
+      result = CURLE_PEER_FAILED_VERIFICATION;
+    }
+
+    if(result == CURLE_OK) {
+      CERT_SIMPLE_CHAIN *pSimpleChain = pChainContext->rgpChain[0];
+      DWORD dwTrustErrorMask = ~(DWORD)(CERT_TRUST_IS_NOT_TIME_NESTED);
+      dwTrustErrorMask &= pSimpleChain->TrustStatus.dwErrorStatus;
+      if(dwTrustErrorMask) {
+        if(dwTrustErrorMask & CERT_TRUST_IS_REVOKED)
+          failf(data, "schannel: CertGetCertificateChain trust error"
+                " CERT_TRUST_IS_REVOKED");
+        else if(dwTrustErrorMask & CERT_TRUST_IS_PARTIAL_CHAIN)
+          failf(data, "schannel: CertGetCertificateChain trust error"
+                " CERT_TRUST_IS_PARTIAL_CHAIN");
+        else if(dwTrustErrorMask & CERT_TRUST_IS_UNTRUSTED_ROOT)
+          failf(data, "schannel: CertGetCertificateChain trust error"
+                " CERT_TRUST_IS_UNTRUSTED_ROOT");
+        else if(dwTrustErrorMask & CERT_TRUST_IS_NOT_TIME_VALID)
+          failf(data, "schannel: CertGetCertificateChain trust error"
+                " CERT_TRUST_IS_NOT_TIME_VALID");
+        else
+          failf(data, "schannel: CertGetCertificateChain error mask: 0x%08x",
+                dwTrustErrorMask);
+        result = CURLE_PEER_FAILED_VERIFICATION;
+      }
+    }
+  }
+
+  if(result == CURLE_OK) {
+    if(conn->ssl_config.verifyhost) {
+      TCHAR cert_hostname_buff[256];
+      DWORD len;
+
+      /* TODO: Fix this for certificates with multiple alternative names.
+      Right now we're only asking for the first preferred alternative name.
+      Instead we'd need to do all via CERT_NAME_SEARCH_ALL_NAMES_FLAG
+      (if WinCE supports that?) and run this section in a loop for each.
+      https://msdn.microsoft.com/en-us/library/windows/desktop/aa376086.aspx
+      curl: (51) schannel: CertGetNameString() certificate hostname
+      (.google.com) did not match connection (google.com)
+      */
+      len = CertGetNameString(pCertContextServer,
+                              CERT_NAME_DNS_TYPE,
+                              CERT_NAME_DISABLE_IE4_UTF8_FLAG,
+                              NULL,
+                              cert_hostname_buff,
+                              256);
+      if(len > 0) {
+        const char *cert_hostname;
+
+        /* Comparing the cert name and the connection hostname encoded as UTF-8
+         * is acceptable since both values are assumed to use ASCII
+         * (or some equivalent) encoding
+         */
+        cert_hostname = Curl_convert_tchar_to_UTF8(cert_hostname_buff);
+        if(!cert_hostname) {
+          result = CURLE_OUT_OF_MEMORY;
+        }
+        else{
+          int match_result;
+
+          match_result = Curl_cert_hostcheck(cert_hostname, conn->host.name);
+          if(match_result == CURL_HOST_MATCH) {
+            infof(data,
+                  "schannel: connection hostname (%s) validated "
+                  "against certificate name (%s)\n",
+                  conn->host.name,
+                  cert_hostname);
+            result = CURLE_OK;
+          }
+          else{
+            failf(data,
+                  "schannel: connection hostname (%s) "
+                  "does not match certificate name (%s)",
+                  conn->host.name,
+                  cert_hostname);
+            result = CURLE_PEER_FAILED_VERIFICATION;
+          }
+          Curl_unicodefree(cert_hostname);
+        }
+      }
+      else {
+        failf(data,
+              "schannel: CertGetNameString did not provide any "
+              "certificate name information");
+        result = CURLE_PEER_FAILED_VERIFICATION;
+      }
+    }
+  }
+
+  if(pChainContext)
+    CertFreeCertificateChain(pChainContext);
+
+  if(pCertContextServer)
+    CertFreeCertificateContext(pCertContextServer);
+
+  return result;
+}
+#endif /* _WIN32_WCE */
+
+#endif /* USE_SCHANNEL */