vtls: encapsulate SSL backend-specific data

So far, all of the SSL backends' private data has been declared as
part of the ssl_connect_data struct, in one big #if .. #elif .. #endif
block.

This can only work as long as the SSL backend is a compile-time option,
something we want to change in the next commits.

Therefore, let's encapsulate the exact data needed by each SSL backend
into a private struct, and let's avoid bleeding any SSL backend-specific
information into urldata.h. This is also necessary to allow multiple SSL
backends to be compiled in at the same time, as e.g. OpenSSL's and
CyaSSL's headers cannot be included in the same .c file.

To avoid too many malloc() calls, we simply append the private structs
to the connectdata struct in allocate_conn().

This requires us to take extra care of alignment issues: struct fields
often need to be aligned on certain boundaries e.g. 32-bit values need to
be stored at addresses that divide evenly by 4 (= 32 bit / 8
bit-per-byte).

We do that by assuming that no SSL backend's private data contains any
fields that need to be aligned on boundaries larger than `long long`
(typically 64-bit) would need. Under this assumption, we simply add a
dummy field of type `long long` to the `struct connectdata` struct. This
field will never be accessed but acts as a placeholder for the four
instances of ssl_backend_data instead. the size of each ssl_backend_data
struct is stored in the SSL backend-specific metadata, to allow
allocate_conn() to know how much extra space to allocate, and how to
initialize the ssl[sockindex]->backend and proxy_ssl[sockindex]->backend
pointers.

This would appear to be a little complicated at first, but is really
necessary to encapsulate the private data of each SSL backend correctly.
And we need to encapsulate thusly if we ever want to allow selecting
CyaSSL and OpenSSL at runtime, as their headers cannot be included within
the same .c file (there are just too many conflicting definitions and
declarations for that).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

1 files changed, 36 insertions, 1 deletions

diff --git a/lib/vtls/schannel.c b/lib/vtls/schannel.c
index 4fb24504d..d3f44018b 100644
--- a/lib/vtls/schannel.c
+++ b/lib/vtls/schannel.c
@@ -46,6 +46,8 @@
 #  error "Can't compile SCHANNEL support without SSPI."
 #endif
 
+#include <schnlsp.h>
+#include <schannel.h>
 #include "curl_sspi.h"
 #include "schannel.h"
 #include "vtls.h"
@@ -127,7 +129,38 @@
  * #define failf(x, y, ...) printf(y, __VA_ARGS__)
  */
 
-#define BACKEND connssl
+/* Structs to store Schannel handles */
+struct curl_schannel_cred {
+  CredHandle cred_handle;
+  TimeStamp time_stamp;
+  int refcount;
+};
+
+struct curl_schannel_ctxt {
+  CtxtHandle ctxt_handle;
+  TimeStamp time_stamp;
+};
+
+struct ssl_backend_data {
+  struct curl_schannel_cred *cred;
+  struct curl_schannel_ctxt *ctxt;
+  SecPkgContext_StreamSizes stream_sizes;
+  size_t encdata_length, decdata_length;
+  size_t encdata_offset, decdata_offset;
+  unsigned char *encdata_buffer, *decdata_buffer;
+  /* encdata_is_incomplete: if encdata contains only a partial record that
+     can't be decrypted without another Curl_read_plain (that is, status is
+     SEC_E_INCOMPLETE_MESSAGE) then set this true. after Curl_read_plain writes
+     more bytes into encdata then set this back to false. */
+  bool encdata_is_incomplete;
+  unsigned long req_flags, ret_flags;
+  CURLcode recv_unrecoverable_err; /* schannel_recv had an unrecoverable err */
+  bool recv_sspi_close_notify; /* true if connection closed by close_notify */
+  bool recv_connection_closed; /* true if connection closed, regardless how */
+  bool use_alpn; /* true if ALPN is used for this connection */
+};
+
+#define BACKEND connssl->backend
 
 static Curl_recv schannel_recv;
 static Curl_send schannel_send;
@@ -1791,6 +1824,8 @@ const struct Curl_ssl Curl_ssl_schannel = {
   0, /* have_ssl_ctx */
   0, /* support_https_proxy */
 
+  sizeof(struct ssl_backend_data),
+
   Curl_schannel_init,                /* init */
   Curl_schannel_cleanup,             /* cleanup */
   Curl_schannel_version,             /* version */