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, 11 insertions, 3 deletions

diff --git a/lib/vtls/gskit.c b/lib/vtls/gskit.c
index 19808c621..5d6bb0c8f 100644
--- a/lib/vtls/gskit.c
+++ b/lib/vtls/gskit.c
@@ -98,7 +98,14 @@
 #define CURL_GSKPROTO_TLSV12_MASK        (1 << CURL_GSKPROTO_TLSV12)
 #define CURL_GSKPROTO_LAST      5
 
-#define BACKEND connssl
+struct ssl_backend_data {
+  gsk_handle handle;
+  int iocport;
+  int localfd;
+  int remotefd;
+};
+
+#define BACKEND connssl->backend
 
 /* Supported ciphers. */
 typedef struct {
@@ -638,7 +645,7 @@ static int pipe_ssloverssl(struct connectdata *conn, int sockindex,
   if(FD_ISSET(BACKEND->remotefd, &fds_write)) {
     /* Try getting data from HTTPS proxy and pipe it upstream. */
     n = 0;
-    i = gsk_secure_soc_read(connproxyssl->handle,
+    i = gsk_secure_soc_read(connproxyssl->backend->handle,
                             buf, sizeof buf, &n);
     switch(i) {
     case GSK_OK:
@@ -664,7 +671,7 @@ static int pipe_ssloverssl(struct connectdata *conn, int sockindex,
     if(n < 0)
       return -1;
     if(n) {
-      i = gsk_secure_soc_write(connproxyssl->handle, buf, n, &m);
+      i = gsk_secure_soc_write(connproxyssl->backend->handle, buf, n, &m);
       if(i != GSK_OK || n != m)
         return -1;
       ret = 1;
@@ -1355,6 +1362,7 @@ const struct Curl_ssl Curl_ssl_gskit = {
   /* TODO: convert to 1 and fix test #1014 (if need) */
   0, /* support_https_proxy */
 
+  sizeof(struct ssl_backend_data),
 
   Curl_gskit_init,                /* init */
   Curl_gskit_cleanup,             /* cleanup */