Clean up crypto library abstraction in build system and source code

libssh2 used to explicitly check for libgcrypt and default to OpenSSL.

Now all possible crypto libraries are checked for explicitly, making
the addition of further crypto libraries both simpler and cleaner.

Makefile.inc

@@ -1,7 +1,18 @@
 CSOURCES = channel.c comp.c crypt.c hostkey.c kex.c mac.c misc.c \
  packet.c publickey.c scp.c session.c sftp.c userauth.c transport.c \
- version.c knownhost.c agent.c openssl.c libgcrypt.c pem.c keepalive.c \
- global.c
+ version.c knownhost.c agent.c pem.c keepalive.c global.c
+if OPENSSL
+CSOURCES += openssl.c
+endif
+if LIBGCRYPT
+CSOURCES += libgcrypt.c
+endif
 
-HHEADERS = libssh2_priv.h openssl.h libgcrypt.h transport.h channel.h \
- comp.h mac.h misc.h packet.h userauth.h session.h sftp.h crypto.h
+HHEADERS = libssh2_priv.h transport.h channel.h comp.h mac.h misc.h \
+ packet.h userauth.h session.h sftp.h crypto.h
+if OPENSSL
+HHEADERS += openssl.h
+endif
+if LIBGCRYPT
+HHEADERS += libgcrypt.h
+endif

configure.ac

@@ -93,7 +93,7 @@ AC_ARG_WITH(libz,
   AC_HELP_STRING([--with-libz],[Use Libz for compression]),
   use_libz=$withval,use_libz=auto)
 
-# Look for OpenSSL (default)
+# Look for OpenSSL
 if test "$use_openssl" != "no" && test "$use_libgcrypt" != "yes"; then
   AC_LIB_HAVE_LINKFLAGS([ssl], [crypto], [#include <openssl/ssl.h>])
   LIBSREQUIRED=libssl,libcrypto
@@ -110,6 +110,11 @@ if test "$ac_cv_libssl" != "yes" && test "$ac_cv_libgcrypt" != "yes"; then
 try --with-libssl-prefix=PATH or --with-libgcrypt-prefix=PATH])
 fi
 
+if test "$ac_cv_libssl" = "yes"; then
+  AC_DEFINE(LIBSSH2_OPENSSL, 1, [Use OpenSSL])
+fi
+AM_CONDITIONAL(OPENSSL, test "$ac_cv_libssl" = "yes")
+
 if test "$ac_cv_libgcrypt" = "yes"; then
   AC_DEFINE(LIBSSH2_LIBGCRYPT, 1, [Use libgcrypt])
 fi

src/crypto.h

@@ -38,10 +38,12 @@
 #ifndef LIBSSH2_CRYPTO_H
 #define LIBSSH2_CRYPTO_H
 
+#ifdef LIBSSH2_OPENSSL
+#include "openssl.h"
+#endif
+
 #ifdef LIBSSH2_LIBGCRYPT
 #include "libgcrypt.h"
-#else
-#include "openssl.h"
 #endif
 
 int _libssh2_rsa_new(libssh2_rsa_ctx ** rsa,

src/openssl.c

@@ -40,8 +40,6 @@
 
 #include "libssh2_priv.h"
 
-#ifndef LIBSSH2_LIBGCRYPT /* compile only if we build with OpenSSL */
-
 #include <string.h>
 
 #ifndef EVP_MAX_BLOCK_LENGTH
@@ -800,5 +798,3 @@ _libssh2_pub_priv_keyfile(LIBSSH2_SESSION *session,
     EVP_PKEY_free(pk);
     return st;
 }
-
-#endif /* !LIBSSH2_LIBGCRYPT */