ssh: create the right callback signature based on build options

When linking against libssh2, create the transport.h such that it
contains its definition for custom crypto and keyboard-interactive
callbacks.

If we don't link against libssh2, create an equivalent signature which
has void pointers instead of pointers to libssh2 structures.

This would be one way to fix #2438.

CMakeLists.txt

@@ -408,6 +408,17 @@ IF (SONAME)
 ENDIF()
 CONFIGURE_FILE(${CMAKE_CURRENT_SOURCE_DIR}/libgit2.pc.in ${CMAKE_CURRENT_BINARY_DIR}/libgit2.pc @ONLY)
 
+IF (LIBSSH2_FOUND)
+	SET(INCLUDE_LIBSSH2 "#include <libssh2.h>")
+	SET(GIT_SSH_PK_FUNC "typedef LIBSSH2_USERAUTH_PUBLICKEY_SIGN_FUNC((*git_cred_sign_callback));")
+	SET(GIT_SSH_KI_FUNC "typedef LIBSSH2_USERAUTH_KBDINT_RESPONSE_FUNC((*git_cred_ssh_interactive_callback));")
+ELSE ()
+	SET(GIT_SSH_PK_FUNC "typedef int (*git_cred_sign_callback)(void *, unsigned char **, size_t *, const unsigned char *, size_t, void **);")
+	SET(GIT_SSH_KI_FUNC "typedef int (*git_cred_ssh_interactive_callback)(const char *, int, const char *, int, int, const void *, void *, void **);")
+ENDIF ()
+CONFIGURE_FILE(${CMAKE_CURRENT_SOURCE_DIR}/include/git2/transport.h.in ${CMAKE_CURRENT_SOURCE_DIR}/include/git2/transport.h @ONLY)
+
+
 IF (MSVC_IDE)
    # Precompiled headers
    SET_TARGET_PROPERTIES(git2 PROPERTIES COMPILE_FLAGS "/Yuprecompiled.h /FIprecompiled.h")

include/git2/transport.h → include/git2/transport.h.in

@@ -11,9 +11,7 @@
 #include "net.h"
 #include "types.h"
 
-#ifdef GIT_SSH
-#include <libssh2.h>
-#endif
+@INCLUDE_LIBSSH2@
 
 /**
  * @file git2/transport.h
@@ -61,13 +59,14 @@ typedef struct {
 	char *password;
 } git_cred_userpass_plaintext;
 
-#ifdef GIT_SSH
-typedef LIBSSH2_USERAUTH_PUBLICKEY_SIGN_FUNC((*git_cred_sign_callback));
-typedef LIBSSH2_USERAUTH_KBDINT_RESPONSE_FUNC((*git_cred_ssh_interactive_callback));
-#else
-typedef int (*git_cred_sign_callback)(void *, ...);
-typedef int (*git_cred_ssh_interactive_callback)(void *, ...);
-#endif
+/*
+ * This defines the callbacks for custom public key signatures and
+ * keyboard-interactive authentication. It is replaced at build-time
+ * with either the libssh2 signature or a dummy signature that's close
+ * enough but with void pointers instead of libssh2 structures.
+ */
+@GIT_SSH_PK_FUNC@
+@GIT_SSH_KI_FUNC@
 
 /**
  * A ssh key from disk