PGP: Implement OpenPGP using librpm API

It implements the original librepo OpenPGP API using librpm API instead
of GpgMe. It implements its own keyring for public keys. Each key with
its subkeys is stored in its own file.

The original GpgMe based implementation was moved to the "gpg_gpgme.c"
file. So it is still present and can be activated by the USE_GPGME option
in "CMakeList.txt".
This commit will leave the original GpgMe implementation enabled by default
in CMakeList.txt. In the .spec file it switches to the librpm API for
Fedora >= 39.

Requirement:
A new rpm library is needed that supports OpenPGP ASCII Armored signature
parsing. Tested with sequoia based rpm OpenPGP backend.

Missing (requires support in the rpm library):
- Setting the `can_sign` property. It now always returns TRUE.
- Fingerprint for subkeys. An empty string is now returned.
- Return all user IDs. Now only one returns

Notes:
In the Python tests, pgp tests that should succeed were disabled. This is
because librepo lacks a Python API for working with OpenGPG keys.
The Python tests manipulate the keyring directly using GpgMe. Of course,
this only works if the librepo library uses the original GpgMe backend.

CMakeLists.txt

@@ -5,6 +5,7 @@ OPTION (ENABLE_TESTS "Build test?" ON)
 OPTION (ENABLE_DOCS "Build docs?" ON)
 OPTION (WITH_ZCHUNK "Build with zchunk support" ON)
 OPTION (ENABLE_PYTHON "Build Python bindings" ON)
+OPTION (USE_GPGME "Use GpgMe (instead of rpm library) for OpenPGP key support" ON)
 
 INCLUDE (${CMAKE_SOURCE_DIR}/VERSION.cmake)
 SET (VERSION "${LIBREPO_MAJOR}.${LIBREPO_MINOR}.${LIBREPO_PATCH}")
@@ -32,8 +33,12 @@ PKG_CHECK_MODULES(GLIB2 glib-2.0>=2.66 gio-2.0 REQUIRED)
 PKG_SEARCH_MODULE(LIBCRYPTO REQUIRED libcrypto openssl)
 PKG_CHECK_MODULES(LIBXML2 libxml-2.0 REQUIRED)
 FIND_PACKAGE(CURL 7.52.0 REQUIRED)
-FIND_PACKAGE(Gpgme REQUIRED)
 
+IF (USE_GPGME)
+    FIND_PACKAGE(Gpgme REQUIRED)
+ELSE (USE_GPGME)
+    PKG_CHECK_MODULES(RPM REQUIRED rpm>=4.18.0)
+ENDIF (USE_GPGME)
 
 IF (WITH_ZCHUNK)
 PKG_CHECK_MODULES(ZCHUNKLIB zck>=0.9.11 REQUIRED)

librepo.spec

@@ -8,6 +8,12 @@
 %bcond_without zchunk
 %endif
 
+%if 0%{?fedora} >= 39
+%bcond_with use_gpgme
+%else
+%bcond_without use_gpgme
+%endif
+
 %global dnf_conflict 2.8.8
 
 Name:           librepo
@@ -24,7 +30,11 @@ BuildRequires:  gcc
 BuildRequires:  check-devel
 BuildRequires:  doxygen
 BuildRequires:  pkgconfig(glib-2.0) >= 2.66
+%if %{with use_gpgme}
 BuildRequires:  gpgme-devel
+%else
+BuildRequires:  pkgconfig(rpm) >= 4.18.0
+%endif
 BuildRequires:  libattr-devel
 BuildRequires:  libcurl-devel >= %{libcurl_version}
 BuildRequires:  pkgconfig(libxml-2.0)
@@ -66,7 +76,9 @@ Python 3 bindings for the librepo library.
 %autosetup -p1
 
 %build
-%cmake %{!?with_zchunk:-DWITH_ZCHUNK=OFF}
+%cmake \
+    -DWITH_ZCHUNK=%{?with_zchunk:ON}%{!?with_zchunk:OFF} \
+    -DUSE_GPGME=%{?with_use_gpgme:ON}%{!?with_use_gpgme:OFF}
 %cmake_build
 
 %check

librepo/CMakeLists.txt

@@ -1,4 +1,4 @@
-SET (librepo_SRCS
+LIST(APPEND librepo_SRCS
      checksum.c
      downloader.c
      downloadtarget.c
@@ -20,7 +20,13 @@ SET (librepo_SRCS
      xmlparser.c
      yum.c)
 
-SET(librepo_HEADERS
+IF(USE_GPGME)
+    LIST(APPEND librepo_SRCS gpg_gpgme.c)
+ELSE(USE_GPGME)
+    LIST(APPEND librepo_SRCS gpg_rpm.c)
+ENDIF(USE_GPGME)
+
+LIST(APPEND librepo_HEADERS
     checksum.h
     fastestmirror.h
     gpg.h
@@ -44,10 +50,11 @@ SET(librepo_HEADERS
     downloader.h
     downloadtarget.h)
 
-SET(librepo_internal_HEADERS
+LIST(APPEND librepo_internal_HEADERS
     downloader_internal.h
     downloadtarget_internal.h
     fastestmirror_internal.h
+    gpg_internal.h
     handle_internal.h
     repoconf_internal.h
     result_internal.h
@@ -60,9 +67,14 @@ TARGET_LINK_LIBRARIES(librepo
                         ${LIBXML2_LIBRARIES}
                         ${CURL_LIBRARY}
                         ${LIBCRYPTO_LIBRARIES}
-                        ${GPGME_VANILLA_LIBRARIES}
                         ${GLIB2_LIBRARIES}
                      )
+IF (USE_GPGME)
+    TARGET_LINK_LIBRARIES(librepo ${GPGME_VANILLA_LIBRARIES})
+ELSE(USE_GPGME)
+    TARGET_LINK_LIBRARIES(librepo ${RPM_LIBRARIES})
+ENDIF (USE_GPGME)
+
 IF (WITH_ZCHUNK)
     TARGET_LINK_LIBRARIES(librepo ${ZCHUNKLIB_LIBRARIES})
 ENDIF (WITH_ZCHUNK)