image: Truly dynamic backend registration

This allows one backend to provide multiple types.  For example, our
TarBackend can provide optional .gz, .bz2, and .xz compression.

4 files changed, 132 insertions, 8 deletions

diff --git a/image/backends/CMakeLists.txt b/image/backends/CMakeLists.txt
index f3c7f5d..726d4eb 100644
--- a/image/backends/CMakeLists.txt
+++ b/image/backends/CMakeLists.txt
@@ -1,4 +1,16 @@
 set(BACKEND_SRCS
-        ${CMAKE_CURRENT_SOURCE_DIR}/basic.cc
-        PARENT_SCOPE
+        basic.cc
 )
+
+set(BACKEND_LIBS "")
+
+find_package(LibArchive)
+
+if(LibArchive_FOUND)
+    list(APPEND BACKEND_SRCS tar.cc)
+    list(APPEND BACKEND_LIBS ${LibArchive_LIBRARIES})
+endif()
+
+add_library(hi-backends ${BACKEND_SRCS})
+target_link_libraries(hi-backends ${BACKEND_LIBS})
+install(TARGETS hi-backends DESTINATION lib)
diff --git a/image/backends/basic.cc b/image/backends/basic.cc
index bec3e41..0aa1afa 100644
--- a/image/backends/basic.cc
+++ b/image/backends/basic.cc
@@ -15,10 +15,8 @@
 namespace Horizon {
 namespace Image {
 
-std::vector<BackendDescriptor> known_backends = {
-   {"tar", "Create a tarball (.tar)", [](std::string, std::string){ return nullptr; } },
-   {"squashfs", "Create a SquashFS image (.squashfs)", [](std::string, std::string){ return nullptr; } }
-};
+std::vector<BackendDescriptor> known_backends
+__attribute__ ((init_priority(200)));
 
 const std::vector<BackendDescriptor> BackendManager::available_backends() {
     return known_backends;
diff --git a/image/backends/basic.hh b/image/backends/basic.hh
index 95b94ae..d57a9ac 100644
--- a/image/backends/basic.hh
+++ b/image/backends/basic.hh
@@ -47,9 +47,9 @@ public:
 
     /*! The intermediate directory which contains the sysroot the image
      *  should contain. */
-    const std::string &ir_dir;
+    const std::string ir_dir;
     /*! The path at which to write the image. */
-    const std::string &out_path;
+    const std::string out_path;
 };
 
 struct BackendDescriptor {
diff --git a/image/backends/tar.cc b/image/backends/tar.cc
new file mode 100644
index 0000000..d4ed584
--- /dev/null
+++ b/image/backends/tar.cc
@@ -0,0 +1,114 @@
+/*
+ * tar.cc - Implementation of the tarball Horizon Image Creation backend
+ * image, the image processing utilities for
+ * Project Horizon
+ *
+ * Copyright (c) 2020 Adélie Linux and contributors.  All rights reserved.
+ * This code is licensed under the AGPL 3.0 license, as noted in the
+ * LICENSE-code file in the root directory of this repository.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+#include <archive.h>
+#include "basic.hh"
+#include "util/output.hh"
+
+namespace Horizon {
+namespace Image {
+
+class TarBackend : public BasicBackend {
+public:
+    enum CompressionType {
+        None,
+        GZip,
+        BZip2,
+        XZ
+    };
+
+private:
+    CompressionType comp;
+    struct archive *a;
+
+public:
+    TarBackend(std::string ir, std::string out, CompressionType _c = None)
+        : BasicBackend(ir, out), comp(_c) {};
+
+    int prepare() override {
+        int res;
+
+        a = archive_write_new();
+        archive_write_set_format_pax_restricted(a);
+
+        switch(comp) {
+        case None:
+            break;
+        case GZip:
+            archive_write_add_filter_gzip(a);
+            break;
+        case BZip2:
+            archive_write_add_filter_bzip2(a);
+            break;
+        case XZ:
+            archive_write_add_filter_xz(a);
+            break;
+        }
+
+        res = archive_write_open_filename(a, this->out_path.c_str()) < ARCHIVE_OK;
+        if(res < ARCHIVE_OK) {
+            if(res < ARCHIVE_WARN) {
+                output_error("tar backend", archive_error_string(a));
+                return res;
+            } else {
+                output_warning("tar backend", archive_error_string(a));
+            }
+        }
+
+        return 0;
+    }
+
+    int create() override {
+        return 0;
+    }
+
+    int finalise() override {
+        archive_write_close(a);
+        archive_write_free(a);
+
+        return 0;
+    }
+};
+
+__attribute__((constructor(400)))
+void register_tar_backend() {
+    BackendManager::register_backend(
+    {"tar", "Create a tarball (.tar)",
+        [](std::string ir_dir, std::string out_path) {
+            return new TarBackend(ir_dir, out_path);
+        }
+    });
+
+    BackendManager::register_backend(
+    {"tgz", "Create a tarball with GZ compression (.tar.gz)",
+        [](std::string ir_dir, std::string out_path) {
+            return new TarBackend(ir_dir, out_path, TarBackend::GZip);
+        }
+    });
+
+    BackendManager::register_backend(
+    {"tbz", "Create a tarball with BZip2 compression (.tar.bz2)",
+        [](std::string ir_dir, std::string out_path) {
+            return new TarBackend(ir_dir, out_path, TarBackend::BZip2);
+        }
+    });
+
+    BackendManager::register_backend(
+    {"txz", "Create a tarball with XZ compression (.tar.xz)",
+        [](std::string ir_dir, std::string out_path) {
+            return new TarBackend(ir_dir, out_path, TarBackend::XZ);
+        }
+    });
+}
+
+}
+}