Add repository "summary" file and metalink support

For Fedora and potentially other distributions which use globally
distributed mirrors, metalink is a popular solution to redirect
clients to a dynamic set of mirrors.

In order to make metalink work though, it needs *one* file which can
be checksummed.  (Well, potentially we could explode all refs into the
metalink.xml, but that would be a lot more invasive, and a bit weird
as we'd end up checksumming the checksum file).

This commit adds a new command:

$ ostree summary -u

To regenerate the summary file.  Can only be run by one process at a
time.

After that's done, the metalink can be generated based on it, and the
client fetch code will parse and load it.

https://bugzilla.gnome.org/show_bug.cgi?id=729585

Makefile-libostree.am

@@ -112,6 +112,8 @@ if USE_LIBSOUP
 libostree_1_la_SOURCES += \
 	src/libostree/ostree-fetcher.h \
 	src/libostree/ostree-fetcher.c \
+	src/libostree/ostree-metalink.h \
+	src/libostree/ostree-metalink.c \
 	src/libostree/ostree-repo-pull.c \
 	$(NULL)
 libostree_1_la_CFLAGS += $(OT_INTERNAL_SOUP_CFLAGS)

Makefile-ostree.am

@@ -40,6 +40,7 @@ ostree_SOURCES = src/ostree/main.c \
 	src/ostree/ot-builtin-remote.c \
 	src/ostree/ot-builtin-reset.c \
 	src/ostree/ot-builtin-rev-parse.c \
+	src/ostree/ot-builtin-summary.c \
 	src/ostree/ot-builtin-show.c \
 	src/ostree/ot-builtin-static-delta.c \
 	src/ostree/ot-main.h \

Makefile-tests.am

@@ -31,6 +31,7 @@ testfiles = test-basic \
 	test-pull-archive-z \
 	test-pull-corruption \
 	test-pull-large-metadata \
+	test-pull-metalink \
 	test-pull-resume \
 	test-gpg-signed-commit \
 	test-admin-deploy-syslinux \

src/libostree/ostree-core.h

@@ -117,6 +117,15 @@ typedef enum {
 #define OSTREE_COMMIT_GVARIANT_STRING "(a{sv}aya(say)sstayay)"
 #define OSTREE_COMMIT_GVARIANT_FORMAT G_VARIANT_TYPE (OSTREE_COMMIT_GVARIANT_STRING)
 
+/**
+ * OSTREE_SUMMARY_GVARIANT_FORMAT:
+ *
+ * refs: a(s(taya{sv})) - Map of ref name -> (latest commit size, latest commit checksum, additional metadata), sorted by ref name
+ * extensions: a{sv} - Additional metadata, none defined at the current time
+ */
+#define OSTREE_SUMMARY_GVARIANT_STRING "(a(s(taya{sv}))a{sv})"
+#define OSTREE_SUMMARY_GVARIANT_FORMAT G_VARIANT_TYPE (OSTREE_SUMMARY_GVARIANT_STRING)
+
 /**
  * OstreeRepoMode:
  * @OSTREE_REPO_MODE_BARE: Files are stored as themselves; can only be written as root