rpmmd/dnf-json: support chain dependency solving

Add a new `rpmmdImpl` method `chainDepsolve`, which is able to
depsolve multiple chained package sets as separate DNF transactions
layered on top of each other.

This new method allows to depsolve the `blueprint` package set on top of
the base image package set (usually called `packages`).

Introduce a helper function `chainPackageSets` for constructing
arguments to the `chainDepsolve` method based on the provided arguments:
 - slice of package set names to chain as transactions
 - map of package sets
 - slice of system repositories used by all package sets
 - map of package-set-specific repositories

Extend `dnf-json` with a new command `chain-depsolve` allowing to
depsolve multiple transaction in a row, layered on top of each other.

Add unit tests where appropriate.

dnf-json

@@ -247,6 +247,59 @@ class Solver():
             "dependencies": dependencies
         }
 
+    def chain_depsolve(self, transactions):
+        last_transaction = []
+
+        for idx, transaction in enumerate(transactions):
+            self.base.reset(goal=True)
+            self.base.sack.reset_excludes()
+
+            # don't install weak-deps for transactions after the 1st transaction
+            if idx > 0:
+                self.base.conf.install_weak_deps=False
+
+            # set the packages from the last transaction as installed
+            for installed_pkg in last_transaction:
+                self.base.package_install(installed_pkg, strict=True)
+
+            # depsolve the current transaction
+            self.base.install_specs(
+                transaction.get("package-specs"),
+                transaction.get("exclude-specs"),
+                reponame=[str(id) for id in transaction.get("repos")])
+            self.base.resolve()
+
+            # store the current transaction result
+            last_transaction.clear()
+            for tsi in self.base.transaction:
+                # Avoid using the install_set() helper, as it does not guarantee
+                # a stable order
+                if tsi.action not in dnf.transaction.FORWARD_ACTIONS:
+                    continue
+                last_transaction.append(tsi.pkg)
+
+        dependencies = []
+        for package in last_transaction:
+            dependencies.append({
+                "name": package.name,
+                "epoch": package.epoch,
+                "version": package.version,
+                "release": package.release,
+                "arch": package.arch,
+                "repo_id": package.repoid,
+                "path": package.relativepath,
+                "remote_location": package.remote_location(),
+                "checksum": (
+                    f"{hawkey.chksum_name(package.chksum[0])}:"
+                    f"{package.chksum[1].hex()}"
+                )
+            })
+
+        return {
+            "checksums": self._repo_checksums(),
+            "dependencies": dependencies
+        }
+
 
 class DnfJsonRequestHandler(BaseHTTPRequestHandler):
     """
@@ -354,6 +407,10 @@ class DnfJsonRequestHandler(BaseHTTPRequestHandler):
                                 )
                             )
                             log.info("depsolve success")
+                        elif command == "chain-depsolve":
+                            self.response_success(
+                                solver.chain_depsolve(arguments["transactions"])
+                            )
 
                     except dnf.exceptions.MarkingErrors as e:
                         log.info("error install_specs")