Add content reader to decouple NFS file reads [RHELDST-26339]

The API to read content of the push items strongly depends
on their presence as file on NFS or locally-mounted filesystem.
However, with advent of new push item sources, it likely that
the push items might not be stored as a file or be locally available.

Hence, pushitems will have an `opener` that is capable to fetch
the corresponding bits and provide them as `content()`. `Source`
will define the `opener` while creating the pushitems to get the
bit from the specific content source. This will transfer the
responsibility to fetch the content from the consumer that is
using the content/pushitems to the `Source` and corresponding
`pushitem` here, abstracting the reading mechanism from the user
and provide flexibility to fetch from different locations/protocols.

src/pushsource/_impl/list_cmd.py

@@ -33,6 +33,10 @@
 
 LOG = logging.getLogger("pushsource-ls")
 
+EXCLUDED_ATTRIBUTES = [
+    "_content",
+]
+
 
 def format_python(item):
     return repr(item) + ","
@@ -49,8 +53,26 @@ def format_python_black(item):
     return out
 
 
+def _filter_attributes(attribute, _):
+    return attribute.alias not in EXCLUDED_ATTRIBUTES
+
+
+def _callable_to_str(value):
+    if not callable(value):
+        return value
+
+    return getattr(value, "__name__", repr(value))
+
+
 def format_yaml(item):
-    data = {type(item).__name__: attr.asdict(item, recurse=True)}
+    data = {
+        type(item).__name__: attr.asdict(
+            item,
+            recurse=True,
+            filter=_filter_attributes,
+            value_serializer=lambda _self, _field, value: _callable_to_str(value),
+        )
+    }
     return yaml.dump([data], Dumper=yaml.SafeDumper)
 
 

src/pushsource/_impl/model/base.py

@@ -16,6 +16,8 @@
     optional,
     optional_str,
 )
+from ..reader import PushItemReader
+from ..utils.openers import open_src_local
 
 
 LOG = logging.getLogger("pushsource")
@@ -178,6 +180,11 @@ def _default_build_info(self):
     doesn't enforce this.
     """
 
+    opener = attr.ib(type=callable, default=open_src_local, repr=False)
+    """Callable that gets the content of this push item. The content could be
+    retrived from `content()` method"""
+
+
     def with_checksums(self):
         """Return a copy of this push item with checksums present.
 
@@ -248,3 +255,12 @@ def with_checksums(self):
             updated_sums[attribute] = hasher.hexdigest()
 
         return attr.evolve(self, **updated_sums)
+
+    def content(self):
+        """Returns a read-only, non-seekable content of this push item.
+
+        Returns:
+            :class:`~io.BufferedReader`
+                A non-seekable object of the push item content
+        """
+        return PushItemReader(self.opener(self))

src/pushsource/_impl/reader.py

@@ -0,0 +1,23 @@
+from io import BufferedReader, SEEK_SET, UnsupportedOperation
+
+
+class PushItemReader(BufferedReader):
+    # Internal class to ensure that the file-like content object returned by
+    # the push items are read-only and non-seekable with a name attribute.
+    def __init__(self, raw, name=None, **kwargs):
+        super(PushItemReader, self).__init__(raw, **kwargs)
+
+        # Attempt to assign name from the raw object if none is provided
+        self._name = name or getattr(super(), "name", None)
+        if not self._name:
+            raise ValueError("'name' not provided or availble from 'raw' object")
+
+    @property
+    def name(self):
+        return self._name or super().name()
+
+    def seekable(self):
+        return False
+
+    def seek(self, offset, whence=SEEK_SET):
+        raise UnsupportedOperation(f"Seek unsupported while reading {self.name}")

src/pushsource/_impl/utils/openers.py

@@ -0,0 +1,5 @@
+def open_src_local(item):
+    # default opener for the push items
+    # assumes that the item's 'src' points to the
+    # locally-accessible file
+    return open(item.src, "rb")

tests/baseline/cases/direct-cgw.yml

@@ -15,6 +15,7 @@ items:
     - dest
     md5sum: null
     name: cgw.yaml
+    opener: open_src_local
     origin: direct
     sha256sum: null
     signing_key: null

tests/baseline/cases/direct-comps.yml

@@ -14,6 +14,7 @@ items:
     dest: []
     md5sum: null
     name: mycomps.xml
+    opener: open_src_local
     origin: direct
     sha256sum: null
     signing_key: null

tests/baseline/cases/direct-dir.yml

@@ -15,6 +15,7 @@ items:
     - /destdir
     md5sum: null
     name: srcdir
+    opener: open_src_local
     origin: direct
     sha256sum: null
     signing_key: null

tests/baseline/cases/direct-file.yml

@@ -18,6 +18,7 @@ items:
     display_order: null
     md5sum: null
     name: custom-filename
+    opener: open_src_local
     origin: direct
     sha256sum: null
     signing_key: null

tests/baseline/cases/direct-modulemd-src.yml

@@ -14,6 +14,7 @@ items:
     dest: []
     md5sum: null
     name: modules.src.txt
+    opener: open_src_local
     origin: direct
     sha256sum: null
     signing_key: null

tests/baseline/cases/direct-modulemd.yml

@@ -14,6 +14,7 @@ items:
     dest: []
     md5sum: null
     name: my-best-module
+    opener: open_src_local
     origin: direct
     sha256sum: null
     signing_key: null

tests/baseline/cases/direct-productid.yml

@@ -17,6 +17,7 @@ items:
     - repo3
     md5sum: null
     name: some-cert
+    opener: open_src_local
     origin: direct
     products:
     - architecture:

tests/baseline/cases/direct-rpm.yml

@@ -15,6 +15,7 @@ items:
     md5sum: null
     module_build: null
     name: test.rpm
+    opener: open_src_local
     origin: custom-origin
     sha256sum: null
     signing_key: A1B2C3