add CRAN support

add CRAN support using https://cran.r-project.org/src/contrib/PACKAGES

docs/usage.rst

@@ -506,6 +506,17 @@ Check `MetaCPAN <https://metacpan.org/>`_ for updates.
 cpan
   The name used on CPAN, e.g. ``YAML``.
 
+Check CRAN
+~~~~~~~~~~
+::
+
+  source = "cran"
+
+Check `CRAN <https://cran.r-project.org/>`_ for updates.
+
+cran
+  The name used on CRAN, e.g. ``ggplot2``.
+
 Check Packagist
 ~~~~~~~~~~~~~~~
 ::

nvchecker_source/cran.py

@@ -0,0 +1,25 @@
+# MIT licensed
+# Copyright (c) 2021- hubutui <hot123tea123@gmail.com>
+import configparser
+
+from nvchecker.api import session
+
+CRAN_URL = 'https://cran.r-project.org/src/contrib/PACKAGES'
+
+async def get_versions(url: str):
+    result = {}
+    res = await session.get(url)
+    config = configparser.ConfigParser()
+    for item in res.body.decode("UTF-8").split("\n\n"):
+        if item.startswith("Package: "):
+            rpkgname = item.split('\n')[0].replace(' ', '').split(':')[1]
+            config.read_string(f"[{rpkgname}]\n" + item)
+            result[rpkgname] = config[rpkgname]["version"]
+
+    return result
+
+async def get_version(name, conf, *, cache, **kwargs):
+    rpkgname = conf.get('cran', name)
+    versions = await cache.get(CRAN_URL, get_versions)
+
+    return versions[rpkgname]

tests/test_cran.py

@@ -0,0 +1,11 @@
+# MIT licensed
+# Copyright (c) 2021- hubutui <hot123tea123@gmail.com>
+
+import pytest
+
+pytestmark = [pytest.mark.asyncio, pytest.mark.needs_net]
+
+async def test_cran(get_version):
+    assert await get_version("ggplot2", {
+        "source": "cran",
+    }) == "3.3.3"