Add support for debian

Signed-off-by: Tushar Goel <tushar.goel.dav@gmail.com>

Author: TG1999

src/packageurl/contrib/purl2url.py

@@ -593,6 +593,57 @@ def build_alpm_download_url(purl_str):
     return url
 
 
+def normalize_version(version: str) -> str:
+    """
+    Remove the epoch (if any) from a Debian version.
+    E.g., "1:2.4.47-2" becomes "2.4.47-2"
+    """
+    if ":" in version:
+        _, v = version.split(":", 1)
+        return v
+    return version
+
+
+@download_router.route("pkg:deb/.*")
+def build_deb_download_url(purl_str: str) -> str:
+    """
+    Construct a download URL for a Debian or Ubuntu package PURL.
+    Supports optional 'repository_url' in qualifiers.
+    """
+    p = PackageURL.from_string(purl_str)
+
+    name = p.name
+    version = p.version
+    qualifiers = p.qualifiers or {}
+    arch = qualifiers.get("arch")
+    repository_url = qualifiers.get("repository_url")
+
+    # Use repository_url if provided, otherwise fall back to distro-specific default
+    if repository_url:
+        base_url = repository_url.rstrip("/")
+    else:
+        namespace = (p.namespace or "debian").lower()
+        if namespace == "debian":
+            base_url = "https://deb.debian.org/debian"
+        elif namespace == "ubuntu":
+            base_url = "http://archive.ubuntu.com/ubuntu"
+        else:
+            raise NotImplementedError(f"Unsupported distro namespace: {namespace}")
+
+    # Normalize version (e.g., remove epoch)
+    norm_version = normalize_version(version)
+
+    # Build filename
+    if arch == "source":
+        filename = f"{name}_{norm_version}.dsc"
+    else:
+        filename = f"{name}_{norm_version}_{arch}.deb"
+
+    pool_path = f"/pool/main/{name[0].lower()}/{name}"
+
+    return f"{base_url}{pool_path}/{filename}"
+
+
 def get_repo_download_url(purl):
     """
     Return ``download_url`` if present in ``purl`` qualifiers or

tests/contrib/test_purl2url.py

@@ -110,6 +110,8 @@ def test_purl2url_get_download_url():
         "pkg:luarocks/hisham/luafilesystem@1.8.0-1": "https://luarocks.org/luafilesystem-1.8.0-1.src.rock",
         "pkg:conda/absl-py@0.4.1?build=py36h06a4308_0&channel=main&subdir=linux-64&type=tar.bz2": "https://repo.anaconda.com/pkgs/main/linux-64/absl-py-0.4.1-py36h06a4308_0.tar.bz2",
         "pkg:alpm/arch/pacman@6.0.1-1?arch=x86_64": "https://archive.archlinux.org/packages/p/pacman/pacman-6.0.1-1-x86_64.pkg.tar.zst",
+        "pkg:deb/debian/attr@1:2.4.48-6?arch=amd64": "https://deb.debian.org/debian/pool/main/a/attr/attr_2.4.48-6_amd64.deb",
+        "pkg:deb/debian/attr@1:2.4.48-6?arch=amd64&repository_url=http://archive.debian.org/debian": "http://archive.debian.org/debian/pool/main/a/attr/attr_2.4.48-6_amd64.deb",
         # From `download_url` qualifier
         "pkg:github/yarnpkg/yarn@1.3.2?download_url=https://github.com/yarnpkg/yarn/releases/download/v1.3.2/yarn-v1.3.2.tar.gz&version_prefix=v": "https://github.com/yarnpkg/yarn/releases/download/v1.3.2/yarn-v1.3.2.tar.gz",
         "pkg:generic/lxc-master.tar.gz?download_url=https://salsa.debian.org/lxc-team/lxc/-/archive/master/lxc-master.tar.gz": "https://salsa.debian.org/lxc-team/lxc/-/archive/master/lxc-master.tar.gz",