Add docker based grype backend

pygrype/__init__.py

@@ -1,3 +1,4 @@
 from .grype import Grype
 from .core.backends.binary import GrypeBinaryBackend
+from .core.backends.docker import GrypeDockerBackend
 

pygrype/core/backends/docker.py

@@ -0,0 +1,50 @@
+import subprocess
+from subprocess import CompletedProcess
+
+from pygrype.core.backends.base import GrypeBackend
+
+
+DOCKER_EXE = 'docker'
+IMAGE_NAME = 'anchore/grype'
+
+
+class GrypeDockerBackend(GrypeBackend):
+
+    def __init__(self, tag: str = "latest") -> None:
+        self.tag: str = tag
+        super().__init__()
+
+    @property
+    def docker_image(self) -> str:
+        return f"{IMAGE_NAME}:{self.tag}"
+
+    def ensure_backend(self):
+        try:
+            # Check if Docker is installed
+            subprocess.run(
+                [DOCKER_EXE, '--version'],
+                check=True,
+                stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE
+            )
+        except subprocess.CalledProcessError:
+            raise Exception("Docker is not installed or not available in the PATH.")
+
+        try:
+            # Ensure the required Docker image is available
+            subprocess.run(
+                [DOCKER_EXE, 'pull', self.docker_image],
+                check=True,
+                stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE
+            )
+        except subprocess.CalledProcessError:
+            raise Exception(f"Failed to pull the required Docker image '{self.docker_image}'.")
+
+    @property
+    def executable_string(self) -> str:
+        return DOCKER_EXE
+
+    def execute(self, *args) -> CompletedProcess:
+        docker_args = ['run', '--rm', self.docker_image] + list(args)
+        return super().execute(*docker_args)