Get input from commandline when instance(s) not provided

Author: Talha Malik

jsonschema/cli.py

@@ -22,6 +22,10 @@ def _json_file(path):
         return json.load(file)
 
 
+def _read_from_stdin():
+    return json.loads(sys.stdin.read())
+
+
 parser = argparse.ArgumentParser(
     description="JSON Schema Validation CLI",
 )
@@ -83,8 +87,9 @@ def run(arguments, stdout=sys.stdout, stderr=sys.stderr):
     validator.check_schema(arguments["schema"])
 
     errored = False
-    for instance in arguments["instances"] or ():
+    for instance in arguments["instances"] or (_read_from_stdin(),):
         for error in validator.iter_errors(instance):
             stderr.write(error_format.format(error=error))
             errored = True
+
     return errored

jsonschema/tests/test_cli.py

@@ -1,4 +1,4 @@
-from unittest import TestCase
+from unittest import TestCase, mock
 import json
 import subprocess
 import sys
@@ -149,3 +149,22 @@ def test_version(self):
         )
         version = version.decode("utf-8").strip()
         self.assertEqual(version, __version__)
+
+    @mock.patch("sys.stdin")
+    def test_piping(self, mock_stdin):
+        mock_stdin.read.return_value = "{}"
+        stdout, stderr = NativeIO(), NativeIO()
+        exit_code = cli.run(
+            {
+                "validator": fake_validator(),
+                "schema": {},
+                "instances": [],
+                "error_format": "{error.message}",
+            },
+            stdout=stdout,
+            stderr=stderr,
+        )
+        mock_stdin.read.assert_called_once_with()
+        self.assertFalse(stdout.getvalue())
+        self.assertFalse(stderr.getvalue())
+        self.assertEqual(exit_code, 0)