Add --env-file and --env-json options. Fixes #608

telepresence/cli.py

@@ -302,6 +302,25 @@ def parse_args(args=None) -> argparse.Namespace:
         )
     )
 
+    parser.add_argument(
+        "--env-json",
+        metavar="FILENAME",
+        default=None,
+        help="Also emit the remote environment to a file as a JSON blob."
+    )
+
+    parser.add_argument(
+        "--env-file",
+        metavar="FILENAME",
+        default=None,
+        help=(
+            "Also emit the remote environment to an env file in Docker "
+            "Compose format. "
+            "See https://docs.docker.com/compose/env-file/ for more "
+            "information on the limitations of this format."
+        )
+    )
+
     group = parser.add_mutually_exclusive_group()
     group.add_argument(
         "--run-shell",

telepresence/main.py

@@ -28,7 +28,7 @@
 from telepresence.output import Output
 from telepresence.proxy import start_proxy, connect
 from telepresence.mount import mount_remote
-from telepresence.remote_env import get_remote_env
+from telepresence.remote_env import get_remote_env, write_env_files
 from telepresence.startup import analyze_args
 from telepresence.usage_tracking import call_scout
 
@@ -89,6 +89,9 @@ def shutdown(signum, frame):
         # Handle filesystem stuff (pod name, ssh object)
         mount_dir = mount_remote(session)
 
+        # Maybe write environment files
+        write_env_files(session)
+
         # Set up outbound networking (pod name, ssh object)
         # Launch user command with the correct environment (...)
         if args.method == "container":

telepresence/remote_env.py

@@ -13,10 +13,10 @@
 # limitations under the License.
 
 import argparse
-from json import loads
+from json import loads, dump
 from subprocess import CalledProcessError
 from time import time, sleep
-from typing import Dict
+from typing import Dict, Tuple, List
 
 from telepresence.remote import RemoteInfo
 from telepresence.runner import Runner
@@ -80,3 +80,52 @@ def get_remote_env(
     else:
         return exit("Error: Failed to get environment variables")
     return env
+
+
+def serialize_as_env_file(env: Dict[str, str]) -> Tuple[str, List[str]]:
+    """
+    Render an env file as defined by Docker Compose
+    https://docs.docker.com/compose/env-file/
+
+    - Compose expects each line in an env file to be in VAR=VAL format.
+    - Lines beginning with # are processed as comments and ignored.
+    - Blank lines are ignored.
+    - There is no special handling of quotation marks.
+      This means that they are part of the VAL.
+
+    Unstated but implied is that values cannot include newlines.
+    """
+    res = []
+    skipped = []
+    for key, value in sorted(env.items()):
+        if "\n" in value:
+            skipped.append(key)
+        else:
+            res.append("{}={}\n".format(key, value))
+    return "".join(res), skipped
+
+
+def write_env_files(session) -> None:
+    args = session.args
+    env = session.env
+    if args.env_json:
+        try:
+            with open(args.env_json, "w") as env_json_file:
+                dump(env, env_json_file, sort_keys=True, indent=4)
+        except IOError as exc:
+            print("Failed to write environment as JSON: {}".format(exc))
+
+    if args.env_file:
+        try:
+            data, skipped = serialize_as_env_file(env)
+            with open(args.env_file, "w") as env_file:
+                env_file.write(data)
+            if skipped:
+                print(
+                    "Skipped these environment keys when writing env "
+                    "file because the associated values have newlines:"
+                )
+                for key in skipped:
+                    print(key)
+        except IOError as exc:
+            print("Failed to write environment as env file: {}".format(exc))