fix: preserve existing mimeapps.list entries when installing web url handler

src/deadline/client/cli/_deadline_web_url.py

@@ -1,5 +1,6 @@
 # Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 
+import configparser
 import os
 import re
 import sys
@@ -215,13 +216,81 @@
 MimeType=x-scheme-handler/{DEADLINE_URL_SCHEME_NAME}
 """
 
-        mimeapps_file_content = f"""[Default Applications]
-x-scheme-handler/{DEADLINE_URL_SCHEME_NAME}={DEADLINE_URL_SCHEME_NAME}.desktop;
-"""
         with open(desktop_file_path, "w") as desktop_file:
             desktop_file.write(desktop_file_content)
-        with open(mimeapps_list_file_path, "w") as mimeapps_list_file:
-            mimeapps_list_file.write(mimeapps_file_content)
+
+        # Read/parse any existing mimeapps.list and add/update ONLY the deadline
+        # handler entry, preserving all other default-application associations.
+        # Opening in "w" mode would truncate the file and destroy unrelated
+        # associations (browser, PDF, mailto, etc.), causing permanent data loss.
+        # interpolation=None avoids treating "%" in values specially, and
+        # optionxform=str preserves the case of mime-type/scheme keys.
+        # strict=False tolerates duplicate keys/sections (last value wins),
+        # which real-world mimeapps.list files written by other desktop tools
+        # have historically contained; the default strict=True would turn an
+        # otherwise-usable file into a hard install failure.
+        mimeapps = configparser.ConfigParser(interpolation=None, strict=False)
+        mimeapps.optionxform = str  # type: ignore[assignment,method-assign]
+
+        if os.path.isfile(mimeapps_list_file_path):
+            # A pre-existing mimeapps.list that is not valid INI can still make
+            # configparser raise even with strict=False (MissingSectionHeaderError
+            # for a key before any section header, UnicodeDecodeError for a
+            # non-text file, ...). Surface these as a DeadlineOperationError for
+            # consistency with the rest of this function rather than crashing the
+            # CLI with a raw traceback.
+            try:
+                mimeapps.read(mimeapps_list_file_path)
+            except (configparser.Error, UnicodeDecodeError) as e:
+                raise DeadlineOperationError(
+                    f"Failed to install the handler for {DEADLINE_URL_SCHEME_NAME} URLs: "
+                    f"could not parse existing {mimeapps_list_file_path}:\n{e}"
+                ) from e
+
+        if not mimeapps.has_section("Default Applications"):
+            mimeapps.add_section("Default Applications")
+        mimeapps.set(
+            "Default Applications",
+            f"x-scheme-handler/{DEADLINE_URL_SCHEME_NAME}",
+            f"{DEADLINE_URL_SCHEME_NAME}.desktop;",
+        )
+
+        # Write atomically: rendering to a temp file in the same directory and
+        # os.replace()-ing it into place means the original mimeapps.list is only
+        # replaced once the new content is fully and successfully written. Opening
+        # the destination directly in "w" mode would truncate it before write()
+        # runs, so a crash/kill/disk-full mid-write would leave it empty or partial
+        # -- losing exactly the unrelated associations this change protects.
+        import stat
+        import tempfile
+
+        # tempfile.mkstemp() creates the temp file with mode 0600, and os.replace()
+        # keeps that mode on the final file. That would silently drop the
+        # permissions of a pre-existing mimeapps.list, and for the all_users case
+        # (/usr/share/applications/mimeapps.list, written as root) would leave a
+        # system-wide file that other users' desktop environments cannot read.
+        # Preserve the existing file's mode, or default to 0644 for a new file.
+        if os.path.isfile(mimeapps_list_file_path):
+            mimeapps_list_file_mode = stat.S_IMODE(os.stat(mimeapps_list_file_path).st_mode)
+        else:
+            mimeapps_list_file_mode = 0o644
+
+        dir_name = os.path.dirname(mimeapps_list_file_path)
+        fd, tmp_path = tempfile.mkstemp(dir=dir_name, prefix=".mimeapps.list.", suffix=".tmp")
+        try:
+            with os.fdopen(fd, "w") as tmp_file:
+                mimeapps.write(tmp_file, space_around_delimiters=False)
+            os.chmod(tmp_path, mimeapps_list_file_mode)
+            os.replace(tmp_path, mimeapps_list_file_path)
+        except BaseException:
+            try:
+                os.unlink(tmp_path)
+            except OSError:
+                # Best-effort temp file cleanup; the original exception below is
+                # the actual failure to surface, and a leftover temp file is
+                # harmless compared to masking it.
+                pass
+            raise
 
         try:
             subprocess.run(["update-desktop-database", entry_dir], check=True)