[PATCH v2 8/8] lib/config.nix: Validate configuration parameters

[Demi Marie Obenour <demiobenour@gmail.com>]

Wrong values for the version or update URL will cause very confusing
build-time or runtime errors.  Provide a better user experience by
validating them up-front.

Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
---
 lib/config.nix | 41 +++++++++++++++++++++++++++++++++++------
 1 file changed, 35 insertions(+), 6 deletions(-)

diff --git a/lib/config.nix b/lib/config.nix
index 5b6b95013734202b7e2e01d5ffce313080658006..660a2427447fd9851e60e955da6bd1a5d71cfdac 100644
--- a/lib/config.nix
+++ b/lib/config.nix
@@ -19,10 +19,39 @@ let
     inherit default;
   } else config;
   finalConfig = default // callConfig config;
+
+  # Only allow unreserved characters, : (for port numbers), /, and %-encoding.
+  # The rest of the code is allowed to assume that these are the only characters
+  # in the update URL.
+  # Do not use [:alnum:] or [:hexdigit:] as they depend on the locale in POSIX.
+  # Query strings and fragment identifiers break appending
+  # /SHA256SUMS and /SHA256SUMS.gpg to a URL.
+  # [, ], {, and } would cause globbing in curl.
+  url-regex = "^https?://([ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789:./~-]|%[ABCDEFabcdef0123456789]{2})+$";
+  update-url = finalConfig.update-url;
+
+  # Only allow a numeric version for now.
+  number_re = "(0|[1-9][0-9]{0,2})";
+  version_re = "^(${number_re}\\.){2}${number_re}$";
 in
-  finalConfig // {
-    update-signing-key = builtins.path {
-      name = "signing-key";
-      path = finalConfig.update-signing-key;
-    };
-  }
+  if !builtins.isString update-url then
+    builtins.abort "Update URL must be a string, not ${builtins.typeOf update-url}"
+  else if builtins.match "^https?://.*" update-url == null then
+    builtins.abort "Update URL ${builtins.toJSON update-url} has unsupported scheme (not https:// or http://) or is invalid"
+  else if builtins.match url-regex update-url == null then
+    builtins.abort "Update URL ${builtins.toJSON update-url} has forbidden characters"
+  else if builtins.substring (builtins.stringLength update-url - 1) 1 update-url == "/" then
+    builtins.abort "Update URL ${builtins.toJSON update-url} must not end with /"
+  else if !builtins.isString finalConfig.version then
+    builtins.abort "Version must be a string, not ${builtins.typeOf finalConfig.version}"
+  else if builtins.match version_re finalConfig.version == null then
+    builtins.abort "Version ${builtins.toJSON finalConfig.version} is invalid"
+  else if !builtins.isPath finalConfig.update-signing-key then
+    builtins.abort "Update verification key file is of type ${builtins.typeOf finalConfig.update-signing-key}, not path"
+  else
+    finalConfig // {
+      update-signing-key = builtins.path {
+        name = "signing-key";
+        path = finalConfig.update-signing-key;
+      };
+    }

-- 
2.51.2