From 204d00caf409dd9e08277263ddebf36d5d1c68db Mon Sep 17 00:00:00 2001
From: Bill <bill@bballou.com>
Date: Thu, 1 Jan 2026 14:06:31 -0500
Subject: [PATCH] feat: add host_header config for Docker networking

When Grist validates the Host header (common with reverse proxy setups),
internal Docker networking fails because requests arrive with
Host: container-name instead of the external domain.

The new host_header config option allows overriding the Host header
sent to Grist while still connecting via internal Docker hostnames.
---
 config.yaml.example           | 8 ++++++++
 src/grist_mcp/config.py       | 2 ++
 src/grist_mcp/grist_client.py | 2 ++
 3 files changed, 12 insertions(+)

diff --git a/config.yaml.example b/config.yaml.example
index 96f50df..130180b 100644
--- a/config.yaml.example
+++ b/config.yaml.example
@@ -23,6 +23,14 @@ documents:
     doc_id: pN0zE5sT2qP7x
     api_key: ${GRIST_PERSONAL_API_KEY}
 
+  # Docker networking example: connect via internal hostname,
+  # but send the external domain in the Host header
+  docker-grist:
+    url: http://grist:8080
+    doc_id: abc123
+    api_key: ${GRIST_API_KEY}
+    host_header: grist.example.com  # Required when Grist validates Host header
+
 # Agent tokens with access scopes
 tokens:
   - token: REPLACE_WITH_GENERATED_TOKEN
diff --git a/src/grist_mcp/config.py b/src/grist_mcp/config.py
index a2c7c54..3ac81af 100644
--- a/src/grist_mcp/config.py
+++ b/src/grist_mcp/config.py
@@ -14,6 +14,7 @@ class Document:
     url: str
     doc_id: str
     api_key: str
+    host_header: str | None = None  # Override Host header for Docker networking
 
 
 @dataclass
@@ -78,6 +79,7 @@ def load_config(config_path: str) -> Config:
             url=doc_data["url"],
             doc_id=doc_data["doc_id"],
             api_key=doc_data["api_key"],
+            host_header=doc_data.get("host_header"),
         )
 
     # Parse tokens
diff --git a/src/grist_mcp/grist_client.py b/src/grist_mcp/grist_client.py
index 97468eb..e66bfae 100644
--- a/src/grist_mcp/grist_client.py
+++ b/src/grist_mcp/grist_client.py
@@ -17,6 +17,8 @@ class GristClient:
         self._doc = document
         self._base_url = f"{document.url.rstrip('/')}/api/docs/{document.doc_id}"
         self._headers = {"Authorization": f"Bearer {document.api_key}"}
+        if document.host_header:
+            self._headers["Host"] = document.host_header
         self._timeout = timeout
 
     async def _request(self, method: str, path: str, **kwargs) -> dict: