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fix: inject Accept header in MCP middleware to prevent 406 errors (#571)

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Some MCP clients (e.g., Claude Code) don't send an Accept header,
causing the MCP SDK to reject requests with 406 Not Acceptable. The
middleware now ensures Accept includes application/json and
text/event-stream when missing.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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DK09876 2026-03-13 13:33:30 -07:00 committed by GitHub
parent 32b00cea4f
commit 836fd81e19
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1 changed files with 9 additions and 0 deletions
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hindsight-api-slim/hindsight_api/api/mcp.py
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@ -381,6 +381,15 @@ class MCPMiddleware:
# Clear root_path since we're passing directly to the app # Clear root_path since we're passing directly to the app
new_scope["root_path"] = "" new_scope["root_path"] = ""
# Ensure Accept header includes required MIME types for MCP SDK.
# Some clients (e.g., Claude Code) don't send Accept, causing
# the SDK to reject with 406 Not Acceptable.
accept_header = self._get_header(new_scope, "accept")
if not accept_header or "text/event-stream" not in accept_header:
headers = [(k, v) for k, v in new_scope.get("headers", []) if k.lower() != b"accept"]
headers.append((b"accept", b"application/json, text/event-stream"))
new_scope["headers"] = headers
# Wrap send to rewrite the SSE endpoint URL to include bank_id if using path-based routing. # Wrap send to rewrite the SSE endpoint URL to include bank_id if using path-based routing.
# Only rewrite SSE (text/event-stream) responses to avoid corrupting tool results # Only rewrite SSE (text/event-stream) responses to avoid corrupting tool results
# that might contain the literal string "data: /messages". # that might contain the literal string "data: /messages".