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Error Handling

pcp_mcp.errors

Error mapping from httpx to MCP ToolErrors.

PCPConnectionError

Bases: PCPError

Cannot connect to pmproxy.

PCPError

Bases: Exception

Base PCP error.

PCPMetricNotFoundError

Bases: PCPError

Metric does not exist.

handle_pcp_error 

handle_pcp_error(e: Exception, operation: str) -> ToolError

Convert PCP/httpx exceptions to MCP ToolErrors.

Uses isinstance() checks instead of match/case class patterns for resilience against module reloading (e.g., FastMCP's FileSystemProvider), which can create different class identities that break structural pattern matching.

Parameters:

Name Type Description Default
e Exception

The exception to convert.

 required
operation str

Description of the operation that failed.

 required

Returns:

Type Description
ToolError

A ToolError with an appropriate message.
Source code in src/pcp_mcp/errors.py 
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def handle_pcp_error(e: Exception, operation: str) -> ToolError:
    """Convert PCP/httpx exceptions to MCP ToolErrors.

    Uses isinstance() checks instead of match/case class patterns for resilience
    against module reloading (e.g., FastMCP's FileSystemProvider), which can
    create different class identities that break structural pattern matching.

    Args:
        e: The exception to convert.
        operation: Description of the operation that failed.

    Returns:
        A ToolError with an appropriate message.
    """
    if isinstance(e, httpx.ConnectError):
        return ToolError("Cannot connect to pmproxy. Is it running? (systemctl start pmproxy)")

    if isinstance(e, httpx.HTTPStatusError):
        if e.response.status_code == 400:
            return ToolError(f"Bad request during {operation}: {e.response.text}")
        if e.response.status_code == 404:
            return ToolError(f"Metric not found during {operation}")
        return ToolError(f"pmproxy error ({e.response.status_code}): {e.response.text}")

    if isinstance(e, httpx.TimeoutException):
        return ToolError(f"Request timed out during {operation}")

    if isinstance(e, PCPMetricNotFoundError):
        return ToolError(f"Metric not found: {e}")

    if isinstance(e, PCPConnectionError):
        return ToolError(str(e))

    return ToolError(f"Error during {operation}: {e}")