Allow customization of Counter, Histogram, Gauge

[extreme4all]

Problem statement:

I want to add extra buckets to the Histogram.

Currently i don't think i can modify these variables because they are not initialized with the class

Proposed Solution

initialize the variables within the class, allow users to either add their own kwargs or add their own Counter, Histogram, Gauge

class PrometheusMiddleware(BaseHTTPMiddleware):
    def __init__(self, app: ASGIApp, filter_unhandled_paths: bool = False,
                 counter_kwargs: Optional[Dict[str, Any]] = None,
                 histogram_kwargs: Optional[Dict[str, Any]] = None,
                 gauge_kwargs: Optional[Dict[str, Any]] = None) -> None:
        super().__init__(app)
        self.filter_unhandled_paths = filter_unhandled_paths
        
        # Default values, can be overridden by kwargs
        counter_kwargs = counter_kwargs or {}
        histogram_kwargs = histogram_kwargs or {}
        gauge_kwargs = gauge_kwargs or {}
        
        self.REQUESTS = Counter(
            "starlette_requests_total",
            "Total count of requests by method and path.",
            ["method", "path_template"],
            **counter_kwargs
        )
        self.RESPONSES = Counter(
            "starlette_responses_total",
            "Total count of responses by method, path and status codes.",
            ["method", "path_template", "status_code"],
            **counter_kwargs
        )
        self.REQUESTS_PROCESSING_TIME = Histogram(
            "starlette_requests_processing_time_seconds",
            "Histogram of requests processing time by path (in seconds)",
            ["method", "path_template"],
            **histogram_kwargs
        )
        self.EXCEPTIONS = Counter(
            "starlette_exceptions_total",
            "Total count of exceptions raised by path and exception type",
            ["method", "path_template", "exception_type"],
            **counter_kwargs
        )
        self.REQUESTS_IN_PROGRESS = Gauge(
            "starlette_requests_in_progress",
            "Gauge of requests by method and path currently being processed",
            ["method", "path_template"],
            **gauge_kwargs
        )

or

class PrometheusMiddleware(BaseHTTPMiddleware):
    def __init__(self, app: ASGIApp, filter_unhandled_paths: bool = False,
                 requests_counter: Optional[Counter] = None,
                 responses_counter: Optional[Counter] = None,
                 processing_time_histogram: Optional[Histogram] = None,
                 exceptions_counter: Optional[Counter] = None,
                 requests_in_progress_gauge: Optional[Gauge] = None) -> None:
        super().__init__(app)
        self.filter_unhandled_paths = filter_unhandled_paths
        
        # Use provided metrics or default to the ones defined below
        self.REQUESTS = requests_counter or Counter(
            "starlette_requests_total",
            "Total count of requests by method and path.",
            ["method", "path_template"]
        )
        self.RESPONSES = responses_counter or Counter(
            "starlette_responses_total",
            "Total count of responses by method, path and status codes.",
            ["method", "path_template", "status_code"]
        )
        self.REQUESTS_PROCESSING_TIME = processing_time_histogram or Histogram(
            "starlette_requests_processing_time_seconds",
            "Histogram of requests processing time by path (in seconds)",
            ["method", "path_template"]
        )
        self.EXCEPTIONS = exceptions_counter or Counter(
            "starlette_exceptions_total",
            "Total count of exceptions raised by path and exception type",
            ["method", "path_template", "exception_type"]
        )
        self.REQUESTS_IN_PROGRESS = requests_in_progress_gauge or Gauge(
            "starlette_requests_in_progress",
            "Gauge of requests by method and path currently being processed",
            ["method", "path_template"]
        )