feat(resources): resource support, list_metrics, targets, tsdb_stats

Resource support, under the prefix of "prometheus://". Initial support
via a few resources, including prometheus://list_metrics,
prometheus://targets, and prometheus://tsdb_stats.

Still learning all this shit and trying to understand the functional
differences and when a tool is more appropriate than a resource and
vice-versa, so I don't even know quite how correct/useful this is yet.

Signed-off-by: TJ Hoplock <[email protected]>

Author: tjhop

pkg/mcp/resources.go

@@ -0,0 +1,80 @@
+package mcp
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/mark3labs/mcp-go/mcp"
+)
+
+var (
+	// Resources
+	resourcePrefix = "prometheus://"
+
+	listMetricsResource = mcp.NewResource(
+		resourcePrefix+"list_metrics",
+		"List metrics",
+		mcp.WithResourceDescription("List metrics available"),
+		mcp.WithMIMEType("application/json"),
+	)
+
+	targetsResource = mcp.NewResource(
+		resourcePrefix+"targets",
+		"Targets",
+		mcp.WithResourceDescription("Overview of the current state of the Prometheus target discovery"),
+		mcp.WithMIMEType("application/json"),
+	)
+
+	tsdbStatsResource = mcp.NewResource(
+		resourcePrefix+"tsdb_stats",
+		"TSDB Stats",
+		mcp.WithResourceDescription("Usage and cardinality statistics from the TSDB"),
+		mcp.WithMIMEType("application/json"),
+	)
+)
+
+func listMetricsResourceHandler(ctx context.Context, request mcp.ReadResourceRequest) ([]mcp.ResourceContents, error) {
+	metrics, err := labelValuesApiCall(ctx, "__name__", nil, time.Time{}, time.Time{})
+	if err != nil {
+		return nil, fmt.Errorf("error getting metric names: %w", err)
+	}
+
+	return []mcp.ResourceContents{
+		mcp.TextResourceContents{
+			URI:      resourcePrefix + "list_metrics",
+			MIMEType: "application/json",
+			Text:     metrics,
+		},
+	}, nil
+}
+
+func targetsResourceHandler(ctx context.Context, request mcp.ReadResourceRequest) ([]mcp.ResourceContents, error) {
+	targets, err := targetsApiCall(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("error getting target info: %w", err)
+	}
+
+	return []mcp.ResourceContents{
+		mcp.TextResourceContents{
+			URI:      resourcePrefix + "targets",
+			MIMEType: "application/json",
+			Text:     targets,
+		},
+	}, nil
+}
+
+func tsdbStatsResourceHandler(ctx context.Context, request mcp.ReadResourceRequest) ([]mcp.ResourceContents, error) {
+	tsdbStats, err := tsdbStatsApiCall(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("error processing tsdb stats: %w", err)
+	}
+
+	return []mcp.ResourceContents{
+		mcp.TextResourceContents{
+			URI:      resourcePrefix + "tsdb_stats",
+			MIMEType: "application/json",
+			Text:     tsdbStats,
+		},
+	}, nil
+}

pkg/mcp/server.go

@@ -13,16 +13,22 @@ func NewServer(logger *slog.Logger) *server.MCPServer {
 
 	// TODO: remove/improve this hook?
 	// hooks.AddBeforeCallTool(func(ctx context.Context, id any, message *mcp.CallToolRequest) {
-		// logger.Debug("Before Call Tool", "id", id, "tool_request", message)
+	// logger.Debug("Before Call Tool", "id", id, "tool_request", message)
 	// })
 
 	mcpServer := server.NewMCPServer(
 		"prometheus-mcp-server",
 		version.Info(),
 		server.WithLogging(),
 		server.WithHooks(hooks),
+		server.WithResourceCapabilities(true, true),
 	)
 
+	// add resources
+	mcpServer.AddResource(listMetricsResource, listMetricsResourceHandler)
+	mcpServer.AddResource(targetsResource, targetsResourceHandler)
+	mcpServer.AddResource(tsdbStatsResource, tsdbStatsResourceHandler)
+
 	// add tools
 	mcpServer.AddTool(alertmanagersTool, alertmanagersToolHandler)
 	mcpServer.AddTool(buildinfoTool, buildinfoToolHandler)