fix: rest probe endpoint (#39)

Fix health probe endpoints.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Bug Fixes**
* Fixed a potential crash in load balancing when no servers are
available.
* Updated API endpoints to use standardized blockchain protocol paths
for improved compatibility.
  * Simplified error reporting for status validation.

* **Chores**
  * Updated dependency management for monitoring library.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: cloud-j-luna

go.mod

@@ -6,6 +6,7 @@ require (
 	github.com/cometbft/cometbft v0.38.12
 	github.com/cosmos/cosmos-sdk v0.50.13
 	github.com/prometheus/client_golang v1.22.0
+	github.com/prometheus/client_model v0.6.1
 	github.com/spf13/cobra v1.9.1
 	github.com/spf13/viper v1.19.0
 	github.com/stretchr/testify v1.10.0
@@ -112,7 +113,6 @@ require (
 	github.com/petermattis/goid v0.0.0-20240813172612-4fcff4a6cae7 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
-	github.com/prometheus/client_model v0.6.1 // indirect
 	github.com/prometheus/common v0.62.0 // indirect
 	github.com/prometheus/procfs v0.15.1 // indirect
 	github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475 // indirect

internal/proxy/balancer.go

@@ -128,7 +128,10 @@ func (rr *LatencyBased) NextServer(_ *http.Request) *Server {
 	}
 
 	// Fallback, shouldn't be reached if rates are normalized
-	return rr.servers[len(rr.servers)-1].Server
+	if len(rr.servers) > 0 {
+		return rr.servers[len(rr.servers)-1].Server
+	}
+	return nil
 }
 
 // Update updates the list of available servers and their corresponding rates

internal/proxy/balancer_test.go

@@ -79,6 +79,17 @@ func TestRoundRobin_NextServer(t *testing.T) {
 	}
 }
 
+func TestLatencyBased_NextServer_EmptyServers(t *testing.T) {
+	lb := NewLatencyBased(slog.New(slog.NewTextHandler(os.Stdout, nil)))
+	lb.Update([]*Server{})
+
+	// Should return nil when no servers are available
+	server := lb.NextServer(nil)
+	if server != nil {
+		t.Errorf("expected nil server when no servers available, got %v", server)
+	}
+}
+
 func TestLatencyBased_NextServer(t *testing.T) {
 	servers := []*Server{
 		{

internal/seed/probes.go

@@ -118,7 +118,7 @@ func RESTProbe(ctx context.Context, node Node) (Status, error) {
 	start := time.Now()
 	client := &http.Client{}
 
-	req, err := http.NewRequest("GET", fmt.Sprintf("%s/syncing", node.Address), nil)
+	req, err := http.NewRequest("GET", fmt.Sprintf("%s/cosmos/base/tendermint/v1beta1/syncing", node.Address), nil)
 	if err != nil {
 		return Status{}, fmt.Errorf("creating REST client request: %w", err)
 	}
@@ -130,7 +130,7 @@ func RESTProbe(ctx context.Context, node Node) (Status, error) {
 	defer resp.Body.Close()
 
 	if resp.StatusCode != 200 {
-		return Status{}, fmt.Errorf("unexpected status from REST client [%d %s]: %w", resp.StatusCode, resp.Status, err)
+		return Status{}, fmt.Errorf("unexpected status from REST client [%d %s]", resp.StatusCode, resp.Status)
 	}
 
 	body, err := io.ReadAll(resp.Body)
@@ -143,7 +143,7 @@ func RESTProbe(ctx context.Context, node Node) (Status, error) {
 		return Status{}, fmt.Errorf("unmarshaling body from REST client response: %w", err)
 	}
 
-	latestBlockReq, err := http.NewRequest("GET", fmt.Sprintf("%s/blocks/latest", node.Address), nil)
+	latestBlockReq, err := http.NewRequest("GET", fmt.Sprintf("%s/cosmos/base/tendermint/v1beta1/blocks/latest", node.Address), nil)
 	if err != nil {
 		return Status{}, fmt.Errorf("creating REST client request: %w", err)
 	}
@@ -155,7 +155,7 @@ func RESTProbe(ctx context.Context, node Node) (Status, error) {
 	defer latestBlockResp.Body.Close()
 
 	if latestBlockResp.StatusCode != 200 {
-		return Status{}, fmt.Errorf("unexpected status from REST client [%d %s]: %w", latestBlockResp.StatusCode, latestBlockResp.Status, err)
+		return Status{}, fmt.Errorf("unexpected status from REST client [%d %s]", latestBlockResp.StatusCode, latestBlockResp.Status)
 	}
 
 	latestBlockBody, err := io.ReadAll(latestBlockResp.Body)