Caplin: Update BlobSidecars Beacon API endpoint to the latest specs

cl/beacon/beaconhttp/args.go

@@ -5,6 +5,7 @@ import (
 	"net/http"
 	"regexp"
 	"strconv"
+	"strings"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/ledgerwatch/erigon-lib/common"
@@ -168,9 +169,13 @@ func Uint64FromQueryParams(r *http.Request, name string) (*uint64, error) {
 
 // decode a list of strings from the query params
 func StringListFromQueryParams(r *http.Request, name string) ([]string, error) {
-	str := r.URL.Query().Get(name)
-	if str == "" {
+	values := r.URL.Query()[name]
+	if len(values) == 0 {
 		return nil, nil
 	}
+
+	// Combine all values into a single string, separating by comma
+	str := strings.Join(values, ",")
+
 	return regexp.MustCompile(`\s*,\s*`).Split(str, -1), nil
 }

cl/beacon/handler/blobs.go

@@ -3,6 +3,7 @@ package handler
 import (
 	"fmt"
 	"net/http"
+	"strconv"
 
 	"github.com/ledgerwatch/erigon/cl/beacon/beaconhttp"
 	"github.com/ledgerwatch/erigon/cl/cltypes"
@@ -51,13 +52,33 @@ func (a *ApiHandler) GetEthV1BeaconBlobSidecars(w http.ResponseWriter, r *http.R
 	if err != nil {
 		return nil, err
 	}
-
+	strIdxs, err := beaconhttp.StringListFromQueryParams(r, "indices")
+	if err != nil {
+		return nil, err
+	}
 	resp := solid.NewStaticListSSZ[*cltypes.BlobSidecar](696969, blobSidecarSSZLenght)
 	if !found {
 		return beaconhttp.NewBeaconResponse(resp), nil
 	}
-	for _, v := range out {
-		resp.Append(v)
+	if len(strIdxs) == 0 {
+		for _, v := range out {
+			resp.Append(v)
+		}
+	} else {
+		included := make(map[uint64]struct{})
+		for _, idx := range strIdxs {
+			i, err := strconv.ParseUint(idx, 10, 64)
+			if err != nil {
+				return nil, err
+			}
+			included[i] = struct{}{}
+		}
+		for _, v := range out {
+			if _, ok := included[v.Index]; ok {
+				resp.Append(v)
+			}
+		}
 	}
+
 	return beaconhttp.NewBeaconResponse(resp), nil
 }