cmd/geth, cmd/utils: geth attach with custom headers (#25829)

This PR makes it possible to set custom headers, in particular for two scenarios: 

- geth attach
- geth commands which can use --remotedb, e..g geth db inspect

The ability to use custom headers is typically useful for connecting to cloud-apis, e.g. providing an infura- or alchemy key, or for that matter access-keys for environments behind cloudflare.  

Co-authored-by: Felix Lange <fjl@twurst.com>

cmd/utils/flags.go

@@ -18,10 +18,13 @@
 package utils
 
 import (
+	"context"
 	"crypto/ecdsa"
+	"errors"
 	"fmt"
 	"math"
 	"math/big"
+	"net/http"
 	"os"
 	"path/filepath"
 	godebug "runtime/debug"
@@ -976,6 +979,13 @@ var (
 		Value:    metrics.DefaultConfig.InfluxDBOrganization,
 		Category: flags.MetricsCategory,
 	}
+
+	HttpHeaderFlag = &cli.StringSliceFlag{
+		Name:     "header",
+		Aliases:  []string{"H"},
+		Usage:    "Pass custom headers to the RPC server wheng using --" + RemoteDBFlag.Name + " or the geth attach console.",
+		Category: flags.NetworkingCategory,
+	}
 )
 
 var (
@@ -995,6 +1005,7 @@ var (
 		DataDirFlag,
 		AncientFlag,
 		RemoteDBFlag,
+		HttpHeaderFlag,
 	}
 )
 
@@ -2125,8 +2136,12 @@ func MakeChainDatabase(ctx *cli.Context, stack *node.Node, readonly bool) ethdb.
 	)
 	switch {
 	case ctx.IsSet(RemoteDBFlag.Name):
-		log.Info("Using remote db", "url", ctx.String(RemoteDBFlag.Name))
-		chainDb, err = remotedb.New(ctx.String(RemoteDBFlag.Name))
+		log.Info("Using remote db", "url", ctx.String(RemoteDBFlag.Name), "headers", len(ctx.StringSlice(HttpHeaderFlag.Name)))
+		client, err := DialRPCWithHeaders(ctx.String(RemoteDBFlag.Name), ctx.StringSlice(HttpHeaderFlag.Name))
+		if err != nil {
+			break
+		}
+		chainDb = remotedb.New(client)
 	case ctx.String(SyncModeFlag.Name) == "light":
 		chainDb, err = stack.OpenDatabase("lightchaindata", cache, handles, "", readonly)
 	default:
@@ -2148,6 +2163,30 @@ func IsNetworkPreset(ctx *cli.Context) bool {
 	return false
 }
 
+func DialRPCWithHeaders(endpoint string, headers []string) (*rpc.Client, error) {
+	if endpoint == "" {
+		return nil, errors.New("endpoint must be specified")
+	}
+	if strings.HasPrefix(endpoint, "rpc:") || strings.HasPrefix(endpoint, "ipc:") {
+		// Backwards compatibility with geth < 1.5 which required
+		// these prefixes.
+		endpoint = endpoint[4:]
+	}
+	var opts []rpc.ClientOption
+	if len(headers) > 0 {
+		var customHeaders = make(http.Header)
+		for _, h := range headers {
+			kv := strings.Split(h, ":")
+			if len(kv) != 2 {
+				return nil, fmt.Errorf("invalid http header directive: %q", h)
+			}
+			customHeaders.Add(kv[0], kv[1])
+		}
+		opts = append(opts, rpc.WithHeaders(customHeaders))
+	}
+	return rpc.DialOptions(context.Background(), endpoint, opts...)
+}
+
 func MakeGenesis(ctx *cli.Context) *core.Genesis {
 	var genesis *core.Genesis
 	switch {