Add flag for specifying an extra http header in RPC requests (#48)

Conduit wanted to be able to specify an http header, this would allow
them to pin the indexer to a specific node.

client/jsonrpc/client.go

@@ -27,10 +27,11 @@ const (
 )
 
 type rpcClient struct {
-	client  *retryablehttp.Client
-	cfg     Config
-	log     *slog.Logger
-	bufPool *sync.Pool
+	client      *retryablehttp.Client
+	cfg         Config
+	log         *slog.Logger
+	bufPool     *sync.Pool
+	httpHeaders map[string]string
 }
 
 func NewClient(log *slog.Logger, cfg Config) (*rpcClient, error) { // revive:disable-line:unexported-return
@@ -61,6 +62,7 @@ func NewClient(log *slog.Logger, cfg Config) (*rpcClient, error) { // revive:dis
 				return new(bytes.Buffer)
 			},
 		},
+		httpHeaders: cfg.HTTPHeaders,
 	}
 	// lets validate RPC node is up & reachable
 	_, err := rpc.LatestBlockNumber()
@@ -112,6 +114,11 @@ func (c *rpcClient) getResponseBody(
 	if err != nil {
 		return err
 	}
+	if c.httpHeaders != nil {
+		for k, v := range c.httpHeaders {
+			req.Header.Set(k, v)
+		}
+	}
 	resp, err := c.client.Do(req)
 	if err != nil {
 		return fmt.Errorf("failed to send request for method %s: %w", method, err)

client/jsonrpc/models.go

@@ -5,4 +5,5 @@ import "time"
 type Config struct {
 	URL          string
 	PollInterval time.Duration
+	HTTPHeaders  map[string]string
 }

cmd/main.go

@@ -9,6 +9,7 @@ import (
 	"log/slog"
 	"os"
 	"os/signal"
+	"strings"
 	stdsync "sync"
 	"syscall"
 	"time"
@@ -48,10 +49,20 @@ func main() {
 	var wg stdsync.WaitGroup
 	var rpcClient jsonrpc.BlockchainClient
 
+	rpcHTTPHeaders := make(map[string]string)
+	if cfg.RPCNode.ExtraHTTPHeader != "" {
+		pair := strings.Split(cfg.RPCNode.ExtraHTTPHeader, ",")
+		// We've validated this list has two elements
+		key := strings.Trim(pair[0], " ")
+		value := strings.Trim(pair[1], " ")
+		logger.Info("Adding extra HTTP header to RPC requests", "key", key, "value", value)
+		rpcHTTPHeaders[key] = value
+	}
 	switch cfg.RPCStack {
 	case models.OpStack:
 		rpcClient, err = jsonrpc.NewOpStackClient(logger, jsonrpc.Config{
-			URL: cfg.RPCNode.NodeURL,
+			URL:         cfg.RPCNode.NodeURL,
+			HTTPHeaders: rpcHTTPHeaders,
 		})
 	default:
 		stdlog.Fatalf("unsupported RPC stack: %s", cfg.RPCStack)

config/config.go

@@ -2,6 +2,8 @@ package config
 
 import (
 	"errors"
+	"fmt"
+	"strings"
 	"time"
 
 	"github.com/duneanalytics/blockchain-ingester/models"
@@ -21,13 +23,20 @@ func (d DuneClient) HasError() error {
 }
 
 type RPCClient struct {
-	NodeURL string `long:"rpc-node-url" env:"RPC_NODE_URL" description:"URL for the blockchain node"`
+	NodeURL         string `long:"rpc-node-url" env:"RPC_NODE_URL" description:"URL for the blockchain node"`
+	ExtraHTTPHeader string `long:"rpc-http-header" env:"RPC_HTTP_HEADER" description:"Extra HTTP header to send with RPC requests. On the form 'key,value'"` // nolint:lll
 }
 
 func (r RPCClient) HasError() error {
 	if r.NodeURL == "" {
 		return errors.New("RPC node URL is required")
 	}
+	if r.ExtraHTTPHeader != "" {
+		header := strings.Split(r.ExtraHTTPHeader, ",")
+		if len(header) != 2 {
+			return fmt.Errorf("invalid rpc http header: expected 'key,value', got '%s'", r.ExtraHTTPHeader)
+		}
+	}
 	return nil
 }