feat: UX improvements

examples/gateway-car/README.md

@@ -26,7 +26,7 @@ Then, you can start the gateway with:
 ./gateway -c data.car -p 8040
 ```
 
-Now you can access the gateway in [localhost:8040](http://localhost:8040). It will
+Now you can access the gateway in [127.0.0.1:8040](http://127.0.0.1:8040). It will
 behave like a regular IPFS Gateway, except for the fact that all contents are provided
 from the CAR file. Therefore, things such as IPNS resolution and fetching contents
 from nodes in the IPFS network won't work.

examples/gateway-car/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"errors"
 	"flag"
 	"io"
 	"log"
@@ -9,6 +10,7 @@ import (
 	"strconv"
 
 	"github.com/ipfs/go-blockservice"
+	"github.com/ipfs/go-cid"
 	offline "github.com/ipfs/go-ipfs-exchange-offline"
 	"github.com/ipfs/go-libipfs/gateway"
 	carblockstore "github.com/ipld/go-car/v2/blockstore"
@@ -19,7 +21,7 @@ func main() {
 	portPtr := flag.Int("p", 8080, "port to run this gateway from")
 	flag.Parse()
 
-	blockService, f, err := newBlockServiceFromCAR(*carFilePtr)
+	blockService, root, f, err := newBlockServiceFromCAR(*carFilePtr)
 	if err != nil {
 		log.Fatal(err)
 	}
@@ -32,28 +34,38 @@ func main() {
 
 	handler := newHandler(gateway, *portPtr)
 
-	address := ":" + strconv.Itoa(*portPtr)
-	log.Printf("Listening on %s", address)
+	address := "127.0.0.1:" + strconv.Itoa(*portPtr)
+	log.Printf("Listening on http://%s", address)
+	log.Printf("Hosting CAR root at http://%s/ipfs/%s", address, root.String())
 
 	if err := http.ListenAndServe(address, handler); err != nil {
 		log.Fatal(err)
 	}
 }
 
-func newBlockServiceFromCAR(filepath string) (blockservice.BlockService, io.Closer, error) {
+func newBlockServiceFromCAR(filepath string) (blockservice.BlockService, *cid.Cid, io.Closer, error) {
 	r, err := os.Open(filepath)
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, nil, err
 	}
 
 	bs, err := carblockstore.NewReadOnly(r, nil)
 	if err != nil {
 		_ = r.Close()
-		return nil, nil, err
+		return nil, nil, nil, err
+	}
+
+	roots, err := bs.Roots()
+	if err != nil {
+		return nil, nil, nil, err
+	}
+
+	if len(roots) == 0 {
+		return nil, nil, nil, errors.New("provided CAR file has no roots")
 	}
 
 	blockService := blockservice.New(bs, offline.Exchange(bs))
-	return blockService, r, nil
+	return blockService, &roots[0], r, nil
 }
 
 func newHandler(gw *blocksGateway, port int) http.Handler {

examples/gateway-car/main_test.go

@@ -16,7 +16,7 @@ const (
 )
 
 func newTestServer() (*httptest.Server, io.Closer, error) {
-	blockService, f, err := newBlockServiceFromCAR("./test.car")
+	blockService, _, f, err := newBlockServiceFromCAR("./test.car")
 	if err != nil {
 		return nil, nil, err
 	}