Add remote-download command to CLI

cli/cli_command/BUILD

@@ -15,6 +15,7 @@ go_library(
         "//cli/login",
         "//cli/plugin",
         "//cli/printlog",
+        "//cli/remote_download",
         "//cli/remotebazel",
         "//cli/update",
         "//cli/upload",

cli/cli_command/cli_command.go

@@ -11,6 +11,7 @@ import (
 	"github.com/buildbuddy-io/buildbuddy/cli/login"
 	"github.com/buildbuddy-io/buildbuddy/cli/plugin"
 	"github.com/buildbuddy-io/buildbuddy/cli/printlog"
+	"github.com/buildbuddy-io/buildbuddy/cli/remote_download"
 	"github.com/buildbuddy-io/buildbuddy/cli/remotebazel"
 	"github.com/buildbuddy-io/buildbuddy/cli/update"
 	"github.com/buildbuddy-io/buildbuddy/cli/upload"
@@ -83,6 +84,11 @@ var Commands = []Command{
 		Help:    "Runs a bazel command in the cloud with BuildBuddy's hosted bazel service.",
 		Handler: remotebazel.HandleRemoteBazel,
 	},
+	{
+		Name:    "remote-download",
+		Help:    "Fetches a remote asset via an intermediate cache.",
+		Handler: remote_download.HandleRemoteDownload,
+	},
 	{
 		Name:    "update",
 		Help:    "Updates the bb CLI to the latest version.",

cli/remote_download/BUILD

@@ -0,0 +1,23 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "remote_download",
+    srcs = ["remote_download.go"],
+    importpath = "github.com/buildbuddy-io/buildbuddy/cli/remote_download",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//cli/arg",
+        "//cli/login",
+        "//proto:remote_asset_go_proto",
+        "//proto:remote_execution_go_proto",
+        "//proto:resource_go_proto",
+        "//server/remote_cache/digest",
+        "//server/util/flag",
+        "//server/util/grpc_client",
+        "@com_github_mattn_go_isatty//:go-isatty",
+        "@org_golang_google_grpc//status",
+        "@org_golang_google_protobuf//types/known/durationpb",
+    ],
+)
+
+package(default_visibility = ["//cli:__subpackages__"])

cli/remote_download/remote_download.go

@@ -0,0 +1,128 @@
+package remote_download
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"strings"
+
+	"github.com/buildbuddy-io/buildbuddy/cli/arg"
+	"github.com/buildbuddy-io/buildbuddy/cli/login"
+	"github.com/buildbuddy-io/buildbuddy/server/remote_cache/digest"
+	"github.com/buildbuddy-io/buildbuddy/server/util/flag"
+	"github.com/buildbuddy-io/buildbuddy/server/util/grpc_client"
+	"github.com/mattn/go-isatty"
+	"google.golang.org/protobuf/types/known/durationpb"
+
+	rapb "github.com/buildbuddy-io/buildbuddy/proto/remote_asset"
+	repb "github.com/buildbuddy-io/buildbuddy/proto/remote_execution"
+	rspb "github.com/buildbuddy-io/buildbuddy/proto/resource"
+	gstatus "google.golang.org/grpc/status"
+)
+
+var (
+	flags = flag.NewFlagSet("remote-download", flag.ContinueOnError)
+
+	target             = flags.String("target", login.DefaultApiTarget, "Remote gRPC target. Must support bytestream and remote asset APIs.")
+	remoteInstanceName = flags.String("remote_instance_name", "", "Remote instance name - typically acts as a cache namespace.")
+	digestFunction     = flags.String("digest_function", "", "Digest function specifying how the blob is cached. Must be supported by the remote server.")
+	timeout            = flags.Duration("timeout", 0, "Fetch timeout.")
+	qualifiers         = flag.New(flags, "qualifier", []string{}, "Qualifiers in NAME=VALUE format.")
+
+	usage = `
+usage: bb ` + flags.Name() + ` <url>
+
+Fetches a file via an intermediate cache server and prints the resulting
+cache resource name to stdout.
+
+The resource can be downloaded using 'bb download':
+
+	bb fetch <url> | xargs bb download
+
+The "checksum.sri" qualifier can be used to specify a checksum.
+Example:
+
+	SHA256=$(curl -fsSL https://example.com | sha256sum | awk '{print $1}')
+	SRI="sha256-$(echo "$SHA256" | xxd -r -p | base64 -w 0)"
+	bb remote-download --qualifier=checksum.sri="$SRI" https://example.com
+`
+)
+
+func HandleRemoteDownload(args []string) (int, error) {
+	if err := arg.ParseFlagSet(flags, args); err != nil {
+		if err == flag.ErrHelp {
+			log.Print(usage)
+			return 1, nil
+		}
+		return -1, err
+	}
+
+	uris := flags.Args()
+	if len(uris) == 0 {
+		return -1, fmt.Errorf("missing <url> argument")
+	}
+	if len(uris) != 1 {
+		return -1, fmt.Errorf("only one URL argument is supported")
+	}
+
+	parsedDigestFunction := repb.DigestFunction_SHA256
+	if *digestFunction != "" {
+		df, err := digest.ParseFunction(*digestFunction)
+		if err != nil {
+			return -1, fmt.Errorf("invalid --digest_function %q", *digestFunction)
+		}
+		parsedDigestFunction = df
+	}
+
+	conn, err := grpc_client.DialSimpleWithoutPooling(*target)
+	if err != nil {
+		return -1, fmt.Errorf("dial %q: %s", *target, err)
+	}
+	defer conn.Close()
+
+	ctx := context.Background()
+
+	var timeoutProto *durationpb.Duration
+	if *timeout > 0 {
+		timeoutProto = durationpb.New(*timeout)
+	}
+	req := &rapb.FetchBlobRequest{
+		InstanceName:   *remoteInstanceName,
+		Uris:           uris,
+		DigestFunction: parsedDigestFunction,
+		Timeout:        timeoutProto,
+		// TODO: OldestContentAccepted
+	}
+	for _, q := range *qualifiers {
+		name, value, ok := strings.Cut(q, "=")
+		if !ok {
+			return -1, fmt.Errorf("invalid qualifier (expected NAME=VALUE)")
+		}
+		req.Qualifiers = append(req.Qualifiers, &rapb.Qualifier{
+			Name:  name,
+			Value: value,
+		})
+		fmt.Printf("Qualifier name: %q value: %q\n", name, value)
+	}
+	client := rapb.NewFetchClient(conn)
+	resp, err := client.FetchBlob(ctx, req)
+	if err != nil {
+		return -1, fmt.Errorf("fetch blob: %w", err)
+	}
+
+	if err := gstatus.ErrorProto(resp.GetStatus()); err != nil {
+		return -1, err
+	}
+
+	rn := digest.NewResourceName(resp.GetBlobDigest(), *remoteInstanceName, rspb.CacheType_CAS, resp.GetDigestFunction())
+	dl, err := rn.DownloadString()
+	if err != nil {
+		return -1, fmt.Errorf("convert resource name to string: %w", err)
+	}
+	fmt.Print(dl)
+	if isatty.IsTerminal(os.Stdout.Fd()) {
+		fmt.Println()
+	}
+	return 0, nil
+}

server/remote_asset/fetch_server/fetch_server.go

@@ -359,7 +359,7 @@ func mirrorToCache(
 	}
 	defer rsp.Body.Close()
 	if rsp.StatusCode < 200 || rsp.StatusCode >= 400 {
-		return nil, status.UnavailableErrorf("failed to fetch %q: HTTP %s", uri, err)
+		return nil, status.UnavailableErrorf("failed to fetch %q: HTTP %s", uri, rsp.Status)
 	}
 
 	// If we know what the hash should be and the content length is known,