fix(core/node): unwrap fx error in node construction

Author: schomatis

cmd/ipfs/daemon.go

@@ -427,7 +427,6 @@ func daemonFunc(req *cmds.Request, re cmds.ResponseEmitter, env cmds.Environment
 
 	node, err := core.NewNode(req.Context, ncfg)
 	if err != nil {
-		log.Error("error from node construction: ", err)
 		return err
 	}
 	node.IsDaemon = true

core/builder.go

@@ -2,13 +2,16 @@ package core
 
 import (
 	"context"
+	"fmt"
+	"reflect"
 	"sync"
 	"time"
 
 	"github.com/ipfs/go-ipfs/core/bootstrap"
 	"github.com/ipfs/go-ipfs/core/node"
 
 	"github.com/ipfs/go-metrics-interface"
+	"go.uber.org/dig"
 	"go.uber.org/fx"
 )
 
@@ -75,11 +78,11 @@ func NewNode(ctx context.Context, cfg *BuildCfg) (*IpfsNode, error) {
 	}()
 
 	if app.Err() != nil {
-		return nil, app.Err()
+		return nil, logAndUnwrapFxError(app.Err())
 	}
 
 	if err := app.Start(ctx); err != nil {
-		return nil, err
+		return nil, logAndUnwrapFxError(err)
 	}
 
 	// TODO: How soon will bootstrap move to libp2p?
@@ -89,3 +92,46 @@ func NewNode(ctx context.Context, cfg *BuildCfg) (*IpfsNode, error) {
 
 	return n, n.Bootstrap(bootstrap.DefaultBootstrapConfig)
 }
+
+// Log the entire `app.Err()` but return only the innermost one to the user
+// given the full error can be very long (as it can expose the entire build
+// graph in a single string).
+//
+// The fx.App error exposed through `app.Err()` normally contains un-exported
+// errors from its low-level `dig` package:
+// * https://github.com/uber-go/dig/blob/5e5a20d/error.go#L82
+// These usually wrap themselves in many layers to expose where in the build
+// chain did the error happen. Although useful for a developer that needs to
+// debug it, it can be very confusing for a user that just wants the IPFS error
+// that he can probably fix without being aware of the entire chain.
+// Unwrapping everything is not the best solution as there can be useful
+// information in the intermediate errors, mainly in the next to last error
+// that locates which component is the build error coming from, but it's the
+// best we can do at the moment given all errors in dig are private and we
+// just have the generic `RootCause` API.
+func logAndUnwrapFxError(fxAppErr error) error {
+	if fxAppErr == nil {
+		return nil
+	}
+
+	log.Error("constructing the node: ", fxAppErr)
+
+	err := fxAppErr
+	for {
+		extractedErr := dig.RootCause(err)
+		// Note that the `RootCause` name is misleading as it just unwraps only
+		// *one* error layer at a time, so we need to continuously call it.
+		if !reflect.TypeOf(extractedErr).Comparable() {
+			// Some internal errors are not comparable (e.g., `dig.errMissingTypes`
+			// which is a slice) and we can't go further.
+			break
+		}
+		if extractedErr == err {
+			// We didn't unwrap any new error in the last call, reached the innermost one.
+			break
+		}
+		err = extractedErr
+	}
+
+	return fmt.Errorf("constructing the node (see log for full detail): %w", err)
+}

go.mod

@@ -104,6 +104,7 @@ require (
 	github.com/whyrusleeping/go-sysinfo v0.0.0-20190219211824-4a357d4b90b1
 	github.com/whyrusleeping/multiaddr-filter v0.0.0-20160516205228-e903e4adabd7
 	go.opencensus.io v0.23.0
+	go.uber.org/dig v1.12.0
 	go.uber.org/fx v1.15.0
 	go.uber.org/zap v1.19.1
 	golang.org/x/crypto v0.0.0-20210921155107-089bfa567519