Named error for `no components`

Update the previous `invalid path` error to match the error returned
from `SplitAbsPath`.

core/pathresolver.go

@@ -3,7 +3,6 @@ package core
 import (
 	"errors"
 	"strings"
-	"fmt"
 
 	context "github.com/ipfs/go-ipfs/Godeps/_workspace/src/golang.org/x/net/context"
 
@@ -32,7 +31,7 @@ func Resolve(ctx context.Context, n *IpfsNode, p path.Path) (*merkledag.Node, er
 		seg := p.Segments()
 
 		if len(seg) < 2 || seg[1] == "" { // just "/<protocol/>" without further segments
-			return nil, fmt.Errorf("invalid path: %s", string(p))
+			return nil, path.ErrNoComponents
 		}
 
 		extensions := seg[2:]

core/pathresolver_test.go

@@ -4,18 +4,22 @@ import (
 	"testing"
 
 	path "github.com/ipfs/go-ipfs/path"
-	"strings"
 )
 
-func TestResolveInvalidPath(t *testing.T) {
+func TestResolveNoComponents(t *testing.T) {
 	n, err := NewMockNode()
 	if n == nil || err != nil {
-		t.Fatal("Should have constructed.", err)
+		t.Fatal("Should have constructed a mock node", err)
+	}
+
+	_, err = Resolve(n.Context(), n, path.Path("/ipns/"))
+	if err != path.ErrNoComponents {
+		t.Fatal("Should error with no components (/ipns/).", err)
 	}
 
 	_, err = Resolve(n.Context(), n, path.Path("/ipfs/"))
-	if !strings.HasPrefix(err.Error(), "invalid path") {
-		t.Fatal("Should get invalid path.", err)
+	if err != path.ErrNoComponents {
+		t.Fatal("Should error with no components (/ipfs/).", err)
 	}
 
 }

path/resolver.go

@@ -4,6 +4,7 @@ package path
 import (
 	"fmt"
 	"time"
+	"errors"
 
 	mh "github.com/ipfs/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-multihash"
 	"github.com/ipfs/go-ipfs/Godeps/_workspace/src/golang.org/x/net/context"
@@ -14,6 +15,10 @@ import (
 
 var log = u.Logger("path")
 
+// Paths after a protocol must contain at least one component
+var ErrNoComponents = errors.New(
+	"path must contain at least one component")
+
 // ErrNoLink is returned when a link is not found in a path
 type ErrNoLink struct {
 	name string
@@ -43,7 +48,7 @@ func SplitAbsPath(fpath Path) (mh.Multihash, []string, error) {
 
 	// if nothing, bail.
 	if len(parts) == 0 {
-		return nil, nil, fmt.Errorf("ipfs path must contain at least one component")
+		return nil, nil, ErrNoComponents
 	}
 
 	// first element in the path is a b58 hash (for now)