command: simplify errors

capability/command/command.go

@@ -1,54 +1,11 @@
 package command
 
 import (
-	"errors"
 	"fmt"
 	"strings"
 )
 
-const (
-	separator = "/"
-)
-
-// ErrNew indicates that the wrapped error was encountered while creating
-// a new Command.
-var ErrNew = errors.New("failed to create Command from elems")
-
-// ErrParse indicates that the wrapped error was encountered while
-// attempting to parse a string as a Command.
-var ErrParse = errors.New("failed to parse Command")
-
-// ErrorJoin indicates that the wrapped error was encountered while
-// attempting to join a new segment to a Command.
-var ErrJoin = errors.New("failed to join segments to Command")
-
-// ErrRequiresLeadingSlash is returned when a parsing a string that
-// doesn't start with a [leading slash character].
-//
-// [leading slash character]: https://github.com/ucan-wg/spec#segment-structure
-var ErrRequiresLeadingSlash = parseError("a command requires a leading slash character")
-
-// ErrDisallowsTrailingSlash is returned when parsing a string that [ends
-// with a trailing slash character].
-//
-// [ends with a trailing slash character]: https://github.com/ucan-wg/spec#segment-structure
-var ErrDisallowsTrailingSlash = parseError("a command must not include a trailing slash")
-
-// ErrUCANNamespaceReserved is returned to indicate that a Command's
-// first segment would contain the [reserved "ucan" namespace].
-//
-// [reserved "ucan" namespace]: https://github.com/ucan-wg/spec#ucan-namespace
-var ErrUCANNamespaceReserved = errors.New("the UCAN namespace is reserved")
-
-// ErrRequiresLowercase is returned if a Command contains, or would contain,
-// [uppercase unicode characters].
-//
-// [uppercase unicode characters]: https://github.com/ucan-wg/spec#segment-structure
-var ErrRequiresLowercase = parseError("UCAN path segments must must not contain upper-case characters")
-
-func parseError(msg string) error {
-	return fmt.Errorf("%w: %s", ErrParse, msg)
-}
+const separator = "/"
 
 var _ fmt.Stringer = (*Command)(nil)
 
@@ -66,18 +23,8 @@ type Command struct {
 // New creates a validated command from the provided list of segment
 // strings.  An error is returned if an invalid Command would be
 // formed
-func New(segments ...string) (*Command, error) {
-	return newCommand(ErrNew, segments...)
-}
-
-func newCommand(err error, segments ...string) (*Command, error) {
-	if len(segments) > 0 && segments[0] == "ucan" {
-		return nil, fmt.Errorf("%w: %w", err, ErrUCANNamespaceReserved)
-	}
-
-	cmd := Command{segments}
-
-	return &cmd, nil
+func New(segments ...string) *Command {
+	return &Command{segments: segments}
 }
 
 // Parse verifies that the provided string contains the required
@@ -100,7 +47,16 @@ func Parse(s string) (*Command, error) {
 
 	// The leading slash will result in the first element from strings.Split
 	// being an empty string which is removed as strings.Join will ignore it.
-	return newCommand(ErrParse, strings.Split(s, "/")[1:]...)
+	return &Command{strings.Split(s, "/")[1:]}, nil
+}
+
+// MustParse is the same as Parse, but panic() if the parsing fail.
+func MustParse(s string) *Command {
+	c, err := Parse(s)
+	if err != nil {
+		panic(err)
+	}
+	return c
 }
 
 // [Top] is the most powerful capability.
@@ -111,22 +67,19 @@ func Parse(s string) (*Command, error) {
 //
 // [Top]: https://github.com/ucan-wg/spec#-aka-top
 func Top() *Command {
-	cmd, _ := New()
-
-	return cmd
+	return New()
 }
 
 // IsValid returns true if the provided string is a valid UCAN command.
 func IsValid(s string) bool {
 	_, err := Parse(s)
-
 	return err == nil
 }
 
 // Join appends segments to the end of this command using the required
 // segment separator.
-func (c *Command) Join(segments ...string) (*Command, error) {
-	return newCommand(ErrJoin, append(c.segments, segments...)...)
+func (c *Command) Join(segments ...string) *Command {
+	return &Command{append(c.segments, segments...)}
 }
 
 // Segments returns the ordered segments that comprise the Command as a
@@ -138,5 +91,5 @@ func (c *Command) Segments() []string {
 // String returns the composed representation the command.  This is also
 // the required wire representation (before IPLD encoding occurs.)
 func (c *Command) String() string {
-	return "/" + strings.Join([]string(c.segments), "/")
+	return "/" + strings.Join(c.segments, "/")
 }

capability/command/command_errors.go

@@ -0,0 +1,21 @@
+package command
+
+import "fmt"
+
+// ErrRequiresLeadingSlash is returned when a parsing a string that
+// doesn't start with a [leading slash character].
+//
+// [leading slash character]: https://github.com/ucan-wg/spec#segment-structure
+var ErrRequiresLeadingSlash = fmt.Errorf("a command requires a leading slash character")
+
+// ErrDisallowsTrailingSlash is returned when parsing a string that [ends
+// with a trailing slash character].
+//
+// [ends with a trailing slash character]: https://github.com/ucan-wg/spec#segment-structure
+var ErrDisallowsTrailingSlash = fmt.Errorf("a command must not include a trailing slash")
+
+// ErrRequiresLowercase is returned if a Command contains, or would contain,
+// [uppercase unicode characters].
+//
+// [uppercase unicode characters]: https://github.com/ucan-wg/spec#segment-structure
+var ErrRequiresLowercase = fmt.Errorf("UCAN path segments must must not contain upper-case characters")

capability/command/command_test.go

@@ -73,7 +73,6 @@ func TestParseCommand(t *testing.T) {
 				t.Parallel()
 
 				cmd, err := command.Parse(testcase.inp)
-				require.ErrorIs(t, err, command.ErrParse)
 				require.ErrorIs(t, err, testcase.err)
 				require.Nil(t, cmd)
 			})
@@ -134,20 +133,6 @@ func invalidTestcases(t *testing.T) []errorTestcase {
 			},
 			err: command.ErrDisallowsTrailingSlash,
 		},
-		{
-			testcase: testcase{
-				name: "only reserved ucan namespace",
-				inp:  "/ucan",
-			},
-			err: command.ErrUCANNamespaceReserved,
-		},
-		{
-			testcase: testcase{
-				name: "reserved ucan namespace prefix",
-				inp:  "/ucan/elem0/elem1/elem2",
-			},
-			err: command.ErrUCANNamespaceReserved,
-		},
 		{
 			testcase: testcase{
 				name: "uppercase character are present",