feat(pointer): better performance through directly managed pointers

pointer.go

@@ -16,6 +16,8 @@ import (
 	"strings"
 )
 
+const defaultPointerAllocationSize = 32
+
 // Parse parses str into a Pointer structure.
 // str may be a pointer or a url string.
 // If a url string, Parse will use the URL's fragment component
@@ -35,6 +37,25 @@ func Parse(str string) (Pointer, error) {
 	return parse(u.Fragment)
 }
 
+// IsEmpty is a utility function to check if the Pointer
+// is empty / nil equivalent
+func (p Pointer) IsEmpty() bool {
+	return len(p) == 0
+}
+
+// Head returns the root of the Pointer
+func (p Pointer) Head() *string {
+	if len(p) == 0 {
+		return nil
+	}
+	return &p[0]
+}
+
+// Tail returns everything after the Pointer head
+func (p Pointer) Tail() Pointer {
+	return Pointer(p[1:])
+}
+
 // The ABNF syntax of a JSON Pointer is:
 // json-pointer    = *( "/" reference-token )
 // reference-token = *( unescaped / escaped )
@@ -62,6 +83,12 @@ func parse(str string) (Pointer, error) {
 // Pointer represents a parsed JSON pointer
 type Pointer []string
 
+// NewPointer creates a Pointer with a pre-allocated block of memory
+// to avoid repeated slice expansions
+func NewPointer() Pointer {
+	return make([]string, 0, defaultPointerAllocationSize)
+}
+
 // String implements the stringer interface for Pointer,
 // giving the escaped string
 func (p Pointer) String() (str string) {
@@ -104,6 +131,14 @@ func (p Pointer) Descendant(path string) (Pointer, error) {
 	return append(p, dpath...), nil
 }
 
+// RawDescendant extends the pointer with 1 or more path tokens
+// The function itself is unsafe as it doesnt fully parse the input
+// and assumes the user is directly managing the pointer
+// This allows for much faster pointer management
+func (p Pointer) RawDescendant(path ...string) Pointer {
+	return append(p, path...)
+}
+
 // Evaluation of each reference token begins by decoding any escaped
 // character sequence.  This is performed by first transforming any
 // occurrence of the sequence '~1' to '/', and then transforming any

pointer_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"reflect"
+	"strings"
 	"testing"
 )
 
@@ -60,15 +61,15 @@ func TestParse(t *testing.T) {
 		{"#/foo", "/foo", ""},
 		{"#/foo/", "/foo/", ""},
 
-		{"://", "", "parse ://: missing protocol scheme"},
+		{"://", "", "missing protocol scheme"},
 		{"#7", "", "non-empty references must begin with a '/' character"},
 		{"", "", ""},
 		{"https://example.com#", "", ""},
 	}
 
 	for i, c := range cases {
 		got, err := Parse(c.raw)
-		if !(err == nil && c.err == "" || err != nil && err.Error() == c.err) {
+		if !(err == nil && c.err == "" || err != nil && strings.Contains(err.Error(), c.err)) {
 			t.Errorf("case %d error mismatch. expected: '%s', got: '%s'", i, c.err, err)
 			continue
 		}