Add helper methods to work with IndexInternalID

.github/workflows/tests.yml

@@ -8,12 +8,12 @@ jobs:
   test:
     strategy:
       matrix:
-        go-version: [1.20.x, 1.21.x, 1.22.x]
+        go-version: [1.23.x, 1.24.x, 1.25.x]
         platform: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.platform }}
     steps:
     - name: Install Go
-      uses: actions/setup-go@v1
+      uses: actions/setup-go@v5
       with:
         go-version: ${{ matrix.go-version }}
     - name: Checkout code

index.go

@@ -17,6 +17,8 @@ package index
 import (
 	"bytes"
 	"context"
+	"encoding/binary"
+	"fmt"
 	"reflect"
 )
 
@@ -185,17 +187,48 @@ func (tfv *TermFieldVector) Size() int {
 		len(tfv.Field) + len(tfv.ArrayPositions)*sizeOfUint64
 }
 
-// IndexInternalID is an opaque document identifier interal to the index impl
+// IndexInternalID is an opaque document identifier internal to the index impl
 type IndexInternalID []byte
 
+// NewIndexInternalID encodes a uint64 into an 8-byte big-endian ID, reusing `buf` when possible.
+func NewIndexInternalID(buf []byte, in uint64) IndexInternalID {
+	if len(buf) != 8 {
+		if cap(buf) >= 8 {
+			buf = buf[0:8]
+		} else {
+			buf = make([]byte, 8)
+		}
+	}
+	binary.BigEndian.PutUint64(buf, in)
+	return buf
+}
+
+// NewIndexInternalIDFrom creates a new IndexInternalID by copying from `other`, reusing `buf` when possible.
+func NewIndexInternalIDFrom(buf IndexInternalID, other IndexInternalID) IndexInternalID {
+	buf = buf[:0]
+	return append(buf, other...)
+}
+
+// Equals checks if two IndexInternalID values are equal.
 func (id IndexInternalID) Equals(other IndexInternalID) bool {
 	return id.Compare(other) == 0
 }
 
+// Compare compares two IndexInternalID values lexicographically. For IDs created
+// by NewIndexInternalID, this comparison order matches the order of their uint64 values
+// due to big-endian encoding.
 func (id IndexInternalID) Compare(other IndexInternalID) int {
 	return bytes.Compare(id, other)
 }
 
+// Value returns the uint64 value encoded in the IndexInternalID.
+func (id IndexInternalID) Value() (uint64, error) {
+	if len(id) != 8 {
+		return 0, fmt.Errorf("wrong len for IndexInternalID: %q", id)
+	}
+	return binary.BigEndian.Uint64(id), nil
+}
+
 type TermFieldDoc struct {
 	Term    string
 	ID      IndexInternalID