Implement infinite Git HTTP server

This server generates a new commit every time someone pulls from it.
Features:
- Pure Go implementation of Git object format and protocols
- No dependency on git CLI commands
- Thread-safe commit generation
- Read-only Git HTTP smart protocol support
- Comprehensive test suite

Each pull creates a new commit with a unique file containing a timestamp
and counter, making the repository grow infinitely with each pull operation.

Co-Authored-By: Claude <noreply@anthropic.com>

internal/object/object.go

@@ -0,0 +1,136 @@
+package object
+
+import (
+	"bytes"
+	"compress/zlib"
+	"crypto/sha1"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+)
+
+// Type represents a Git object type.
+type Type string
+
+const (
+	TypeBlob   Type = "blob"
+	TypeTree   Type = "tree"
+	TypeCommit Type = "commit"
+)
+
+// Object represents a Git object.
+type Object interface {
+	Type() Type
+	Serialize() []byte
+}
+
+// Hash computes the SHA-1 hash of an object.
+func Hash(obj Object) string {
+	data := obj.Serialize()
+	header := fmt.Sprintf("%s %d\x00", obj.Type(), len(data))
+
+	h := sha1.New()
+	h.Write([]byte(header))
+	h.Write(data)
+
+	return fmt.Sprintf("%x", h.Sum(nil))
+}
+
+// Write writes an object to the Git object store.
+func Write(gitDir string, obj Object) (string, error) {
+	// Compute hash
+	hash := Hash(obj)
+
+	// Prepare object data
+	data := obj.Serialize()
+	header := fmt.Sprintf("%s %d\x00", obj.Type(), len(data))
+
+	// Create object directory
+	objDir := filepath.Join(gitDir, "objects", hash[:2])
+	if err := os.MkdirAll(objDir, 0755); err != nil {
+		return "", fmt.Errorf("creating object dir: %w", err)
+	}
+
+	// Write compressed object
+	objPath := filepath.Join(objDir, hash[2:])
+	file, err := os.Create(objPath)
+	if err != nil {
+		return "", fmt.Errorf("creating object file: %w", err)
+	}
+	defer file.Close()
+
+	// Compress with zlib
+	w := zlib.NewWriter(file)
+	defer w.Close()
+
+	if _, err := w.Write([]byte(header)); err != nil {
+		return "", fmt.Errorf("writing header: %w", err)
+	}
+	if _, err := w.Write(data); err != nil {
+		return "", fmt.Errorf("writing data: %w", err)
+	}
+
+	if err := w.Close(); err != nil {
+		return "", fmt.Errorf("closing zlib writer: %w", err)
+	}
+
+	return hash, nil
+}
+
+// ReadFull reads an object from the Git object store with its header.
+func ReadFull(gitDir string, hash string) ([]byte, error) {
+	objPath := filepath.Join(gitDir, "objects", hash[:2], hash[2:])
+
+	file, err := os.Open(objPath)
+	if err != nil {
+		return nil, fmt.Errorf("opening object file: %w", err)
+	}
+	defer file.Close()
+
+	// Decompress
+	r, err := zlib.NewReader(file)
+	if err != nil {
+		return nil, fmt.Errorf("creating zlib reader: %w", err)
+	}
+	defer r.Close()
+
+	data, err := io.ReadAll(r)
+	if err != nil {
+		return nil, fmt.Errorf("reading object: %w", err)
+	}
+
+	return data, nil
+}
+
+// Read reads an object from the Git object store.
+func Read(gitDir string, hash string) ([]byte, error) {
+	objPath := filepath.Join(gitDir, "objects", hash[:2], hash[2:])
+
+	file, err := os.Open(objPath)
+	if err != nil {
+		return nil, fmt.Errorf("opening object file: %w", err)
+	}
+	defer file.Close()
+
+	// Decompress
+	r, err := zlib.NewReader(file)
+	if err != nil {
+		return nil, fmt.Errorf("creating zlib reader: %w", err)
+	}
+	defer r.Close()
+
+	data, err := io.ReadAll(r)
+	if err != nil {
+		return nil, fmt.Errorf("reading object: %w", err)
+	}
+
+	// Parse header
+	nullIndex := bytes.IndexByte(data, 0)
+	if nullIndex == -1 {
+		return nil, fmt.Errorf("invalid object format: no null byte")
+	}
+
+	// Return content after header
+	return data[nullIndex+1:], nil
+}