rewrite private name map storage to support build caching

import_obfuscation.go

@@ -7,10 +7,8 @@ import (
 	"bufio"
 	"bytes"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"os"
-	"path/filepath"
 	"sort"
 	"strings"
 
@@ -47,18 +45,17 @@ type privateImports struct {
 	privateNames []string
 }
 
-func appendPrivateNameMap(nameMap map[string]string, packageDirectory string) error {
-	file, err := os.Open(filepath.Join(packageDirectory, garbleMapFile))
-	if errors.Is(err, os.ErrNotExist) {
-		return nil
-	}
-	if err != nil {
-		return err
-	}
-	defer file.Close()
+func appendPrivateNameMap(pkg *goobj2.Package, nameMap map[string]string) error {
+	for _, member := range pkg.ArchiveMembers {
+		if member.ArchiveHeader.Name != garbleMapHeaderName {
+			continue
+		}
 
-	if err := json.NewDecoder(file).Decode(&nameMap); err != nil {
-		return err
+		serializedMap := member.ArchiveHeader.Data
+		if err := json.Unmarshal(serializedMap[:bytes.IndexByte(serializedMap, 0x00)], &nameMap); err != nil {
+			return err
+		}
+		return nil
 	}
 	return nil
 }
@@ -87,8 +84,7 @@ func obfuscateImports(objPath, importCfgPath string) (garbledImports, privateNam
 
 			pkgs = append(pkgs, pkgInfo{pkg, info.Path, private})
 
-			packageDir := filepath.Dir(info.Path)
-			if err := appendPrivateNameMap(privateNameMap, packageDir); err != nil {
+			if err := appendPrivateNameMap(pkg, privateNameMap); err != nil {
 				return nil, nil, fmt.Errorf("error parsing name map %s at %s: %v", pkgPath, info.Path, err)
 			}
 		}

main.go

@@ -31,6 +31,8 @@ import (
 	"time"
 	"unicode"
 
+	"github.com/Binject/debug/goobj2"
+
 	"golang.org/x/mod/module"
 	"golang.org/x/mod/semver"
 	"golang.org/x/tools/go/ast/astutil"
@@ -115,7 +117,7 @@ var (
 	seed []byte
 )
 
-const garbleMapFile = "garble.map"
+const garbleMapHeaderName = "garble/nameMap"
 
 func saveListedPackages(w io.Writer, flags, patterns []string) error {
 	args := []string{"list", "-json", "-deps", "-export"}
@@ -664,17 +666,34 @@ func transformCompile(args []string) ([]string, error) {
 	}
 
 	if len(privateNameMap) > 0 {
-		outputDirectory := filepath.Dir(flagValue(flags, "-o"))
+		objPath := flagValue(flags, "-o")
+		importcfg := flagValue(flags, "-importcfg")
+		deferred = append(deferred, func() error {
+			importCfg, err := goobj2.ParseImportCfg(importcfg)
+			if err != nil {
+				return err
+			}
 
-		file, err := os.Create(filepath.Join(outputDirectory, garbleMapFile))
-		if err != nil {
-			return nil, err
-		}
-		defer file.Close()
+			pkg, err := goobj2.Parse(objPath, pkgPath, importCfg)
+			if err != nil {
+				return err
+			}
 
-		if err := json.NewEncoder(file).Encode(privateNameMap); err != nil {
-			return nil, err
-		}
+			data, err := json.Marshal(privateNameMap)
+			if err != nil {
+				return err
+			}
+
+			pkg.ArchiveMembers = append(pkg.ArchiveMembers, goobj2.ArchiveMember{
+				ArchiveHeader: goobj2.ArchiveHeader{
+					Name: garbleMapHeaderName,
+					Size: int64(len(data)),
+					Data: data,
+				},
+			})
+
+			return pkg.Write(objPath)
+		})
 	}
 
 	return append(flags, newPaths...), nil