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// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package modindex contains code for building and searching an index to
// the Go module cache. The directory containing the index, returned by
// IndexDir(), contains a file index-name-<ver> that contains the name
// of the current index. We believe writing that short file is atomic.
// ReadIndex reads that file to get the file name of the index.
// WriteIndex writes an index with a unique name and then
// writes that name into a new version of index-name-<ver>.
// (<ver> stands for the CurrentVersion of the index format.)
package modindex
import (
"path/filepath"
"slices"
"strings"
"time"
"golang.org/x/mod/semver"
)
// Create always creates a new index for the go module cache that is in cachedir.
func Create(cachedir string) error {
_, err := indexModCache(cachedir, true)
return err
}
// Update the index for the go module cache that is in cachedir,
// If there is no existing index it will build one.
// If there are changed directories since the last index, it will
// write a new one and return true. Otherwise it returns false.
func Update(cachedir string) (bool, error) {
return indexModCache(cachedir, false)
}
// indexModCache writes an index current as of when it is called.
// If clear is true the index is constructed from all of GOMODCACHE
// otherwise the index is constructed from the last previous index
// and the updates to the cache. It returns true if it wrote an index,
// false otherwise.
func indexModCache(cachedir string, clear bool) (bool, error) {
cachedir, err := filepath.Abs(cachedir)
if err != nil {
return false, err
}
cd := Abspath(cachedir)
future := time.Now().Add(24 * time.Hour) // safely in the future
ok, err := modindexTimed(future, cd, clear)
if err != nil {
return false, err
}
return ok, nil
}
// modindexTimed writes an index current as of onlyBefore.
// If clear is true the index is constructed from all of GOMODCACHE
// otherwise the index is constructed from the last previous index
// and all the updates to the cache before onlyBefore.
// It returns true if it wrote a new index, false if it wrote nothing.
func modindexTimed(onlyBefore time.Time, cachedir Abspath, clear bool) (bool, error) {
var curIndex *Index
if !clear {
var err error
curIndex, err = ReadIndex(string(cachedir))
if clear && err != nil {
return false, err
}
// TODO(pjw): check that most of those directories still exist
}
cfg := &work{
onlyBefore: onlyBefore,
oldIndex: curIndex,
cacheDir: cachedir,
}
if curIndex != nil {
cfg.onlyAfter = curIndex.Changed
}
if err := cfg.buildIndex(); err != nil {
return false, err
}
if len(cfg.newIndex.Entries) == 0 && curIndex != nil {
// no changes from existing curIndex, don't write a new index
return false, nil
}
if err := cfg.writeIndex(); err != nil {
return false, err
}
return true, nil
}
type work struct {
onlyBefore time.Time // do not use directories later than this
onlyAfter time.Time // only interested in directories after this
// directories from before onlyAfter come from oldIndex
oldIndex *Index
newIndex *Index
cacheDir Abspath
}
func (w *work) buildIndex() error {
// The effective date of the new index should be at least
// slightly earlier than when the directories are scanned
// so set it now.
w.newIndex = &Index{Changed: time.Now(), Cachedir: w.cacheDir}
dirs := findDirs(string(w.cacheDir), w.onlyAfter, w.onlyBefore)
if len(dirs) == 0 {
return nil
}
newdirs, err := byImportPath(dirs)
if err != nil {
return err
}
// for each import path it might occur only in newdirs,
// only in w.oldIndex, or in both.
// If it occurs in both, use the semantically later one
if w.oldIndex != nil {
for _, e := range w.oldIndex.Entries {
found, ok := newdirs[e.ImportPath]
if !ok {
w.newIndex.Entries = append(w.newIndex.Entries, e)
continue // use this one, there is no new one
}
if semver.Compare(found[0].version, e.Version) > 0 {
// use the new one
} else {
// use the old one, forget the new one
w.newIndex.Entries = append(w.newIndex.Entries, e)
delete(newdirs, e.ImportPath)
}
}
}
// get symbol information for all the new diredtories
getSymbols(w.cacheDir, newdirs)
// assemble the new index entries
for k, v := range newdirs {
d := v[0]
pkg, names := processSyms(d.syms)
if pkg == "" {
continue // PJW: does this ever happen?
}
entry := Entry{
PkgName: pkg,
Dir: d.path,
ImportPath: k,
Version: d.version,
Names: names,
}
w.newIndex.Entries = append(w.newIndex.Entries, entry)
}
// sort the entries in the new index
slices.SortFunc(w.newIndex.Entries, func(l, r Entry) int {
if n := strings.Compare(l.PkgName, r.PkgName); n != 0 {
return n
}
return strings.Compare(l.ImportPath, r.ImportPath)
})
return nil
}
func (w *work) writeIndex() error {
return writeIndex(w.cacheDir, w.newIndex)
}
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