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apkindex.go
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apkindex.go
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package apk
import (
"archive/tar"
"bufio"
"bytes"
"compress/gzip"
"encoding/base64"
"fmt"
"io"
"os"
"strconv"
"strings"
"text/template"
"time"
"github.com/MakeNowJust/heredoc/v2"
)
const apkIndexFilename = "APKINDEX"
const descriptionFilename = "DESCRIPTION"
// Go template for generating the APKINDEX file from an ApkIndex struct
var apkIndexTemplate = template.Must(template.New(apkIndexFilename).Funcs(
template.FuncMap{
// Helper function to join slice of string by space
"join": func(s []string) string {
return strings.Join(s, " ")
},
}).Parse(heredoc.Doc(`C:{{.ChecksumString}}
P:{{.Name}}
V:{{.Version}}
{{- if .Arch}}
A:{{.Arch}}
{{- end }}
{{- if .Size}}
S:{{.Size}}
{{- end }}
{{- if .InstalledSize}}
I:{{.InstalledSize}}
{{- end}}
T:{{.Description}}
{{- if .URL}}
U:{{.URL}}
{{- end}}
{{- if .License}}
L:{{.License}}
{{- end}}
{{- if .Origin}}
o:{{.Origin}}
{{- end}}
{{- if .Maintainer}}
m:{{.Maintainer}}
{{- end}}
{{- if and .BuildTime (not .BuildTime.IsZero)}}
t:{{.BuildTime.Unix}}
{{- end}}
{{- if .RepoCommit}}
c:{{.RepoCommit}}
{{- end}}
{{- if .Dependencies}}
D:{{join .Dependencies}}
{{- end}}
{{- if .InstallIf}}
i:{{.InstallIf}}
{{- end}}
{{- if .Provides}}
p:{{join .Provides}}
{{- end}}
{{- if .ProviderPriority}}
k:{{.ProviderPriority}}
{{- end}}
`)))
type APKIndex struct { //nolint:revive
Signature []byte
Description string
Packages []*Package
}
// Splitting empty string results in single element array with one empty string, which would
// be treated as package with empty name.
func splitRepeatedField(val string) []string {
if val == "" {
return nil
}
return strings.Split(val, " ")
}
// ParsePackageIndex parses a plain (uncompressed) APKINDEX file. It returns an
// ApkIndex struct
func ParsePackageIndex(apkIndexUnpacked io.Reader) ([]*Package, error) {
if closer, ok := apkIndexUnpacked.(io.Closer); ok {
defer closer.Close()
}
indexScanner := bufio.NewScanner(apkIndexUnpacked)
// We have seen alpine's community/coq package a provides line with 72KB of data in it.
// The default MaxScanTokenSize for bufio.Scanner is 64KB. We allow buf to allocate up
// to 1MB but give it a starting buffer size of 16KB (default is 4KB) because we always
// end up having to resize, and 16KB should avoid an extra alloc, whereas the 1MB allows
// us to alloc enough to handle alpine (and hopefully we never have to revisit this).
buf := make([]byte, 16*1024)
meg := 1024 * 1024
indexScanner.Buffer(buf, meg)
pkg := &Package{}
linenr := 1
packages := []*Package{}
for indexScanner.Scan() {
line := indexScanner.Text()
if len(line) == 0 {
if pkg.Name != "" {
packages = append(packages, pkg)
}
pkg = &Package{}
continue
}
if len(line) > 1 && line[1:2] != ":" {
return nil, fmt.Errorf("cannot parse line %d: expected \":\" in not found", linenr)
}
token := line[:1]
val := line[2:]
switch token {
case "P":
pkg.Name = val
case "V":
pkg.Version = val
case "A":
pkg.Arch = val
case "L":
pkg.License = val
case "T":
pkg.Description = val
case "o":
pkg.Origin = val
case "m":
pkg.Maintainer = val
case "U":
pkg.URL = val
case "D":
pkg.Dependencies = splitRepeatedField(val)
case "p":
pkg.Provides = splitRepeatedField(val)
case "c":
pkg.RepoCommit = val
case "t":
i, err := strconv.ParseInt(val, 10, 64)
if err != nil {
return nil, fmt.Errorf("cannot parse build time %s: %w", val, err)
}
pkg.BuildDate = i
pkg.BuildTime = time.Unix(i, 0).UTC()
case "i":
pkg.InstallIf = splitRepeatedField(val)
case "S":
size, err := strconv.ParseUint(val, 10, 64)
if err != nil {
return nil, fmt.Errorf("cannot parse size field %s: %w", val, err)
}
pkg.Size = size
case "I":
installedSize, err := strconv.ParseUint(val, 10, 64)
if err != nil {
return nil, fmt.Errorf("cannot parse installed size field %s: %w", val, err)
}
pkg.InstalledSize = installedSize
case "k":
priority, err := strconv.ParseUint(val, 10, 64)
if err != nil {
return nil, fmt.Errorf("cannot parse provider priority field %s: %w", val, err)
}
pkg.ProviderPriority = priority
case "C":
// Handle SHA1 checksums:
if strings.HasPrefix(val, "Q1") {
checksum, err := base64.StdEncoding.DecodeString(val[2:])
if err != nil {
return nil, err
}
pkg.Checksum = checksum
}
}
linenr++
}
return packages, indexScanner.Err()
}
func IndexFromArchive(archive io.ReadCloser) (*APKIndex, error) {
gzipReader, err := gzip.NewReader(archive)
if err != nil {
return nil, err
}
defer gzipReader.Close()
tarReader := tar.NewReader(gzipReader)
apkindex := &APKIndex{}
for {
hdr, err := tarReader.Next()
if err == io.EOF {
break
}
if err != nil {
return nil, err
}
switch hdr.Name {
case apkIndexFilename:
apkindex.Packages, err = ParsePackageIndex(io.NopCloser(tarReader))
if err != nil {
return nil, err
}
case descriptionFilename:
description, err := io.ReadAll(tarReader)
if err != nil {
return nil, err
}
apkindex.Description = string(description)
default:
if strings.HasPrefix(hdr.Name, ".SIGN.") {
var err error
apkindex.Signature, err = io.ReadAll(tarReader)
if err != nil {
return nil, err
}
} else {
return nil, fmt.Errorf("unexpected file found in APKINDEX: %s", hdr.Name)
}
}
}
return apkindex, nil
}
func ArchiveFromIndex(apkindex *APKIndex) (archive io.Reader, err error) {
// Execute the template and append output for each package in the index
var apkindexContents bytes.Buffer
for _, pkg := range apkindex.Packages {
if len(pkg.Name) == 0 {
continue
}
err = apkIndexTemplate.Execute(&apkindexContents, pkg)
if err != nil {
return nil, fmt.Errorf("failed to parse template for package %s: %w", pkg.Name, err)
}
}
// Create the tarball
var tarballContents bytes.Buffer
gw := gzip.NewWriter(&tarballContents)
defer gw.Close()
tw := tar.NewWriter(gw)
defer tw.Close()
// Add APKINDEX and DESCRIPTION files to the tarball
for _, item := range []struct {
filename string
contents []byte
}{
{apkIndexFilename, apkindexContents.Bytes()},
{descriptionFilename, []byte(apkindex.Description)},
} {
var info os.FileInfo = &tarballItemFileInfo{item.filename, int64(len(item.contents))}
header, err := tar.FileInfoHeader(info, item.filename)
if err != nil {
return nil, fmt.Errorf("creating tar header for %s: %w", item.filename, err)
}
header.Name = item.filename
if err := tw.WriteHeader(header); err != nil {
return nil, fmt.Errorf("writing tar header for %s: %w", item.filename, err)
}
if _, err = io.Copy(tw, bytes.NewReader(item.contents)); err != nil {
return nil, fmt.Errorf("copying tar contents for %s: %w", item.filename, err)
}
}
// Return io.ReadCloser representing the tarball
return &tarballContents, nil
}
// This type implements os.FileInfo, allowing us to construct
// a tar header without needing to run os.Stat on a file
type tarballItemFileInfo struct {
name string
size int64
}
func (info *tarballItemFileInfo) Name() string { return info.name }
func (info *tarballItemFileInfo) Size() int64 { return info.size }
func (info *tarballItemFileInfo) Mode() os.FileMode { return 0644 }
func (info *tarballItemFileInfo) ModTime() time.Time { return time.Time{} }
func (info *tarballItemFileInfo) IsDir() bool { return false }
func (info *tarballItemFileInfo) Sys() interface{} { return nil }
var _ os.FileInfo = (*tarballItemFileInfo)(nil)