motiejus/undocker
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reading files using size and offsets

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This commit is contained in:
Motiejus Jakštys 2021-05-24 00:11:58 +03:00
parent b622d991cf
commit 76ab2a9c82
2 changed files with 48 additions and 41 deletions
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29
lxcconfig/lxcconfig.go
View File

@ -35,6 +35,12 @@ type (
Env []string
}
// offsetSize is a tuple which stores file offset and size
offsetSize struct {
offset int64
size int64
}
// dockerManifest is manifest.json
dockerManifest []struct {
Config string `json:"Config"`
@ -93,7 +99,7 @@ func (l lxcConfig) WriteTo(wr io.Writer) error {
func getDockerConfig(rd io.ReadSeeker) (dockerConfig, error) {
tr := tar.NewReader(rd)
// get offsets to all json files rd the archive
jsonOffsets := map[string]int64{}
jsonOffsets := map[string]offsetSize{}
for {
hdr, err := tr.Next()
if err == io.EOF {
@ -109,7 +115,10 @@ func getDockerConfig(rd io.ReadSeeker) (dockerConfig, error) {
if err != nil {
return dockerConfig{}, err
}
jsonOffsets[hdr.Name] = here
jsonOffsets[hdr.Name] = offsetSize{
offset: here,
size: hdr.Size,
}
}
// manifest is the docker manifest rd the image
@ -129,21 +138,17 @@ func getDockerConfig(rd io.ReadSeeker) (dockerConfig, error) {
return config, nil
}
//TODO: don't seek to files, read them.
func parseJSON(rd io.ReadSeeker, offsets map[string]int64, fname string, c interface{}) error {
configOffset, ok := offsets[fname]
fmt.Printf("jumping to %s in %x\n", fname, configOffset)
func parseJSON(rd io.ReadSeeker, offsets map[string]offsetSize, fname string, c interface{}) error {
osize, ok := offsets[fname]
if !ok {
return fmt.Errorf("file %s not found", fname)
}
if _, err := rd.Seek(configOffset, io.SeekStart); err != nil {
if _, err := rd.Seek(osize.offset, io.SeekStart); err != nil {
return fmt.Errorf("seek to %s: %w", fname, err)
}
tr := tar.NewReader(rd)
if _, err := tr.Next(); err != nil {
return err
}
dec := json.NewDecoder(tr)
lrd := io.LimitReader(rd, osize.size)
dec := json.NewDecoder(lrd)
if err := dec.Decode(c); err != nil {
return fmt.Errorf("decode %s: %w", fname, err)
}

32
lxcconfig/lxcconfig_test.go
View File

@ -4,6 +4,7 @@ import (
"archive/tar"
"bytes"
"encoding/json"
"strings"
"testing"
"github.com/motiejus/code/undocker/internal/tartest"
@ -23,12 +24,13 @@ func TestLXCConfig(t *testing.T) {
docker: dockerConfig{
Architecture: "amd64",
},
want: `lxc.include = LXC_TEMPLATE_CONFIG/common.conf
lxc.architecture = amd64
lxc.execute.cmd = '/bin/sh'
`,
want: strings.Join([]string{
`lxc.include = LXC_TEMPLATE_CONFIG/common.conf`,
`lxc.architecture = amd64`,
`lxc.execute.cmd = '/bin/sh'`,
``,
}, "\n"),
},
/*
{
name: "all fields",
docker: dockerConfig{
@ -43,15 +45,16 @@ lxc.execute.cmd = '/bin/sh'
},
},
},
want: `lxc.include = LXC_TEMPLATE_CONFIG/common.conf
lxc.architecture = amd64
lxc.execute.cmd = '/entrypoint.sh /bin/sh -c echo foo'
lxc.init.cwd = /x
lxc.environment = LONGNAME="Foo Bar"
lxc.environment = SHELL=/bin/tcsh
`,
want: strings.Join([]string{
`lxc.include = LXC_TEMPLATE_CONFIG/common.conf`,
`lxc.architecture = amd64`,
`lxc.execute.cmd = '/entrypoint.sh /bin/sh -c echo foo'`,
`lxc.init.cwd = /x`,
`lxc.environment = LONGNAME="Foo Bar"`,
`lxc.environment = SHELL=/bin/tcsh`,
``,
}, "\n"),
},
*/
}
for _, tt := range tests {
@ -60,10 +63,9 @@ lxc.execute.cmd = '/bin/sh'
Name: "manifest.json",
Contents: bytes.NewBufferString(`[{"Config":"config.json"}]`),
}
_ = manifest
archive := tartest.Tarball{
manifest,
//tt.docker,
tt.docker,
}
in := bytes.NewReader(archive.Buffer().Bytes())
var buf bytes.Buffer