README
¶
simplecache 
The simplecache package provides support for reading Chromium simple cache v6 or v7.
Learn more: http://www.chromium.org/developers/design-documents/network-stack/disk-cache/very-simple-backend
See the example_test.go for an example of how to read an image from cache in testdata.
This project also includes a tool to read the cache from command line, read this README.
Short cache format
The simple cache contains different files:
| Filename | Description |
|---|---|
| index | Fake index file |
| #####_0 | Data stream file |
| #####_1 | Data stream file |
| #####_s | Data stream file |
| index-dir/the-real-index | The real index file |
Fake index file format (index)
| offset | size | value | description |
|---|---|---|---|
| 0 | 8 | 0x656e74657220796f | Magic |
| 8 | 4 | 7 | Version |
| 12 | 8 | 0x0 | Padding |
Real index file format (the-real-index)
Overview:
- File header
- Last write reason (starting v7)
- Index table
- Last modified
File header
The index file header (struct indexHeader) is 36 bytes in size and consists of:
| offset | size | value | description |
|---|---|---|---|
| 0 | 4 | Payload size | |
| 4 | 4 | Payload CRC32 | |
| 8 | 8 | 0x656e74657220796f | Magic |
| 16 | 4 | 7 | Version |
| 20 | 8 | Number of entries | |
| 28 | 8 | Cache size |
Index table
The index table is an array of entries. An entry (struct indexEntry) is 24 bytes in size and consists of:
| offset | size | value | description |
|---|---|---|---|
| 0 | 8 | Hash | |
| 8 | 8 | Last used | |
| 16 | 8 | Size |
Data stream file format (#####_0)
Overview:
- File header
- URL
- Data stream (stream 1)
- Stream EOF
- HTTP headers (stream 0)
- (optionally) the SHA256 of the URL
- Stream EOF
File header
The index file header (struct entryHeader) is 20 bytes in size and consists of:
| offset | size | value | description |
|---|---|---|---|
| 0 | 8 | 0xfcfb6d1ba7725c30 | Magic |
| 8 | 4 | 5 | Version |
| 12 | 4 | URL length | |
| 16 | 4 | URL MD5 |
Stream EOF
The separator (struct entryEOF) contains information about the stream above. It is 20 bytes in size and consists of:
| offset | size | value | description |
|---|---|---|---|
| 0 | 8 | 0xf4fa6f45970d41d8 | Magic |
| 8 | 4 | Flag | |
| 12 | 4 | stream CRC32 | |
| 16 | 4 | stream size |
| value | description |
|---|---|
| 0 | |
| 1 | the stream has CRC32 |
| 2 | the URL has SHA256 |
| 3 | 1 + 2 |
Data stream file format (#####_1)
Overview:
- File header
- URL
- Data stream (stream 2)
- Stream EOF
Data stream file format (#####_s)
Overview:
- File header
- many of the following:
- Range header
- Range data stream
File header
The index file header (struct entryHeader) is 20 bytes in size and consists of:
| offset | size | value | description |
|---|---|---|---|
| 0 | 8 | 0xfcfb6d1ba7725c30 | Magic |
| 8 | 4 | 7 | Version |
| 12 | 4 | URL length | |
| 16 | 4 | URL MD5 |
Range header
The range header (struct sparseRangeHeader) contains information about the following range stream. It is 28 bytes in size and consists of:
| offset | size | value | description |
|---|---|---|---|
| 0 | 8 | 0xeb97bf016553676b | Magic |
| 8 | 8 | stream offset | |
| 16 | 8 | stream size | |
| 24 | 4 | stream CRC32 |
Documentation
¶
Overview ¶
Package simplecache provides support for reading Chromium simple cache. http://www.chromium.org/developers/design-documents/network-stack/disk-cache/very-simple-backend
Example ¶
Example gets an entry from the cache and prints it to stdout.
package main
import (
"fmt"
"image/png"
"log"
"github.com/schorlet/simplecache"
)
func main() {
entry, err := simplecache.Get("https://golang.org/doc/gopher/pkg.png", "testdata")
if err != nil {
log.Fatal(err)
}
fmt.Println(entry.URL)
header, err := entry.Header()
if err != nil {
log.Fatal(err)
}
for _, key := range []string{"Status", "Content-Length", "Content-Type"} {
fmt.Printf("%s: %s\n", key, header.Get(key))
}
body, err := entry.Body()
if err != nil {
log.Fatal(err)
}
defer body.Close()
config, err := png.DecodeConfig(body)
if err != nil {
log.Fatal(err)
}
fmt.Printf("PNG image data, %d x %d\n", config.Width, config.Height)
}
Output: https://golang.org/doc/gopher/pkg.png Status: 200 Content-Length: 5409 Content-Type: image/png PNG image data, 83 x 120
Index ¶
Examples ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func URLs ¶
URLs returns all the URLs currently stored in the cache.
On linux, valid cache paths are:
~/.cache/chromium/Default/Cache ~/.cache/chromium/Default/Media Cache
URLs reads the files named "path/index" and "path/index-dir/the-real-index" and every entry files named "path/hash(url)_0" where hash is read from the-real-index file.
An error is returned if the format of the index files is unexpected.
Types ¶
type Entry ¶
type Entry struct {
URL string
// contains filtered or unexported fields
}
Entry represents a HTTP response as stored in the cache. Each entry is stored in a file named "path/hash(url)_0".
func Get ¶
Get returns the Entry for the specified URL. An error is returned if the format of the entry does not match the one expected.
Source Files
Directories
¶
| Path | Synopsis |
|---|---|
|
cmd
|
|
|
simplecache
Command simplecache helps reading chromium simple cache v6 or v7.
|
Command simplecache helps reading chromium simple cache v6 or v7. |