Difference between pages "Gzip" and "Google Chrome"

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+
Google Chrome is a [[Web Browser|web browser]] developed by Google Inc.
  
== File format ==
+
== Configuration ==
The gzip file (.gz) format consists of:
+
The Google Chrome configuration can be found in the '''Preferences''' file.
* a file header
+
* optional headers
+
** extra fields
+
** original file name
+
** comment
+
** header checksum
+
* compressed data (commonly used compression method DEFLATE, without zlib header)
+
* a file footer
+
  
{| class="wikitable"
+
On Linux
! align="left"| Characteristics
+
<pre>
! Description
+
/home/$USER/.config/google-chrome/Default/Preferences
|-
+
</pre>
| Byte order
+
| little-endian
+
|-
+
| Date and time values
+
| Filetime in UTC
+
|-
+
| Character string
+
| ISO 8859-1 (LATIN-1)
+
|}
+
  
=== File header ===
+
On MacOS-X
The file header is 10 bytes in size and contains:
+
<pre>
{| class="wikitable"
+
/Users/$USER/Library/Application Support/Google/Chrome/Default/Preferences
! align="left"| Offset
+
</pre>
! Size
+
! Value
+
! Description
+
|-
+
| 0
+
| 2
+
| 0x1f 0x8b
+
| Signature (or identification byte 1 and 2)
+
|-
+
| 2
+
| 1
+
|
+
| Compression Method
+
|-
+
| 3
+
| 1
+
|
+
| Flags
+
|-
+
| 4
+
| 4
+
|
+
| Last modification time <br> Contains a POSIX timestamp.
+
|-
+
| 8
+
| 1
+
|
+
| Compression flags (or extra flags)
+
|-
+
| 9
+
| 1
+
|
+
| Operating system <br> Value that indicates on which operating system the gzip file was created.
+
|}
+
  
==== Compression method ====
+
On Windows XP
 +
<pre>
 +
C:\Documents and Settings\%USERNAME%\Local Settings\Application Data\Google\Chrome\User Data\Default\Preferences
 +
</pre>
  
{| class="wikitable"
+
On Windows Vista and later
! align="left"| Value
+
<pre>
! Identifier
+
C:\Users\%USERNAME%\AppData\Local\Google\Chrome\User Data\Default\Preferences
! Description
+
</pre>
|-
+
| 0 - 7
+
|
+
| Reserved
+
|-
+
| 8
+
| deflate
+
| deflate compressed data
+
|}
+
  
==== Flags ====
+
Or for '''Chromium'''
  
{| class="wikitable"
+
On Linux
! align="left"| Value
+
<pre>
! Identifier
+
/home/$USER/.config/chromium/Default/Preferences
! Description
+
</pre>
|-
+
| 0x01
+
| FTEXT
+
| If set the uncompressed data needs to be treated as text instead of binary data. <br> This flag hints end-of-line conversion for cross-platform text files but does not enforce it.
+
|-
+
| 0x02
+
| FHCRC
+
| The file contains a header checksum (CRC-16)
+
|-
+
| 0x04
+
| FEXTRA
+
| The file contains extra fields
+
|-
+
| 0x08
+
| FNAME
+
| The file contains an original file name string
+
|-
+
| 0x10
+
| FCOMMENT
+
| The file contains comment
+
|-
+
| 0x20
+
|
+
| Reserved
+
|-
+
| 0x40
+
|
+
| Reserved
+
|-
+
| 0x80
+
|
+
| Reserved
+
|}
+
  
<b>Notes:</b>
+
On MacOS-X
* Reserved flags bits must be zero.
+
<pre>
* The FHCRC bit was never set by versions of gzip up to 1.2.4, even though it was documented with a different meaning in gzip 1.2.4.
+
/Users/$USER/Library/Application Support/Chromium/Default/Preferences
 +
</pre>
  
==== Compression flags ====
+
On Windows XP
This value contains flags specific to the compression method.
+
<pre>
 +
C:\Documents and Settings\%USERNAME%\Local Settings\Application Data\Chromium\User Data\Default\Preferences
 +
</pre>
  
===== Compression flags - deflate =====
+
On Windows Vista and later
If compression method value is 8 (deflate) the following compression flags can be used:
+
<pre>
{| class="wikitable"
+
C:\Users\%USERNAME%\AppData\Local\Chromium\User Data\Default\Preferences
! align="left"| Value
+
</pre>
! Identifier
+
! Description
+
|-
+
| 0x02
+
|
+
| compressor used maximum compression, slowest algorithm
+
|-
+
| 0x04
+
|
+
| compressor used fastest algorithm
+
|}
+
  
==== Operating System ====
+
=== Plugins ===
{| class="wikitable"
+
! align="left"| Value
+
! Identifier
+
! Description
+
|-
+
| 0
+
|
+
| FAT filesystem (MS-DOS, OS/2, NT/Win32)
+
|-
+
| 1
+
|
+
| Amiga
+
|-
+
| 2
+
|
+
| VMS (or OpenVMS)
+
|-
+
| 3
+
|
+
| Unix
+
|-
+
| 4
+
|
+
| VM/CMS
+
|-
+
| 5
+
|
+
| Atari TOS
+
|-
+
| 6
+
|
+
| HPFS filesystem (OS/2, NT)
+
|-
+
| 7
+
|
+
| Macintosh
+
|-
+
| 8
+
|
+
| Z-System
+
|-
+
| 9
+
|
+
| CP/M
+
|-
+
| 10
+
|
+
| TOPS-20
+
|-
+
| 11
+
|
+
| NTFS filesystem (NT)
+
|-
+
| 12
+
|
+
| QDOS
+
|-
+
| 13
+
|
+
| Acorn RISCOS
+
|-
+
| 255
+
|
+
| unknown
+
|}
+
  
=== Optional headers ===
+
Information about plugins can be found under the "plugins section" of the Preferences file.
==== Extra fields ====
+
This value is present in the file if the FEXTRA flag is set in the file header flags.
+
  
The extra field are variable of size and contains:
+
=== DNS Prefetching ===
{| class="wikitable"
+
! align="left"| Offset
+
! Size
+
! Value
+
! Description
+
|-
+
| 0
+
| 2
+
|
+
| Extra field data size <br> Value in bytes.
+
|-
+
| 2
+
| ...
+
|
+
| Extra field data
+
|}
+
  
==== Original file name ====
+
DNS is prefetched for related sites, e.g. links on the page.
This value is present in the file if the FNAME flag is set in the file header flags.
+
This behavior is controlled by the setting "Predict network actions to improve page load performance", which is enabled by default.
  
This is the original name of the file being compressed, with any directory components removed, and, if the file being compressed is on a file system with case insensitive names, forced to lower case.
+
If enabled the Preferences file contains:
 +
<pre>
 +
  "dns_prefetching": {
 +
      "enabled": true,
 +
</pre>
  
Contains an ISO 8859-1 (LATIN-1) string with end-of-string character.
+
If disabled the Preferences file contains:
 +
<pre>
 +
  "dns_prefetching": {
 +
      "enabled": false,
 +
</pre>
  
==== Comment ====
+
== Start-up DNS queries ==
This value is present in the file if the FCOMMENT flag is set in the file header flags.
+
  
Contains an ISO 8859-1 (LATIN-1) string with end-of-string character. Line breaks should be denoted by a single line feed character.
+
When Chrome starts it queries for several non-existing hostnames that consists of a 10 random characters, E.g.
 +
<pre>
 +
ttrgoiknff.mydomain.com
 +
bxjhgftsyu.mydomain.com
 +
yokjbjiagd.mydomain.com
 +
</pre>
  
==== Header checksum ====
+
This is used to determine if your ISP is hijacking NXDOMAIN results [http://www.google.com/support/forum/p/Chrome/thread?tid=3511015c72a7b314&hl=en].
The header checksum contain a CRC-16 that consists of the two least significant bytes of the CRC-32 for all bytes of the gzip header up to and not including the CRC-16.
+
  
=== File footer ===
+
== Disk Cache ==
The file footer is 8 bytes in size and contains:
+
Google Chrome uses multiple caches, from [http://src.chromium.org/viewvc/chrome/trunk/src/net/base/cache_type.h?view=markup]:
{| class="wikitable"
+
<pre>
! align="left"| Offset
+
// The types of caches that can be created.
! Size
+
enum CacheType {
! Value
+
    DISK_CACHE,  // Disk is used as the backing storage.
! Description
+
    MEMORY_CACHE,  // Data is stored only in memory.
|-
+
    MEDIA_CACHE,  // Optimized to handle media files.
| 0
+
    APP_CACHE,  // Backing store for an AppCache.
| 4
+
    SHADER_CACHE, // Backing store for the GL shader cache.
|
+
    PNACL_CACHE, // Backing store the PNaCl translation cache
| Checksum (CRC-32)
+
};
|-
+
</pre>
| 4
+
 
| 4
+
The Google Chrome disk cache can be found in:
|
+
 
| Uncompressed data size <br> Value in bytes.
+
On Linux
|}
+
 
 +
<pre>
 +
/home/$USER/.cache/chromium/Default/Cache/
 +
/home/$USER/.cache/google-chrome/Default/Cache/
 +
/home/$USER/.config/chromium/Default/Cache/
 +
/home/$USER/.config/google-chrome/Default/Cache/
 +
</pre>
 +
 
 +
<pre>
 +
/home/$USER/.cache/chromium/Default/Media Cache/
 +
/home/$USER/.cache/google-chrome/Default/Media Cache/
 +
/home/$USER/.config/chromium/Default/Media Cache/
 +
/home/$USER/.config/google-chrome/Default/Media Cache/
 +
</pre>
 +
 
 +
 
 +
<pre>
 +
/home/$USER/.config/chromium/Default/Application Cache/Cache/
 +
/home/$USER/.config/google-chrome/Default/Application Cache/Cache/
 +
</pre>
 +
 
 +
 
 +
<pre>
 +
/home/$USER/.config/chromium/Default/GPUCache/
 +
/home/$USER/.config/google-chrome/Default/GPUCache/
 +
</pre>
 +
 
 +
<pre>
 +
/home/$USER/.cache/chromium/PnaclTranslationCache/
 +
/home/$USER/.cache/google-chrome/PnaclTranslationCache/
 +
</pre>
 +
 
 +
On MacOS-X
 +
<pre>
 +
/Users/$USER/Caches/Chromium/Default/Cache/
 +
/Users/$USER/Caches/Google/Chrome/Default/Cache/
 +
</pre>
 +
 
 +
On Windows XP
 +
<pre>
 +
C:\Documents and Settings\%USERNAME%\Local Settings\Application Data\Chromium\User Data\Cache\
 +
C:\Documents and Settings\%USERNAME%\Local Settings\Application Data\Google\Chrome\User Data\Cache\
 +
</pre>
 +
 
 +
On Windows Vista and later
 +
<pre>
 +
C:\Users\%USERNAME%\AppData\Local\Google\Chromium\Default\Cache\
 +
C:\Users\%USERNAME%\AppData\Local\Google\Chrome\User Data\Default\Cache\
 +
</pre>
 +
 
 +
The Chrome Cache contains different files with the following file names:
 +
* index
 +
* data_#; where # contains a decimal digit.
 +
* f_######; where # contains a hexadecimal digit.
 +
 
 +
For more info see Chrome developers site [http://www.chromium.org/developers/design-documents/network-stack/disk-cache].
 +
 
 +
== History ==
 +
Chrome stores the history of visited sites in a file named '''History'''. This file uses the [[SQLite database format]].
 +
 
 +
The '''History''' file can be found in same location as the '''Preferences''' file.
 +
 
 +
There is also '''Archived History''' that predates information in the '''History''' file.
 +
Note that the '''Archived History''' only contains visits.
 +
 
 +
=== Timestamps ===
 +
The '''History''' file uses the different timestamps.
 +
 
 +
==== visits.visit_time ====
 +
 
 +
The '''visits.visit_time''' is in (the number of) microseconds since January 1, 1601 UTC
 +
 
 +
Some Python code to do the conversion into human readable format:
 +
<pre>
 +
date_string = datetime.datetime( 1601, 1, 1 )
 +
            + datetime.timedelta( microseconds=timestamp )
 +
</pre>
 +
 
 +
Note that this timestamp is not the same as a Windows filetime which is (the number of) 100 nanoseconds since January 1, 1601 UTC
 +
 
 +
==== downloads.start_time ====
 +
 
 +
The '''downloads.start_time''' is in (the number of) seconds since January 1, 1970 UTC
 +
 
 +
Some Python code to do the conversion into human readable format:
 +
<pre>
 +
date_string = datetime.datetime( 1970, 1, 1 )
 +
            + datetime.timedelta( seconds=timestamp )
 +
</pre>
 +
 
 +
=== Example queries ===
 +
Some example queries:
 +
 
 +
To get an overview of the visited sites:
 +
<pre>
 +
SELECT datetime(((visits.visit_time/1000000)-11644473600), "unixepoch"), urls.url, urls.title FROM urls, visits WHERE urls.id = visits.url;
 +
</pre>
 +
 
 +
Note that the visit_time conversion looses precision.
 +
 
 +
To get an overview of the downloaded files:
 +
<pre>
 +
SELECT datetime(downloads.start_time, "unixepoch"), downloads.url, downloads.full_path, downloads.received_bytes, downloads.total_bytes FROM downloads;
 +
</pre>
 +
 
 +
How the information of the downloaded files is stored in the database can vary per version of Chrome as of version 26:
 +
<pre>
 +
SELECT datetime(((downloads.start_time/1000000)-11644473600), "unixepoch"), downloads.target_path, downloads_url_chains.url, downloads.received_bytes, downloads.total_bytes \
 +
FROM downloads, downloads_url_chains WHERE downloads.id = downloads_url_chains.id;
 +
</pre>
  
 
== See Also ==
 
== See Also ==
* [[bz2 file]]
+
 
 +
* [[SQLite database format]]
  
 
== External Links ==
 
== External Links ==
 +
* [http://en.wikipedia.org/wiki/Google_Chrome Wikipedia article on Google Chrome]
 +
* [http://www.chromium.org/user-experience/user-data-directory The Chromium Projects - User Data Directory]
 +
* [http://www.chromium.org/developers/design-documents/network-stack/disk-cache Chrome Disk Cache]
 +
* [http://www.google.com/support/forum/p/Chrome/thread?tid=3511015c72a7b314&hl=en Chrome support forum article random 10 character hostnames on startup]
 +
* [http://www.useragentstring.com/pages/Chrome/ Chrome User Agent strings]
 +
* [http://computer-forensics.sans.org/blog/2010/01/21/google-chrome-forensics/ Google Chrome Forensics] by [[Kristinn Guðjónsson]], January 21, 2010
 +
* [http://linuxsleuthing.blogspot.ch/2013/02/cashing-in-on-google-chrome-cache.html?m=1 Cashing in on the Google Chrome Cache], [[John Lehr]], February 24, 2013
 +
* [http://www.obsidianforensics.com/blog/history-index-files-removed-from-chrome/ History Index files removed from Chrome v30], by Ryan Benson, October 2, 2013
 +
* [https://hindsight-internet-history.googlecode.com/files/Evolution_of_Chrome_Databases.png Evolution of Chrome Databases], by Ryan Benson, November 12, 2013
  
* [http://www.gzip.org/format.txt The gzip file format], by the [http://www.gzip.org/ gzip project]
+
== Tools ==
* [http://www.gzip.org/algorithm.txt The gzip compression algorithm], by the [http://www.gzip.org/ gzip project]
+
=== Open Source ===
* [http://tools.ietf.org/html/rfc1952 RFC1952: GZIP file format specification version 4.3], by [[IETF]]
+
* [https://code.google.com/p/hindsight-internet-history/ hindsight-internet-history]
* [http://en.wikipedia.org/wiki/Gzip Wikipedia: gzip]
+
  
[[Category:File Formats]]
+
[[Category:Applications]]
 +
[[Category:Web Browsers]]

Revision as of 03:50, 30 April 2014

Google Chrome is a web browser developed by Google Inc.

Configuration

The Google Chrome configuration can be found in the Preferences file.

On Linux

/home/$USER/.config/google-chrome/Default/Preferences

On MacOS-X

/Users/$USER/Library/Application Support/Google/Chrome/Default/Preferences

On Windows XP

C:\Documents and Settings\%USERNAME%\Local Settings\Application Data\Google\Chrome\User Data\Default\Preferences

On Windows Vista and later

C:\Users\%USERNAME%\AppData\Local\Google\Chrome\User Data\Default\Preferences

Or for Chromium

On Linux

/home/$USER/.config/chromium/Default/Preferences

On MacOS-X

/Users/$USER/Library/Application Support/Chromium/Default/Preferences

On Windows XP

C:\Documents and Settings\%USERNAME%\Local Settings\Application Data\Chromium\User Data\Default\Preferences

On Windows Vista and later

C:\Users\%USERNAME%\AppData\Local\Chromium\User Data\Default\Preferences

Plugins

Information about plugins can be found under the "plugins section" of the Preferences file.

DNS Prefetching

DNS is prefetched for related sites, e.g. links on the page. This behavior is controlled by the setting "Predict network actions to improve page load performance", which is enabled by default.

If enabled the Preferences file contains:

   "dns_prefetching": {
      "enabled": true,

If disabled the Preferences file contains:

   "dns_prefetching": {
      "enabled": false,

Start-up DNS queries

When Chrome starts it queries for several non-existing hostnames that consists of a 10 random characters, E.g.

ttrgoiknff.mydomain.com
bxjhgftsyu.mydomain.com
yokjbjiagd.mydomain.com

This is used to determine if your ISP is hijacking NXDOMAIN results [1].

Disk Cache

Google Chrome uses multiple caches, from [2]:

// The types of caches that can be created.
enum CacheType {
    DISK_CACHE,  // Disk is used as the backing storage.
    MEMORY_CACHE,  // Data is stored only in memory.
    MEDIA_CACHE,  // Optimized to handle media files.
    APP_CACHE,  // Backing store for an AppCache.
    SHADER_CACHE, // Backing store for the GL shader cache.
    PNACL_CACHE, // Backing store the PNaCl translation cache
};

The Google Chrome disk cache can be found in:

On Linux

/home/$USER/.cache/chromium/Default/Cache/
/home/$USER/.cache/google-chrome/Default/Cache/
/home/$USER/.config/chromium/Default/Cache/
/home/$USER/.config/google-chrome/Default/Cache/
/home/$USER/.cache/chromium/Default/Media Cache/
/home/$USER/.cache/google-chrome/Default/Media Cache/
/home/$USER/.config/chromium/Default/Media Cache/
/home/$USER/.config/google-chrome/Default/Media Cache/


/home/$USER/.config/chromium/Default/Application Cache/Cache/
/home/$USER/.config/google-chrome/Default/Application Cache/Cache/


/home/$USER/.config/chromium/Default/GPUCache/
/home/$USER/.config/google-chrome/Default/GPUCache/
/home/$USER/.cache/chromium/PnaclTranslationCache/
/home/$USER/.cache/google-chrome/PnaclTranslationCache/

On MacOS-X

/Users/$USER/Caches/Chromium/Default/Cache/
/Users/$USER/Caches/Google/Chrome/Default/Cache/

On Windows XP

C:\Documents and Settings\%USERNAME%\Local Settings\Application Data\Chromium\User Data\Cache\
C:\Documents and Settings\%USERNAME%\Local Settings\Application Data\Google\Chrome\User Data\Cache\

On Windows Vista and later

C:\Users\%USERNAME%\AppData\Local\Google\Chromium\Default\Cache\
C:\Users\%USERNAME%\AppData\Local\Google\Chrome\User Data\Default\Cache\

The Chrome Cache contains different files with the following file names:

  • index
  • data_#; where # contains a decimal digit.
  • f_######; where # contains a hexadecimal digit.

For more info see Chrome developers site [3].

History

Chrome stores the history of visited sites in a file named History. This file uses the SQLite database format.

The History file can be found in same location as the Preferences file.

There is also Archived History that predates information in the History file. Note that the Archived History only contains visits.

Timestamps

The History file uses the different timestamps.

visits.visit_time

The visits.visit_time is in (the number of) microseconds since January 1, 1601 UTC

Some Python code to do the conversion into human readable format:

date_string = datetime.datetime( 1601, 1, 1 )
            + datetime.timedelta( microseconds=timestamp )

Note that this timestamp is not the same as a Windows filetime which is (the number of) 100 nanoseconds since January 1, 1601 UTC

downloads.start_time

The downloads.start_time is in (the number of) seconds since January 1, 1970 UTC

Some Python code to do the conversion into human readable format:

date_string = datetime.datetime( 1970, 1, 1 )
            + datetime.timedelta( seconds=timestamp )

Example queries

Some example queries:

To get an overview of the visited sites:

SELECT datetime(((visits.visit_time/1000000)-11644473600), "unixepoch"), urls.url, urls.title FROM urls, visits WHERE urls.id = visits.url;

Note that the visit_time conversion looses precision.

To get an overview of the downloaded files:

SELECT datetime(downloads.start_time, "unixepoch"), downloads.url, downloads.full_path, downloads.received_bytes, downloads.total_bytes FROM downloads;

How the information of the downloaded files is stored in the database can vary per version of Chrome as of version 26:

SELECT datetime(((downloads.start_time/1000000)-11644473600), "unixepoch"), downloads.target_path, downloads_url_chains.url, downloads.received_bytes, downloads.total_bytes \
FROM downloads, downloads_url_chains WHERE downloads.id = downloads_url_chains.id;

See Also

External Links

Tools

Open Source