Tips – Page 9 – Guy Rutenberg

Make Offline Mirror of a Site using `wget`

Sometimes you want to create an offline copy of a site that you can take and view even without internet access. Using wget you can make such copy easily:

wget --mirror --convert-links --adjust-extension --page-requisites 
--no-parent http://example.org

Explanation of the various flags:

--mirror – Makes (among other things) the download recursive.
--convert-links – convert all the links (also to stuff like CSS stylesheets) to relative, so it will be suitable for offline viewing.
--adjust-extension – Adds suitable extensions to filenames (html or css) depending on their content-type.
--page-requisites – Download things like CSS style-sheets and images required to properly display the page offline.
--no-parent – When recursing do not ascend to the parent directory. It useful for restricting the download to only a portion of the site.

Alternatively, the command above may be shortened:

wget -mkEpnp http://example.org

Note: that the last p is part of np (--no-parent) and hence you see p twice in the flags.

Comparison of Hebrew Fonts on Kindle Paperwhite

I’ve decided to compare the looks of four, freely available Hebrew fonts, on the Amazon Kindle Paperwhite.

Bootstrap: Combining `input-append` and `input-block-level`

If you have a button appended to an input control in Bootstrap, and you want it fill the entire width, it’s not sufficient to add the input-block-level to the input itself but this CSS class also needs to be added to the surrounding .input-append div. For example:

<div class="input-append input-block-level">
	<input type="text" class="search-query input-block-level" name="q" placeholder="Search">
	<button type="submit" class="btn btn-primary">Search</button>
</div>

Applying .input-block-level to only one of the elments (either the div or the input) just doesn’t work.

Enabling C++11 (C++0x) in CMake

Going over some CMakeLists.txt files I’ve written, I came across the following snippet:

include(CheckCXXCompilerFlag)
CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
if(COMPILER_SUPPORTS_CXX11)
	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
elseif(COMPILER_SUPPORTS_CXX0X)
	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")
else()
        message(STATUS "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support. Please use a different C++ compiler.")
endif()

Various compiler versions of gcc and clang use different flags to specify C++11 support, namely older ones accept -std=c++0x and newer one -std=c++11. The above snippets detects which is the right one for the compiler being used and adds the flag to the CXX_FLAGS.

View `man` Pages Properly in gVim

Vim’s ability to display man pages easily using the K mapping often comes handy. It been bothering me for a while, that the same thing doesn’t work properly in gVim, which I use more. The reason is that Vim’s ability to display man pages depends on having a terminal emulator, which just isn’t true for gVim, hence the garbled display of man pages one sees if he tries viewing a man page in gVim.

Today, I found a way around this limitation. It turns out, Vim comes with support for displaying man pages in a split window, and does it perfectly – colors, links and all the necessary stuff. The first line, enables this feature which includes by default the K mapping to open the man page in a new split. The second part, which I find very convenient, makes the regular K do the same in gVim. And unlike the original mapping, it also accepts a count before, so pressing 3K will search the 3 man section of the keyword under the cursor.

" Properly display man pages
" ==========================
runtime ftplugin/man.vim
if has("gui_running")
	nnoremap K :<C-U>exe "Man" v:count "<C-R><C-W>"<CR>
endif

Highlight Whitespace at End-of-Line in Vim

Usually trailing whitespace is undesirable. Using vim’s :match command you can easily highlight those trailing whitespace:

:match Error /\s\+$/

This can be combined with autocmd and inserted to ~/.vimrc to highlight trailing whitespace only for certain files:

autocmd Filetype python match Error /\s\+$/

Preventing Directory Traversal in Python

Consider the following use case:

PREFIX = '/home/user/files/'
full_path = os.path.join(PREFIX, filepath)
read(full_path, 'rb')
...

Assuming that filepath is user-controlled, a malicious user user might attempt a directory traversal (like setting filepath to ../../../etc/passwd). How can we make sure that filepath cannot traverse “above” our prefix? There are of course numerous solutions to sanitizing input against directory traversalthat. The easiest way (that I came up with) to do so in python is:

filepath = os.normpath('/' + filepath).lstrip('/')

It works because it turns the path into an absolute path, normalizes it and makes it relative again. As one cannot traverse above /, it effectively ensures that the filepath cannot go outside of PREFIX.

Post updated: see the comments below for explanation of the changes.

Ubuntu Freezes When Booting with Degraded Raid

I tried testing my software raid (mdadm) setup by removing one of the disks. When I tried to boot the degraded system, the system hanged displaying a purple screen. If I try booting the system in recovery mode, I get the following error:

** WARNING: There appears to be one or more degraded RAID devices ** The system my have suffered a hardware fault, such as a disk drive failure. The root device may depend on the RAID devices being online. Do you wish to start the degraded RAID? [y/N]: — ** WARNING: There appears to be one or more degraded RAID devices **
The system my have suffered a hardware fault, such as a disk drive failure. The root device may depend on the RAID devices being online.
Do you wish to start the degraded RAID? [y/N]:

Galaxy S2 – Clearing Logs on an Unrooted Phone

I have a Samsung Galaxy S2 using an unrooted stock ROM. Lately, I couldn’t update any of my apps, or install new ones as every time I tried it would complain about Insufficient storage available. This was weird, as according to my phone the apps took less than 600MB and still I barely 200MB of free space in my device memory.

Using CyanogenMod’s Apps on Official ROM

Every since I switched back from using CyanogenMod ROM to the official ROM (due to modem problems) I missed some of the custom apps. It turns out to be really install those apps. You just need to download CyanogenMod and extract the relevant APKs from system/app/ and copy over the phone. To install them you’ll need to enable installation of apps from unknown source in Settings->Security. It’s best to get a CyanogenMod version that corresponds to your ROM’s version, but I successfully installed apps also from newer CyanogenMod releases.