Sunday, June 24, 2018

Skip the Pre-Commit Hook on Git Rebase or Merge

When you want to skip the git pre-commit hook for a single commit, it's easy — you just add the --no-verify flag (or -n for short) to the git commit command:

git commit --no-verify

But to skip multiple commits executed by another git command, like rebase or merge, the --no-verify flag doesn't work. The best way I've found to skip the pre-commit hook in that case is to code the hook to check for a custom environment variable (I like to use NO_VERIFY), and skip the pre-commit logic if it's not empty. For example, the script in my Google Java Format Pre-Commit Hook has a block of code like this at the top of the file, which skips the main functionality of the pre-commit hook if the NO_VERIFY environment variable has been set to anything other than an empty string:

if [ "$NO_VERIFY" ]; then
    echo 'pre-commit hook skipped' 1>&2
    exit 0

So when I want to skip that pre-commit hook when doing a complicated rebase or merge, I simply run the following commands in the same shell:

export NO_VERIFY=1
git rebase -i master # or `git merge some-branch` or whatever
export NO_VERIFY=

Monday, June 18, 2018

Google Java Format Pre-Commit Hook

My team decided to standardize on the Google Java Style Guide for formatting Java code; and not finding a drop-in git pre-commit hook for the Google Java Format library, I whipped one up and pushed it to GitHub as the Google Java Format Pre-Commit Hook project.

To use it, clone the repo, and link its script as the .git/hooks/pre-commit script in whatever project you want to use it with (or call it from your existing .git/hooks/pre-commit script, if you already have one). The script automatically downloads the Google Java Format library, and runs it over all staged .java files whenever you make a commit (and fails the commit if there are any formatting issues it can't automatically clean up).

You can skip the hook by including the --no-verify flag on an individual commit, or by setting the NO_VERIFY environment variable in your shell to be not empty prior to running a sequence of commits (like a merge or rebase). Full details for install and usage are in the project README.

Sunday, May 20, 2018

OpenDKIM Key Retrieval Failed

I set up OpenDKIM on my mailserver years ago, but while I got it working for signing just fine, I could never get it working for verification. Whenever I'd receive a message signed with DKIM, I'd see an error message like this in my mailserver logs:

May  4 01:20:20 mail opendkim[24874]: 7EE5982132: key retrieval failed (s=20161025, '' query timed out

When I tried dig on the DNS record listed in the logs, however, I was able to retrieve it just fine:

dig TXT

Recently I set aside some time to "dig" into it further. I found I could use the opendkim-testkey command to at least reproduce the issue (instead of having to keep sending test emails from other accounts to myself). For example, the following command tries to retrieve the DKIM key from the DNS TXT record (20161025 is the DKIM selector and is the signing domain):

opendkim-testkey -s 20161025 -d

This command gave me the same "query timed out" error message that I saw in my logs. Through a lot of trial and error, I figured out that I could avoid the error by setting the Nameservers property in my /etc/opendkim.conf file to an external DNS server (any external one will do), and restarting the OpenDKIM daemon. I've been running my mailserver on an Ubuntu EC2 instance, and apparently OpenDKIM does not like something about the combination of the Ubuntu DNS resolver and the internal EC2 DNS servers.

So, I added this line to my /etc/opendkim.conf, restarted the OpenDKIM daemon, and now I no longer see the "key retrieval failed" error message in my logs (instead I get a nice Authentication-Results header added by OpenDKIM to my incoming mail)!:

Nameservers is Cloudflare's DNS servers — but any external DNS servers should work. One thing to keep in mind with using external DNS servers is that if your network has a stateless firewall, you need to allow inbound access to UDP in the "ephemeral" port range. If you're using EC2's Network ACLs (and not just using the defaults), this means adding a rule like the following to the ACL for the subnet in which your mailserver lives (32768-61000 is Ubuntu's ephemeral port range):

Rule #: [any number lower than your DENY rules]
Type: Custom UDP Rule
Protocol: UDP (17)
Port Range: 32768-61000
Allow/Deny: ALLOW

Sunday, April 30, 2017

Jenkins Install-Plugin Remoting Deprecated

Installing and setting up Jenkins through an automated process can be tricky. The new, safer CLI (Command Line Interface) that was implemented for Jenkins 2.54 adds another twist to the process. That twist is the "remoting" mechanism for using the CLI has been deprecated, and turned off by default — but it's still the only way to install plugins via the CLI.

So now, to install plugins through automation, you first have to turn remoting back on. You can do that by changing the enabled element in the jenkins.CLI.xml config file (located in the root of your Jenkins home directory) to true, like so:

<?xml version='1.0' encoding='UTF-8'?>

And then restart Jenkins. Now you can use the remoting protocol with the CLI — but it's no longer the default protocol, so you have to specify it explicitly via the -remoting flag, like so (for example to install the ant plugin):

java -jar jenkins-cli.jar -remoting -s http://localhost:8080 \
    install-plugin ant \
    --username admin \
    --password-file secrets/initialAdminPassword

If you don't enable remoting and/or specify the -remoting flag, you'll get an error like this from the CLI:

ERROR: Bad Credentials. Search the server log for 18058afb-86ed-4cc8-856f-b128918cbe8b for more details.

And you'll see this in the Jenkins server log:

INFO: CLI login attempt failed: 18058afb-86ed-4cc8-856f-b128918cbe8b
org.acegisecurity.BadCredentialsException: Failed to read secrets/initialAdminPassword; nested exception is hudson.AbortException: This command is requesting the deprecated -remoting mode. See
        at hudson.cli.CLICommand.main(
        at hudson.cli.CLIAction$PlainCliEndpointResponse$

Once you've got all your plugins installed, you probably will want to go back and disable remoting (by changing the enabled element in the jenkins.CLI.xml config file back to false and restarting Jenkins; or manually via the "Enable CLI over Remoting" checkbox on Jenkins' "Manage Jenkins > Configure Global Security" page).

Sunday, July 10, 2016

JPGPJ: A new Java GPG Library

The Bouncy Castle PGP implementation is the "standard" GPG/PGP library in Java, and it's quite solid — but it's cumbersome to use directly, since it pretty much forces you to learn and use the raw primitives of the OpenPGP spec (RFC 4880). Also, while there is some helpful example code in the Bouncy Castle examples package (and snippets from the same examples have been copied and pasted into a bunch of Stack Overflow answers), the example code is (appropriately?) cryptic, and covers only a limited subset of functionality in each example.

Encrypting with JPGPJ

So I wrote a small library, JPGPJ, to wrap the Bouncy Castle PGP implementation with a simple API for encrypting and decrypting files. It makes interoperating with the standard gpg command-line client (GnuPGP) a breeze. This is all you need to do to encrypt a file with Bob's public key, and sign it with Alice's private key:

new Encryptor(
    new Key(new File("path/to/my/keys/alice-sec.gpg"), "password123"),
    new Key(new File("path/to/my/keys/bob-pub.gpg"))
    new File("path/to/plaintext.txt"),
    new File("path/to/ciphertext.txt.gpg")

The above Java code does the same thing as following gpg command (where Alice has an `alice` secret key and a `bob` public key on her keyring, and enters "password123" when prompted for her passphrase):

gpg --sign --encrypt --local-user alice --recipient alice --recipient bob \
    --output path/to/ciphertext.txt.gpg path/to/plaintext.txt

JPGPJ is set up to do the right thing by default — sign and encrypt — but if you just want to encrypt without signing, that's easy, too — just set the encryptor's signingAlgoritm property to Unsigned:

Encryptor encryptor = new Encryptor(
    new Key(new File("path/to/my/keys/bob-pub.gpg"))
    new File("path/to/plaintext.txt"),
    new File("path/to/ciphertext.txt.gpg")

To encode with ASCII Armor (ie produce Base64-encoded content, instead of binary content), just turn on the encryptor's asciiArmored flag:

Encryptor encryptor = new Encryptor(
    new Key(new File("path/to/my/keys/bob-pub.gpg"))
    new File("path/to/plaintext.txt"),
    new File("path/to/ciphertext.txt.asc")

Decrypting with JPGPJ

Decrypting is just as easy. JPGPJ handles signed or unsigned, encrypted or unencrypted, compressed or uncompressed, ascii-armored or binary messages all the same way. Its default setting is to require messages to be signed by a known key; so for example, to decrypt a message signed by Alice's private key and encrypted with Bob's public key (requiring Alice's public key to verify and Bob's private key to decrypt), this is all the Java you need:

new Decryptor(
    new Key(new File("path/to/my/keys/alice-pub.gpg")),
    new Key(new File("path/to/my/keys/bob-sec.gpg"), "b0bru1z!")
    new File("path/to/ciphertext.txt.gpg"),
    new File("path/back-to/plaintext.txt")

The above Java code does the same thing as the following gpg command (where Bob has a `bob` secret key and an `alice` public key on his keyring, and enters "b0bru1z!" when prompted for his passphrase):

gpg --decrypt --output path/back-to/plaintext.txt path/to/ciphertext.txt.gpg

If the message can't be verified by any known key (that is, any key with which the decryptor had been configured), JPGPJ will raise a VerificationException. If the message can't be decrypted by any known private key (that is, any private key with which the decryptor had been configured), JPGPJ will raise a DecryptionException.

To ignore signatures (in other words, decrypt a message successfully regardless of whether it was signed or not), simply turn off the decryptor's verificationRequired flag:

Decryptor decryptor = new Decryptor(
    new Key(new File("path/to/my/keys/bob-sec.gpg"), "b0bru1z!")
    new File("path/to/ciphertext.txt.gpg"),
    new File("path/back-to/plaintext.txt")

Keys in JPGPJ

The key data used by JPGPJ is simply what get when you export a key from GnuPG, like with the following gpg command for a public key:

gpg --export alice > path/to/my/keys/alice-pub.gpg

Or this gpg command to export a private key (which exports both the public and private parts of the key, encrypted with the same password that the key has on your GnuPG keyring):

gpg --export-secret-keys bob > path/to/my/keys/bob-sec.gpg

If you encode keys with ASCII Armor when you export them (via the GnuPG --armor flag), you can load them the same way in JPGPJ; and you can also embed ascii-armored keys as strings in your source code, if you find that more convenient than using external files (see the Key Rings wiki page for more details on loading and using keys in JPGPJ).

Sunday, May 22, 2016

Powerline Subversion Status

For a while I've been using Jasper N. Brouwer's Powerline Gitstatus plugin for the nifty Powerline shell prompt, and it's become a pretty much indispensable part of my Git workflow. I haven't been able to find something comparable for subversion, so I created something myself: Powerline SVN Status. Here's a screenshot of it in action:

Powerline SVN Status Screenshot

I don't use Subversion all that much any more — mainly for a few older projects — but when I do, having a plugin like this makes my life easier, reminding me when I have some changes I need to check in, or if I have some untracked files I need to add. It's also really helpful when you've switched to a branch, having a branch indicator to remind you that you're not looking at the trunk anymore.

This plugin is just a simple Python class that calls svn info and svn status when in a Subversion working directory. With Powerline all set up, you can simply install it via Pip:

pip install powerline-svnstatus
And then add the following block to your Powerline segment configuration to activate it (I put this in my ~/.config/powerline/themes/shell/default_leftonly.json file):
    "function": "powerline_svnstatus.svnstatus",
    "priority": 40

Saturday, May 14, 2016

Ubuntu 16.04 with Java 7 Timezone Data

As I found when upgrading to Ubuntu 16.04, Java 7 is no longer in the main Ubuntu repository — you have to install it via the OpenJDK PPA. That works nicely, but unfortunately this PPA doesn't include any timezone data.

In previous releases of Ubuntu, Java 6 and 7 timezone data were included via the tzdata-java package; but this package isn't available for Ubuntu 16.04. So I created a new tzdata-java PPA just for Ubuntu 16.04 (Xenial). You can install it like this:

sudo apt-add-repository ppa:justinludwig/tzdata
sudo apt-get install tzdata-java

To update my previous blog post: as a set of Ansible tasks, installing Java 7 on Ubuntu 16.04 now just works like this:

- name: register java 7 ppas
  become: yes
  apt_repository: repo={{ item }}
  - 'ppa:openjdk-r/ppa'
  - 'ppa:justinludwig/tzdata'

- name: install java 7 packages
  become: yes
  apt: pkg={{ item }}
  - openjdk-7-jdk
  - tzdata-java