Validate DCO on Travis

Copied straight from Docker, replacing github.com/docker/docker
with github.com/docker/fig in .validate.

Signed-off-by: Ben Firshman <ben@firshman.co.uk>

.travis.yml

@@ -7,5 +7,6 @@ install:
 - pip install -r requirements.txt
 - pip install -r requirements-dev.txt
 script:
+ - script/validate-dco
  - flake8 fig
  - nosetests tests/unit

script/.validate

@@ -0,0 +1,33 @@
+#!/bin/bash
+
+if [ -z "$VALIDATE_UPSTREAM" ]; then
+	# this is kind of an expensive check, so let's not do this twice if we
+	# are running more than one validate bundlescript
+	
+	VALIDATE_REPO='https://github.com/docker/fig.git'
+	VALIDATE_BRANCH='master'
+	
+	if [ "$TRAVIS" = 'true' -a "$TRAVIS_PULL_REQUEST" != 'false' ]; then
+		VALIDATE_REPO="https://github.com/${TRAVIS_REPO_SLUG}.git"
+		VALIDATE_BRANCH="${TRAVIS_BRANCH}"
+	fi
+	
+	VALIDATE_HEAD="$(git rev-parse --verify HEAD)"
+	
+	git fetch -q "$VALIDATE_REPO" "refs/heads/$VALIDATE_BRANCH"
+	VALIDATE_UPSTREAM="$(git rev-parse --verify FETCH_HEAD)"
+	
+	VALIDATE_COMMIT_LOG="$VALIDATE_UPSTREAM..$VALIDATE_HEAD"
+	VALIDATE_COMMIT_DIFF="$VALIDATE_UPSTREAM...$VALIDATE_HEAD"
+	
+	validate_diff() {
+		if [ "$VALIDATE_UPSTREAM" != "$VALIDATE_HEAD" ]; then
+			git diff "$VALIDATE_COMMIT_DIFF" "$@"
+		fi
+	}
+	validate_log() {
+		if [ "$VALIDATE_UPSTREAM" != "$VALIDATE_HEAD" ]; then
+			git log "$VALIDATE_COMMIT_LOG" "$@"
+		fi
+	}
+fi

script/validate-dco

@@ -0,0 +1,56 @@
+#!/bin/bash
+
+source "$(dirname "$BASH_SOURCE")/.validate"
+
+adds=$(validate_diff --numstat | awk '{ s += $1 } END { print s }')
+dels=$(validate_diff --numstat | awk '{ s += $2 } END { print s }')
+notDocs="$(validate_diff --numstat | awk '$3 !~ /^docs\// { print $3 }')"
+
+: ${adds:=0}
+: ${dels:=0}
+
+# "Username may only contain alphanumeric characters or dashes and cannot begin with a dash"
+githubUsernameRegex='[a-zA-Z0-9][a-zA-Z0-9-]+'
+
+# https://github.com/docker/docker/blob/master/CONTRIBUTING.md#sign-your-work
+dcoPrefix='Signed-off-by:'
+dcoRegex="^(Docker-DCO-1.1-)?$dcoPrefix ([^<]+) <([^<>@]+@[^<>]+)>( \\(github: ($githubUsernameRegex)\\))?$"
+
+check_dco() {
+	grep -qE "$dcoRegex"
+}
+
+if [ $adds -eq 0 -a $dels -eq 0 ]; then
+	echo '0 adds, 0 deletions; nothing to validate! :)'
+elif [ -z "$notDocs" -a $adds -le 1 -a $dels -le 1 ]; then
+	echo 'Congratulations!  DCO small-patch-exception material!'
+else
+	commits=( $(validate_log --format='format:%H%n') )
+	badCommits=()
+	for commit in "${commits[@]}"; do
+		if [ -z "$(git log -1 --format='format:' --name-status "$commit")" ]; then
+			# no content (ie, Merge commit, etc)
+			continue
+		fi
+		if ! git log -1 --format='format:%B' "$commit" | check_dco; then
+			badCommits+=( "$commit" )
+		fi
+	done
+	if [ ${#badCommits[@]} -eq 0 ]; then
+		echo "Congratulations!  All commits are properly signed with the DCO!"
+	else
+		{
+			echo "These commits do not have a proper '$dcoPrefix' marker:"
+			for commit in "${badCommits[@]}"; do
+				echo " - $commit"
+			done
+			echo
+			echo 'Please amend each commit to include a properly formatted DCO marker.'
+			echo
+			echo 'Visit the following URL for information about the Docker DCO:'
+			echo ' https://github.com/docker/docker/blob/master/CONTRIBUTING.md#sign-your-work'
+			echo
+		} >&2
+		false
+	fi
+fi