% Mini-projet : Exécuter un validateur XML au sein d'un containeur % Didier Richard % rèv. 0.0.1 du 31/01/2016

---

Use docker to validate an XML file

The objective is to check whether an XML file is well formed and validates against a given schema.

In order to build to docker images, we start by writing the shell that checks the XML/XSD files. Let's call it xsdlint.sh. Once xsdlint.sh is tested, we write the Dockerfile and then build the images. Finally, we test the image under multiple use case :

• no arguments given : check that --help is passed to xsdlint.sh ;
• give path to files and xml file : check that the validation is done ;
• don't give path to files : check that validation raises an error !

The XML/XSD script linter

The shortest path to write such a linter is to use xmllint from the libxml2 project. We assume that libxml2-utils is installed in the host (or any ubuntu 14.04 VM).

The xsdlint.sh looks like :

#!/bin/bash
#
# Vérifie si un fichier XML est bien formé et valide
#
# Constantes :
VERSION="0.0.1"
# Variables globales :
unset show
#
# Exécute ou affiche une commande
# $1 : code de sortie en erreur
# $2 : commande à exécuter
run () {
  local code=$1
  local cmd=$2
  if [ -n "${show}" ] ; then
    echo "cmd: ${cmd}"
  else
    eval ${cmd}
  fi
  [ $? -ne 0 ] && {
    echo "Oops #################"
    exit ${code}
  }
  exit 0
}
#
# Affichage d'erreur
# $1 : code de sortie
# $@ : message
echoerr () {
    local code=$1
    shift
    echo "$@" 1>&2
    usage ${code}
}
#
# Usage du shell :
# $1 : code de sortie
usage () {
  cat >&2 <<EOF
usage: `basename $0` [--help -h] | [pathToXSD] pathToXML

    --help, -h    : prints this help and exits

    pathToXSD : path to XML schema. If none, it is derived from pathToXML
    pathToXML : path to XML file.
EOF
exit $1
}
#
# main
#
while [ $# -gt 0 ]; do
  case $1 in
  --help|-h)
    usage 0
    ;;
  --show|-s)
    show=true
    ;;
  *)
    if [ "z$xsd" = "z" ] ; then
        xsd="$1"
    elif [ "z$xml" = "z" ] ; then
        xml="$1"
    fi
    ;;
  esac
  shift
done

[ ! -n "$xsd" ] && {
    echoerr 2 "Fichier XML absent"
}

[ ! -n "$xml" ] && {
    xml=$xsd
    xsd="${xml%xml}xsd"
    [ ! -e $xsd ] && {
        # no xsd found
        unset xsd
    }
}
[ ! -e $xml ] && {
    echoerr 3 "Fichier ${xml} absent"
}
cmdToExec="xmllint --noout"
[ ! -z "$xsd" ] && {
    cmdToExec="${cmdToExec} --schema ${xsd}"
}
cmdToExec="${cmdToExec} ${xml}"
run 100 "${cmdToExec}"

exit 0

We can test it :

• no parameters are given :

$ ./xsdlint.sh
Fichier XML absent
usage: xsdlint.sh [--help -h] | [pathToXSD] pathToXML

    --help, -h    : prints this help and exits

    pathToXSD : path to XML schema. If none, it is derived from pathToXML
    pathToXML : path to XML file.

• option --help :

$ ./xsdlint.sh --help
usage: xsdlint.sh [--help -h] | [pathToXSD] pathToXML

    --help, -h    : prints this help and exits

    pathToXSD : path to XML schema. If none, it is derived from pathToXML
    pathToXML : path to XML file.

• with an XML file that does not exist :

$ ./xsdlint.sh oops.xml
Fichier oops.xml absent
usage: xsdlint.sh [--help -h] | [pathToXSD] pathToXML

    --help, -h    : prints this help and exits

    pathToXSD : path to XML schema. If none, it is derived from pathToXML
    pathToXML : path to XML file.

• with an XML file that dost exist, but not the XSD schema, checks what is done :

$ ./xsdlint.sh --show ok.xml 
cmd: xmllint --noout ok.xml

• with an XML file and its XSD schema, schema what is done :

$ ./xsdlint.sh --show /data/git/xml2-a/exos/stagiaires.xml
cmd: xmllint --noout --schema /data/git/xml2-a/exos/stagiaires.xsd /data/git/xml2-a/exos/stagiaires.xml

• same test, but now run the validation :

$ ./xsdlint.sh /data/git/xml2-a/exos/stagiaires.xml
/data/git/xml2-a/exos/stagiaires.xml validates

• same test, but now give the XSD file explicitely :

$ ./xsdlint.sh stagiaires.xsd /data/git/xml2-a/exos/stagiaires.xml
/data/git/xml2-a/exos/stagiaires.xml validates

Create the docker image

The Dockerfile is based on alpine:3.3. It installs the bash and libxml2-utils packages, then copy the xsdlint.sh shell script into the image. It also defined the default command as xsdlint.sh and, when no arguments are given to the container (at the run stage), it passes in the --help option to the default command. The file is then as follows :

FROM alpine:3.3
MAINTAINER Didier Richard <didier.richard@ign.fr>
RUN \
    apk update && \
    apk add --no-cache --update-cache bash libxml2-utils && \
    rm -rf /var/cache/apk/*
COPY xsdlint.sh /usr/bin/xsdlint.sh
ENTRYPOINT ["xsdlint.sh"]
CMD ["--help"]

Let's run it and build a versionned image, also taggued latest :

$ docker build -t dgricci/xmllint:0.0.1 -t dgricci/xmllint:latest .
Sending build context to Docker daemon 39.42 kB
Step 1 : FROM alpine:3.3
 ---> 0d81fc72e790
Step 2 : MAINTAINER Didier Richard <didier.richard@ign.fr>
 ---> Running in d34f3b2f1de2
 ---> 2eac89ad17d0
Removing intermediate container d34f3b2f1de2
Step 3 : RUN apk update &&     apk add --no-cache --update-cache bash libxml2-utils &&     rm -rf /var/cache/apk/*
 ---> Running in d5f49af5211f
fetch http://dl-4.alpinelinux.org/alpine/v3.3/main/x86_64/APKINDEX.tar.gz
fetch http://dl-4.alpinelinux.org/alpine/v3.3/community/x86_64/APKINDEX.tar.gz
v3.3.1-79-gd691e49 [http://dl-4.alpinelinux.org/alpine/v3.3/main]
v3.3.1-59-g48b0368 [http://dl-4.alpinelinux.org/alpine/v3.3/community]
OK: 5859 distinct packages available
fetch http://dl-4.alpinelinux.org/alpine/v3.3/main/x86_64/APKINDEX.tar.gz
fetch http://dl-4.alpinelinux.org/alpine/v3.3/main/x86_64/APKINDEX.tar.gz
fetch http://dl-4.alpinelinux.org/alpine/v3.3/community/x86_64/APKINDEX.tar.gz
fetch http://dl-4.alpinelinux.org/alpine/v3.3/community/x86_64/APKINDEX.tar.gz
(1/7) Installing ncurses-terminfo-base (6.0-r6)
(2/7) Installing ncurses-terminfo (6.0-r6)
(3/7) Installing ncurses-libs (6.0-r6)
(4/7) Installing readline (6.3.008-r4)
(5/7) Installing bash (4.3.42-r3)
Executing bash-4.3.42-r3.post-install
(6/7) Installing libxml2 (2.9.3-r0)
(7/7) Installing libxml2-utils (2.9.3-r0)
Executing busybox-1.24.1-r7.trigger
OK: 14 MiB in 18 packages
 ---> f82916b86628
Removing intermediate container d5f49af5211f
Step 4 : COPY xsdlint.sh /usr/bin/xsdlint.sh
 ---> 865bf12c576f
Removing intermediate container c5ebe419f6da
Step 5 : ENTRYPOINT xsdlint.sh
 ---> Running in 5c8edcbae4f2
 ---> caa3009adbe8
Removing intermediate container 5c8edcbae4f2
Step 6 : CMD --help
 ---> Running in fd8cae33e9fb
 ---> 120adefa82ab
Removing intermediate container fd8cae33e9fb
Successfully built 120adefa82ab

Let's check the images first :

$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED VIRTUAL     SIZE
dgricci/xmllint     0.0.1               120adefa82ab        49 seconds ago      9.795 MB
dgricci/xmllint     latest              120adefa82ab        49 seconds ago      9.795 MB
...

Run the image

• no arguments, check --help is passed in :

$ docker run --rm dgricci/xmllint
usage: xsdlint.sh [--help -h] | [pathToXSD] pathToXML

    --help, -h    : prints this help and exits

    pathToXSD : path to XML schema. If none, it is derived from pathToXML
    pathToXML : path to XML file.

• mount path to xml and checks :

$ docker run --rm -v /data:/data:ro dgricci/xmllint /data/git/xml2-a/exos/stagiaires.xml
/data/git/xml2-a/exos/stagiaires.xml validates

• same, but verify what is done :

$ docker run --rm -v /data:/data:ro dgricci/xmllint --show /data/git/xml2-a/exos/stagiaires.xml
cmd: xmllint --noout --schema /data/git/xml2-a/exos/stagiaires.xsd /data/git/xml2-a/exos/stagiaires.xml

• now with a non-existing XML file :

$ docker run --rm -v /data:/data:ro dgricci/xmllint /data/git/xml2-a/exos/oops.xml
Fichier /data/git/xml2-a/exos/oops.xml absent
usage: xsdlint.sh [--help -h] | [pathToXSD] pathToXML

    --help, -h    : prints this help and exits

    pathToXSD : path to XML schema. If none, it is derived from pathToXML
    pathToXML : path to XML file.

Et voilà !

fin du document¹

Footnotes

1. document généré via $ pandoc -V fontsize=10pt -V geometry:"top=2cm, bottom=2cm, left=1cm, right=1cm" -s -N --toc -o xmllint.pdf README.md{.bash} ↩