Implementation of docker pull and docker push commands without docker client via HTTP requests

We had 2 bags of grass, 75 tablets of mescaline unix environment, docker repository and task to implement docker pull and docker push commands without docker client.

UPD:
Question: What is all this for?
Answer: Load testing of the product (NOT by means of bash, scripts are provided for educational purposes). It was decided not to use the docker client to reduce additional layers (within reasonable limits) and, accordingly, emulate a higher load. As a result, all system delays of the docker client were removed. Received a relatively clean load directly on the product

First, let's see what these teams do.

So what is docker pull used for? According to the documentation :

"Pull an image or a repository from a registry".

There we find a link to understand images, containers, and storage drivers .

docker image layers, , . registry API.

:

"An “image” is a combination of a JSON manifest and individual layer files. The process of pulling an > image centers around retrieving these two components."

“Pulling an Image Manifest”.

, . : GET /v2/{name}/manifests/{reference}

"The name and reference parameter identify the image and are required. The reference may include a tag or digest."

, :

curl -s -X GET "http://localhost:8081/link/to/docker/registry/v2/centos-11-10/manifests/1.1.1" -H "header_if_needed"

json , . , : "GET /v2/{name}/blobs/{digest}"

“Access to a layer will be gated by the name of the repository but is identified uniquely in the registry by digest.”

digest , .

curl -s -X GET "http://localhost:8081/link/to/docker/registry/v2/centos-11-10/blobs/sha256:f972d139738dfcd1519fd2461815651336ee25a8b54c358834c50af094bb262f" -H "header_if_needed" --output firstLayer

.

file firstLayer

.. tar , .

#!/bin/bash -eu

downloadDir=$1
# url as http://localhost:8081/link/to/docker/registry
url=$2
imageName=$3
tag=$4

# array of layers
layers=($(curl -s -X GET "$url/v2/$imageName/manifests/$tag" | grep -oP '(?<=blobSum" : ").+(?=")'))

# download each layer from array
for layer in "${layers[@]}"; do
    echo "Downloading ${layer}"
    curl -v -X GET "$url/v2/$imageName/blobs/$layer" --output "$downloadDir/$layer.tar"
done

# find all layers, untar them and remove source .tar files
cd "$downloadDir" && find . -name "sha256:*" -exec tar xvf {} \;
rm sha256:*.tar
exit 0

./script.sh dirName “http://localhost:8081/link/to/docker/registry” myAwesomeImage 1.0

2 — docker push

.

. , . .

:

• — "POST /v2/{repoName}/blobs/uploads/"
• ( , .. ) — "PUT /v2/{repoName}/blobs/uploads/{uuid}?digest={digest}
  Content-Length: {size of layer}
  Content-Type: application/octet-stream
  Layer Binary Data".
• — "PUT /v2/{repoName}/manifests/{reference}".

, . (chunked) PATCH :

"PATCH /v2/{repoName}/blobs/uploads/{uuid}
Content-Length: {size of chunk}
Content-Type: application/octet-stream
{Layer Chunk Binary Data}".

, .. 202 4.

:

• 
  2 3 , .

. archlinux:latest

docker pull archlinux

docker save c24fe13d37b9 -o savedArch

tar xvf savedArch

. ,

cat manifest.json | json_pp

. , .

, .

config . 2 ( ), mediaType :

echo ‘{
   "schemaVersion": 2,
   "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
   "config": {
      "mediaType": "application/vnd.docker.container.image.v1+json",
      "size": config_size,
      "digest": "config_hash"
   },
   "layers": [
      ’ > manifest.json

. json :

{
         "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
         "size": ${layersSizes[$i]},
         "digest": \"sha256:${layersNames[$i]}\"
      },

.

sed -i "s/config_size/$configSize/g; s/config_hash/$configName/g" $manifestFile

Now you can initiate the boot process and save yourself uuid, which should be accompanied by all subsequent requests.

The full script looks something like this:

#!/bin/bash -eux

imageDir=$1
# url as http://localhost:8081/link/to/docker/registry
url=$2
repoName=$3
tag=$4
manifestFile=$(readlink -f ${imageDir}/manifestCopy)
configFile=$(readlink -f $(find $imageDir -name "*.json" ! -name "manifest.json"))

# calc layers sha 256 sum, rename them accordingly, and add info about each to manifest file
function prepareLayersForUpload() {
  info_file=$imageDir/info
  # lets calculate layers sha256 and use it as layers names further
  layersNames=($(find $imageDir -name "layer.tar" -exec shasum -a 256 {} \; | cut -d" " -f1))

  # rename layers according to shasums. !!!Set required amount of fields for cut command!!!
  # this part definitely can be done easier but i didn't found another way, sry
  find $imageDir -name "layer.tar" -exec bash -c 'mv {} "$(echo {} | cut -d"/" -f1,2)/$(shasum -a 256 {} | cut -d" " -f1)"' \;

  layersSizes=($(find $imageDir -name "*.tar" -exec ls -l {} \; | awk '{print $5}'))

  for i in "${!layersNames[@]}"; do
    echo "{
         "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
         "size": ${layersSizes[$i]},
         "digest": \"sha256:${layersNames[$i]}\"
      }," >> $manifestFile
  done
  # remove last ','
  truncate -s-2 $manifestFile
  # add closing brakets to keep json consistent
  printf "\n\t]\n}" >> $manifestFile
}

# calc config sha 256 sum and add info about it to manifest
function setConfigProps() {
  configSize=$(ls -l $configFile | awk '{print $5}')
  configName=$(basename $configFile | cut -d"." -f1)

  sed -i "s/config_size/$configSize/g; s/config_hash/$configName/g" $manifestFile
}

#prepare manifest file
prepareLayersForUpload
setConfigProps
cat $manifestFile

# initiate upload and get uuid
uuid=$(curl -s -X POST -I "$url/v2/$repoName/blobs/uploads/" | grep -oP "(?<=Docker-Upload-Uuid: ).+")

# patch layers
# in data-binary we're getting absolute path to layer file
for l in "${!layersNames[@]}"; do
  pathToLayer=$(find $imageDir -name ${layersNames[$l]} -exec readlink -f {} \;)
    curl -v -X PATCH "$url/v2/$repoName/blobs/uploads/$uuid" \
  -H "Content-Length: ${layersSizes[$i]}" \
  -H "Content-Type: application/octet-stream" \
  --data-binary "@$pathToLayer"

# put layer
  curl -v -X PUT "$url/v2/$repoName/blobs/uploads/$uuid?digest=sha256:${layersNames[$i]}" \
  -H 'Content-Type: application/octet-stream' \
  -H "Content-Length: ${layersSizes[$i]}" \
  --data-binary "@$pathToLayer"
done

# patch and put config after all layers
curl -v -X PATCH "$url/v2/$repoName/blobs/uploads/$uuid" \
  -H "Content-Length: $configSize" \
  -H "Content-Type: application/octet-stream" \
  --data-binary "@$configFile"

  curl -v -X PUT "$url/v2/$repoName/blobs/uploads/$uuid?digest=sha256:$configName" \
  -H 'Content-Type: application/octet-stream' \
  -H "Content-Length: $configSize" \
  --data-binary "@$configFile"

# put manifest
curl -v -X PUT "$url/v2/$repoName/manifests/$tag" \
  -H 'Content-Type: application/vnd.docker.distribution.manifest.v2+json' \
  --data-binary "@$manifestFile"

exit 0

we can use a ready-made script:

./uploadImage.sh "~/path/to/saved/image" "http://localhost:8081/link/to/docker/registry" myRepoName 1.0

The article used GNU version tools.

In general, the article does not discover America, but slightly structures the disparate data and supplements the gaps in the documentation. Thank you for reading.