display layer mediaType

[azr]

What would you like to be added:

The mediaType for a layer. on top of digest and command

Why is this needed:

Performances improvements.

Additional context:

I recently discovered that everything is faster with zstd, and I want to check the media type of all the layers of an image. And also, if possible the compression level setting.

[azr]

In the meantime, I used this:

#!/bin/bash

# Check if image name is provided
if [ $# -eq 0 ]; then
    echo "Usage: $0 <image-name>"
    exit 1
fi

IMAGE=$1

# Function to get media types and sizes
get_media_info() {
    local manifest=$1
    local config_media=$(jq -r '.config.mediaType' <<< "$manifest")
    local config_size=$(jq -r '.config.size' <<< "$manifest")
    echo "Config:"
    echo "  mediaType: $config_media"
    echo "  size:      $config_size bytes"
    echo "Layers:"
    jq -r '.layers[] | "  \(.mediaType)\n    size: \(.size) bytes"' <<< "$manifest"
}

# Function to clean image reference
clean_image_ref() {
    local img=$1
    if [[ "$img" == *@* ]]; then
        echo "${img%@*}"
    elif [[ "$img" == *:* ]]; then
        echo "${img%:*}"
    else
        echo "$img"
    fi
}

# Get initial manifest
MANIFEST=$(skopeo inspect --raw "docker://$IMAGE")
MEDIA_TYPE=$(jq -r '.mediaType // empty' <<< "$MANIFEST")

# Handle manifest lists/indexes
if [[ $MEDIA_TYPE == "application/vnd.docker.distribution.manifest.list.v2+json" ]] ||
   [[ $MEDIA_TYPE == "application/vnd.oci.image.index.v1+json" ]]; then
    echo "Found manifest list/index, searching for linux/amd64..."
    DIGEST=$(jq -r '.manifests[] | select(.platform.architecture == "amd64" and .platform.os == "linux").digest' <<< "$MANIFEST")

    if [ -z "$DIGEST" ]; then
        echo "No linux/amd64 platform found in manifest list"
        exit 1
    fi

    # Clean image reference and add digest
    CLEAN_REF=$(clean_image_ref "$IMAGE")
    NEW_REF="${CLEAN_REF}@${DIGEST}"
    echo "Fetching image manifest for digest: $DIGEST"
    MANIFEST=$(skopeo inspect --raw "docker://$NEW_REF")
fi

# Process the final manifest
MEDIA_TYPE=$(jq -r '.mediaType // empty' <<< "$MANIFEST")
if [[ $MEDIA_TYPE == "application/vnd.docker.distribution.manifest.v2+json" ]] ||
   [[ $MEDIA_TYPE == "application/vnd.oci.image.manifest.v1+json" ]]; then
    get_media_info "$MANIFEST"
else
    echo "Unsupported manifest media type: $MEDIA_TYPE"
    exit 1
fi

> ./docker-inspect.sh nvidia/cuda:12.3.2-cudnn9-devel-ubuntu22.04
Found manifest list/index, searching for linux/amd64...
Fetching image manifest for digest: sha256:4f00d5116a3679bab6bc13318c8555d7207206de2318e77348a9a93f66e73e21
Config:
  mediaType: application/vnd.docker.container.image.v1+json
  size:      19684 bytes
Layers:
  application/vnd.docker.image.rootfs.diff.tar.gzip
    size: 29536188 bytes
  application/vnd.docker.image.rootfs.diff.tar.gzip
    size: 4622976 bytes
  application/vnd.docker.image.rootfs.diff.tar.gzip
    size: 57074219 bytes
  application/vnd.docker.image.rootfs.diff.tar.gzip
    size: 185 bytes
  application/vnd.docker.image.rootfs.diff.tar.gzip
    size: 6886 bytes
  application/vnd.docker.image.rootfs.diff.tar.gzip
    size: 1287119340 bytes
  application/vnd.docker.image.rootfs.diff.tar.gzip
    size: 63930 bytes
  application/vnd.docker.image.rootfs.diff.tar.gzip
    size: 1684 bytes
  application/vnd.docker.image.rootfs.diff.tar.gzip
    size: 1522 bytes
  application/vnd.docker.image.rootfs.diff.tar.gzip
    size: 2569340468 bytes
  application/vnd.docker.image.rootfs.diff.tar.gzip
    size: 88605 bytes
  application/vnd.docker.image.rootfs.diff.tar.gzip
    size: 675297436 bytes