feat(oci): support OCI images and Ollama models (#2628)

* Support specifying oci:// and ollama:// for model URLs

Fixes: https://github.com/mudler/LocalAI/issues/2527
Fixes: https://github.com/mudler/LocalAI/issues/1028

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* Lower watcher warnings

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* Allow to install ollama models from CLI

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* fixup tests

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* Do not keep file ownership

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* Skip test on darwin

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

---------

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

pkg/oci/ollama.go

@@ -0,0 +1,88 @@
+package oci
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+// Define the main struct for the JSON data
+type Manifest struct {
+	SchemaVersion int           `json:"schemaVersion"`
+	MediaType     string        `json:"mediaType"`
+	Config        Config        `json:"config"`
+	Layers        []LayerDetail `json:"layers"`
+}
+
+// Define the struct for the "config" section
+type Config struct {
+	Digest    string `json:"digest"`
+	MediaType string `json:"mediaType"`
+	Size      int    `json:"size"`
+}
+
+// Define the struct for each item in the "layers" array
+type LayerDetail struct {
+	Digest    string `json:"digest"`
+	MediaType string `json:"mediaType"`
+	Size      int    `json:"size"`
+}
+
+func OllamaModelManifest(image string) (*Manifest, error) {
+	// parse the repository and tag from `image`. `image` should be for e.g. gemma:2b, or foobar/gemma:2b
+
+	// if there is a : in the image, then split it
+	// if there is no : in the image, then assume it is the latest tag
+	tag, repository, image := ParseImageParts(image)
+
+	// get e.g. https://registry.ollama.ai/v2/library/llama3/manifests/latest
+	req, err := http.NewRequest("GET", "https://registry.ollama.ai/v2/"+repository+"/"+image+"/manifests/"+tag, nil)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Accept", "application/vnd.docker.distribution.manifest.v2+json")
+	client := &http.Client{}
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+
+	// parse the JSON response
+	var manifest Manifest
+	err = json.NewDecoder(resp.Body).Decode(&manifest)
+	if err != nil {
+		return nil, err
+	}
+
+	return &manifest, nil
+}
+
+func OllamaModelBlob(image string) (string, error) {
+	manifest, err := OllamaModelManifest(image)
+	if err != nil {
+		return "", err
+	}
+	// find a application/vnd.ollama.image.model in the mediaType
+
+	for _, layer := range manifest.Layers {
+		if layer.MediaType == "application/vnd.ollama.image.model" {
+			return layer.Digest, nil
+		}
+	}
+
+	return "", nil
+}
+
+func OllamaFetchModel(image string, output string, statusWriter func(ocispec.Descriptor) io.Writer) error {
+	_, repository, imageNoTag := ParseImageParts(image)
+
+	blobID, err := OllamaModelBlob(image)
+	if err != nil {
+		return err
+	}
+
+	return FetchImageBlob(fmt.Sprintf("registry.ollama.ai/%s/%s", repository, imageNoTag), blobID, output, statusWriter)
+}