server: allow mixed-case model names on push, pull, cp, and create (#7676)

This change allows for mixed-case model names to be pushed, pulled,
copied, and created, which was previously disallowed because the Ollama
registry was backed by a Docker registry that enforced a naming
convention that disallowed mixed-case names, which is no longer the
case.

This does not break existing, intended, behaviors.

Also, make TestCase test a story of creating, updating, pulling, and
copying a model with case variations, ensuring the model's manifest is
updated correctly, and not duplicated across different files with
different case variations.

server/images.go

@@ -13,6 +13,7 @@ import (
 	"io"
 	"log"
 	"log/slog"
+	"net"
 	"net/http"
 	"net/url"
 	"os"
@@ -1071,6 +1072,21 @@ func makeRequestWithRetry(ctx context.Context, method string, requestURL *url.UR
 	return nil, errUnauthorized
 }
 
+// testMakeRequestDialContext specifies the dial function for the http client in
+// makeRequest. It can be used to resolve hosts in model names to local
+// addresses for testing. For example, the model name ("example.com/my/model")
+// can be directed to push/pull from "127.0.0.1:1234".
+//
+// This is not safe to set across goroutines. It should be set in
+// the main test goroutine, and not by tests marked to run in parallel with
+// t.Parallel().
+//
+// It should be cleared after use, otherwise it will affect other tests.
+//
+// Ideally we would have some set this up the stack, but the code is not
+// structured in a way that makes this easy, so this will have to do for now.
+var testMakeRequestDialContext func(ctx context.Context, network, addr string) (net.Conn, error)
+
 func makeRequest(ctx context.Context, method string, requestURL *url.URL, headers http.Header, body io.Reader, regOpts *registryOptions) (*http.Response, error) {
 	if requestURL.Scheme != "http" && regOpts != nil && regOpts.Insecure {
 		requestURL.Scheme = "http"
@@ -1105,6 +1121,9 @@ func makeRequest(ctx context.Context, method string, requestURL *url.URL, header
 	}
 
 	resp, err := (&http.Client{
+		Transport: &http.Transport{
+			DialContext: testMakeRequestDialContext,
+		},
 		CheckRedirect: regOpts.CheckRedirect,
 	}).Do(req)
 	if err != nil {