server : Support multimodal completion and embeddings prompts in JSON format (#15108)

- Use server_tokens in more places in server and util.cpp
- Convert most functions that used llama_tokens to server_tokens
- Modify input tokenizer to handle JSON objects as subprompts
- Break out MTMD prompt parsing into utility function
- Support JSON objects with multimodal_data arrays for MTMD prompts along with other existing types
- Add capability to model endpoint to indicate if client can send multimodal data
- Add tests.

tools/server/tests/unit/test_completion.py

@@ -6,6 +6,8 @@ from utils import *
 
 server = ServerPreset.tinyllama2()
 
+JSON_MULTIMODAL_KEY = "multimodal_data"
+JSON_PROMPT_STRING_KEY = "prompt_string"
 
 @pytest.fixture(autouse=True)
 def create_server():
@@ -231,6 +233,28 @@ def test_nocache_long_input_prompt():
     })
     assert res.status_code == 400
 
+def test_json_prompt_no_mtmd():
+    global server
+    server.start()
+    res = server.make_request("POST", "/completion", data={
+        "prompt": { JSON_PROMPT_STRING_KEY: "I believe the meaning of life is" },
+        "seed": 42,
+        "temperature": 1.0,
+        "cache_prompt": False,
+    })
+    assert res.status_code == 200
+
+def test_json_prompt_mtm_error_when_not_supported():
+    global server
+    server.start()
+    res = server.make_request("POST", "/completion", data={
+        "prompt": { JSON_PROMPT_STRING_KEY: "I believe the meaning of life is <__media__>", JSON_MULTIMODAL_KEY: "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk+A8AAQUBAScY42YAAAAASUVORK5CYII=" },
+        "seed": 42,
+        "temperature": 1.0,
+        "cache_prompt": False,
+    })
+    # MTMD is disabled on this model, so this should fail.
+    assert res.status_code != 200
 
 def test_completion_with_tokens_input():
     global server
@@ -269,6 +293,20 @@ def test_completion_with_tokens_input():
     assert len(res.body) == 2
     assert res.body[0]["content"] == res.body[1]["content"]
 
+    # mixed JSON and tokens
+    res = server.make_request("POST", "/completion", data={
+        "prompt": [
+            tokens,
+            {
+                JSON_PROMPT_STRING_KEY: "I believe the meaning of life is",
+            },
+        ],
+    })
+    assert res.status_code == 200
+    assert type(res.body) == list
+    assert len(res.body) == 2
+    assert res.body[0]["content"] == res.body[1]["content"]
+
     # mixed string and tokens in one sequence
     res = server.make_request("POST", "/completion", data={
         "prompt": [1, 2, 3, 4, 5, 6, prompt_str, 7, 8, 9, 10, prompt_str],