[Frontend]: Support base64 embedding (#5935)

Co-authored-by: Cyrus Leung <cyrus.tl.leung@gmail.com>

tests/entrypoints/openai/test_embedding.py

@@ -1,3 +1,6 @@
+import base64
+
+import numpy as np
 import openai
 import pytest
 import ray
@@ -109,3 +112,33 @@ async def test_batch_embedding(embedding_client: openai.AsyncOpenAI,
     assert embeddings.usage.completion_tokens == 0
     assert embeddings.usage.prompt_tokens == 17
     assert embeddings.usage.total_tokens == 17
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "model_name",
+    [EMBEDDING_MODEL_NAME],
+)
+async def test_batch_base64_embedding(embedding_client: openai.AsyncOpenAI,
+                                      model_name: str):
+    input_texts = [
+        "Hello my name is",
+        "The best thing about vLLM is that it supports many different models"
+    ]
+
+    responses_float = await embedding_client.embeddings.create(
+        input=input_texts, model=model_name, encoding_format="float")
+
+    responses_base64 = await embedding_client.embeddings.create(
+        input=input_texts, model=model_name, encoding_format="base64")
+
+    decoded_responses_base64_data = []
+    for data in responses_base64.data:
+        decoded_responses_base64_data.append(
+            np.frombuffer(base64.b64decode(data.embedding),
+                          dtype="float").tolist())
+
+    assert responses_float.data[0].embedding == decoded_responses_base64_data[
+        0]
+    assert responses_float.data[1].embedding == decoded_responses_base64_data[
+        1]