community[minor]: llamafile embeddings support (#17976)

* **Description:** adds `LlamafileEmbeddings` class implementation for
generating embeddings using
[llamafile](https://github.com/Mozilla-Ocho/llamafile)-based models.
Includes related unit tests and notebook showing example usage.
* **Issue:** N/A
* **Dependencies:** N/A

libs/community/langchain_community/embeddings/llamafile.py

@@ -0,0 +1,119 @@
+import logging
+from typing import List, Optional
+
+import requests
+from langchain_core.embeddings import Embeddings
+from langchain_core.pydantic_v1 import BaseModel
+
+logger = logging.getLogger(__name__)
+
+
+class LlamafileEmbeddings(BaseModel, Embeddings):
+    """Llamafile lets you distribute and run large language models with a
+    single file.
+
+    To get started, see: https://github.com/Mozilla-Ocho/llamafile
+
+    To use this class, you will need to first:
+
+    1. Download a llamafile.
+    2. Make the downloaded file executable: `chmod +x path/to/model.llamafile`
+    3. Start the llamafile in server mode with embeddings enabled:
+
+        `./path/to/model.llamafile --server --nobrowser --embedding`
+
+    Example:
+        .. code-block:: python
+
+            from langchain_community.embeddings import LlamafileEmbeddings
+            embedder = LlamafileEmbeddings()
+            doc_embeddings = embedder.embed_documents(
+                [
+                    "Alpha is the first letter of the Greek alphabet",
+                    "Beta is the second letter of the Greek alphabet",
+                ]
+            )
+            query_embedding = embedder.embed_query(
+                "What is the second letter of the Greek alphabet"
+            )
+
+    """
+
+    base_url: str = "http://localhost:8080"
+    """Base url where the llamafile server is listening."""
+
+    request_timeout: Optional[int] = None
+    """Timeout for server requests"""
+
+    def _embed(self, text: str) -> List[float]:
+        try:
+            response = requests.post(
+                url=f"{self.base_url}/embedding",
+                headers={
+                    "Content-Type": "application/json",
+                },
+                json={
+                    "content": text,
+                },
+                timeout=self.request_timeout,
+            )
+        except requests.exceptions.ConnectionError:
+            raise requests.exceptions.ConnectionError(
+                f"Could not connect to Llamafile server. Please make sure "
+                f"that a server is running at {self.base_url}."
+            )
+
+        # Raise exception if we got a bad (non-200) response status code
+        response.raise_for_status()
+
+        contents = response.json()
+        if "embedding" not in contents:
+            raise KeyError(
+                "Unexpected output from /embedding endpoint, output dict "
+                "missing 'embedding' key."
+            )
+
+        embedding = contents["embedding"]
+
+        # Sanity check the embedding vector:
+        # Prior to llamafile v0.6.2, if the server was not started with the
+        # `--embedding` option, the embedding endpoint would always return a
+        # 0-vector. See issue:
+        # https://github.com/Mozilla-Ocho/llamafile/issues/243
+        # So here we raise an exception if the vector sums to exactly 0.
+        if sum(embedding) == 0.0:
+            raise ValueError(
+                "Embedding sums to 0, did you start the llamafile server with "
+                "the `--embedding` option enabled?"
+            )
+
+        return embedding
+
+    def embed_documents(self, texts: List[str]) -> List[List[float]]:
+        """Embed documents using a llamafile server running at `self.base_url`.
+        llamafile server should be started in a separate process before invoking
+        this method.
+
+        Args:
+            texts: The list of texts to embed.
+
+        Returns:
+            List of embeddings, one for each text.
+        """
+        doc_embeddings = []
+        for text in texts:
+            doc_embeddings.append(self._embed(text))
+        return doc_embeddings
+
+    def embed_query(self, text: str) -> List[float]:
+        """Embed a query using a llamafile server running at `self.base_url`.
+        llamafile server should be started in a separate process before invoking
+        this method.
+
+        Args:
+            text: The text to embed.
+
+        Returns:
+            Embeddings for the text.
+        """
+        return self._embed(text)