Merge #4456

4456: Add Ollama as an embeddings provider r=dureuill a=jakobklemm

# Pull Request

## Related issue
[Related Discord Thread](https://discord.com/channels/1006923006964154428/1211977150316683305)

## What does this PR do?
- Adds Ollama as a provider of Embeddings besides HuggingFace and OpenAI under the name `ollama`
- Adds the environment variable `MEILI_OLLAMA_URL` to set the embeddings URL of an Ollama instance with a default value of `http://localhost:11434/api/embeddings` if no variable is set
- Changes some of the structs and functions in `openai.rs` to be public so that they can be shared.
- Added more error variants for Ollama specific errors
- It uses the model `nomic-embed-text` as default, but any string value is allowed, however it won't automatically check if the model actually exists or is an embedding model

Tested against Ollama version `v0.1.27` and the `nomic-embed-text` model.

## PR checklist
Please check if your PR fulfills the following requirements:
- [x] Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
- [x] Have you read the contributing guidelines?
- [x] Have you made sure that the title is accurate and descriptive of the changes?

Co-authored-by: Jakob Klemm <jakob@jeykey.net>
Co-authored-by: Louis Dureuil <louis.dureuil@gmail.com>

milli/src/vector/error.rs

@@ -2,6 +2,7 @@ use std::path::PathBuf;
 
 use hf_hub::api::sync::ApiError;
 
+use super::ollama::OllamaError;
 use crate::error::FaultSource;
 use crate::vector::openai::OpenAiError;
 
@@ -71,6 +72,17 @@ pub enum EmbedErrorKind {
     OpenAiRuntimeInit(std::io::Error),
     #[error("initializing web client for sending embedding requests failed: {0}")]
     InitWebClient(reqwest::Error),
+    // Dedicated Ollama error kinds, might have to merge them into one cohesive error type for all backends.
+    #[error("unexpected response from Ollama: {0}")]
+    OllamaUnexpected(reqwest::Error),
+    #[error("sent too many requests to Ollama: {0}")]
+    OllamaTooManyRequests(OllamaError),
+    #[error("received internal error from Ollama: {0}")]
+    OllamaInternalServerError(OllamaError),
+    #[error("model not found. Meilisearch will not automatically download models from the Ollama library, please pull the model manually: {0}")]
+    OllamaModelNotFoundError(OllamaError),
+    #[error("received unhandled HTTP status code {0} from Ollama")]
+    OllamaUnhandledStatusCode(u16),
 }
 
 impl EmbedError {
@@ -129,6 +141,26 @@ impl EmbedError {
     pub fn openai_initialize_web_client(inner: reqwest::Error) -> Self {
         Self { kind: EmbedErrorKind::InitWebClient(inner), fault: FaultSource::Runtime }
     }
+
+    pub(crate) fn ollama_unexpected(inner: reqwest::Error) -> EmbedError {
+        Self { kind: EmbedErrorKind::OllamaUnexpected(inner), fault: FaultSource::Bug }
+    }
+
+    pub(crate) fn ollama_model_not_found(inner: OllamaError) -> EmbedError {
+        Self { kind: EmbedErrorKind::OllamaModelNotFoundError(inner), fault: FaultSource::User }
+    }
+
+    pub(crate) fn ollama_too_many_requests(inner: OllamaError) -> EmbedError {
+        Self { kind: EmbedErrorKind::OllamaTooManyRequests(inner), fault: FaultSource::Runtime }
+    }
+
+    pub(crate) fn ollama_internal_server_error(inner: OllamaError) -> EmbedError {
+        Self { kind: EmbedErrorKind::OllamaInternalServerError(inner), fault: FaultSource::Runtime }
+    }
+
+    pub(crate) fn ollama_unhandled_status_code(code: u16) -> EmbedError {
+        Self { kind: EmbedErrorKind::OllamaUnhandledStatusCode(code), fault: FaultSource::Bug }
+    }
 }
 
 #[derive(Debug, thiserror::Error)]
@@ -195,6 +227,13 @@ impl NewEmbedderError {
         }
     }
 
+    pub fn ollama_could_not_determine_dimension(inner: EmbedError) -> NewEmbedderError {
+        Self {
+            kind: NewEmbedderErrorKind::CouldNotDetermineDimension(inner),
+            fault: FaultSource::User,
+        }
+    }
+
     pub fn openai_invalid_api_key_format(inner: reqwest::header::InvalidHeaderValue) -> Self {
         Self { kind: NewEmbedderErrorKind::InvalidApiKeyFormat(inner), fault: FaultSource::User }
     }