repeated "content-type" in headers when send https request to models api

[chench53]

Describe the bug
When sending a request to the api point of a model, the "content-type" will be repeated twice, like this following:

POST /compatible-mode/v1/embeddings HTTP/1.1
content-type: application/json
content-type: application/json
authorization: Bearer sk-abc
accept: /
host: dashscope.aliyuncs.com
content-length: 53

{"input":["hello Tabby"],"model":"text-embedding-v3"}

This may cause the model http api providers return an error.

Information about your version
tabby 0.26.0

Information about your GPU
(I use remote model http api, so I think it is irrelevant)
NVIDIA-SMI 470.141.03 Driver Version: 470.141.03 CUDA Version: 11.4

Additional context
Some model http api providers may require very strict http schema, even they claim the apis are compatible with openai.
This could happen when use alibaba cloud model studio. I found the alibaba embedding model api keep returning errors. After remove the redundant content-type in requests, the api works fine.

In this code snippet in file /crates/http-api-bindings/src/embedding/openai.rs:

        let request_builder = self
            .client
            .post(&self.api_endpoint)
            .json(&request)
            .header("content-type", "application/json")
            .bearer_auth(&self.api_key);

I don't think the line .header("content-type", "application/json") is necessary, because the header "content-type" is already set to "application/json" by the previous .json(&request), Check this json function in reqwest:

    pub fn json<T: Serialize + ?Sized>(mut self, json: &T) -> RequestBuilder {
        let mut error = None;
        if let Ok(ref mut req) = self.request {
            match serde_json::to_vec(json) {
                Ok(body) => {
                    if !req.headers().contains_key(CONTENT_TYPE) {
                        req.headers_mut()
                            .insert(CONTENT_TYPE, HeaderValue::from_static("application/json"));
                    }
                    *req.body_mut() = Some(body.into());
                }
                Err(err) => error = Some(crate::error::builder(err)),
            }
        }
        if let Some(err) = error {
            self.request = Err(err);
        }
        self
    }

Or you can put .header("content-type", "application/json") before the .json function.

Maybe it exist for some compatibility reasons?

[wsxiaoys]

Thank you for reporting the bug. It appears that the simplest solution is to remove the line .header("content-type", "application/json")