cmd: support OLLAMA_CLIENT_HOST environment variable (#262)

* cmd: support OLLAMA_HOST environment variable

This commit adds support for the OLLAMA_HOST environment
variable. This variable can be used to specify the host to which
the client should connect. This is useful when the client is
running somewhere other than the host where the server is running.

The new api.FromEnv function is used to read configure clients from the
environment. Clients wishing to use the environment variable being
consistent with the Ollama CLI can use this new function.

* Update api/client.go

Co-authored-by: Jeffrey Morgan <jmorganca@gmail.com>

* Update api/client.go

Co-authored-by: Jeffrey Morgan <jmorganca@gmail.com>

---------

Co-authored-by: Jeffrey Morgan <jmorganca@gmail.com>

api/client.go

@@ -9,10 +9,17 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"os"
+)
+
+const DefaultHost = "localhost:11434"
+
+var (
+	envHost = os.Getenv("OLLAMA_HOST")
 )
 
 type Client struct {
-	base    url.URL
+	Base    url.URL
 	HTTP    http.Client
 	Headers http.Header
 }
@@ -33,14 +40,34 @@ func checkError(resp *http.Response, body []byte) error {
 	return apiError
 }
 
+// Host returns the default host to use for the client. It is determined in the following order:
+// 1. The OLLAMA_HOST environment variable
+// 2. The default host (localhost:11434)
+func Host() string {
+	if envHost != "" {
+		return envHost
+	}
+	return DefaultHost
+}
+
+// FromEnv creates a new client using Host() as the host. An error is returns
+// if the host is invalid.
+func FromEnv() (*Client, error) {
+	u, err := url.Parse(Host())
+	if err != nil {
+		return nil, err
+	}
+	return &Client{Base: *u}, nil
+}
+
 func NewClient(hosts ...string) *Client {
-	host := "127.0.0.1:11434"
+	host := DefaultHost
 	if len(hosts) > 0 {
 		host = hosts[0]
 	}
 
 	return &Client{
-		base: url.URL{Scheme: "http", Host: host},
+		Base: url.URL{Scheme: "http", Host: host},
 		HTTP: http.Client{},
 	}
 }
@@ -57,7 +84,7 @@ func (c *Client) do(ctx context.Context, method, path string, reqData, respData
 		reqBody = bytes.NewReader(data)
 	}
 
-	url := c.base.JoinPath(path).String()
+	url := c.Base.JoinPath(path).String()
 
 	req, err := http.NewRequestWithContext(ctx, method, url, reqBody)
 	if err != nil {
@@ -105,7 +132,7 @@ func (c *Client) stream(ctx context.Context, method, path string, data any, fn f
 		buf = bytes.NewBuffer(bts)
 	}
 
-	request, err := http.NewRequestWithContext(ctx, method, c.base.JoinPath(path).String(), buf)
+	request, err := http.NewRequestWithContext(ctx, method, c.Base.JoinPath(path).String(), buf)
 	if err != nil {
 		return err
 	}