Improve error message when Ollama is not installed

Author: ccreutzi

+llms/+utils/errorMessageCatalog.m

@@ -77,4 +77,5 @@
 catalog("llms:unsupportedDatatypeInPrototype") = "Invalid data type ''{1}'' in prototype. Prototype must be a struct, composed of numerical, string, logical, categorical, or struct.";
 catalog("llms:incorrectResponseFormat") = "Invalid response format. Response format must be ""text"", ""json"", a struct, or a string with a JSON Schema definition.";
 catalog("llms:OllamaStructuredOutputNeeds05") = "Structured output is not supported for Ollama version {1}. Use version 0.5.0 or newer.";
+catalog("llms:noOllamaFound") = "Unable to connect to Ollama. Check that {1} is a valid endpoint and ensure that Ollama is installed and running.";
 end

ollamaChat.m

@@ -236,7 +236,7 @@
                 streamFun = this.StreamFun;
             end
 
-            try % just for nicer errors, reducing the stack depth shown
+            try
                 [text, message, response] = llms.internal.callOllamaChatAPI(...
                     nvp.ModelName, messagesStruct, this.FunctionsStruct, ...
                     Temperature=nvp.Temperature, ToolChoice=toolChoice, ...
@@ -247,6 +247,10 @@
                     TimeOut=nvp.TimeOut, StreamFun=streamFun, ...
                     Endpoint=nvp.Endpoint);
             catch e
+                if e.identifier == "MATLAB:webservices:ConnectionRefused"
+                    error("llms:noOllamaFound",llms.utils.errorMessageCatalog.getMessage("llms:noOllamaFound",nvp.Endpoint));
+                end
+                % for nicer errors, throw instead of rethrow, reducing the stack depth shown
                 throw(e);
             end 
 

tests/tollamaChat.m

@@ -277,6 +277,12 @@ function doReturnErrors(testCase)
             testCase.verifyError(@() generate(chat,"hi!"), "llms:apiReturnedError");
         end
 
+        function errorNoOllamaServer(testCase)
+            % we expect no server running on this port
+            chat = ollamaChat("mistral",Endpoint="127.0.0.1:11433");
+            testCase.verifyError(@() generate(chat,"hi!"), "llms:noOllamaFound");
+        end
+
         function invalidInputsConstructor(testCase, InvalidConstructorInput)
             testCase.verifyError(@() ollamaChat(testCase.defaultModelName, InvalidConstructorInput.Input{:}), InvalidConstructorInput.Error);
         end