llm: do not silently fail for supplied, but invalid formats (#8130)

Changes in #8002 introduced fixes for bugs with mangling JSON Schemas.
It also fixed a bug where the server would silently fail when clients
requested invalid formats. It also, unfortunately, introduced a bug
where the server would reject requests with an empty format, which
should be allowed.

The change in #8127 updated the code to allow the empty format, but also
reintroduced the regression where the server would silently fail when
the format was set, but invalid.

This commit fixes both regressions. The server does not reject the empty
format, but it does reject invalid formats. It also adds tests to help
us catch regressions in the future.

Also, the updated code provides a more detailed error message when a
client sends a non-empty, but invalid format, echoing the invalid format
in the response.

This commits also takes the opportunity to remove superfluous linter
checks.

.golangci.yaml

@@ -8,8 +8,6 @@ linters:
     - containedctx
     - contextcheck
     - errcheck
-    - exportloopref
-    - gci
     - gocheckcompilerdirectives
     - gofmt
     - gofumpt
@@ -30,8 +28,6 @@ linters:
     - wastedassign
     - whitespace
 linters-settings:
-  gci:
-    sections: [standard, default, localmodule]
   staticcheck:
     checks:
       - all

llm/server.go

@@ -674,21 +674,6 @@ type CompletionResponse struct {
 }
 
 func (s *llmServer) Completion(ctx context.Context, req CompletionRequest, fn func(CompletionResponse)) error {
-	if err := s.sem.Acquire(ctx, 1); err != nil {
-		if errors.Is(err, context.Canceled) {
-			slog.Info("aborting completion request due to client closing the connection")
-		} else {
-			slog.Error("Failed to acquire semaphore", "error", err)
-		}
-		return err
-	}
-	defer s.sem.Release(1)
-
-	// put an upper limit on num_predict to avoid the model running on forever
-	if req.Options.NumPredict < 0 || req.Options.NumPredict > 10*s.options.NumCtx {
-		req.Options.NumPredict = 10 * s.options.NumCtx
-	}
-
 	request := map[string]any{
 		"prompt":            req.Prompt,
 		"stream":            true,
@@ -714,6 +699,39 @@ func (s *llmServer) Completion(ctx context.Context, req CompletionRequest, fn fu
 		"cache_prompt":      true,
 	}
 
+	if len(req.Format) > 0 {
+		switch {
+		case bytes.Equal(req.Format, []byte(`""`)):
+			// fallthrough
+		case bytes.Equal(req.Format, []byte(`"json"`)):
+			request["grammar"] = grammarJSON
+		case bytes.HasPrefix(req.Format, []byte("{")):
+			// User provided a JSON schema
+			g := llama.SchemaToGrammar(req.Format)
+			if g == nil {
+				return fmt.Errorf("invalid JSON schema in format")
+			}
+			request["grammar"] = string(g)
+		default:
+			return fmt.Errorf("invalid format: %q; expected \"json\" or a valid JSON Schema", req.Format)
+		}
+	}
+
+	if err := s.sem.Acquire(ctx, 1); err != nil {
+		if errors.Is(err, context.Canceled) {
+			slog.Info("aborting completion request due to client closing the connection")
+		} else {
+			slog.Error("Failed to acquire semaphore", "error", err)
+		}
+		return err
+	}
+	defer s.sem.Release(1)
+
+	// put an upper limit on num_predict to avoid the model running on forever
+	if req.Options.NumPredict < 0 || req.Options.NumPredict > 10*s.options.NumCtx {
+		req.Options.NumPredict = 10 * s.options.NumCtx
+	}
+
 	// Make sure the server is ready
 	status, err := s.getServerStatusRetry(ctx)
 	if err != nil {
@@ -722,16 +740,6 @@ func (s *llmServer) Completion(ctx context.Context, req CompletionRequest, fn fu
 		return fmt.Errorf("unexpected server status: %s", status.ToString())
 	}
 
-	if bytes.Equal(req.Format, []byte(`"json"`)) {
-		request["grammar"] = grammarJSON
-	} else if bytes.HasPrefix(req.Format, []byte("{")) {
-		g := llama.SchemaToGrammar(req.Format)
-		if g == nil {
-			return fmt.Errorf("invalid JSON schema in format")
-		}
-		request["grammar"] = string(g)
-	}
-
 	// Handling JSON marshaling with special characters unescaped.
 	buffer := &bytes.Buffer{}
 	enc := json.NewEncoder(buffer)

llm/server_test.go

@@ -0,0 +1,63 @@
+package llm
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/ollama/ollama/api"
+	"golang.org/x/sync/semaphore"
+)
+
+func TestLLMServerCompletionFormat(t *testing.T) {
+	// This test was written to fix an already deployed issue. It is a bit
+	// of a mess, and but it's good enough, until we can refactoring the
+	// Completion method to be more testable.
+
+	ctx, cancel := context.WithCancel(context.Background())
+	s := &llmServer{
+		sem: semaphore.NewWeighted(1), // required to prevent nil panic
+	}
+
+	checkInvalid := func(format string) {
+		t.Helper()
+		err := s.Completion(ctx, CompletionRequest{
+			Options: new(api.Options),
+			Format:  []byte(format),
+		}, nil)
+
+		want := fmt.Sprintf("invalid format: %q; expected \"json\" or a valid JSON Schema", format)
+		if err == nil || !strings.Contains(err.Error(), want) {
+			t.Fatalf("err = %v; want %q", err, want)
+		}
+	}
+
+	checkInvalid("X")   // invalid format
+	checkInvalid(`"X"`) // invalid JSON Schema
+
+	cancel() // prevent further processing if request makes it past the format check
+
+	checkCanceled := func(err error) {
+		t.Helper()
+		if !errors.Is(err, context.Canceled) {
+			t.Fatalf("Completion: err = %v; expected context.Canceled", err)
+		}
+	}
+
+	valids := []string{`"json"`, `{"type":"object"}`, ``, `""`}
+	for _, valid := range valids {
+		err := s.Completion(ctx, CompletionRequest{
+			Options: new(api.Options),
+			Format:  []byte(valid),
+		}, nil)
+		checkCanceled(err)
+	}
+
+	err := s.Completion(ctx, CompletionRequest{
+		Options: new(api.Options),
+		Format:  nil, // missing format
+	}, nil)
+	checkCanceled(err)
+}