write_file improvements

main_test.go

@@ -2389,3 +2389,139 @@ func TestSanitizeMessagesCleansReasoningContent(t *testing.T) {
   }
 }
 
+func TestWriteFileOmittedOrZeroOffsetDoesNotAppend(t *testing.T) {
+  tmp := t.TempDir()
+  target := filepath.Join(tmp, "test.txt")
+
+  // Create file with initial content
+  if err := os.WriteFile(target, []byte("EXISTING"), 0644); err != nil {
+    t.Fatalf("failed to write initial file: %v", err)
+  }
+
+  // 1. Direct writeFile with offset 0: writes starting at offset 0, does NOT append
+  res, err := writeFile(target, 0, 0, "PREFIX_")
+  if err != nil {
+    t.Fatalf("writeFile: %v", err)
+  }
+  if !strings.Contains(res, "Successfully wrote 7 bytes") {
+    t.Errorf("unexpected res: %q", res)
+  }
+  data, err := os.ReadFile(target)
+  if err != nil {
+    t.Fatalf("readFile: %v", err)
+  }
+  if string(data) != "PREFIX_EXISTING" {
+    t.Errorf("expected 'PREFIX_EXISTING', got %q", string(data))
+  }
+
+  // 2. AL tool dispatch with offset omitted completely: must start writing at offset 0, NOT append
+  srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+    var req struct {
+      Messages []Message `json:"messages"`
+    }
+    json.NewDecoder(r.Body).Decode(&req)
+    for _, m := range req.Messages {
+      if m.Role == "tool" {
+        w.Write([]byte(`{"choices":[{"message":{"role":"assistant","content":"done"}}]}`))
+        return
+      }
+    }
+    // Tool call without "offset" parameter
+    args, _ := json.Marshal(map[string]any{
+      "path":    target,
+      "content": "START_",
+    })
+    w.Write([]byte(fmt.Sprintf(`{"choices":[{"message":{"role":"assistant","content":null,"tool_calls":[{"id":"c1","type":"function","function":{"name":"write_file","arguments":%s}}]}}]}`, strconv.Quote(string(args)))))
+  }))
+  defer srv.Close()
+
+  cfg := defCfg
+  cfg.Endpoint = srv.URL
+  cfg.Stream = false
+  cfg.APIKey = "-"
+  _, _, err = AL(context.Background(), &cfg, []Message{{Role: "user", Content: strp("write")}})
+  if err != nil {
+    t.Fatalf("AL: %v", err)
+  }
+
+  data, err = os.ReadFile(target)
+  if err != nil {
+    t.Fatalf("readFile: %v", err)
+  }
+  if string(data) != "START_PREFIX_EXISTING" {
+    t.Errorf("expected 'START_PREFIX_EXISTING', got %q", string(data))
+  }
+
+  // 3. AL tool dispatch with explicit offset: 0
+  srv2 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+    var req struct {
+      Messages []Message `json:"messages"`
+    }
+    json.NewDecoder(r.Body).Decode(&req)
+    for _, m := range req.Messages {
+      if m.Role == "tool" {
+        w.Write([]byte(`{"choices":[{"message":{"role":"assistant","content":"done"}}]}`))
+        return
+      }
+    }
+    args, _ := json.Marshal(map[string]any{
+      "path":      target,
+      "offset":    0,
+      "del_bytes": 0,
+      "content":   "ZERO_",
+    })
+    w.Write([]byte(fmt.Sprintf(`{"choices":[{"message":{"role":"assistant","content":null,"tool_calls":[{"id":"c1","type":"function","function":{"name":"write_file","arguments":%s}}]}}]}`, strconv.Quote(string(args)))))
+  }))
+  defer srv2.Close()
+
+  cfg.Endpoint = srv2.URL
+  _, _, err = AL(context.Background(), &cfg, []Message{{Role: "user", Content: strp("write zero")}})
+  if err != nil {
+    t.Fatalf("AL: %v", err)
+  }
+
+  data, err = os.ReadFile(target)
+  if err != nil {
+    t.Fatalf("readFile: %v", err)
+  }
+  if string(data) != "ZERO_START_PREFIX_EXISTING" {
+    t.Errorf("expected 'ZERO_START_PREFIX_EXISTING', got %q", string(data))
+  }
+
+  // 4. AL tool dispatch with offset: null
+  srv3 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+    var req struct {
+      Messages []Message `json:"messages"`
+    }
+    json.NewDecoder(r.Body).Decode(&req)
+    for _, m := range req.Messages {
+      if m.Role == "tool" {
+        w.Write([]byte(`{"choices":[{"message":{"role":"assistant","content":"done"}}]}`))
+        return
+      }
+    }
+    args, _ := json.Marshal(map[string]any{
+      "path":    target,
+      "offset":  nil,
+      "content": "NULL_",
+    })
+    w.Write([]byte(fmt.Sprintf(`{"choices":[{"message":{"role":"assistant","content":null,"tool_calls":[{"id":"c1","type":"function","function":{"name":"write_file","arguments":%s}}]}}]}`, strconv.Quote(string(args)))))
+  }))
+  defer srv3.Close()
+
+  cfg.Endpoint = srv3.URL
+  _, _, err = AL(context.Background(), &cfg, []Message{{Role: "user", Content: strp("write null")}})
+  if err != nil {
+    t.Fatalf("AL: %v", err)
+  }
+
+  data, err = os.ReadFile(target)
+  if err != nil {
+    t.Fatalf("readFile: %v", err)
+  }
+  if string(data) != "NULL_ZERO_START_PREFIX_EXISTING" {
+    t.Errorf("expected 'NULL_ZERO_START_PREFIX_EXISTING', got %q", string(data))
+  }
+}
+
+