Long Conversation Variable Descriptions Cause "Internal Server Error" When Editing Chatflow

[QuantumGhost]

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Dify version

1.8.1

Cloud or Self Hosted

Cloud

Steps to reproduce

Import the following DSL and edit it.

DSL

app:
  description: ''
  icon: 🤖
  icon_background: '#FFEAD5'
  mode: advanced-chat
  name: conversation variable desc length
  use_icon_as_answer_icon: false
dependencies:
- current_identifier: null
  type: marketplace
  value:
    marketplace_plugin_unique_identifier: langgenius/openai:0.1.0@539dc0dde8ecaa84e61b8eeb154c3bb7fbc9caa80afd83763dd5860a725d2742
kind: app
version: 0.4.0
workflow:
  conversation_variables:
  - description: =====94a7f93b7d03ac3405c3fb7da00705b65265f3f01620976a2fb22dbeb8e26ea77f1c4a54b052e6c02a5f03cf0a2dcc809dd80771bfe1401a4e7cf99aeae1f8fbf8692750b414ea541caa0c0816cce948f54812a1c33ce48b6d1f98024f103b9bcff6aaca2af723a6cc1c90fd8446db60588ff22a2ea1b443993fec7200a5f46474a9===
    id: 091bfe21-8e0e-4f2d-b1ef-5a9429d6b5b5
    name: test
    selector:
    - conversation
    - test
    value: '1234'
    value_type: string
  environment_variables: []
  features:
    file_upload:
      allowed_file_extensions:
      - .JPG
      - .JPEG
      - .PNG
      - .GIF
      - .WEBP
      - .SVG
      allowed_file_types:
      - image
      allowed_file_upload_methods:
      - local_file
      - remote_url
      enabled: false
      fileUploadConfig:
        audio_file_size_limit: 50
        batch_count_limit: 5
        file_size_limit: 15
        image_file_size_limit: 10
        video_file_size_limit: 100
        workflow_file_upload_limit: 10
      image:
        enabled: false
        number_limits: 3
        transfer_methods:
        - local_file
        - remote_url
      number_limits: 3
    opening_statement: ''
    retriever_resource:
      enabled: true
    sensitive_word_avoidance:
      enabled: false
    speech_to_text:
      enabled: false
    suggested_questions: []
    suggested_questions_after_answer:
      enabled: false
    text_to_speech:
      enabled: false
      language: ''
      voice: ''
  graph:
    edges:
    - data:
        sourceType: start
        targetType: llm
      id: 1757581230524-llm
      source: '1757581230524'
      sourceHandle: source
      target: llm
      targetHandle: target
      type: custom
    - data:
        sourceType: llm
        targetType: answer
      id: llm-answer
      source: llm
      sourceHandle: source
      target: answer
      targetHandle: target
      type: custom
    nodes:
    - data:
        desc: ''
        selected: false
        title: Start
        type: start
        variables: []
      height: 54
      id: '1757581230524'
      position:
        x: 80
        y: 282
      positionAbsolute:
        x: 80
        y: 282
      sourcePosition: right
      targetPosition: left
      type: custom
      width: 244
    - data:
        context:
          enabled: false
          variable_selector: []
        desc: ''
        memory:
          query_prompt_template: '{{#sys.query#}}


            {{#sys.files#}}'
          role_prefix:
            assistant: ''
            user: ''
          window:
            enabled: false
            size: 10
        model:
          completion_params:
            temperature: 0.7
          mode: chat
          name: gpt-3.5-turbo-0125
          provider: langgenius/openai/openai
        prompt_template:
        - role: system
          text: ''
        selected: false
        title: LLM
        type: llm
        variables: []
        vision:
          enabled: false
      height: 90
      id: llm
      position:
        x: 380
        y: 282
      positionAbsolute:
        x: 380
        y: 282
      sourcePosition: right
      targetPosition: left
      type: custom
      width: 244
    - data:
        answer: '{{#llm.text#}}'
        desc: ''
        selected: false
        title: Answer
        type: answer
        variables: []
      height: 105
      id: answer
      position:
        x: 680
        y: 282
      positionAbsolute:
        x: 680
        y: 282
      sourcePosition: right
      targetPosition: left
      type: custom
      width: 244
    viewport:
      x: 0
      y: 0
      zoom: 1

Problem Description

Currently, conversation variables in Dify have no length limit for their descriptions, allowing users to create variables with arbitrarily long descriptions. However, draft variables are restricted to a maximum of 256 characters.

When fetching draft variables for conversation variables during the drafting process, the system copies conversation variables to draft variables, including their descriptions as-is. Due to this length mismatch, the operation can fail and result in an "Internal Server Error" when attempting to save draft variables.

Additionally, excessively long descriptions may cause performance issues since conversation variable descriptions are stored inline as part of the workflow graph.

✔️ Expected Behavior

No error occurred while editing chatflow.

❌ Actual Behavior

A popup shows while editing chatflow.

[dosubot]

This error happens because conversation variable descriptions have no length limit, but draft variables enforce a 256-character maximum. When you edit a chatflow, Dify copies conversation variable descriptions to draft variables without truncating or validating the length. If a description exceeds 256 characters, the backend throws an exception, resulting in the "Internal Server Error" popup you see. The relevant code in the API controller does not perform length checks before syncing the draft workflow, so any violation triggers a generic error rather than a user-friendly message (source).

Workaround: Keep conversation variable descriptions under 256 characters until this is addressed.
Suggestion: If you can modify the code, add validation or truncation for descriptions before saving draft variables. Improving error handling to surface a clear validation message instead of a generic server error would also help.

Recent PRs have refactored variable handling and improved type safety, but none directly fix this length mismatch or add user-facing validation (source).

To reply, just mention @dosu.

---

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[fsea]

The issue is not about how long it is, but whether it exists or not. Even if the instantaneous variable value is only 1 character long, it will still report an error; however, if there is no variable, it will not report an error.

[QuantumGhost]

@fsea I believe we might be discussing different issues here.

The bug I fixed in #25541 specifically relates to conversation variable descriptions that exceed 256 characters causing an "Internal Server Error" when editing chatflows. This happens because conversation variables don't have length limits, but draft variables are restricted to 256 characters maximum.

From your description, it sounds like you're encountering a different issue where the mere presence of any conversation variable (regardless of description length) triggers an error, while the absence of variables works fine.

Could you provide more details about the specific error you're experiencing? For example:

• What error message do you see?
• Does it also show "Internal Server Error" or something different?
• Are you able to share a minimal DSL that reproduces your issue?

This would help us determine if we're dealing with separate bugs that need different fixes.

[tomy-kyu]

Since I suspected this issue might also be occurring in my environment, I'm attaching the logs generated by the API container for your reference.This environment is self-hosted, though.

In my case, after applying up to 1b0f92a, I encountered the same issue when creating a new workflow and clicking the Publish button.
The same issue also occurs when clicking to update an existing app (chat flow).

2025-09-13 00:19:41.417 ERROR [Dummy-1] [app.py:875] - Exception on /console/api/apps/6500cdcc-8e59-4ddb-8888-a182581bdd97/workflows/publish [POST]
Traceback (most recent call last):
  File "/app/api/.venv/lib/python3.12/site-packages/flask/app.py", line 917, in full_dispatch_request
    rv = self.dispatch_request()
         ^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/api/.venv/lib/python3.12/site-packages/flask/app.py", line 902, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)  # type: ignore[no-any-return]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/api/.venv/lib/python3.12/site-packages/flask_restx/api.py", line 402, in wrapper
    resp = resource(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/api/.venv/lib/python3.12/site-packages/flask/views.py", line 110, in view
    return current_app.ensure_sync(self.dispatch_request)(**kwargs)  # type: ignore[no-any-return]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/api/.venv/lib/python3.12/site-packages/flask_restx/resource.py", line 41, in dispatch_request
    resp = meth(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/app/api/controllers/console/wraps.py", line 215, in decorated
    return view(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/app/api/libs/login.py", line 62, in decorated_view
    return current_app.ensure_sync(func)(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/api/controllers/console/wraps.py", line 37, in decorated
    return view(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/app/api/controllers/console/app/wraps.py", line 56, in decorated_view
    return view_func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/api/controllers/console/app/workflow.py", line 516, in post
    workflow = workflow_service.publish_workflow(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/api/services/workflow_service.py", line 273, in publish_workflow
    workflow = Workflow.new(
               ^^^^^^^^^^^^^
  File "/app/api/models/workflow.py", line 174, in new
    workflow.environment_variables = environment_variables or []
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/api/models/workflow.py", line 396, in environment_variables
    origin_variables_dictionary = {var.id: var for var in self.environment_variables}
                                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/api/models/workflow.py", line 357, in environment_variables
    environment_variables_dict: dict[str, Any] = json.loads(self._environment_variables)
                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/json/__init__.py", line 339, in loads
    raise TypeError(f'the JSON object must be str, bytes or bytearray, '
TypeError: the JSON object must be str, bytes or bytearray, not NoneType

[tomy-kyu]

Please note that this issue has not occurred in tenants updated to 874406d or earlier. Therefore, we suspect there is some problem with the commit content from that point onward up to the present.
Thank you for your cooperation.