René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"ServerMessageEndOfCallReport can't parse payloads from Voice Agent because camelCase fields aren't honored","articleBody":"**Description**  \nWhen receiving a payload from a Vapi Voice Agent, the `ServerMessageEndOfCallReport` model in the `server-sdk-python` fails to parse the incoming JSON. The payload uses **camelCase field names** (e.g., `endedReason`, `endTime`, `secondsFromStart`), but the SDK model expects **snake_case** (`ended_reason`, `end_time`, `seconds_from_start`).  \n\nAlthough the generated model defines aliases using `FieldMetadata(alias=\"...\")`, those aliases are not actually used during model validation. As a result, the SDK throws large validation errors stating that required fields are missing.\n\n---\n\n**Example**\n\n```python\nfrom vapi_server_sdk.models import ServerMessageEndOfCallReport\n\nmsg = {\n    \"timestamp\": 1762133576209,\n    \"type\": \"end-of-call-report\",\n    \"endedReason\": \"customer-ended-call\",\n    \"analysis\": {\"summary\": \"...\", \"successEvaluation\": \"true\"},\n    \"artifact\": {\n        \"messages\": [\n            {\n                \"role\": \"bot\",\n                \"message\": \"Hi, this is a test.\",\n                \"time\": 1762133501000.0,\n                \"endTime\": 1762133502000.0,\n                \"secondsFromStart\": 1.0,\n            }\n        ],\n        \"transcript\": \"AI: Hi, this is a test.\"\n    }\n}\n\nServerMessageEndOfCallReport.model_validate(msg)\n```\n\n**Actual behavior**\n\n```bash\n80 validation errors for ServerMessageEndOfCallReport  \nended_reason  \n  Field required [type=missing, input_value={...}, input_type=dict]  \nartifact.messages.0.BotMessage.end_time  \n  Field required [type=missing, input_value={...}, input_type=dict]  \nartifact.messages.0.BotMessage.seconds_from_start  \n  Field required [type=missing, input_value={...}, input_type=dict]  \n...\n```\n\n---\n\n**Expected behavior**  \nThe SDK should correctly parse the Voice Agent’s camelCase JSON payload, populating the corresponding snake_case model fields using Pydantic’s alias handling.\n\n---\n\n**Root cause**  \nThe generated models use Fern’s custom `FieldMetadata(alias=\"...\")` annotations instead of Pydantic’s native `Field(alias=\"...\")`.  \nPydantic v2 does **not** honor those aliases when parsing input (`model_validate`, `__init__`), only when serializing output (`model_dump(by_alias=True)`).  \n\nThis means that incoming camelCase payloads from the Voice Agent (which follow the documented API schema) cannot be deserialized without manual key remapping.\n\n---\n\n**Workarounds**\n\nConvert the incoming JSON keys from camelCase → snake_case before validation:\n\n```python\nimport re  \nfrom typing import Any, Mapping\n\nCAMEL_RE = re.compile(r'(?\u003c!^)(?=[A-Z])')\n\ndef camel_to_snake(name: str) -\u003e str:\n    return CAMEL_RE.sub('_', name).lower()\n\ndef normalize_keys(obj: Any) -\u003e Any:\n    if isinstance(obj, Mapping):\n        return {camel_to_snake(k): normalize_keys(v) for k, v in obj.items()}\n    elif isinstance(obj, list):\n        return [normalize_keys(x) for x in obj]\n    else:\n        return obj\n\nnormalized = normalize_keys(msg)  \nServerMessageEndOfCallReport.model_validate(normalized)\n```\n\nOr manually subclass the model to redeclare fields using `pydantic.Field(alias=\"...\")`.\n\n---\n\n**Proposed fix**  \n- Update code generation for `server-sdk-python` to use **`pydantic.Field(alias=...)`** rather than `FieldMetadata(alias=...)`, ensuring proper alias resolution during validation.  \n- Alternatively, update the SDK’s `UncheckedBaseModel` to include:  \n\n```python\nmodel_config = ConfigDict(populate_by_name=True)\n```\n\nand propagate real Pydantic alias definitions into the generated models.\n\n---\n\n**Environment**  \n- SDK: `vapi/server-sdk-python`\n- SDK Version: 1.7.3\n- Pydantic: 2.12.3 \n- Python: 3.11\n- Platform: macOS\n\n---\n\n**Impact**  \nPayloads received from Voice Agents fail validation because camelCase fields aren’t recognized. This breaks out-of-the-box use of the server SDK for handling voice agent events.\n","author":{"url":"https://github.com/pratyushsahay","@type":"Person","name":"pratyushsahay"},"datePublished":"2025-11-03T07:08:22.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/18/server-sdk-python/issues/18"}