[REQ] Feature Request Description

Is your feature request related to a problem? Please describe.

Whenever I generate a typescript-node API client, the generated code does not respect different return types for different status codes. For example, if 200 returns a user and 400 returns an error, the error gets parsed as a user and thus the error message is lost!

Describe the solution you'd like

There's a generated bit of code that looks like this:

if (error) {
    reject(error);
} else {
    body = ObjectSerializer.deserialize(body, "OrganizationMember");
    if (response.statusCode && response.statusCode >= 200 && response.statusCode <= 299) {
        resolve({ response: response, body: body });
    } else {
        reject(new HttpError(response, body, response.statusCode));
    }
}

Ideally, it should follow the json specifications where different status codes return different types.

"200": {
"description": "Success",
"content": {
"text/plain": {
"schema": {
"$ref": "#/components/schemas/RefreshTokenSuccessResponse"
}
},
"application/json": {
"schema": {
"$ref": "#/components/schemas/RefreshTokenSuccessResponse"
}
},
"text/json": {
"schema": {
"$ref": "#/components/schemas/RefreshTokenSuccessResponse"
}
}
}
},
"400": {
"description": "Bad Request",
"content": {
"text/plain": {
"schema": {
"$ref": "#/components/schemas/ProblemDetails"
}
},
"application/json": {
"schema": {
"$ref": "#/components/schemas/ProblemDetails"
}
},
"text/json": {
"schema": {
"$ref": "#/components/schemas/ProblemDetails"
}
}
}
},
"404": {
"description": "Not Found",
"content": {
"text/plain": {
"schema": {
"$ref": "#/components/schemas/ProblemDetails"
}
},
"application/json": {
"schema": {
"$ref": "#/components/schemas/ProblemDetails"
}
},
"text/json": {
"schema": {
"$ref": "#/components/schemas/ProblemDetails"
}
}
}
},
"500": {
"description": "Server Error",
"content": {
"text/plain": {
"schema": {
"$ref": "#/components/schemas/ProblemDetails"
}
},
"application/json": {
"schema": {
"$ref": "#/components/schemas/ProblemDetails"
}
},
"text/json": {
"schema": {
"$ref": "#/components/schemas/ProblemDetails"
}
}
}
}

This can be a configurable mode called "strictStatusTypes" and resolve like so:

if (error) {
    reject(error);
} else if (response.statusCode === 200) 
    resolve({ response: response, body: ObjectSerializer.deserialize(body, "OrganizationMember") });
} else if (response.statusCode === 400) {
    reject(new HttpError(response, ObjectSerializer.deserialize(body, "ProblemDetails"), response.statusCode));
} else if ....

Describe alternatives you've considered

An easier solution to the issue would be to just leave the body alone when there's an error and use a raw JSON object without the parse.

if (error) {
    reject(error);
} else {
    if (response.statusCode && response.statusCode >= 200 && response.statusCode <= 299) {
        body = ObjectSerializer.deserialize(body, "OrganizationMember");
        resolve({ response: response, body: body });
    } else {
        reject(new HttpError(response, body, response.statusCode));
    }
}

Additional context

Whenever the success status has no body (e.g. 201, 202, ...) the error body is left untouched which makes this behavior really inconsistent!

Start with the typescript-node generator path that emits the shown response-handling code, then trace how OpenAPI response status codes and schemas are represented. Done means generated clients can optionally use a strictStatusTypes mode that deserializes each status code with its specified response type, while preserving the proposed behavior for unspecified modes.