[Bug]: estimatePosition GraphQL API returns error

[bglownia]

Problem encountered

Graphql request to https://api.n07.testnet.vega.xyz/graphql

query EstimatePosition($marketId: ID!, $openVolume: String!, $orders: [OrderInfo!], $collateralAvailable: String) {
  estimatePosition(
    marketId: $marketId
    openVolume: $openVolume
    orders: $orders
    collateralAvailable: $collateralAvailable
  ) {
    margin {
      worstCase {
        maintenanceLevel
        searchLevel
        initialLevel
        collateralReleaseLevel
        __typename
      }
      bestCase {
        maintenanceLevel
        searchLevel
        initialLevel
        collateralReleaseLevel
        __typename
      }
      __typename
    }
    liquidation {
      worstCase {
        open_volume_only
        including_buy_orders
        including_sell_orders
        __typename
      }
      bestCase {
        open_volume_only
        including_buy_orders
        including_sell_orders
        __typename
      }
      __typename
    }
    __typename
  }
}

{
  "marketId": "4cb06ca74c44c2c4aea5018ca9106bd771ee0f8904fa4127bcab637bd17801a1",
  "openVolume": "1",
  "orders": [  
    {
      "isMarketOrder": true,
      "price": "0",
      "remaining": "1",
      "side": "SIDE_SELL"
    }
  ],
  "collateralAvailable": "321578449"
}

returns error

{"errors":[{"message":"","path":["estimatePosition"],"extensions":{"code":2,"type":"Unknown"}}],"data":{"estimatePosition":null}}

It happens when openPosition + remaining can be zero. Open volume = 1 and order remaining is 1 on sell side .

[gordsport]

@MuthuVega - please can you catch up with @bglownia and see if we can reproduce this in tests.

[EVODelavega]

After reading through the code for the EstimatePosition call in datanode/api/trading_data_v2.go, it would appear that this is caused by the liquidation estimate calculations returning an error in case the liquidation price could not be determined. This error is not handled, but rather returned straight back to EstimatePosition where it results, and sends back an error response:

calculateLiquidationPrice returns an error if the price is not defined here:

func calculateLiquidationPrice(openVolume num.Decimal, currentPrice, collateralAvailable num.Decimal, linearSlippageFactor, quadraticSlippageFactor, riskFactorLong, riskFactorShort num.Decimal) (num.Decimal, error) {
	rf := riskFactorLong
	if openVolume.IsNegative() {
		rf = riskFactorShort
	}

	denominator := calculateSlippageFactor(openVolume, linearSlippageFactor, quadraticSlippageFactor).Add(openVolume.Abs().Mul(rf)).Sub(openVolume)
	if denominator.IsZero() {
		return num.DecimalZero(), fmt.Errorf("liquidation price not defined")
	}

	ret := collateralAvailable.Sub(openVolume.Mul(currentPrice)).Div(denominator)
	if ret.IsNegative() {
		return num.DecimalZero(), nil
	}
	return ret, nil
}

Which is passed back up to EstimatePosition here:

	var liquidationEstimate *v2.LiquidationEstimate
	if req.CollateralAvailable != nil && len(*req.CollateralAvailable) > 0 {
		liquidationEstimate, err = t.computeLiquidationPriceRange(
			collateralAvailable,
			req.OpenVolume,
			buyOrders,
			sellOrders,
			marketObservable,
			positionFactor,
			linearSlippageFactor,
			quadraticSlippageFactor,
			rf)

		if err != nil {
			return nil, err
		}
	}

Where we just check if err != nil, and in that case return nil, err. Whether we should return an empty liquidation estimate, return some type of approximation (if we can), or are right in returning an error is something that needs to be decided on

[bglownia]

API fails also with

{
  "marketId": "4cb06ca74c44c2c4aea5018ca9106bd771ee0f8904fa4127bcab637bd17801a1",
  "openVolume": "1",
  "orders": [  
    {
      "isMarketOrder": true,
      "price": "0",
      "remaining": "1",
      "side": "SIDE_SELL"
    },
    {
      "isMarketOrder": true,
      "price": "0",
      "remaining": "100",
      "side": "SIDE_SELL"
    }
  ],
  "collateralAvailable": "123"
}

but not with

{
  "marketId": "4cb06ca74c44c2c4aea5018ca9106bd771ee0f8904fa4127bcab637bd17801a1",
  "openVolume": "1",
  "orders": [  
    {
      "isMarketOrder": true,
      "price": "0",
      "remaining": "2",
      "side": "SIDE_SELL"
    },
    {
      "isMarketOrder": true,
      "price": "0",
      "remaining": "99",
      "side": "SIDE_SELL"
    }
  ],
  "collateralAvailable": "123"
}

[gordsport]

Tests for this can be seen in the market sim:

• feat: add test for estimate position vega-market-sim#425