Update coinrank error handling & fallback

- It was possible to return USD results for non-USD requests  when data was expired or if there was an error in the fetched data.
- Ensure we always return accurate non-USD prices if possible, falling back to the cached data if necessary.

Author: Jon-edge

src/exchangeRateRouter.ts

@@ -28,6 +28,7 @@ import {
   addIso,
   fromCode,
   isIsoCode,
+  logger,
   normalizeDate,
   subIso,
   toCode,
@@ -329,62 +330,110 @@ const getRedisMarkets = async (
   const now = new Date()
   const nowTimestamp = now.getTime()
 
-  const jsonString = await getAsync(`${REDIS_COINRANK_KEY_PREFIX}_${fiatCode}`)
-  let redisResult: CoinrankRedis = JSON.parse(jsonString)
-
-  if (fiatCode !== defaultFiatCode) {
-    const lastUpdated =
-      redisResult != null ? new Date(redisResult.lastUpdate).getTime() : 0
-
-    // If no result in redis or it's out of date
-    if (redisResult == null || nowTimestamp - lastUpdated > EXPIRE_TIME) {
-      // Attempt to scale prices by foreign exchange rate
+  try {
+    // First try to get data for the requested fiat code
+    const jsonString = await getAsync(
+      `${REDIS_COINRANK_KEY_PREFIX}_${fiatCode}`
+    )
 
-      // Get exchange rate
-      const result = await fetch(
-        `${ratesServerAddress}/v2/exchangeRate?currency_pair=${defaultFiatCode}_${fiatCode}`
-      )
-      const resultJson = await result.json()
-      const { exchangeRate } = asExchangeRateResponse(resultJson)
-      const rate = Number(exchangeRate)
+    // Only parse if jsonString is not null/undefined
+    let redisResult: CoinrankRedis | undefined
+    if (jsonString !== null && jsonString !== undefined) {
+      try {
+        redisResult = JSON.parse(jsonString)
+
+        // If we have valid data that hasn't expired, return it
+        const lastUpdated =
+          redisResult != null ? new Date(redisResult.lastUpdate).getTime() : 0
+        if (nowTimestamp - lastUpdated <= EXPIRE_TIME) {
+          return redisResult
+        }
+        // We have cached data but it's expired - we'll try to refresh it below
+        // but will fall back to this expired data if refresh fails
+      } catch (e) {
+        // JSON parsing error, redisResult remains undefined
+        logger(`Error parsing Redis data for ${fiatCode}: ${e}`)
+        // Continue to try to get fresh data
+      }
+    }
 
-      // Get USD rankings
-      const jsonString = await getAsync(
-        `${REDIS_COINRANK_KEY_PREFIX}_${defaultFiatCode}`
-      )
-      redisResult = JSON.parse(jsonString)
-      let { markets } = redisResult
-
-      // Modify fiat-related fields with the forex rate
-      markets = markets.map(m => ({
-        ...m,
-        marketCap: m.marketCap * rate,
-        price: m.price * rate,
-        volume24h: m.volume24h * rate,
-        high24h: m.high24h * rate,
-        low24h: m.low24h * rate,
-        priceChange24h: m.priceChange24h * rate,
-        marketCapChange24h: m.marketCapChange24h * rate,
-        circulatingSupply: m.circulatingSupply * rate,
-        totalSupply: m.totalSupply * rate,
-        maxSupply: m.maxSupply * rate,
-        allTimeHigh: m.allTimeHigh * rate,
-        allTimeLow: m.allTimeLow * rate
-      }))
-
-      // Update redis cache
-      const redisData: CoinrankRedis = {
-        markets,
-        lastUpdate: now.toISOString()
+    // If we need to convert from USD (either no data or expired data)
+    if (fiatCode !== defaultFiatCode) {
+      try {
+        // Get exchange rate
+        const result = await fetch(
+          `${ratesServerAddress}/v2/exchangeRate?currency_pair=${defaultFiatCode}_${fiatCode}`
+        )
+        if (!result.ok) {
+          throw new Error(`Exchange rate API returned status ${result.status}`)
+        }
+
+        const resultJson = await result.json()
+        const { exchangeRate } = asExchangeRateResponse(resultJson)
+        const rate = Number(exchangeRate)
+
+        // Validate the rate
+        if (rate == null || isNaN(rate) || rate <= 0) {
+          throw new Error(`Invalid exchange rate: ${exchangeRate}`)
+        }
+
+        // Get USD rankings
+        const usdJsonString = await getAsync(
+          `${REDIS_COINRANK_KEY_PREFIX}_${defaultFiatCode}`
+        )
+        if (usdJsonString == null) {
+          throw new Error(`No USD data available in Redis`)
+        }
+
+        const usdRedisResult = JSON.parse(usdJsonString)
+        let { markets } = usdRedisResult
+
+        // Modify fiat-related fields with the forex rate
+        markets = markets.map(m => ({
+          ...m,
+          marketCap: m.marketCap * rate,
+          price: m.price * rate,
+          volume24h: m.volume24h * rate,
+          high24h: m.high24h * rate,
+          low24h: m.low24h * rate,
+          priceChange24h: m.priceChange24h * rate,
+          marketCapChange24h: m.marketCapChange24h * rate,
+          circulatingSupply: m.circulatingSupply * rate,
+          totalSupply: m.totalSupply * rate,
+          maxSupply: m.maxSupply * rate,
+          allTimeHigh: m.allTimeHigh * rate,
+          allTimeLow: m.allTimeLow * rate
+        }))
+
+        // Update redis cache
+        const redisData: CoinrankRedis = {
+          markets,
+          lastUpdate: now.toISOString()
+        }
+        await setAsync(
+          `${REDIS_COINRANK_KEY_PREFIX}_${fiatCode}`,
+          JSON.stringify(redisData)
+        )
+
+        return redisData
+      } catch (e) {
+        logger(`Error converting USD data to ${fiatCode}: ${e}`)
+        // If conversion fails but we have cached data (even if expired), return that
+        if (redisResult != null) {
+          logger(`Falling back to cached data for ${fiatCode}`)
+          return redisResult
+        }
+        // Only return undefined if we have no cached data at all
+        return undefined
       }
-      await setAsync(
-        `${REDIS_COINRANK_KEY_PREFIX}_${fiatCode}`,
-        JSON.stringify(redisData)
-      )
+    } else {
+      // For USD requests when data is missing or expired
+      return redisResult
     }
+  } catch (e) {
+    logger(`Error in getRedisMarkets for ${fiatCode}: ${e}`)
+    return undefined
   }
-
-  return redisResult
 }
 
 const sendCoinrankList: express.RequestHandler = async (