journal2clickhouse: coerce things that look like strings back to strings

There's binary data sometimes, but on the whole I don't care about preserving
it properly (sorry), so let's just coerce it to a string if it is supposed to
go into a "proper" field.

go/journal2clickhouse/journal2clickhouse.go

@@ -185,11 +185,49 @@ func insertIntoClickhouse(ctx context.Context, chAddr string, rows []interface{}
 	return doInsert(ctx, chAddr, "logger.systemd_scrape", mostRecentRows)
 }
 
+func coerceToByteSlice(n []interface{}) ([]byte, bool) {
+	// Fast fail.
+	nInt, isInt := n[0].(int)
+	nFloat, isFloat := n[0].(float64)
+	_, isByte := n[0].(byte)
+	if !isInt && !isByte && !isFloat {
+		return nil, false
+	} else if isInt && (nInt >= 256 || nInt < 0) {
+		return nil, false
+	} else if isFloat && float64(byte(nFloat)) != nFloat {
+		return nil, false
+	}
+
+	out := make([]byte, len(n))
+	for idx, vInterface := range n {
+		vInt, okInt := vInterface.(int)
+		vByte, okByte := vInterface.(byte)
+		vFloat, okFloat := vInterface.(float64)
+		switch {
+		case okInt:
+			if vInt >= 256 || vInt < 0 {
+				return nil, false
+			}
+			out[idx] = byte(vInt)
+		case okByte:
+			out[idx] = vByte
+		case okFloat:
+			out[idx] = byte(vFloat)
+			if float64(out[idx]) != vFloat {
+				return nil, false
+			}
+		default:
+			return nil, false
+		}
+	}
+	return out, true
+}
+
 func parseLog(d map[string]interface{}) (map[string]interface{}, error) {
 	data := make(map[string]interface{})
 	extraData := make(map[string]interface{})
 
-	msgID := fmt.Sprintf("_HOSTNAME: %v; __REALTIME_TIMESTAMP: %v; MESSAGE: %v", data["_HOSTNAME"], data["__REALTIME_TIMESTAMP"], data["MESSAGE"])
+	msgID := fmt.Sprintf("_HOSTNAME: %v; __REALTIME_TIMESTAMP: %v; __CURSOR: %v; MESSAGE: %v", d["_HOSTNAME"], d["__REALTIME_TIMESTAMP"], d["__CURSOR"], d["MESSAGE"])
 
 	for origField, newField := range fieldMap {
 		v, ok := d[origField]
@@ -199,10 +237,23 @@ func parseLog(d map[string]interface{}) (map[string]interface{}, error) {
 
 		// Check if this is a slice...
 		if vs, ok := v.([]interface{}); ok {
-			// extraData gets all values after the first one, we keep the first one.
+			// This might be a []byte, though.
-			log.Printf("[%v] origField %v newField %v got a repeated message; keeping only the first element", msgID, origField, newField)
+			vbytes, ok := coerceToByteSlice(vs)
-			extraData[origField] = vs[1:]
+			if ok {
-			v = vs[0]
+				v = string(vbytes)
+			} else {
+				// extraData gets all values after the first one, we keep the first one.
+				log.Printf("[%v] origField %v newField %v got a repeated message; keeping only the first element", msgID, origField, newField)
+				extraData[origField] = vs[1:]
+				v = vs[0]
+			}
+		}
+		if vs, ok := v.([]interface{}); ok {
+			// It's possible we had a [][]byte, so now coerce this again.
+			vbytes, ok := coerceToByteSlice(vs)
+			if ok {
+				v = string(vbytes)
+			}
 		}
 
 		transformer := fieldTransform[newField]