Sort inferred fields for first event (#450)

FileWriter expects sorted events so position of fields matter. 
This is because it looks for data using offsets. 

This fixes an issue where events sent during the first 
minute of server's operation were getting lost.

Author: trueleo

server/src/event/format/json.rs

@@ -24,6 +24,7 @@ use arrow_array::RecordBatch;
 use arrow_json::reader::{infer_json_schema_from_iterator, ReaderBuilder};
 use arrow_schema::{DataType, Field, Fields, Schema};
 use datafusion::arrow::util::bit_util::round_upto_multiple_of_64;
+use itertools::Itertools;
 use serde_json::Value;
 use std::{collections::HashMap, sync::Arc};
 
@@ -73,7 +74,12 @@ impl EventFormat for Event {
                         return Err(anyhow!("Could not merge schema of this event with that of the existing stream. {:?}", err));
                     }
                     is_first = true;
-                    infer_schema.fields.iter().cloned().collect()
+                    infer_schema
+                        .fields
+                        .iter()
+                        .cloned()
+                        .sorted_by(|a, b| a.name().cmp(b.name()))
+                        .collect()
                 }
                 Err(err) => {
                     return Err(anyhow!(