doc: improve explainer

Author: Devdutt Shenoi

src/response.rs

@@ -16,9 +16,10 @@
  *
  */
 
-use crate::{handlers::http::query::QueryError, utils::arrow::record_batches_to_json};
 use datafusion::arrow::record_batch::RecordBatch;
-use serde_json::{json, Map, Value};
+use serde_json::{json, Value};
+
+use crate::{handlers::http::query::QueryError, utils::arrow::record_batches_to_json};
 
 pub struct QueryResponse {
     pub records: Vec<RecordBatch>,
@@ -28,9 +29,9 @@ pub struct QueryResponse {
 }
 
 impl QueryResponse {
-    /// TODO: maybe this can be futher optimized by directly converting `arrow` to `serde_json` instead of serializing to bytes
+    /// Convert into a JSON response
     pub fn to_json(&self) -> Result<Value, QueryError> {
-        let mut json: Vec<Map<String, Value>> = record_batches_to_json(&self.records)?;
+        let mut json = record_batches_to_json(&self.records)?;
 
         if self.fill_null {
             for object in json.iter_mut() {

src/utils/arrow/mod.rs

@@ -22,20 +22,20 @@ use std::{
     sync::Arc,
 };
 
+use arrow::error::Result;
 use arrow_array::{ArrayRef, RecordBatch, StringArray, TimestampMillisecondArray, UInt64Array};
-use arrow_schema::{ArrowError, DataType, Field, Schema, TimeUnit};
+use arrow_schema::{DataType, Field, Schema, TimeUnit};
 use arrow_select::take::take;
+pub use batch_adapter::adapt_batch;
 use chrono::{DateTime, Utc};
 use itertools::Itertools;
-
-pub mod batch_adapter;
-pub mod flight;
-
-pub use batch_adapter::adapt_batch;
 use serde_json::{Map, Value};
 
 use crate::event::DEFAULT_TIMESTAMP_KEY;
 
+pub mod batch_adapter;
+pub mod flight;
+
 /// Converts a slice of record batches to JSON.
 ///
 /// # Arguments
@@ -46,9 +46,10 @@ use crate::event::DEFAULT_TIMESTAMP_KEY;
 /// * Result<Vec<Map<String, Value>>>
 ///
 /// A vector of JSON objects representing the record batches.
-pub fn record_batches_to_json(
-    records: &[RecordBatch],
-) -> Result<Vec<Map<String, Value>>, ArrowError> {
+///
+/// TODO: maybe this can be futher optimized by directly converting `arrow`
+///       to an in-memory type instead of serializing to bytes.
+pub fn record_batches_to_json(records: &[RecordBatch]) -> Result<Vec<Map<String, Value>>> {
     let buf = vec![];
     let mut writer = arrow_json::ArrayWriter::new(buf);
     for record in records {
@@ -101,7 +102,7 @@ pub fn add_parseable_fields(
     rb: RecordBatch,
     p_timestamp: DateTime<Utc>,
     p_custom_fields: &HashMap<String, String>,
-) -> Result<RecordBatch, ArrowError> {
+) -> Result<RecordBatch> {
     // Return Result for proper error handling
 
     // Add custom fields in sorted order