feat(wal_inspect): Make table_name_index optional for line proto writing

This will allow for decoding a WAL into line protocol without connecting
to a catalog service (or having an equivalent name lookup mechanism).

wal_inspect/src/lib.rs

@@ -15,6 +15,7 @@
     missing_debug_implementations,
     missing_docs
 )]
+use std::borrow::Cow;
 use std::io::Write;
 
 use data_types::{NamespaceId, TableId};
@@ -62,7 +63,7 @@ where
     namespaced_output: HashMap<NamespaceId, W>,
     new_write_sink: F,
 
-    table_name_index: HashMap<TableId, String>,
+    table_name_index: Option<HashMap<TableId, String>>,
 }
 
 impl<W, F> LineProtoWriter<W, F>
@@ -100,10 +101,13 @@ where
 {
     /// Constructs a new [`LineProtoWriter`] that uses `new_write_sink` to
     /// get the destination for each line protocol write by its namespace ID.
-    /// The `table_name_index` must provide a mapping from all table IDs to
-    /// table name to recover the measurement name, as WAL write entries do
-    /// not contain this information.
-    pub fn new(new_write_sink: F, table_name_index: HashMap<TableId, String>) -> Self {
+    ///
+    /// The optional `table_name_index` is used to provide a mapping for all table IDs
+    /// to the corresponding table name to recover the measurement name, as WAL write
+    /// entries do not contain this information. If supplied, the index MUST be exhaustive.
+    ///
+    /// If no index is given then measurement names are written as table IDs.
+    pub fn new(new_write_sink: F, table_name_index: Option<HashMap<TableId, String>>) -> Self {
         Self {
             namespaced_output: HashMap::new(),
             new_write_sink,
@@ -135,7 +139,7 @@ where
 
 fn write_batches_as_line_proto<W>(
     sink: &mut W,
-    table_name_index: &HashMap<TableId, String>,
+    table_name_index: &Option<HashMap<TableId, String>>,
     table_batches: HashMap<i64, MutableBatch>,
 ) -> Result<(), WriteError>
 where
@@ -144,14 +148,18 @@ where
     for (table_id, mb) in table_batches {
         let schema = mb.schema(schema::Projection::All)?;
         let record_batch = mb.to_arrow(schema::Projection::All)?;
-        let measurement_name = table_name_index.get(&TableId::new(table_id)).ok_or(
-            WriteError::ConvertToLineProtocolFailed(format!(
-                "missing table name for id {}",
-                &table_id
-            )),
-        )?;
+        let table_id = TableId::new(table_id);
+        let measurement_name = match table_name_index {
+            Some(idx) => Cow::Borrowed(idx.get(&table_id).ok_or(
+                WriteError::ConvertToLineProtocolFailed(format!(
+                    "missing table name for id {}",
+                    &table_id
+                )),
+            )?),
+            None => Cow::Owned(table_id.to_string()),
+        };
         sink.write_all(
-            convert_to_lines(measurement_name, &schema, &record_batch)
+            convert_to_lines(&measurement_name, &schema, &record_batch)
                 .map_err(WriteError::ConvertToLineProtocolFailed)?
                 .as_slice(),
         )?;
@@ -210,7 +218,7 @@ mod tests {
             wal.reader_for_segment(closed.id())
                 .expect("failed to open reader for closed segment"),
         );
-        let mut writer = LineProtoWriter::new(|_| Ok(Vec::<u8>::new()), table_name_index);
+        let mut writer = LineProtoWriter::new(|_| Ok(Vec::<u8>::new()), Some(table_name_index));
 
         let decoded_entries = decoder
             .into_iter()
@@ -315,7 +323,7 @@ mod tests {
             wal.reader_for_segment(closed.id())
                 .expect("failed to open reader for closed segment"),
         );
-        let mut writer = LineProtoWriter::new(|_| Ok(Vec::<u8>::new()), table_name_index);
+        let mut writer = LineProtoWriter::new(|_| Ok(Vec::<u8>::new()), Some(table_name_index));
 
         // The translator should be able to read all 2 good entries containing 4 write ops
         let decoded_entries = decoder
@@ -359,6 +367,39 @@ mod tests {
         });
     }
 
+    #[test]
+    fn write_line_proto_without_index() {
+        let mut sink = Vec::<u8>::new();
+        let batches = lines_to_batches(
+            r#"m1,t=foo v=1i 1
+m2,t=bar v="arán" 1"#,
+            0,
+        )
+        .expect("failed to create batches from line proto")
+        .into_iter()
+        // Trim the non-numeric characters from the batches to make ID derivation deterministic
+        // (map enumeration is not ordered).
+        .map(|(table_name, batch)| {
+            (
+                table_name
+                    .trim_matches(|c| !char::is_numeric(c))
+                    .parse::<i64>()
+                    .expect("failed to convert table name to id"),
+                batch,
+            )
+        })
+        .collect();
+
+        write_batches_as_line_proto(&mut sink, &None, batches)
+            .expect("write back to line proto should succeed");
+
+        assert_eq!(
+            String::from_utf8(sink).expect("invalid output"),
+            r#"1,t=foo v=1i 1
+2,t=bar v="arán" 1"#
+        );
+    }
+
     fn build_indexes<'a>(
         iter: impl IntoIterator<Item = (&'a str, TableId)>,
     ) -> (HashMap<String, TableId>, HashMap<TableId, String>) {