trxcllnt commented on code in PR #14:
URL: https://github.com/apache/arrow-js/pull/14#discussion_r2103290165


##########
src/ipc/reader.ts:
##########
@@ -369,9 +389,51 @@ abstract class RecordBatchReaderImpl<T extends TypeMap = 
any> implements RecordB
             new Vector(data)) :
             new Vector(data)).memoize() as Vector;
     }
-    protected _loadVectors(header: metadata.RecordBatch, body: any, types: 
(Field | DataType)[]) {
+    protected _loadVectors(header: metadata.RecordBatch, body: Uint8Array, 
types: (Field | DataType)[]) {
         return new VectorLoader(body, header.nodes, header.buffers, 
this.dictionaries, this.schema.metadataVersion).visitMany(types);
     }
+
+    private _decompressBuffers(header: metadata.RecordBatch, body: Uint8Array, 
codec: Codec): { decommpressedBody: Uint8Array; buffers: 
metadata.BufferRegion[] } {
+        const decompressedBuffers: Uint8Array[] = [];
+        const newBufferRegions: metadata.BufferRegion[] = [];
+
+        let currentOffset = 0;
+        for (const { offset, length } of header.buffers) {
+            if (length === 0) {
+                decompressedBuffers.push(new Uint8Array(0));
+                newBufferRegions.push(new metadata.BufferRegion(currentOffset, 
0));
+                continue;
+            }
+            const byteBuf = new flatbuffers.ByteBuffer(body.subarray(offset, 
offset + length));
+            const uncompressedLenth = bigIntToNumber(byteBuf.readInt64(0));
+
+
+            const bytes = byteBuf.bytes().subarray(LENGTH_OF_PREFIX_DATA);
+
+            const decompressed = (uncompressedLenth === 
LENGTH_NO_COMPRESSED_DATA)
+                ? bytes
+                : codec.decode!(bytes);
+
+            decompressedBuffers.push(decompressed);
+
+            const padding = (DEFAULT_ALIGNMENT - (currentOffset % 
DEFAULT_ALIGNMENT)) % DEFAULT_ALIGNMENT;
+            currentOffset += padding;
+            newBufferRegions.push(new metadata.BufferRegion(currentOffset, 
decompressed.length));
+            currentOffset += decompressed.length;
+        }
+
+        const totalSize = currentOffset;
+        const combined = new Uint8Array(totalSize);
+
+        for (const [i, decompressedBuffer] of decompressedBuffers.entries()) {
+            combined.set(decompressedBuffer, newBufferRegions[i].offset);

Review Comment:
   I can take a look at adding it to the writer. I wouldn't want to merge this 
PR without at least a limited set of tests, and verifying we can read what we 
write is the easiest way to do that.



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