stream: fixup from memory issue / batch yielding

Author: jasnell

lib/internal/streams/new/from.js

@@ -35,6 +35,11 @@ const {
 // Shared TextEncoder instance for string conversion.
 const encoder = new TextEncoder();
 
+// Maximum number of chunks to yield per batch from from(Uint8Array[]).
+// Bounds peak memory when arrays flow through transforms, which must
+// allocate output for the entire batch at once.
+const FROM_BATCH_SIZE = 128;
+
 // =============================================================================
 // Type Guards and Detection
 // =============================================================================
@@ -458,7 +463,11 @@ function fromSync(input) {
     };
   }
 
-  // Fast path: Uint8Array[] - yield as a single batch
+  // Fast path: Uint8Array[] - yield in bounded sub-batches.
+  // Yielding the entire array as one batch forces downstream transforms
+  // to process all data at once, causing peak memory proportional to total
+  // data volume. Sub-batching keeps peak memory bounded while preserving
+  // the throughput benefit of batched processing.
   if (ArrayIsArray(input)) {
     if (input.length === 0) {
       return {
@@ -475,7 +484,13 @@ function fromSync(input) {
         const batch = input;
         return {
           *[SymbolIterator]() {
-            yield batch;
+            if (batch.length <= FROM_BATCH_SIZE) {
+              yield batch;
+            } else {
+              for (let i = 0; i < batch.length; i += FROM_BATCH_SIZE) {
+                yield ArrayPrototypeSlice(batch, i, i + FROM_BATCH_SIZE);
+              }
+            }
           },
         };
       }
@@ -514,7 +529,11 @@ function from(input) {
     };
   }
 
-  // Fast path: Uint8Array[] - yield as a single batch
+  // Fast path: Uint8Array[] - yield in bounded sub-batches.
+  // Yielding the entire array as one batch forces downstream transforms
+  // to process all data at once, causing peak memory proportional to total
+  // data volume. Sub-batching keeps peak memory bounded while preserving
+  // the throughput benefit of batched processing.
   if (ArrayIsArray(input)) {
     if (input.length === 0) {
       return {
@@ -530,7 +549,13 @@ function from(input) {
         const batch = input;
         return {
           async *[SymbolAsyncIterator]() {
-            yield batch;
+            if (batch.length <= FROM_BATCH_SIZE) {
+              yield batch;
+            } else {
+              for (let i = 0; i < batch.length; i += FROM_BATCH_SIZE) {
+                yield ArrayPrototypeSlice(batch, i, i + FROM_BATCH_SIZE);
+              }
+            }
           },
         };
       }