Apply byte-range options to default Web-file responses

.changeset/curly-files-range.md

@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+Apply byte range and chunk size options to default Web file responses.

packages/effect/src/unstable/http/HttpPlatform.ts

@@ -156,14 +156,42 @@ export const layer = Layer.effect(HttpPlatform)(
           { contentLength, headers, status, statusText }
         )
       },
-      fileWebResponse(file, status, statusText, headers, _options) {
-        return Response.stream(
-          Stream.fromReadableStream({
+      fileWebResponse(file, status, statusText, headers, options) {
+        const offset = Number(options?.offset ?? 0)
+        const bytesToRead = options?.bytesToRead !== undefined ? Number(options.bytesToRead) : undefined
+        const chunkSize = options?.chunkSize !== undefined ? Math.max(1, Number(options.chunkSize)) : Infinity
+        const end = offset + (bytesToRead ?? Infinity)
+        const stream = end <= offset
+          ? Stream.empty
+          : Stream.fromReadableStream({
             evaluate: () => file.stream() as ReadableStream<Uint8Array>,
             onError: identity
-          }),
-          { headers, status, statusText }
-        )
+          }).pipe(
+            Stream.mapAccum(
+              () => 0,
+              (position, bytes) => {
+                const next = position + bytes.length
+                const start = Math.min(Math.max(offset - position, 0), bytes.length)
+                const stop = Math.min(Math.max(end - position, 0), bytes.length)
+                const chunks: Array<{ readonly bytes: Uint8Array; readonly done: boolean }> = []
+                for (let index = start; index < stop; index += chunkSize) {
+                  chunks.push({
+                    bytes: bytes.subarray(index, Math.min(index + chunkSize, stop)),
+                    done: next >= end && index + chunkSize >= stop
+                  })
+                }
+                return [next, chunks]
+              }
+            ),
+            Stream.takeUntil((chunk) => chunk.done),
+            Stream.map((chunk) => chunk.bytes)
+          )
+        return Response.stream(stream, {
+          contentLength: bytesToRead ?? file.size - offset,
+          headers,
+          status,
+          statusText
+        })
       }
     }))
 ).pipe(Layer.provide(Etag.layerWeak))

packages/effect/test/unstable/http/HttpPlatform.test.ts

@@ -0,0 +1,43 @@
+import { assert, describe, it } from "@effect/vitest"
+import { Effect, FileSystem, Stream } from "effect"
+import { HttpPlatform } from "effect/unstable/http"
+
+describe("HttpPlatform", () => {
+  const file = {
+    name: "file.bin",
+    lastModified: 0,
+    size: 4,
+    type: "application/octet-stream",
+    stream: () => new Blob([new Uint8Array([1, 2, 3, 4])]).stream()
+  }
+
+  it.effect("honors Web file offset and byte count", () =>
+    Effect.gen(function*() {
+      const platform = yield* HttpPlatform.HttpPlatform
+      const response = yield* platform.fileWebResponse(file, { offset: 1, bytesToRead: 2 })
+      assert.strictEqual(response.body._tag, "Stream")
+      if (response.body._tag === "Stream") {
+        assert.strictEqual(response.body.contentLength, 2)
+        const bytes = yield* Stream.mkUint8Array(response.body.stream)
+        assert.deepStrictEqual(Array.from(bytes), [2, 3])
+      }
+    }).pipe(
+      Effect.provide(HttpPlatform.layer),
+      Effect.provideService(FileSystem.FileSystem, {} as any)
+    ))
+
+  it.effect("honors Web file chunk size", () =>
+    Effect.gen(function*() {
+      const platform = yield* HttpPlatform.HttpPlatform
+      const response = yield* platform.fileWebResponse(file, { offset: 0, bytesToRead: 4, chunkSize: 2 })
+      assert.strictEqual(response.body._tag, "Stream")
+      if (response.body._tag === "Stream") {
+        assert.strictEqual(response.body.contentLength, 4)
+        const chunks = yield* Stream.runCollect(response.body.stream)
+        assert.deepStrictEqual(chunks.map((chunk) => Array.from(chunk)), [[1, 2], [3, 4]])
+      }
+    }).pipe(
+      Effect.provide(HttpPlatform.layer),
+      Effect.provideService(FileSystem.FileSystem, {} as any)
+    ))
+})