perf(runtime/fs): optimize readFile by using a single large buffer (#12057)

* perf(runtime/fs): optimize readFile by using a single large buffer
* handle extended/truncated files during read

Allocate an extra byte in our read buffer to detect "overflow" then fallback to unsized readAll for remainder of extended file, this is a slowpath that should rarely happen in practice

2 files changed, 71 insertions, 41 deletions

diff --git a/runtime/js/12_io.js b/runtime/js/12_io.js
index a15015351..d5cf14e55 100644
--- a/runtime/js/12_io.js
+++ b/runtime/js/12_io.js
@@ -11,6 +11,7 @@
   const {
     Uint8Array,
     ArrayPrototypePush,
+    MathMin,
     TypedArrayPrototypeSubarray,
     TypedArrayPrototypeSet,
   } = window.__bootstrap.primordials;
@@ -96,10 +97,7 @@
     return nread === 0 ? null : nread;
   }
 
-  async function read(
-    rid,
-    buffer,
-  ) {
+  async function read(rid, buffer) {
     if (buffer.length === 0) {
       return 0;
     }
@@ -117,10 +115,10 @@
     return await core.opAsync("op_write_async", rid, data);
   }
 
-  const READ_PER_ITER = 32 * 1024;
+  const READ_PER_ITER = 16 * 1024; // 16kb, see https://github.com/denoland/deno/issues/10157
 
-  async function readAll(r) {
-    return await readAllInner(r);
+  function readAll(r) {
+    return readAllInner(r);
   }
   async function readAllInner(r, options) {
     const buffers = [];
@@ -138,20 +136,7 @@
       throw new DOMException("The read operation was aborted.", "AbortError");
     }
 
-    let totalLen = 0;
-    for (const buf of buffers) {
-      totalLen += buf.byteLength;
-    }
-
-    const contents = new Uint8Array(totalLen);
-
-    let n = 0;
-    for (const buf of buffers) {
-      TypedArrayPrototypeSet(contents, buf, n);
-      n += buf.byteLength;
-    }
-
-    return contents;
+    return concatBuffers(buffers);
   }
 
   function readAllSync(r) {
@@ -161,12 +146,16 @@
       const buf = new Uint8Array(READ_PER_ITER);
       const read = r.readSync(buf);
       if (typeof read == "number") {
-        ArrayPrototypePush(buffers, new Uint8Array(buf.buffer, 0, read));
+        ArrayPrototypePush(buffers, buf.subarray(0, read));
       } else {
         break;
       }
     }
 
+    return concatBuffers(buffers);
+  }
+
+  function concatBuffers(buffers) {
     let totalLen = 0;
     for (const buf of buffers) {
       totalLen += buf.byteLength;
@@ -183,6 +172,57 @@
     return contents;
   }
 
+  function readAllSyncSized(r, size) {
+    const buf = new Uint8Array(size + 1); // 1B to detect extended files
+    let cursor = 0;
+
+    while (cursor < size) {
+      const sliceEnd = MathMin(size + 1, cursor + READ_PER_ITER);
+      const slice = buf.subarray(cursor, sliceEnd);
+      const read = r.readSync(slice);
+      if (typeof read == "number") {
+        cursor += read;
+      } else {
+        break;
+      }
+    }
+
+    // Handle truncated or extended files during read
+    if (cursor > size) {
+      // Read remaining and concat
+      return concatBuffers([buf, readAllSync(r)]);
+    } else { // cursor == size
+      return buf.subarray(0, cursor);
+    }
+  }
+
+  async function readAllInnerSized(r, size, options) {
+    const buf = new Uint8Array(size + 1); // 1B to detect extended files
+    let cursor = 0;
+    const signal = options?.signal ?? null;
+    while (!signal?.aborted && cursor < size) {
+      const sliceEnd = MathMin(size + 1, cursor + READ_PER_ITER);
+      const slice = buf.subarray(cursor, sliceEnd);
+      const read = await r.read(slice);
+      if (typeof read == "number") {
+        cursor += read;
+      } else {
+        break;
+      }
+    }
+    if (signal?.aborted) {
+      throw new DOMException("The read operation was aborted.", "AbortError");
+    }
+
+    // Handle truncated or extended files during read
+    if (cursor > size) {
+      // Read remaining and concat
+      return concatBuffers([buf, await readAllInner(r, options)]);
+    } else {
+      return buf.subarray(0, cursor);
+    }
+  }
+
   window.__bootstrap.io = {
     iterSync,
     iter,
@@ -195,5 +235,7 @@
     readAll,
     readAllInner,
     readAllSync,
+    readAllSyncSized,
+    readAllInnerSized,
   };
 })(this);
diff --git a/runtime/js/40_read_file.js b/runtime/js/40_read_file.js
index 75cfd8074..53ac9b08a 100644
--- a/runtime/js/40_read_file.js
+++ b/runtime/js/40_read_file.js
@@ -4,13 +4,13 @@
 ((window) => {
   const core = window.Deno.core;
   const { open, openSync } = window.__bootstrap.files;
-  const { readAllInner, readAllSync } = window.__bootstrap.io;
+  const { readAllSyncSized, readAllInnerSized } = window.__bootstrap.io;
 
   function readFileSync(path) {
     const file = openSync(path);
     try {
-      const contents = readAllSync(file);
-      return contents;
+      const { size } = file.statSync();
+      return readAllSyncSized(file, size);
     } finally {
       file.close();
     }
@@ -19,31 +19,19 @@
   async function readFile(path, options) {
     const file = await open(path);
     try {
-      const contents = await readAllInner(file, options);
-      return contents;
+      const { size } = await file.stat();
+      return await readAllInnerSized(file, size, options);
     } finally {
       file.close();
     }
   }
 
   function readTextFileSync(path) {
-    const file = openSync(path);
-    try {
-      const contents = readAllSync(file);
-      return core.decode(contents);
-    } finally {
-      file.close();
-    }
+    return core.decode(readFileSync(path));
   }
 
   async function readTextFile(path, options) {
-    const file = await open(path);
-    try {
-      const contents = await readAllInner(file, options);
-      return core.decode(contents);
-    } finally {
-      file.close();
-    }
+    return core.decode(await readFile(path, options));
   }
 
   window.__bootstrap.readFile = {