nodejs · codebytere · Aug 16, 2026
diff --git a/lib/fs.js b/lib/fs.js
@@ -81,6 +81,7 @@ const {
 
 const {
   FSReqCallback,
+  ReadFileJob,
 } = binding;
 const { toPathIfFileURL } = require('internal/url');
 const {
@@ -98,6 +99,7 @@ const {
 const {
   constants: {
     kIoMaxLength,
+    kReadFileBufferLength,
     kMaxUserId,
   },
   copyObject,
@@ -428,10 +430,70 @@ function readFile(path, options, callback) {
     return;
 
   const flagsNumber = stringToFlags(options.flag, 'options.flag');
+  path = getValidatedPath(path);
+  if (options.buffer === undefined) {
+    // Open + fstat + read + close in one thread pool round trip for files of
+    // up to one chunk; larger files come back as an open fd + size and take
+    // the chunked reader below (readFileAfterOneShot). `true`: a handed-back
+    // fd will be closed through fs.close(), so track it as unmanaged.
+    const job = new ReadFileJob(path, flagsNumber, kReadFileBufferLength, true);
+    job.context = context;
+    job.ondone = readFileAfterOneShot;
+    const accessError = job.run(path);
+    if (accessError !== undefined) {
+      // Not scheduled: report it the way the request-based open() did.
+      callback(accessError);
+    }
+    return;
+  }
   const req = new FSReqCallback();
   req.context = context;
   req.oncomplete = readFileAfterOpen;
-  binding.open(getValidatedPath(path), flagsNumber, 0o666, req);
+  binding.open(path, flagsNumber, 0o666, req);
+}
+
+function readFileAfterOneShot(err, buffer, fd, size, closeErr) {
+  const context = this.context;
+  if (err) {
+    context.callback(err);
+    return;
+  }
+  if (fd !== -1) {
+    // (context.read() below performs the abort check for this case.)
+    // Larger than one chunk: continue exactly like after open + fstat.
+    context.fd = fd;
+    context.size = size;
+    if (size > kIoMaxLength) {
+      return context.close(new ERR_FS_FILE_TOO_LARGE(size));
+    }
+    try {
+      context.prepare();
+    } catch (err) {
+      return context.close(err);
+    }
+    context.read();
+    return;
+  }
+  if (closeErr) {
+    context.callback(closeErr);
+    return;
+  }
+  if (context.signal?.aborted) {
+    // An abort that arrived while the read was in flight wins, as it did when
+    // it was noticed between the open/fstat/read steps.
+    context.callback(new AbortError(undefined, { cause: context.signal.reason }));
+    return;
+  }
+  let result = buffer;
+  if (context.encoding) {
+    try {
+      result = buffer.toString(context.encoding);
+    } catch (err) {
+      context.callback(err);
+      return;
+    }
+  }
+  context.callback(null, result);
 }
 
 function tryStatSync(fd, isUserFd) {

diff --git a/lib/internal/fs/promises.js b/lib/internal/fs/promises.js
@@ -1211,26 +1211,32 @@ async function readFileHandleWithUserBuffer(filehandle, options, size) {
   return encoding ? buffer.toString(encoding) : buffer.subarray(0, totalRead);
 }
 
-async function readFileHandle(filehandle, options) {
+async function readFileHandle(filehandle, options, knownRegularFileSize) {
   const signal = options?.signal;
   const encoding = options?.encoding;
   const decoder = encoding && new StringDecoder(encoding);
 
   checkAborted(signal);
 
-  const statFields = await PromisePrototypeThen(
-    binding.fstat(filehandle.fd, false, kUsePromises),
-    undefined,
-    handleErrorFromBinding,
-  );
-
-  checkAborted(signal);
-
   let size = 0;
   let length = 0;
-  if ((statFields[1/* mode */] & S_IFMT) === S_IFREG) {
-    size = statFields[8/* size */];
+  if (knownRegularFileSize !== undefined) {
+    // Handed over by readFile() together with an already open fd.
+    size = knownRegularFileSize;
     length = encoding ? MathMin(size, kReadFileBufferLength) : size;
+  } else {
+    const statFields = await PromisePrototypeThen(
+      binding.fstat(filehandle.fd, false, kUsePromises),
+      undefined,
+      handleErrorFromBinding,
+    );
+
+    checkAborted(signal);
+
+    if ((statFields[1/* mode */] & S_IFMT) === S_IFREG) {
+      size = statFields[8/* size */];
+      length = encoding ? MathMin(size, kReadFileBufferLength) : size;
+    }
   }
   if (length === 0) {
     length = kReadFileUnknownBufferLength;
@@ -2146,10 +2152,49 @@ async function readFile(path, options) {
 
   checkAborted(options.signal);
 
+  if (options.buffer === undefined && vfsState.handlers === null) {
+    // Open + fstat + read + close in one thread pool round trip for files of
+    // up to one chunk; larger files come back as an open fd + size and are
+    // read by readFileHandle() as before.
+    path = getValidatedPath(path);
+    const { 0: buffer, 1: fd, 2: size } = await readFileInOneRoundTrip(path, stringToFlags(flag));
+    if (fd === -1) {
+      checkAborted(options.signal);  // An abort during the read still wins.
+      return options.encoding ? buffer.toString(options.encoding) : buffer;
+    }
+    const filehandle = new FileHandle(new binding.FileHandle(fd));
+    return handleFdClose(readFileHandle(filehandle, options, size), filehandle.close);
+  }
+
   const fd = await open(path, flag, 0o666);
   return handleFdClose(readFileHandle(fd, options), fd.close);
 }
 
+/**
+ * @param {string|Buffer} path Validated path
+ * @param {number} flagsNumber
+ * @returns {Promise<[Buffer|undefined, number, number|undefined]>} [buffer, -1] or [undefined, fd, size]
+ */
+function readFileInOneRoundTrip(path, flagsNumber) {
+  return new Promise((resolve, reject) => {
+    const job = new binding.ReadFileJob(path, flagsNumber, kReadFileBufferLength);
+    job.ondone = (err, buffer, fd, size, closeErr) => {
+      const error = err ?? closeErr;
+      if (error != null) {
+        ErrorCaptureStackTrace(error, readFileInOneRoundTrip);
+        reject(error);
+      } else {
+        resolve([buffer, fd, size]);
+      }
+    };
+    const accessError = job.run(path);
+    if (accessError !== undefined) {
+      ErrorCaptureStackTrace(accessError, readFileInOneRoundTrip);
+      reject(accessError);
+    }
+  });
+}
+
 async function* _watch(filename, options = kEmptyObject) {
   const h = vfsState.handlers;
   if (h !== null) {