Fix doReadv/doWritev discarding partial count on EAGAIN

src/lib/libwasi.js

@@ -202,7 +202,18 @@ var WasiLibrary = {
       var ptr = {{{ makeGetValue('iov', C_STRUCTS.iovec.iov_base, '*') }}};
       var len = {{{ makeGetValue('iov', C_STRUCTS.iovec.iov_len, '*') }}};
       iov += {{{ C_STRUCTS.iovec.__size__ }}};
-      var curr = FS.read(stream, HEAP8, ptr, len, offset);
+      try {
+        var curr = FS.read(stream, HEAP8, ptr, len, offset);
+      } catch (e) {
+        // On a non-blocking stream a subsequent read may would-block after we
+        // already gathered data. POSIX readv is a single gather-read: return
+        // what we have rather than failing the whole call.
+        if (ret > 0 && e instanceof FS.ErrnoError &&
+            (e.errno == {{{ cDefs.EAGAIN }}} || e.errno == {{{ cDefs.EWOULDBLOCK }}})) {
+          break;
+        }
+        throw e;
+      }
       if (curr < 0) return -1;
       ret += curr;
       if (curr < len) break; // nothing more to read
@@ -219,7 +230,18 @@ var WasiLibrary = {
       var ptr = {{{ makeGetValue('iov', C_STRUCTS.iovec.iov_base, '*') }}};
       var len = {{{ makeGetValue('iov', C_STRUCTS.iovec.iov_len, '*') }}};
       iov += {{{ C_STRUCTS.iovec.__size__ }}};
-      var curr = FS.write(stream, HEAP8, ptr, len, offset);
+      try {
+        var curr = FS.write(stream, HEAP8, ptr, len, offset);
+      } catch (e) {
+        // On a non-blocking stream a subsequent write may would-block after we
+        // already sent data. POSIX writev is a single gather-write: return
+        // what we have rather than failing the whole call.
+        if (ret > 0 && e instanceof FS.ErrnoError &&
+            (e.errno == {{{ cDefs.EAGAIN }}} || e.errno == {{{ cDefs.EWOULDBLOCK }}})) {
+          break;
+        }
+        throw e;
+      }
       if (curr < 0) return -1;
       ret += curr;
       if (curr < len) {

test/codesize/test_codesize_cxx_ctors1.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 19183,
-  "a.out.js.gz": 7971,
+  "a.out.js": 19321,
+  "a.out.js.gz": 8000,
   "a.out.nodebug.wasm": 132556,
   "a.out.nodebug.wasm.gz": 49942,
-  "total": 151739,
-  "total_gz": 57913,
+  "total": 151877,
+  "total_gz": 57942,
   "sent": [
     "__cxa_throw",
     "_abort_js",

test/codesize/test_codesize_cxx_ctors2.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 19160,
-  "a.out.js.gz": 7957,
+  "a.out.js": 19298,
+  "a.out.js.gz": 7986,
   "a.out.nodebug.wasm": 131982,
   "a.out.nodebug.wasm.gz": 49601,
-  "total": 151142,
-  "total_gz": 57558,
+  "total": 151280,
+  "total_gz": 57587,
   "sent": [
     "__cxa_throw",
     "_abort_js",

test/codesize/test_codesize_cxx_except.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 23158,
-  "a.out.js.gz": 8955,
+  "a.out.js": 23296,
+  "a.out.js.gz": 8993,
   "a.out.nodebug.wasm": 172466,
   "a.out.nodebug.wasm.gz": 57476,
-  "total": 195624,
-  "total_gz": 66431,
+  "total": 195762,
+  "total_gz": 66469,
   "sent": [
     "__cxa_begin_catch",
     "__cxa_end_catch",

test/codesize/test_codesize_cxx_except_wasm.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 18982,
-  "a.out.js.gz": 7888,
+  "a.out.js": 19120,
+  "a.out.js.gz": 7923,
   "a.out.nodebug.wasm": 147881,
   "a.out.nodebug.wasm.gz": 55369,
-  "total": 166863,
-  "total_gz": 63257,
+  "total": 167001,
+  "total_gz": 63292,
   "sent": [
     "_abort_js",
     "_tzset_js",

test/codesize/test_codesize_cxx_except_wasm_legacy.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 19060,
-  "a.out.js.gz": 7913,
+  "a.out.js": 19198,
+  "a.out.js.gz": 7948,
   "a.out.nodebug.wasm": 145687,
   "a.out.nodebug.wasm.gz": 54986,
-  "total": 164747,
-  "total_gz": 62899,
+  "total": 164885,
+  "total_gz": 62934,
   "sent": [
     "_abort_js",
     "_tzset_js",

test/codesize/test_codesize_cxx_lto.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 18526,
-  "a.out.js.gz": 7665,
+  "a.out.js": 18665,
+  "a.out.js.gz": 7692,
   "a.out.nodebug.wasm": 102063,
   "a.out.nodebug.wasm.gz": 39527,
-  "total": 120589,
-  "total_gz": 47192,
+  "total": 120728,
+  "total_gz": 47219,
   "sent": [
     "a (emscripten_resize_heap)",
     "b (_setitimer_js)",

test/codesize/test_codesize_cxx_mangle.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 23208,
-  "a.out.js.gz": 8976,
+  "a.out.js": 23346,
+  "a.out.js.gz": 9013,
   "a.out.nodebug.wasm": 238895,
   "a.out.nodebug.wasm.gz": 79814,
-  "total": 262103,
-  "total_gz": 88790,
+  "total": 262241,
+  "total_gz": 88827,
   "sent": [
     "__cxa_begin_catch",
     "__cxa_end_catch",

test/codesize/test_codesize_cxx_noexcept.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 19183,
-  "a.out.js.gz": 7971,
+  "a.out.js": 19321,
+  "a.out.js.gz": 8000,
   "a.out.nodebug.wasm": 134556,
   "a.out.nodebug.wasm.gz": 50787,
-  "total": 153739,
-  "total_gz": 58758,
+  "total": 153877,
+  "total_gz": 58787,
   "sent": [
     "__cxa_throw",
     "_abort_js",

test/codesize/test_codesize_file_preload.expected.js

@@ -519,7 +519,17 @@ var onPreRuns = [];
     var ptr = HEAPU32[((iov) >> 2)];
     var len = HEAPU32[(((iov) + (4)) >> 2)];
     iov += 8;
-    var curr = FS.write(stream, HEAP8, ptr, len, offset);
+    try {
+      var curr = FS.write(stream, HEAP8, ptr, len, offset);
+    } catch (e) {
+      // On a non-blocking stream a subsequent write may would-block after we
+      // already sent data. POSIX writev is a single gather-write: return
+      // what we have rather than failing the whole call.
+      if (ret > 0 && e instanceof FS.ErrnoError && (e.errno == 6 || e.errno == 6)) {
+        break;
+      }
+      throw e;
+    }
     if (curr < 0) return -1;
     ret += curr;
     if (curr < len) {

test/codesize/test_codesize_file_preload.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 22239,
-  "a.out.js.gz": 9251,
+  "a.out.js": 22308,
+  "a.out.js.gz": 9277,
   "a.out.nodebug.wasm": 1666,
   "a.out.nodebug.wasm.gz": 945,
-  "total": 23905,
-  "total_gz": 10196,
+  "total": 23974,
+  "total_gz": 10222,
   "sent": [
     "a (fd_write)"
   ],

test/codesize/test_codesize_files_js_fs.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 17831,
-  "a.out.js.gz": 7311,
+  "a.out.js": 17969,
+  "a.out.js.gz": 7342,
   "a.out.nodebug.wasm": 381,
   "a.out.nodebug.wasm.gz": 258,
-  "total": 18212,
-  "total_gz": 7569,
+  "total": 18350,
+  "total_gz": 7600,
   "sent": [
     "a (fd_write)",
     "b (fd_read)",

test/codesize/test_codesize_hello_dylink.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 26190,
-  "a.out.js.gz": 11198,
+  "a.out.js": 26260,
+  "a.out.js.gz": 11231,
   "a.out.nodebug.wasm": 17861,
   "a.out.nodebug.wasm.gz": 9019,
-  "total": 44051,
-  "total_gz": 20217,
+  "total": 44121,
+  "total_gz": 20250,
   "sent": [
     "__syscall_stat64",
     "emscripten_resize_heap",

test/codesize/test_codesize_hello_dylink_all.json

@@ -1,7 +1,7 @@
 {
-  "a.out.js": 268279,
+  "a.out.js": 268425,
   "a.out.nodebug.wasm": 587978,
-  "total": 856257,
+  "total": 856403,
   "sent": [
     "IMG_Init",
     "IMG_Load",

test/fs/test_readv_eagain.c

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2024 The Emscripten Authors.  All rights reserved.
+ * Emscripten is available under two separate licenses, the MIT license and the
+ * University of Illinois/NCSA Open Source License.  Both these licenses can be
+ * found in the LICENSE file.
+ */
+
+// Regression test: a partial gather-read/write on a non-blocking stream must
+// return the bytes already transferred rather than propagating EAGAIN from a
+// later iovec.
+
+#include <assert.h>
+#include <emscripten/emscripten.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/uio.h>
+#include <unistd.h>
+
+int main() {
+  EM_ASM({
+    var eagain = $0;
+
+    // Device that satisfies the first read fully, then would-blocks.
+    var readCalls = 0;
+    var rdev = FS.makedev(64, 0);
+    FS.registerDevice(rdev, {
+      read: (stream, buffer, offset, length, pos) => {
+        if (++readCalls == 1) {
+          for (var i = 0; i < length; i++) buffer[offset + i] = 65 + i;
+          return length;
+        }
+        throw new FS.ErrnoError(eagain);
+      }
+    });
+    FS.mkdev('/rdev', rdev);
+
+    // Device that accepts the first write fully, then would-blocks.
+    var writeCalls = 0;
+    var wdev = FS.makedev(64, 1);
+    FS.registerDevice(wdev, {
+      write: (stream, buffer, offset, length, pos) => {
+        if (++writeCalls == 1) return length;
+        throw new FS.ErrnoError(eagain);
+      }
+    });
+    FS.mkdev('/wdev', wdev);
+  }, EAGAIN);
+
+  int rfd = open("/rdev", O_RDONLY);
+  assert(rfd >= 0);
+  char buf0[4] = {0};
+  char buf1[4] = {0};
+  struct iovec riov[] = {{.iov_base = buf0, .iov_len = 4},
+                         {.iov_base = buf1, .iov_len = 4}};
+  ssize_t nread = readv(rfd, riov, 2);
+  // First iovec filled; second would-block -> partial success, not EAGAIN.
+  assert(nread == 4);
+  assert(memcmp(buf0, "ABCD", 4) == 0);
+  close(rfd);
+
+  int wfd = open("/wdev", O_WRONLY);
+  assert(wfd >= 0);
+  char out0[4] = "ABCD";
+  char out1[4] = "EFGH";
+  struct iovec wiov[] = {{.iov_base = out0, .iov_len = 4},
+                         {.iov_base = out1, .iov_len = 4}};
+  ssize_t nwrite = writev(wfd, wiov, 2);
+  assert(nwrite == 4);
+  close(wfd);
+
+  printf("done\n");
+  return 0;
+}

test/test_core.py

@@ -6037,6 +6037,9 @@ def test_fs_readv(self):
   def test_fs_writev(self):
     self.do_runf('fs/test_writev.c', 'done\n', cflags=['-sFORCE_FILESYSTEM'])
 
+  def test_fs_readv_eagain(self):
+    self.do_runf('fs/test_readv_eagain.c', 'done\n', cflags=['-sFORCE_FILESYSTEM'])
+
   def test_fs_64bit(self):
     if self.get_setting('WASMFS'):
       self.set_setting('FORCE_FILESYSTEM')