Slightly optimize iovec on Windows

libc/sock/iovec2nt.c

@@ -29,15 +29,21 @@
  */
 textwindows size_t __iovec2nt(struct NtIovec iovnt[hasatleast 16],
                               const struct iovec *iov, size_t iovlen) {
-  size_t i, limit;
-  for (limit = 0x7ffff000, i = 0; i < MIN(16, iovlen); ++i) {
-    iovnt[i].buf = iov[i].iov_base;
+  size_t i, j, limit = 0x7ffff000;
+  for (j = i = 0; i < iovlen; ++i) {
+    if (!iov[i].iov_len)
+      continue;
+    if (j == 16)
+      break;
+    iovnt[j].buf = iov[i].iov_base;
     if (iov[i].iov_len < limit) {
-      limit -= (iovnt[i].len = iov[i].iov_len);
+      limit -= (iovnt[j].len = iov[i].iov_len);
+      ++j;
     } else {
-      iovnt[i].len = limit;
+      iovnt[j].len = limit;
+      ++j;
       break;
     }
   }
-  return i;
+  return j;
 }

libc/sysv/consts.sh

@@ -2044,7 +2044,7 @@ syscon	misc	IF_NAMESIZE				0x10			0x10			0x10			0x10			0x10			0x10			0x10			0
 syscon	misc	INTERMEDIATE_C_GOOD			10			10			0			0			0			0			0			0
 syscon	misc	INTERMEDIATE_GOOD			8			8			0			0			0			0			0			0
 
-syscon	misc	IOV_MAX					0x0400			0x0400			0x0400			0x0400			0x0400			0x0400			0x0400			16			# unix consensus & MSG_MAXIOVLEN
+syscon	misc	IOV_MAX					1024			1024			1024			1024			1024			1024			1024			16			# unix consensus & MSG_MAXIOVLEN
 syscon	misc	LINE_MAX				0x0800			0x0800			0x0800			0x0800			0x0800			0x0800			0x0800			0			# unix consensus
 syscon	misc	LINKED_CMD_COMPLETE			10			10			0			0			0			0			0			0
 syscon	misc	LINKED_FLG_CMD_COMPLETE			11			11			0			0			0			0			0			0

libc/sysv/consts/IOV_MAX.S

@@ -1,2 +1,2 @@
 #include "libc/sysv/consts/syscon.internal.h"
-.syscon misc,IOV_MAX,0x0400,0x0400,0x0400,0x0400,0x0400,0x0400,0x0400,16
+.syscon misc,IOV_MAX,1024,1024,1024,1024,1024,1024,1024,16

test/posix/writev_test.c

@@ -0,0 +1,122 @@
+#include <netinet/in.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+#include <unistd.h>
+
+int main() {
+  int sockfd, newsockfd, clientfd;
+  struct sockaddr_in serv_addr, cli_addr;
+  socklen_t clilen;
+  struct iovec iov[2];
+  char buffer[256];
+  ssize_t n;
+  const char *str1 = "";
+  const char *str2 = "Hello from server!\n";
+  const char *str3 = "Hello from client!\n";
+
+  // Create server socket
+  sockfd = socket(AF_INET, SOCK_STREAM, 0);
+  if (sockfd < 0) {
+    perror("socket");
+    return 18;
+  }
+
+  // Bind server socket to localhost:PORT
+  memset(&serv_addr, 0, sizeof(serv_addr));
+  serv_addr.sin_family = AF_INET;
+  serv_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);  // localhost
+  serv_addr.sin_port = 0;
+  if (bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
+    perror("bind");
+    close(sockfd);
+    return 19;
+  }
+  uint32_t addrsize = sizeof(serv_addr);
+  if (getsockname(sockfd, (struct sockaddr *)&serv_addr, &addrsize)) {
+    perror("getsockname");
+    return 20;
+  }
+
+  // Listen for incoming connections
+  if (listen(sockfd, 1) < 0) {
+    perror("listen");
+    close(sockfd);
+    return 21;
+  }
+
+  // Create client socket
+  clientfd = socket(AF_INET, SOCK_STREAM, 0);
+  if (clientfd < 0) {
+    perror("socket");
+    close(sockfd);
+    return 22;
+  }
+
+  // Connect client socket to server
+  if (connect(clientfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
+    perror("connect");
+    close(sockfd);
+    close(clientfd);
+    return 23;
+  }
+
+  // Accept connection on server side
+  clilen = sizeof(cli_addr);
+  newsockfd = accept(sockfd, (struct sockaddr *)&cli_addr, &clilen);
+  if (newsockfd < 0) {
+    perror("accept");
+    close(sockfd);
+    close(clientfd);
+    return 34;
+  }
+
+  // Server writes to client using writev with zero-length iovec
+  iov[0].iov_base = (void *)str1;
+  iov[0].iov_len = 0;  // Zero-length iovec
+  iov[1].iov_base = (void *)str2;
+  iov[1].iov_len = strlen(str2);
+
+  n = writev(newsockfd, iov, 2);
+  if (n != 19)
+    return 13;
+
+  // Client reads data from server
+  memset(buffer, 0, sizeof(buffer));
+  n = read(clientfd, buffer, sizeof(buffer) - 1);
+  if (n < 0) {
+    perror("read");
+    return 14;
+  } else {
+    if (n != 19)
+      return 8;
+  }
+
+  // Client writes to server using writev with zero-length iovec
+  iov[0].iov_base = (void *)str1;
+  iov[0].iov_len = 0;  // Zero-length iovec
+  iov[1].iov_base = (void *)str3;
+  iov[1].iov_len = strlen(str3);
+
+  n = writev(clientfd, iov, 2);
+  if (n != 19)
+    return 9;
+
+  // Server reads data from client
+  memset(buffer, 0, sizeof(buffer));
+  n = read(newsockfd, buffer, sizeof(buffer) - 1);
+  if (n < 0) {
+    perror("ERROR reading from client");
+    return 10;
+  } else if (n != 19) {
+    return 11;
+  }
+
+  // Close all sockets
+  close(newsockfd);
+  close(clientfd);
+  close(sockfd);
+}