From 208d4f9b3b730687d9224f2e372d0728c6b75244 Mon Sep 17 00:00:00 2001
From: Emil Mikulic <emikulic@gmail.com>
Date: Mon, 25 Mar 2013 05:17:32 +1100
Subject: [PATCH] Handle short writes.

---
 buftee.c | 39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/buftee.c b/buftee.c
index ae74b08..552a333 100644
--- a/buftee.c
+++ b/buftee.c
@@ -241,16 +241,17 @@ static void wait_until_writable(const int fd) {
     errx(1, "select() did not return writable fd = %d", fd);
 }
 
-static int xwrite(const int fd, struct buf* const buf) {
-  ssize_t write_ret;
-  int saved_errno;
-  struct timespec t0;
-  struct timespec t1;
+// Returns zero on EOF, dies on error, retries on short write.
+static int write_buf(const int fd, struct buf* const buf) {
+  char* data = buf->data;
+  size_t left = (size_t)buf->len;
 
   for (;;) {
+    struct timespec t0;
+    struct timespec t1;
     get_mono_time(&t0);
-    write_ret = write(fd, buf->data, (size_t)buf->len);
-    saved_errno = errno;
+    ssize_t write_ret = write(fd, data, left);
+    int saved_errno = errno;
     get_mono_time(&t1);
     warn_time("write()", &t0, &t1);
 
@@ -261,17 +262,21 @@ static int xwrite(const int fd, struct buf* const buf) {
         wait_until_writable(fd);
         continue;
       }
-      err(1, "write(fd = %d, count = %d) failed", fd, buf->len);
+      err(1, "write(fd = %d, count = %d) failed", fd, (int)left);
     }
-    if (write_ret == 0)
+    if (write_ret == 0) {
       return 0;  // EOF
+    }
     assert(write_ret >= 0);
-    if (write_ret < buf->len)
-      err(1, "write(fd = %d, count = %d) stopped short (returned %d)",
-          fd, buf->len, (int)write_ret);
-      // FIXME: handle this
-    assert(write_ret == buf->len);
-    return (int)write_ret;
+    if (write_ret < (ssize_t)left) {
+      nblogx("short write(fd = %d, count = %d): wrote %d",
+             fd, (int)left, (int)write_ret);
+      left -= write_ret;
+      data += write_ret;
+      continue;
+    }
+    assert(write_ret == (ssize_t)left);
+    return 1;
   }
 }
 
@@ -327,11 +332,9 @@ static void* writer_routine(void *arg) {
     }
 
     // Write.
-    int write_ret = xwrite(my->fd, buf);
-    if (write_ret == 0) {
+    if (write_buf(my->fd, buf) == 0) {
       errx(1, "fd %d hit EOF", my->fd);
     }
-    assert(write_ret == buf->len);
 
     // Unreference buffer, freeing it if we have to.
     lock(my->mutex);
-- 
2.17.1