All Write errors are fatal

With TLS connections a Write timeout caused by a SetDeadline permanently
breaks the connection. However, the errors are reported as temporary. So
there is no way to determine if it really is recoverable. As these were
the only kind of Write error that was recovered all Write errors are now
fatal to the connection.

https://github.com/jackc/pgx/issues/494
https://github.com/jackc/pgx/issues/506
https://github.com/golang/go/issues/29971

batch.go

@@ -133,11 +133,9 @@ func (b *Batch) Send(ctx context.Context, txOptions *TxOptions) error {
 		b.conn.pendingReadyForQueryCount++
 	}
 
-	n, err := b.conn.conn.Write(buf)
+	_, err = b.conn.conn.Write(buf)
 	if err != nil {
-		if fatalWriteErr(n, err) {
-			b.conn.die(err)
-		}
+		b.conn.die(err)
 		return err
 	}
 

conn.go

@@ -1096,11 +1096,9 @@ func (c *Conn) prepareEx(name, sql string, opts *PrepareExOptions) (ps *Prepared
 	buf = appendDescribe(buf, 'S', name)
 	buf = appendSync(buf)
 
-	n, err := c.conn.Write(buf)
+	_, err = c.conn.Write(buf)
 	if err != nil {
-		if fatalWriteErr(n, err) {
-			c.die(err)
-		}
+		c.die(err)
 		return nil, err
 	}
 	c.pendingReadyForQueryCount++
@@ -1360,11 +1358,9 @@ func (c *Conn) sendPreparedQuery(ps *PreparedStatement, arguments ...interface{}
 	buf = appendExecute(buf, "", 0)
 	buf = appendSync(buf)
 
-	n, err := c.conn.Write(buf)
+	_, err = c.conn.Write(buf)
 	if err != nil {
-		if fatalWriteErr(n, err) {
-			c.die(err)
-		}
+		c.die(err)
 		return err
 	}
 	c.pendingReadyForQueryCount++
@@ -1372,17 +1368,6 @@ func (c *Conn) sendPreparedQuery(ps *PreparedStatement, arguments ...interface{}
 	return nil
 }
 
-// fatalWriteError takes the response of a net.Conn.Write and determines if it is fatal
-func fatalWriteErr(bytesWritten int, err error) bool {
-	// Partial writes break the connection
-	if bytesWritten > 0 {
-		return true
-	}
-
-	netErr, is := err.(net.Error)
-	return !(is && netErr.Timeout())
-}
-
 // Exec executes sql. sql can be either a prepared statement name or an SQL string.
 // arguments should be referenced positionally from the sql string as $1, $2, etc.
 func (c *Conn) Exec(sql string, arguments ...interface{}) (commandTag CommandTag, err error) {
@@ -1791,8 +1776,8 @@ func (c *Conn) execEx(ctx context.Context, sql string, options *QueryExOptions,
 		buf = appendSync(buf)
 
 		c.lastStmtSent = true
-		n, err := c.conn.Write(buf)
-		if err != nil && fatalWriteErr(n, err) {
+		_, err = c.conn.Write(buf)
+		if err != nil {
 			c.die(err)
 			return "", err
 		}

query.go

@@ -418,8 +418,8 @@ func (c *Conn) QueryEx(ctx context.Context, sql string, options *QueryExOptions,
 		buf = appendSync(buf)
 
 		c.lastStmtSent = true
-		n, err := c.conn.Write(buf)
-		if err != nil && fatalWriteErr(n, err) {
+		_, err = c.conn.Write(buf)
+		if err != nil {
 			rows.fatal(err)
 			c.die(err)
 			return rows, err