我试图将矢量用作缓冲区like this，我想知道是否有办法从矢量中取出切片而没有growing it，所以代码喜欢这项工作：
fn example(r: Read) {
let buffer: Vec<u8> = Vec::with_capacity(1024);
let slice: &mut[u8] = &mut buffer;
r.read(slice); // doesnt work since the slice has length zero
}
答案 0 :(得分：5)
如果只是为了获得一小部分容量，那么您将获得一些未初始化的数据。这是不安全的。
您可以使用Vec＆＃39; set_len执行此操作。然而
这是不安全的。读取数据对内存是安全的，但是另一种类型的向量或者set_len的误用可能不是。溢出检查和正确清理很重要。
这可能是一个重大的安全漏洞。
如果您使用非基本类型，则需要考虑恐慌安全。
这样做的基本方法是
unsafe {
buffer.set_len(buffer.capacity());
let new_len = try!(r.read(slice));
buffer.set_len(cmp::min(buffer.len(), new_len));
}
如果您不完全信任cmp::min的实施，则需要read，因为不正确的输出会导致设置的时间过长。
答案 1 :(得分：0)
我想在@Veedrac回答中添加三个细节。
1 - 这是从{% load service_path_extras %}
{% load staticfiles %}
<div class = "well well-light">
<div class="jarviswidget jarviswidget-color-blueDark" id="wid-id-5" data-widget-editbutton="false">
<!-- widget edit box -->
<div class="jarviswidget-editbox">
<!-- This area used as dropdown edit box -->
</div>
<!-- end widget edit box -->
<!-- widget content -->
<div class="widget-body no-padding">
<table id="service_path_table" class="table table-striped table-bordered table-hover" width="100%">
<thead>
<tr>
<th style="text-align:center"data-class="expand" class="col-sm-2"><h1 rel="popover-hover" data-placement="top" data-original-title="Service" data-content="Service is the partition or network segment name for a BU.<br>Click through for historical transitions.<br><br>Services Highlighted in <span class='badge bg-color-yellow'>yellow</span> have transitioned or added within the last 3 days." data-html="true"><strong>Service</strong></h1></th>
<th style="text-align:center"><h1 rel="popover-hover" data-placement="top" data-original-title="IP of Service" data-content="The Destination IP address of the corresponding Service<br>is checked from the HUB: hub1: <pre>sh ip bgp x.x.x.x</pre>" data-html="true"><strong>Service IP</strong></h1></th>
<th style="text-align:center"data-hide="phone"><h1 rel="popover-hover" data-placement="top" data-original-title="Best Path Router Hostname" data-content="The destination Hostname of the best path router. <br>Hover over name for more detail. <br>Click through for Statseeker Device View." data-html="true"><strong>Service Router</strong></h1></th>
<th style="text-align:center"data-hide="phone"><h1 rel="popover-hover" data-placement="top" data-original-title="Service Path Source Location" data-content="Location of running service. <br>Hover for Alternate Paths." data-html="true"><strong>Service Location</strong></h1></th>
<th style="text-align:center"data-hide="phone"><h1 rel="popover-hover" data-placement="top" data-original-title="SNMP Location" data-content="SNMP Location field of the best path router." data-html="true"><strong>Route Detail</strong></h1></th>
<th style="text-align:center"data-hide="phone,tablet"><h1><strong>Since</strong></h1></th>
</tr>
</thead>
<tbody>
{% for row in service_path_table %}
<tr>
{% if row.service_path_name in created_recent_service_names %}
<td align="center" class="success"><h6 rel="popover-hover" data-placement="top" data-original-title="Description" data-content="{{row.service_path_description}}"><strong><a href="/servicepathtable/{{row.service_path_id}}/">{{row.service_path_name}}</a></strong></h6></td>
{% elif row.service_path_name in recent_service_names %}
<td align="center" class="warning"><h6 rel="popover-hover" data-placement="top" data-original-title="Description" data-content="{{row.service_path_description}}"><strong><a href="/servicepathtable/{{row.service_path_id}}/">{{row.service_path_name}}</a></strong></h6></td>
{% else %}
<td align="center"><h6 rel="popover-hover" data-placement="top" data-original-title="Description" data-content="{{row.service_path_description}}"><strong><a href="/servicepathtable/{{row.service_path_id}}/">{{row.service_path_name}}</a></strong></h6></td>
{% endif %}
<td align="center"><h6 rel="popover-hover" data-placement="right" data-original-title="Raw Command Output" data-content="<pre>HTX-JC-HUB-2#{{row.sh_command_output}}</pre>" data-html="true">{{row.service_path_ip}}</td>
<td align="center"><h6 rel="popover-hover" data-placement="top" data-original-title="<h4>Quick Router Information</h4>" data-content="<div class='panel-body no-padding'>
<table class='table table-bordered table-condensed'>
<thead>
<tr>
<th align='center'>IP</th>
<th align='center'>Model</th>
<th>Tunnel Count</th>
<th>CPU One Minute Average</th>
</tr>
</thead>
<tbody>
<tr>
<td align='center'>{{row.ip}}</td>
<td>{{row.model}}</td>
<td align='center'>{{row.tunnel_count}}</td>
<td align='center'>{{row.cpu_uti_last_one_min}}%</td>
</tr>
</tbody>
</table>
</div>" data-html="true"><a href="http://NIM/cgi/nimc02?sort=&report=116&device={{row.hostname|convert_host}}">{{row.hostname}}</a></h6></td>
<td align="center"><h6 rel="popover-hover" data-placement="top" data-original-title="<h4>Alternate Paths</h4>" data-content="<div class='panel-body no-padding'>
<table class='table table-bordered table-condensed'>
<thead>
<tr>
<th>jConnect IP</th>
<th>Pref</th>
<th>Via IP</th>
<th>Loopback IP</th>
</tr>
</thead>
<tbody>
{% if row.alt_path_0_ip %}
<tr>
<td>{{row.alt_path_0_ip}}</td>
<td>{{row.alt_path_0_local_pref}}</td>
<td>{{row.alt_path_0_via_ip}}</td>
<td>{{row.alt_path_0_loopback_ip}}</td>
</tr>
{% endif %}
{% if row.alt_path_1_ip %}
<tr>
<td>{{row.alt_path_1_ip}}</td>
<td>{{row.alt_path_1_local_pref}}</td>
<td>{{row.alt_path_1_via_ip}}</td>
<td>{{row.alt_path_1_loopback_ip}}</td>
</tr>
{% endif %}
{% if row.alt_path_2_ip %}
<tr>
<td>{{row.alt_path_2_ip}}</td>
<td>{{row.alt_path_2_local_pref}}</td>
<td>{{row.alt_path_2_via_ip}}</td>
<td>{{row.alt_path_2_loopback_ip}}</td>
</tr>
{% endif %}
{% if row.alt_path_3_ip %}
<tr>
<td>{{row.alt_path_3_ip}}</td>
<td>{{row.alt_path_3_local_pref}}</td>
<td>{{row.alt_path_3_via_ip}}</td>
<td>{{row.alt_path_3_loopback_ip}}</td>
</tr>
{% endif %}
{% if row.alt_path_4_ip %}
<tr>
<td>{{row.alt_path_4_ip}}</td>
<td>{{row.alt_path_4_local_pref}}</td>
<td>{{row.alt_path_4_via_ip}}</td>
<td>{{row.alt_path_4_loopback_ip}}</td>
</tr>
{% endif %}
</tbody>
</table>
</div>" data-html="true">{{row.snmp_location|get_city}}</h6></td>
<td align="center">{{row.snmp_location}}</td>
<td align="center">{{row.date}}</td>
</tr>
{% endfor %}
</tbody>
</table>
</div>
<!-- end widget content -->
</div>
<!-- end widget div -->
</div>
<script>
$(document).ready(function() {
var responsiveHelper_dt_basic = undefined;
var responsiveHelper_datatable_fixed_column = undefined;
var responsiveHelper_datatable_col_reorder = undefined;
var responsiveHelper_datatable_tabletools = undefined;
var breakpointDefinition = {
tablet : 1024,
phone : 480
};
/* TABLETOOLS */
$('#service_path_table').dataTable({
// Tabletools options:
// https://datatables.net/extensions/tabletools/button_options
"sDom": "<'dt-toolbar'<'col-xs-12 col-sm-6'f><'col-sm-6 col-xs-6 hidden-xs'T>r>"+
"t"+
"<'dt-toolbar-footer'<'col-sm-6 col-xs-12 hidden-xs'i><'col-sm-6 col-xs-12'p>>",
"bPaginate": false,
"oTableTools": {
"aButtons": [
{
"sExtends": "xls",
"sTitle": "ETS_Service_Path_Table",
},
{
"sExtends": "pdf",
"sTitle": "ETS_Service_Path_Table",
"sPdfMessage": "Service Path Table PDF",
"sPdfSize": "letter"
},
{
"sExtends": "copy",
"sButtonText": "Copy to Clipboard",
"oSelectorOpts": { filter: "applied", order: "current" }
},
{
"sExtends": "csv",
"sButtonText": "Export to CSV",
"sTitle": "ETS_Service_Path_Table",
"oSelectorOpts": { filter: "applied", order: "current" }
},
{
"sExtends": "print",
"sButtonText": "Print",
"oSelectorOpts": { filter: "applied", order: "current" }
}
],
"sSwfPath": "http://cdn.datatables.net/tabletools/2.2.2/swf/copy_csv_xls_pdf.swf"
},
"autoWidth" : true,
"preDrawCallback" : function() {
// Initialize the responsive datatables helper once.
if (!responsiveHelper_datatable_tabletools) {
responsiveHelper_datatable_tabletools = new ResponsiveDatatablesHelper($('#service_path_table'), breakpointDefinition);
}
},
"rowCallback" : function(nRow) {
responsiveHelper_datatable_tabletools.createExpandIcon(nRow);
},
"drawCallback" : function(oSettings) {
responsiveHelper_datatable_tabletools.respond();
}
});
})
</script>
创建切片的相关代码，在这两种情况下，切片从向量的开头一直到Vec<T>：
fn deref_mut(&mut self) -> &mut [T]
2 - 有一个optimization in the TcpStream可以避免将内存归零，就像@ Veedrac的替代品一样，但它仅用于self.len而不是read_to_end。执行归零的read从performance reasons
3 - 切片没有关于矢量大小的信息，因此必须更新矢量长度，否则缓冲区将大于数据并且将使用零。