Content-Length报头是一个数字，表示HTTP正文的确切字节长度。HTTP主体在开始行和报头之后的第一个空行之后立即开始。

通常，Content-Length报头用于HTTP 1.1，以便接收方知道当前响应*何时结束，这样连接就可以用于另一个请求。

*……或请求，在请求方法有一个主体的情况下，如POST, PUT或PATCH

或者，可以省略Content-Length头，使用分块的Transfer-Encoding头。

如果Content-Length和Transfer-Encoding头都缺失，则在响应的末尾必须关闭连接。

以下资源是我在学习HTTP时发现的非常有用的指南:

HTTP变得非常简单。

从这里开始:

The Content-Length entity-header field indicates the size of the entity-body, in decimal number of OCTETs, sent to the recipient or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET. Content-Length = "Content-Length" ":" 1*DIGIT An example is Content-Length: 3495 Applications SHOULD use this field to indicate the transfer-length of the message-body, unless this is prohibited by the rules in section 4.4. Any Content-Length greater than or equal to zero is a valid value. Section 4.4 describes how to determine the length of a message-body if a Content-Length is not given. Note that the meaning of this field is significantly different from the corresponding definition in MIME, where it is an optional field used within the "message/external-body" content-type. In HTTP, it SHOULD be sent whenever the message's length can be determined prior to being transferred, unless this is prohibited by the rules in section 4.4.

我的解释是，这意味着“导线上”的长度，即“编码”内容的长度

根据说明书:

The Content-Length entity-header field indicates the size of the entity-body, in decimal number of OCTETs, sent to the recipient or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET. Content-Length = "Content-Length" ":" 1*DIGIT An example is Content-Length: 3495 Applications SHOULD use this field to indicate the transfer-length of the message-body, unless this is prohibited by the rules in section 4.4. Any Content-Length greater than or equal to zero is a valid value. Section 4.4 describes how to determine the length of a message-body if a Content-Length is not given. Note that the meaning of this field is significantly different from the corresponding definition in MIME, where it is an optional field used within the "message/external-body" content-type. In HTTP, it SHOULD be sent whenever the message's length can be determined prior to being transferred, unless this is prohibited by the rules in section 4.4.

一个八位是8位。Content-length是消息体所代表的字节数。

rfc2616

的Content-Length实体报头字段表示 entity-body，十进制形式的OCTETs，发送给接收方 HEAD方法的情况，entity-body的大小 如果请求是GET，则已经发送了。

内容类型是什么并不重要。

延长线在以下职位。

考虑一下你是否有这样的标题:

content-encoding: gzip
content-length: 52098
content-type: text/javascript; charset=UTF-8

内容长度是压缩消息体的大小，以“八位”为单位(即以8位为单位，这恰好是所有现代计算机的“字节”)。

实际消息体的大小可以是其他大小，可能是150280字节。

字符的数量也可以不同，可能是150231个字符，因为一些unicode字符使用多个字节(注意UTF-8是一种标准编码)。

所以，不同的数字取决于你是否关心有多少数据被传输，或者有多少数据被保存，或者有多少符号被看到。当然，不能保证会提供这些头文件。