在查询http标头时（通过winhttpqueryheaders）我收到错误ERROR_WINHTTP_HEADER_NOT_FOUND，即无法找到请求的标头。只有当我请求的数据很大时，才会发生这种情况，对于小数据，它正常工作。
WinHttpQueryHeaders( hRequest,
WINHTTP_QUERY_CONTENT_LENGTH | WINHTTP_QUERY_FLAG_NUMBER,
WINHTTP_HEADER_NAME_BY_INDEX,
&contentLength,
&contentLenBufferSize,
WINHTTP_NO_HEADER_INDEX);
答案 0 :(得分：0)
显然，Content-Length标头不存在，否则WinHttpQueryHeaders()将无法报告ERROR_WINHTTP_HEADER_NOT_FOUND。
在许多情况下，Content-Length标头可选：
如果邮件正在使用 chunked 传输编码（在HTTP 1.1中常用，特别是对于大数据），则需要Content-Length标头 要省略，如果存在，必须。在您的情况下，这是最可能发生的情况。
如果邮件正在使用multipart/...媒体类型（自终止），则可能会省略Content-Length标题。
如果通过关闭套接字终止消息，则可以省略Content-Length标题。
因此，并不总是可以知道消息开头的完整内容长度，有时您只能知道消息结束后的长度。您需要查看Content-Type，Content-Length，Transfer-Encoding和Connection标题，了解每个RFC 2616 Section 4.4的实际情况：
4.4 Message Length
The transfer-length of a message is the length of the message-body as
it appears in the message; that is, after any transfer-codings have
been applied. When a message-body is included with a message, the
transfer-length of that body is determined by one of the following
(in order of precedence):
1.Any response message which "MUST NOT" include a message-body (such
as the 1xx, 204, and 304 responses and any response to a HEAD
request) is always terminated by the first empty line after the
header fields, regardless of the entity-header fields present in
the message.
2.If a Transfer-Encoding header field (section 14.41) is present and
has any value other than "identity", then the transfer-length is
defined by use of the "chunked" transfer-coding (section 3.6),
unless the message is terminated by closing the connection.
3.If a Content-Length header field (section 14.13) is present, its
decimal value in OCTETs represents both the entity-length and the
transfer-length. The Content-Length header field MUST NOT be sent
if these two lengths are different (i.e., if a Transfer-Encoding
header field is present). If a message is received with both a
Transfer-Encoding header field and a Content-Length header field,
the latter MUST be ignored.
4.If the message uses the media type "multipart/byteranges", and the
ransfer-length is not otherwise specified, then this self-
elimiting media type defines the transfer-length. This media type
UST NOT be used unless the sender knows that the recipient can arse
it; the presence in a request of a Range header with ultiple byte-
range specifiers from a 1.1 client implies that the lient can parse
multipart/byteranges responses.
A range header might be forwarded by a 1.0 proxy that does not
understand multipart/byteranges; in this case the server MUST
delimit the message using methods defined in items 1,3 or 5 of
this section.
5.By the server closing the connection. (Closing the connection
cannot be used to indicate the end of a request body, since that
would leave no possibility for the server to send back a response.)
For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
containing a message-body MUST include a valid Content-Length header
field unless the server is known to be HTTP/1.1 compliant. If a
request contains a message-body and a Content-Length is not given,
the server SHOULD respond with 400 (bad request) if it cannot
determine the length of the message, or with 411 (length required) if
it wishes to insist on receiving a valid Content-Length.
All HTTP/1.1 applications that receive entities MUST accept the
"chunked" transfer-coding (section 3.6), thus allowing this mechanism
to be used for messages when the message length cannot be determined
in advance.
Messages MUST NOT include both a Content-Length header field and a
non-identity transfer-coding. If the message does include a non-
identity transfer-coding, the Content-Length MUST be ignored.
When a Content-Length is given in a message where a message-body is
allowed, its field value MUST exactly match the number of OCTETs in
the message-body. HTTP/1.1 user agents MUST notify the user when an
invalid length is received and detected.