web server - Borland Technical Publications

Large data transfer
Note If you specify an invalid value (non numeric/negative number) then the default 4096
value is employed.
Known content length versus unknown
Based on whether content length is known in advance or not, chunked upload mode
can take one of the following two paths:
■
■
chunked upload with known content length
chunked upload with unknown content length
Chunked upload with known content length
In this case, the client knows the content length of the data in advance of the transfer.
The client sets the Content-Length HTTP header before writing out the data. The client
writes out a single response header followed by multiple chunks of data. Apache
receives this from the browser and sends data in the same fashion to the Borland web
container.
The response header contains the following header:
Content-Length=
Chunked upload with unknown content length
HTTP protocol version 1.1 adds a new feature to handle the case of data transfer when
data length is not known in advance. This feature is called HTTP chunking.
In this case, a client does not know the content length of the data in advance of a
transfer. The client does not set the Content-Length HTTP request header. Instead, the
client sets the Transfer-Encoding HTTP request header to a value of chunked as follows:
Transfer-Encoding="chunked"
The client sends the data to the Apache web server as “HTTP chunks”; a single
request header followed by multiple combinations of chunk header, chunk data, and
chunk trailer.
When the Apache web server sees this Transfer-Encoding header, it strips out the
chunk header and chunk trailers and sends the data as normal data chunks to the
Borland web container.
At this time, no major browsers support uploading data without knowing the content
length. In other words, browsers never add a Transfer-Encoding="chunked" header to an
HTTP request. However, a non-browser client can add this header to an HTTP
request.
Implementing non-chunked upload
This is the default transfer of data mode for the IIOP connector. In the non-chunked
upload mode, the Apache web server waits until it has all the data to send. Then it
calculates the content length and sets the Content-Length header to the actual content
length. Apache then sends the request header followed by a single huge data block.
This mode of transfer has high memory requirements both on the Apache web server
and the Borland web container, because the data is cached until all of it is available.
The non-chunked upload mode of transfer has no overhead of extra thread per each
request (in the Borland web container). This download mode works well under both the
HTTP protocol versions 1.0 and 1.1, because the Transfer-Encoding header is never
set in this mode.
Chapter 5: Web server to web container connectivity 51