Publisher review:rproxy adds backwards-compatible extensions to HTTP. rproxy adds backwards-compatible extensions to HTTP that come into operation when two parties to a web request understand the `hsync' encoding. If there are no two that can handle these extensions then they are silently ignored, so that the software will interoperate smoothly with existing systems. These parties might be the user agent (browser), the origin server, or intermediate proxies.
When an rproxy-enabled client requests a resource, it first checks whether it has a cached copy of the resource from a previous request. If it does, then it finds a block-by-block signature of the file, by computing a checksum over consecutive extents of equal length, such as 1024 bytes. The client adds this checksum into a header of the request and transmits the request as usual.
When an rproxy-enabled server receives a request containing a signature, it proceeds to generate the response, perhaps by running a server-side script. It then searches through the new instance body for blocks that have checksums that match those of blocks in the signature from the client. When it finds a match, it decides that the block is repeated from the old instance. Using this information, it generates a diff composed of instructions to copy sections from the old file, and instructions to insert new literal data. In fact, encoding can be performed inline as the response is generated, so large responses can be handled equally well.
The search for matching blocks obviously has to be able to cope with blocks that don't start on aligned boundaries, or it would not be useful in the common case where data is inserted or removed. The algorithm addresses this by supplying for this block both a `weak' CRC checksum, and a `strong' MD4 hash. The weak checksum algorithm is such that the server can efficiently check for a match at every byte offset. If a match is found, then the strong checksum is compared. If both match, the probability is astronomically high that the blocks are in fact identical.
The server also generates and sends down the signature of the new instance. The client is required to store this signature and return it on any future requests in which it wishes to use the cached instance. This mechanism will allow the differencing algorithm to be enhanced in the future without changing the client software. Requirements: ยท librsync
rproxy 0.9.5 is a C/C++ script for PHP Classes scripts design by Martin Pool.
It runs on following operating system: Windows / Linux / Mac OS / BSD / Solaris.
Operating system:Windows / Linux / Mac OS / BSD / Solaris
rproxy 0.9.5 script details 
