Retrieve the first x bytes of a remote file

[dd32]

A commonly useful functionality in HTTP clients is to only request the first x bytes of a document, this can be useful for example, when you only need to fetch the first few KB of a image so as to determine it's dimensions from the initial metadata in the file.

At present, we have no way to offer this through WP_HTTP, The attached patch is a first-scratch effort at adding it. No proper unit tests so far, just casual testing which confirms it working.

Patch

• Supports all 3 transports
• Handles streaming-to-file as well
• Doesn't include Headers in the byte count
• Works with Redirects

I'll add some Unit tests for this soon hopefully.

Other things of note

• Disables Compression support (Well, rather it disables WP_HTTP saying it can support compression, servers may still send compressed data.
• Doesn't work with HTTP 1.1 + Transfer-encoding: Chunked, HTTP 1.1 support is mostly broken at present anyway #23463

Throwing this in for some soak time, I've renamed the parameter from 'first-x-bytes' to 'limit-response-size' - I'm not entirely sure of what naming scheme to use for this though, the name may change if someone can suggest a better option.

In 23605:

WP_HTTP: Enable developers to request the first x bytes of a document using the 'limit-response-size' parameter.
The connection to the remote server will be disconnected after x number of bytes has been received.
See #23472

In 23609:

WP_HTTP: Prevent the 'max_body_length' and 'stream_handle' properties of the curl class from leaking between requests by specifically initializing them in every case. See #23472 & r23605

Fixed?