Fix wrong SCGI XML-RPC body length calculation method

[crux153]

Fix wrong XML-RPC body length calculation method which results in SCGI calls failing when multibyte characters are included.

Description

I discovered that flood calculates XML-RPC body length of an SCGI call simply by using String.prototype.length. This works ok when all payload is consist of single-byte characters.

However, when any multibyte character is included in xml payload, it miscalculate body length as JavaScript's string is UTF-16 and every UTF-8 multibyte characters are single-byte in UTF-16. So while String.prototype.length reports that the length of a UTF-8 character is 1, it may be 2-4 bytes when encoded in UTF-8, which causes rTorrent's XML-RPC server to misbehave.

[Error: XML-RPC fault: Call XML not a proper XML-RPC call. Call is not valid XML. Invalid XML "content". Problem with token at '<...': unclosed token]

This error is thrown when UTF-8 multibyte character is included in XML body, as current implementation of SCGI call builder reports shorter body length than its actual length.

I fixed this issue by calculating body length properly using Node's Buffer.byteLength function, which returns real byte length of UTF-8 encoded string.

Related Issue

#164 #196

I think changes in #196 may be reverted, but not tested.

Motivation and Context

I faced this issue when I tried to add torrents with download path including CJK characters. I wasn't able to use flood since my hard drive is full of directories containing UTF-8 multibyte characters and flood couldn't handle it.

This PR fixes issues with CJK character handling.

How Has This Been Tested?

I'm running the modified source on my machine for several days with bunch of torrents with multibyte character path. No problem so far.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[jfurrow]

Good catch @crux153, thanks for the PR!