feat: ability to recover partial content from broken encoding

[fcisnerosrojo]

--> Problem

What I did:
I wrote a simple email which has two parts (text/plain and text/html) with base64 encoded data, but with one characteristic: both part contents have one extra base64 character (so they are slightly broken). Instead of having 4*n characters, the contents are (4*n)+1 characters long.

What I expected:
ReadParts() returns the root Part, with a FirstChild, and this one with a NextSibling. FirstChild and NextSibling have the partially decoded base64 data (Content != nil, parser recovers partial data from the parts with broken encoding).

What I got:
ReadParts() returns the root Part, with a FirstChild, and this one with a NextSibling. FirstChild and NextSibling have Content == nil (Parser does not recover partial data)
The reason is that for each part a base64.CorruptInputError is thrown, which then is catched by base64CorruptInputCheck(), leaving the part content empty and returning nil error (skipMalformedParts flag on true/false would not change the output).

--> Solution

With this particular scenario, in which there are text/plain and text/html contents, I would like to ignore that specific error (base64.CorruptInputError) and to keep the buffer read at that moment.
But the thing is that there might be different preferences (for now on, "policies"). For example:

• keep the buffer read only when base64.CorruptInputError is raised
• keep the buffer read only when another error is raised
• keep the buffer read only on a base64.CorruptInputError error and when ContentType is text/plain
• keep the buffer read only on a base64.CorruptInputError error and when ContentType is text/plain or text/html
• always keep the buffer read, no matter the error
• and so on ...

To solve this, I added a callback function readPartErrorPolicy to the Parser type, from which it will be possible to decide when to keep the buffer or not when an error is thrown while reading a part content.

When no policy is sent to the parser, default behavior is kept.

Release or branch I am using:
master

[jhillyerd]

Thanks, code looks good overall, but I have some suggestions.

[fcisnerosrojo]

Thanks, code looks good overall, but I have some suggestions.

Thanks for your feedback @jhillyerd ! All suggestions were included in the last commit .

[jhillyerd]

Thanks!

[fcisnerosrojo]

@jhillyerd , can we get a release that includes this feature?

[jhillyerd]

done