Why no BlobItem?

[kelson42]

Searching how to write blobs, i wonder why there is no BlobItem and BlobProvider?! https://libzim.readthedocs.io/en/latest/api/classzim_1_1writer_1_1ContentProvider.html#exhale-class-classzim-1-1writer-1-1contentprovider

[mgautierfr]

The question is more "Why would we need a BlobItem and a BlobProvider ?"

Blob is a small wrapper around a data and a size. You can create is with Blob(const char *data, size_type size)

[kelson42]

@mgautierfr So it's straight to write a string, how to straightly write a blob (like a png content for example)? Do I need to create a a new dedicated contentProvider?

[mgautierfr]

What do you means by "write" a string ?
Adding a item with a content (as a string) into a zim ?

std::string is just a container for char. You can put your png content is a string[*] and you are good (at least, as good as for other content)

[*] There is just a trap, you have to use the version "4" of the constructor (in this doc) and not the version "5" as the png content may contain 0 bytes.

If you don't want to put your content in a string, yes, you have to create a ContentProvider creating Blob from your data/size.

[kelson42]

@mgautierfr Putting a blob in a string is a hack. A string is not (only) a char*. Actually we, with @kelvinhammond are a bit lost on node-libzim because this is unclear. We have tried to put blob in in the StringItem but somehow the binary code get corrupted and almost all our pictures are broken. It seems to me it would be really better to just provide a BlobItem and BlobContentProvider would be far more user friendly.

[mgautierfr]

the binary code get corrupted and almost all our pictures are broken

This is probably because your create the string with std::string(data). With this version of the constructor, the data will stop at the first 0 byte. You should use std::string(data, size)

[mgautierfr]

If you have a data and a size, you can simply create a contentProvider on a string using:
StringProvider(std::string(data, size)).
We could indeed create a constructor StringProvider(data, size) which create the std::string for you.