Handle unspecified siteOrigin

[jfurrow]

If a user doesn't specify siteOrigin, then Batfish will now do the following:

• Throw an error when using prefixUrl.absolute
• Skip sitemap generation and display an explanatory message

I also modified lib/generate-sitemap.js. I added a try/catch block to fix promise resolution, because it turns out the sitemap-static package doesn't accept a callback (check out the function).

Closes #43

@davidtheclark 👀

[davidtheclark]

I think that try-catch is not going to work here, either. On closer inspection, I think we'll have to rely on sitemapWriter emitting its stream events. We should add sitemapWriter.on('error', reject) and sitemapWriter.on('finish', () => resolve()), I think.

[jfurrow]

That makes sense, done!

Is there a reason you used the anonymous function wrapper in your example? Just curious, I wrote it as follows, but I can change it!

sitemapWriter.on('error', reject);
sitemapWriter.on('finish', resolve);

[davidtheclark]

The only reason I had in mind was strict control over the value with which the Promise will resolve. With () => resolve() we can say that this function returns a Promise that resolves with undefined. With just resolve, I'm not exactly sure what it will resolve with — would have to check the Node docs — and I'm not sure it'd be valuable to the consumer of this function.

[jfurrow]

That makes sense! I updated it.

[davidtheclark]

Interested in sending a PR to sitemap-static for fixing the docs in https://github.com/tmcw/sitemap-static#library-api?

[davidtheclark]

Other than that stream-related trickery, looks great 👍