The payloads won't be huge because we're talking about _down_loads, not _up_loads. The biggest payload I've seen was on some filehosting: about 2 KB, 10+ hidden form fields. But that's an "extreme" case, usually it'll be even less - just a download/request/transaction ID and/or a disposable request token to prevent request replay. For instance, Grooveshark's payload is about 100 bytes.
As for Components.isSuccessCode() calls, call it my extra paranoia. The one in onStateChange() is for cases when the connection is interrupted before the response headers arrive. I such cases, accessing the channel properties like responseStatus or contentType will throw and pollute the log. (The only easy way to reproduce that case I can come up with is to refresh the page repeatedly by holding F5/Ctrl+R for a second or two.) I think the one in the beginning of observe() can be safely dropped because if I'm not missing anything, observe() is called either by the browser (who, I think, won't call it for an incomplete/interrupted response) or by MediaSniffer::onStateChange.
And before you merge: there's another comment (DMS.js, line 2566) that AMO auditors probably won't like. Although I don't understand why do you care about their likes. I thought their job is auditing the code, not approving the comments.
As for Components.isSuccessCode() calls, call it my extra paranoia. The one in onStateChange() is for cases when the connection is interrupted before the response headers arrive. I such cases, accessing the channel properties like responseStatus or contentType will throw and pollute the log. (The only easy way to reproduce that case I can come up with is to refresh the page repeatedly by holding F5/Ctrl+R for a second or two.) I think the one in the beginning of observe() can be safely dropped because if I'm not missing anything, observe() is called either by the browser (who, I think, won't call it for an incomplete/interrupted response) or by MediaSniffer::onStateChange.
And before you merge: there's another comment (DMS.js, line 2566) that AMO auditors probably won't like. Although I don't understand why do you care about their likes. I thought their job is auditing the code, not approving the comments.