Wa alaikum as salam.

I haven't been to Shanghai but I've lived/worked in other provinces in China.  I've never had a problem getting halal food anywhere.   When I was in Beijing I swore there were more Muslim restaurants in Hai Dian district than in all of California.  All of the supermarkets carry halal meat.   Just like we have the "K" in the States for Kosher, in China there's a "halal" symbol.  (it's just halal written in arabic)   If you're ever not sure, just ask someone in the store if the food is "hui ming de." 

Going out to eat with your co-workers  shouldn't be so bad.  Every restaurant serves vegetables and Tofu  But I must say the tofu is pretty good.  

Enjoy your stay in China, you're going to have a blast!

Salaam

I guess a rough translation for "hui ming" is Muslim and "de" is a suffix used to show possession or belonging.    If I said something was Mai Guo De, it would mean it was American.    

I don't see why you couldn't eat the vegetarian food.    Just make sure they don't put any meat in your vegetables.  Chinese like to mix meat and vegetables.  Also, pretty much all Chinese understand that Muslims don't eat pork.  But they don't get the concept of "halal" beef, chicken,etc.  So be careful, of people giving you meat and saying "yes yes I know you're muslim this one you can eat."

Salaam

Hmm, I know a lot of Muslims in China that will only eat in Muslim restaurants because of the possibility of the utensils being touched by pork.     This is an issue.  Perhaps you could take it up with an Imam.    I fear giving you an opinion without proper adilla.

Salaam