Ok, after significant trial and error, I've figured out how to do this. I ended up switching to knox, but presumably, you could use a similar strategy with aws-sdk. This is the kind of solution that makes me say, "There has to be a better way than this," but I'm satisfied with anything that works, at this point.
var imgData = "";
client.getFile(key, function(err, fileRes){
fileRes.on('data', function(chunk){
imgData += chunk.toString('binary');
}).on('end', function(){
res.set('Content-Type', pic.mime);
res.set('Content-Length', fileRes.headers['content-length']);
res.send(new Buffer(imgData, 'binary'));
});
});
getFile()
returns data chunks as buffers. One would think you could just pipe the results straight to front end, but for whatever reason, this was the ONLY way I could get the service to return an image correctly. It feels redundant to write a buffer to a binary string, only to write it back into a buffer, but hey, if it works, it works. If anyone finds a more efficient solution, I would love to hear it.