close streams when possible, simplify some code, enforce asynchrony

lib/storage/file.js

@@ -65,7 +65,10 @@ var channelExists = function (filepath, cb) {
 // it also allows the handler to abort reading at any time
 const readMessagesBin = (env, id, start, msgHandler, cb) => {
     const stream = Fs.createReadStream(mkPath(env, id), { start: start });
-    return void readFileBin(stream, msgHandler, cb);
+    return void readFileBin(stream, msgHandler, function (err) {
+        try { stream.close(); } catch (err2) { }
+        cb(err);
+    });
 };
 
 // reads classic metadata from a channel log and aborts
@@ -101,9 +104,6 @@ var getMetadataAtPath = function (Env, path, _cb) {
         if (i++ > 0) {
             console.log("aborting");
             abort();
-            try { stream.close(); } catch (err) {
-                console.log("could not close stream");
-            }
             return void cb();
         }
         var metadata;
@@ -684,6 +684,7 @@ var getChannel = function (
     id,
     callback /*:(err:?Error, chan:?ChainPadServer_ChannelInternal_t)=>void*/
 ) {
+    var callback = Util.once(Util.mkAsync(_callback));
     if (env.channels[id]) {
         var chan = env.channels[id];
         chan.atime = +new Date();
@@ -725,23 +726,20 @@ var getChannel = function (
             delete env.channels[id];
         }
         if (!channel.writeStream) {
-            throw new Error("getChannel() complete called without channel writeStream");
+            throw new Error("getChannel() complete called without channel writeStream"); // XXX
         }
         whenLoaded.forEach(function (wl) { wl(err, (err) ? undefined : channel); });
     };
     var fileExists;
-    var errorState;
     nThen(function (waitFor) {
         checkPath(path, waitFor(function (err, exists) {
             if (err) {
-                errorState = true;
-                complete(err);
-                return;
+                waitFor.abort();
+                return void complete(err);
             }
             fileExists = exists;
         }));
     }).nThen(function (waitFor) {
-        if (errorState) { return; }
         var stream = channel.writeStream = Fs.createWriteStream(path, { flags: 'a' });
         env.openFiles++;
         stream.on('open', waitFor());
@@ -757,7 +755,6 @@ var getChannel = function (
             }
         });
     }).nThen(function () {
-        if (errorState) { return; }
         complete();
     });
 };