address remaining notes in the storage api

storage/file.js

@@ -236,8 +236,7 @@ How to proceed
 //  writeMetadata appends to the dedicated log of metadata amendments
 var writeMetadata = function (env, channelId, data, cb) {
     var path = mkMetadataPath(env, channelId);
-    // XXX appendFile isn't great
+    // TODO see if we can make this any faster by using something other than appendFile
-    // but this is a simple way to get things working
     Fs.appendFile(path, data + '\n', cb);
 };
 
@@ -290,7 +289,11 @@ const mkOffsetCounter = () => {
     });
 };
 
-// XXX write some docs for this magic
+// readMessagesBin asynchronously iterates over the messages in a channel log
+// the handler for each message must call back to read more, which should mean
+// that this function has a lower memory profile than our classic method
+// of reading logs line by line.
+// 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 });
     let keepReading = true;
@@ -341,23 +344,33 @@ var removeChannel = function (env, channelName, cb) {
 
     var CB = Once(cb);
 
+    var errors = 0;
     nThen(function (w) {
         Fs.unlink(channelPath, w(function (err) {
             if (err) {
-                // XXX handle ENOENT and only return an error
+                if (err.code === 'ENOENT') {
-                // if both channel and metadata did not exist...
+                    errors++;
+                    return;
+                }
                 w.abort();
                 CB(labelError("E_CHANNEL_REMOVAL", err));
             }
         }));
         Fs.unlink(metadataPath, w(function (err) {
             if (err) {
-                if (err.code === 'ENOENT') { return; } // proceed if there's no metadata to delete
+                if (err.code === 'ENOENT') {
+                    errors++;
+                    return;
+                } // proceed if there's no metadata to delete
                 w.abort();
                 CB(labelError("E_METADATA_REMOVAL", err));
             }
         }));
     }).nThen(function () {
+        if (errors === 2) {
+            return void CB(labelError('E_REMOVE_CHANNEL', new Error("ENOENT")));
+        }
+
         CB();
     });
 };
@@ -421,12 +434,23 @@ var listChannels = function (root, handler, cb) {
                     if (err) { return void handler(err); } // Is this correct?
 
                     list.forEach(function (item) {
-                        // ignore things that don't match the naming pattern
+                        // ignore hidden files
-                        // XXX don't ignore metadata files if there is no corresponding channel
+                        if (/^\./.test(item)) { return; }
-                        // since you probably want to clean those up
+                        // ignore anything that isn't channel or metadata
-                        if (/^\./.test(item) || !/[0-9a-fA-F]{32}\.ndjson$/.test(item)) { return; }
+                        if (!/^[0-9a-fA-F]{32}(\.metadata?)*\.ndjson$/.test(item)) {
+                            return;
+                        }
+                        if (!/^[0-9a-fA-F]{32}\.ndjson$/.test(item)) {
+                            // this will catch metadata, which we want to ignore if
+                            // the corresponding channel is present
+                            if (list.indexOf(item.replace(/\.metadata/, '')) !== -1) { return; }
+                            // otherwise fall through
+                        }
                         var filepath = Path.join(nestedDirPath, item);
-                        var channel = filepath.replace(/\.ndjson$/, '').replace(/.*\//, '');
+                        var channel = filepath
+                            .replace(/\.ndjson$/, '')
+                            .replace(/\.metadata/, '')
+                            .replace(/.*\//, '');
                         if ([32, 34].indexOf(channel.length) === -1) { return; }
 
                         // otherwise throw it on the pile