begin standardizing our method of streaming lines from files

lib/storage/file.js

@@ -65,7 +65,7 @@ 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(env, stream, msgHandler, cb);
+    return void readFileBin(stream, msgHandler, cb);
 };
 
 // reads classic metadata from a channel log and aborts
@@ -90,7 +90,7 @@ var getMetadataAtPath = function (Env, path, _cb) {
     });
 
     var i = 0;
-    return readFileBin(Env, stream, function (msgObj, readMore, abort) {
+    return readFileBin(stream, function (msgObj, readMore, abort) {
         const line = msgObj.buff.toString('utf8');
 
         if (!line) {
@@ -164,28 +164,16 @@ var clearChannel = function (env, channelId, _cb) {
 };
 
 /*  readMessages is our classic method of reading messages from the disk
-    notably doesn't provide a means of aborting if you finish early
+    notably doesn't provide a means of aborting if you finish early.
+    Internally it uses readFileBin: to avoid duplicating code and to use less memory
 */
-// XXX replicate current API on top of readMessagesBin
-var readMessages = function (path, msgHandler, cb) {
-    var remainder = '';
-    var stream = Fs.createReadStream(path, { encoding: 'utf8' });
-    var complete = function (err) {
-        var _cb = cb;
-        cb = undefined;
-        if (_cb) { _cb(err); }
-    };
-    stream.on('data', function (chunk) {
-        var lines = chunk.split('\n');
-        lines[0] = remainder + lines[0];
-        remainder = lines.pop();
-        lines.forEach(msgHandler);
-    });
-    stream.on('end', function () {
-        msgHandler(remainder);
-        complete();
-    });
-    stream.on('error', function (e) { complete(e); });
+var readMessages = function (path, msgHandler, _cb) {
+    var stream = Fs.createReadStream(path, { start: 0});
+    var cb = Util.once(Util.mkAsync(_cb));
+    return readFileBin(stream, function (msgObj, readMore) {
+        msgHandler(msgObj.buff.toString('utf8'));
+        readMore();
+    }, cb);
 };
 
 /*  getChannelMetadata
@@ -203,23 +191,21 @@ var getChannelMetadata = function (Env, channelId, cb) {
 // low level method for getting just the dedicated metadata channel
 var getDedicatedMetadata = function (env, channelId, handler, cb) {
     var metadataPath = mkMetadataPath(env, channelId);
-    // XXX use readFileBin
-    readMessages(metadataPath, function (line) {
-        if (!line) { return; }
+    var stream = Fs.createReadStream(metadataPath, {start: 0});
+    readFileBin(stream, function (msgObj, readMore) {
+        var line = msgObj.buff.toString('utf8');
         try {
             var parsed = JSON.parse(line);
             handler(null, parsed);
-        } catch (e) {
-            handler(e, line);
+        } catch (err) {
+            handler(err, line);
         }
+        readMore();
     }, function (err) {
-        if (err) {
-            // ENOENT => there is no metadata log
-            if (err.code === 'ENOENT') { return void cb(); }
-            // otherwise stream errors?
-            return void cb(err);
-        }
-        cb();
+        // ENOENT => there is no metadata log
+        if (!err || err.code === 'ENOENT') { return void cb(); }
+        // otherwise stream errors?
+        cb(err);
     });
 };
 
@@ -377,7 +363,7 @@ var removeArchivedChannel = function (env, channelName, cb) {
     });
 };
 
-// XXX use ../plan.js
+// TODO use ../plan.js for a smaller memory footprint
 var listChannels = function (root, handler, cb) {
     // do twenty things at a time
     var sema = Semaphore.create(20);
@@ -793,6 +779,7 @@ var message = function (env, chanName, msg, cb) {
 };
 
 // stream messages from a channel log
+// TODO replace getMessages with readFileBin
 var getMessages = function (env, chanName, handler, cb) {
     getChannel(env, chanName, function (err, chan) {
         if (!chan) {