GitHub - abastardi/nchan: Fast, horizontally scalable, multiprocess pub/sub queuing server and proxy for HTTP, long-polling, Websockets and EventSource (SSE), powered by Nginx.

https://nchan.slact.net

Nchan is a scalable, flexible pub/sub server for the modern web, built as a module for the Nginx web server. It can be configured as a standalone server, or as a shim between your application and hundreds, thousands, or millions of live subscribers. It can buffer messages in memory, on-disk, or via Redis. All connections are handled asynchronously and distributed among any number of worker processes. It can also scale to many Nginx servers with Redis.

Messages are published to channels with HTTP POST requests or Websocket, and subscribed also through Websocket, long-polling, EventSource (SSE), old-fashioned interval polling, and more.

In a web browser, you can use Websocket or EventSource directly, or the NchanSubscriber.js wrapper library. It supports Long-Polling, EventSource, and resumable Websockets, and has a few other added convenience options.

Features

RESTful, HTTP-native API.
Supports Websocket, EventSource (Server-Sent Events), Long-Polling and other HTTP-based subscribers.
No-repeat, no-loss message delivery guarantees with per-channel configurable message buffers.
Subscribe to hundreds of channels over a single subscriber connection.
HTTP request callbacks and hooks for easy integration.
Introspection with channel events and url for monitoring performance statistics.
Fast ephemeral local message storage and optional, slower, persistent storage with Redis.
Horizontally scalable (using Redis).
Highly Available with no single point of failure (using Redis Cluster).

Status and History

The latest Nchan release is v1.0.8 (November 28, 2016) (changelog).

The first iteration of Nchan was written in 2009-2010 as the Nginx HTTP Push Module, and was vastly refactored into its present state in 2014-2016. The present release is in the testing phase. The core features and old functionality are thoroughly tested and stable. Some of the new functionality, especially Redis Cluster may be a bit buggy.

Upgrade from Nginx HTTP Push Module

Although Nchan is backwards-compatible with all Push Module configuration directives, some of the more unusual and rarely used settings have been disabled and will be ignored (with a warning). See the upgrade page for a detailed list of changes and improvements, as well as a full list of incompatibilities.

Does it scale?

Yes it does. Like Nginx, Nchan can easily handle as much traffic as you can throw at it. I've tried to benchmark it, but my benchmarking tools are much slower than Nchan. The data I've gathered is on how long Nchan itself takes to respond to every subscriber after publishing a message -- this excludes TCP handshake times and internal HTTP request parsing. Basically, it measures how Nchan scales assuming all other components are already tuned for scalability. The graphed data are averages of 5 runs with 50-byte messages.

With a well-tuned OS and network stack on commodity server hardware, expect to handle upwards of 300K concurrent subscribers per second at minimal CPU load. Nchan can also be scaled out to multiple Nginx instances using the Redis storage engine, and that too can be scaled up beyond a single-point-of-failure by using Redis Cluster.

Currently, Nchan's main bottleneck is not CPU load but memory bandwidth. This can be improved significantly in future versions with fewer allocations and better use of contiguous memory pools. Please consider supporting Nchan to speed up the work of memory cache optimization.

Install

Download Packages

Arch Linux: nginx-nchan and nginx-nchan-git are available in the Arch User Repository.
Mac OS X: a homebrew package is available. brew tap homebrew/nginx; brew install nginx-full --with-nchan-module
Debian: A dynamic module build is available in the Debian package repository: libnginx-mod-nchan.
Additionally, you can use the pre-built static module packages nginx-common.deb and nginx-extras.deb. Download both and install them with dpkg -i, followed by sudo apt-get -f install.
Ubuntu: nginx-common.ubuntu.deb and nginx-extras.ubuntu.deb. Download both and install them with dpkg -i, followed by sudo apt-get -f install. Who knows when Ubuntu will Nchan to their repository?...
Fedora: Dynamic module builds for Nginx > 1.10.0 are available: nginx-mod-nchan.x86_64.rpm, nginx-mod-nchan.src.rpm.
A statically compiled binary and associated linux nginx installation files are also available as a tarball.

Build From Source

Grab the latest copy of Nginx from nginx.org. Grab the latest Nchan source from github. Follow the instructions for building Nginx, except during the configure stage, add

./configure --add-module=path/to/nchan ...

If you're using Nginx > 1.9.11, you can build Nchan as a dynamic module with --add-dynamic-module=path/to/nchan

Run make, make install, and enjoy. (Caution, contents may be hot.)

Getting Started

Once you've built and installed Nchan, it's very easy to start using. Add two locations to your nginx config:

#...
http {  
  server {
    #...
    
    location = /sub {
      nchan_subscriber;
      nchan_channel_id $arg_id;
    }
    
    location = /pub {
      nchan_publisher;
      nchan_channel_id $arg_id;
    }
  }
}

You can now publish messages to channels by POSTing data to /sub?id=channel_id , and subscribe by pointing Websocket, EventSource, or NchanSubscriber.js to sub/?id=channel_id. It's that simple.

But Nchan is very flexible and highly configurable. So, of course, it can get a lot more complicated...

Conceptual Overview

The basic unit of most pub/sub solutions is the messaging channel. Nchan is no different. Publishers send messages to channels with a certain channel id, and subscribers subscribed to those channels receive them. Some number of messages may be buffered for a time in a channel's message buffer before they are deleted. Pretty simple, right?

Well... the trouble is that nginx configuration does not deal with channels, publishers, and subscribers. Rather, it has several sections for incoming requests to match against server and location sections. Nchan configuration directives map servers and locations onto channel publishing and subscribing endpoints:

#very basic nchan config
worker_processes 5;

http {  
  server {
    listen       80;
    
    location = /sub {
      nchan_subscriber;
      nchan_channel_id foobar;
    }
    
    location = /pub {
      nchan_publisher;
      nchan_channel_id foobar;
    }
  }
}

The above maps requests to the URI /sub onto the channel foobar's subscriber endpoint , and similarly /pub onto channel foobar's publisher endpoint.

Publisher Endpoints

Publisher endpoints are Nginx config locations with the nchan_publisher directive.

Messages can be published to a channel by sending HTTP POST requests with the message contents to the publisher endpoint locations. You can also publish messages through a Websocket connection to the same location.

Publishing Messages

Requests and websocket messages are responded to with information about the channel at time of message publication. Here's an example from publishing with curl:

>  curl --request POST --data "test message" http://127.0.0.1:80/pub

 queued messages: 5
 last requested: 18 sec. ago
 active subscribers: 0
 last message id: 1450755280:0

The response can be in plaintext (as above), JSON, or XML, based on the request's Accept header:

> curl --request POST --data "test message" -H "Accept: text/json" http://127.0.0.2:80/pub

 {"messages": 6, "requested": 55, "subscribers": 0, "last_message_id": "1450755317:0" }

Websocket publishers also receive the same responses when publishing, with the encoding determined by the Accept header present during the handshake.

The response code for an HTTP request is 202 Accepted if no subscribers are present at time of publication, or 201 Created if at least 1 subscriber was present.

Metadata can be added to a message when using an HTTP POST request for publishing. A Content-Type header will be associated as the message's content type (and output to Long-Poll, Interval-Poll, and multipart/mixed subscribers). A X-EventSource-Event header can also be used to associate an EventSource event: line value with a message.

Other Publisher Endpoint Actions

HTTP GET requests return channel information without publishing a message. The response code is 200 if the channel exists, and 404 otherwise:

> curl --request POST --data "test message" http://127.0.0.2:80/pub
  ...

> curl -v --request GET -H "Accept: text/json" http://127.0.0.2:80/pub

 {"messages": 1, "requested": 7, "subscribers": 0, "last_message_id": "1450755421:0" }

HTTP DELETE requests delete a channel and end all subscriber connections. Like the GET requests, this returns a 200 status response with channel info if the channel existed, and a 404 otherwise.

For an in-depth explanation of how settings are applied to channels from publisher locations, see the details page.

Subscriber Endpoints

Subscriber endpoints are Nginx config locations with the nchan_subscriber directive.

Nchan supports several different kinds of subscribers for receiving messages: Websocket, EventSource (Server Sent Events), Long-Poll, Interval-Poll. HTTP chunked transfer, and HTTP multipart/mixed.

Long-Polling

The tried-and-true server-push method supported by every browser out there.
Initiated by sending an HTTP GET request to a channel subscriber endpoint.
The long-polling subscriber walks through a channel's message queue via the built-in cache mechanism of HTTP clients, namely with the "Last-Modified" and "Etag" headers. Explicitly, to receive the next message for given a long-poll subscriber response, send a request with the "If-Modified-Since" header set to the previous response's "Last-Modified" header, and "If-None-Match" likewise set to the previous response's "Etag" header.
Sending a request without a "If-Modified-Since" or "If-None-Match" headers returns the oldest message in a channel's message queue, or waits until the next published message, depending on the value of the nchan_subscriber_first_message config directive.
A message's associated content type, if present, will be sent to this subscriber with the Content-Type header.
Interval-Polling

Works just like long-polling, except if the requested message is not yet available, immediately responds with a 304 Not Modified. There is no way to differentiate between long-poll and interval-poll subscriber requests, so long-polling must be disabled for a subscriber location if you wish to use interval-polling.
Websocket

Bidirectional communication for web browsers. Part of the HTML5 spec. Nchan supports the latest protocol version 13 (RFC 6455).
Initiated by sending a websocket handshake to the desired subscriber endpoint location.
If the websocket connection is closed by the server, the close frame will contain the HTTP response code and status line describing the reason for closing the connection. Server-initiated keep-alive pings can be configured with the nchan_websocket_ping_interval config directive. Websocket extensions are not yet supported.
Messages published through a websocket connection can be forwarded to an upstream application with the nchan_publisher_upstream_request config directive.
Websocket subscribers can use the custom ws+meta.nchan subprotocol to receive message metadata with messages, making websocket connections resumable. Messages received with this subprotocol are of the form
```
id: message_id
content-type: message_content_type
\n
message_data
```
The content-type: line may be omitted.

Messages are delivered in text websocket frames, except if a message's content-type is "application/octet-stream" -- then it is delivered in a binary frame.
EventSource

Also known as Server-Sent Events or SSE, it predates Websockets in the HTML5 spec, and is a very simple protocol.
Initiated by sending an HTTP GET request to a channel subscriber endpoint with the "Accept: text/event-stream" header.
Each message data: segment will be prefaced by the message id: .
To resume a closed EventSource connection from the last-received message, one should start the connection with the "Last-Event-ID" header set to the last message's id.
Unfortunately, browsers don't support setting this header for an EventSource object, so by default the last message id is set either from the "Last-Event-Id" header or the last_event_id url query string argument.
This behavior can be configured via the nchan_subscriber_last_message_id config.
A message's content-type will not be received by an EventSource subscriber, as the protocol makes no provisions for this metadata. A message's associated event type, if present, will be sent to this subscriber with the event: line.
HTTP multipart/mixed

The multipart/mixed MIMEtype was conceived for emails, but hey, why not use it for HTTP? It's easy to parse and includes metadata with each message.
Initiated by including an Accept: multipart/mixed header.
The response headers and the unused "preamble" portion of the response body are sent right away, with the boundary string generated randomly for each subscriber. Each subsequent message will be sent as one part of the multipart message, and will include the message time and tag (Last-Modified and Etag) as well as the optional Content-Type headers.
Each message is terminated with the next multipart message's boundary without a trailing newline. While this conforms to the multipart spec, it is unusual as multipart messages are defined as starting, rather than ending with a boundary.
A message's associated content type, if present, will be sent to this subscriber with the Content-Type header.
HTTP Raw Stream

A simple subscription method similar to the streaming subscriber of the Nginx HTTP Push Stream Module. Messages are appended to the response body, separated by a newline or configurable by nchan_subscriber_http_raw_stream_separator.
HTTP Chunked Transfer

This subscription method uses the chunked Transfer-Encoding to receive messages.
Initiated by explicitly including chunked in the TE header:
TE: chunked (or TE: chunked;q=?? where the qval > 0)
The response headers are sent right away, and each message will be sent as an individual chunk. Note that because a zero-length chunk terminates the transfer, zero-length messages will not be sent to the subscriber.
Unlike the other subscriber types, the chunked subscriber cannot be used with http/2 because it dissallows chunked encoding.

PubSub Endpoint

PubSub endpoints are Nginx config locations with the nchan_pubsub directive.

A combination of publisher and subscriber endpoints, this location treats all HTTP GET requests as subscribers, and all HTTP POST as publishers. One simple use case is an echo server:

  location = /pubsub {
    nchan_pubsub;
    nchan_channel_id foobar;
  }

A more applicable setup may set different publisher and subscriber channel ids:

  location = /pubsub {
    nchan_pubsub;
    nchan_publisher_channel_id foo;
    nchan_subscriber_channel_id bar;
  }

Here, subscribers will listen for messages on channel foo, and publishers will publish messages to channel bar. This can be useful when setting up websocket proxying between web clients and your application.

The Channel ID

So far the examples have used static channel ids, which is not very useful in practice. It can be set to any nginx variable, such as a querystring argument, a header value, or a part of the location url:

  location = /sub_by_ip {
    #channel id is the subscriber's IP address
    nchan_subscriber;
    nchan_channel_id $remote_addr;
  }
  
  location /sub_by_querystring {
    #channel id is the query string parameter chanid
    # GET /sub/sub_by_querystring?foo=bar&chanid=baz will have the channel id set to 'baz'
    nchan_subscriber;
    nchan_channel_id $arg_chanid;
  }

  location ~ /sub/(\w+)$ {
    #channel id is the word after /sub/
    # GET /sub/foobar_baz will have the channel id set to 'foobar_baz'
    # I hope you know your regular expressions...
    nchan_subscriber;
    nchan_channel_id $1; #first capture of the location match
  }

Channel Multiplexing

With channel multiplexing, subscribers can subscribe to up to 255 channels per connection. Messages published to all the specified channels will be delivered in-order to the subscriber. There are two ways to enable multiplexing:

Up to 7 channel ids can be specified for the nchan_channel_id or nchan_channel_subscriber_id config directive:

  location ~ /multisub/(\w+)/(\w+)$ {
    nchan_subscriber;
    nchan_channel_id "$1" "$2" "common_channel";
    #GET /multisub/foo/bar will be subscribed to:
    # channels 'foo', 'bar', and 'common_channel',
    #and will receive messages from all of the above.
  }

For more than 7 channels, nchan_channel_id_split_delimiter can be used to split the nchan_channel_id or nchan_channel_subscriber_id into up to 255 individual channel ids:

  location ~ /multisub-split/(.*)$ {
    nchan_subscriber;
    nchan_channel_id "$1";
    nchan_channel_id_split_delimiter ",";
    #GET /multisub-split/foo,bar,baz,a will be subscribed to:
    # channels 'foo', 'bar', 'baz', and 'a'
    #and will receive messages from all of the above.
  }

Publishing to multiple channels with a single request is also possible, with similar configuration:

  location ~ /multipub/(\w+)/(\w+)$ {
    nchan_publisher;
    nchan_channel_id "$1" "$2" "another_channel";
  }

DELETE requests to a multiplexed channel broadcast the deletion to each of the channels it multiplexes, deletes all their messages and kicks out all clients subscribed to any of the channel ids.

See the details page for more information about using good IDs and keeping channels secure.

Storage

Nchan can stores messages in memory, on disk, or via Redis. Memory storage is much faster, whereas Redis has additional overhead as is considerably slower for publishing messages, but offers near unlimited scalability for broadcast use cases with far more subscribers than publishers.

Memory Storage

This storage method uses a segment of shared memory to store messages and channel data. Large messages as determined by Nginx's caching layer are stored on-disk. The size of the memory segment is configured with nchan_max_reserved_memory. Data stored here is not persistent, and is lost if Nginx is restarted or reloaded.

Redis

Nchan can also store messages and channels on a Redis server, or in a Redis cluster. To use a Redis server, set nchan_use_redis on; and set the server url with nchan_redis_url. These two settings are inheritable by nested locations, so it is enough to set them within an http { } block to enable Redis for all Nchan locations in that block. Different locations can also use different Redis servers.

To use a Redis Cluster, the Redis servers acting as cluster nodes need to be configured in an upstream { } block:

  upstream redis_cluster {
    nchan_redis_server redis://127.0.0.1:7000;
    nchan_redis_server redis://127.0.0.1:7001;
    nchan_redis_server redis://127.0.0.1:7002;
  }

It is best to specify all master cluster nodes, but this is not required -- as long as Nchan can connect to at least 1 node, it will discover and connect to the whole cluster.

To use Redis Cluster in an Nchan location, use the nchan_redis_pass setting:

  location ~ /pubsub/(\w+)$ {
    nchan_channel_id $1;
    nchan_pubsub;
    nchan_redis_pass redis_cluster;
  }

Note that nchan_redis_pass implies nchan_use_redis on;, and that this setting is not inherited by nested locations.

When connecting several Nchan servers to the same Redis server (or cluster), the servers must have their times synced up. Failure to do so may result in missing and duplicated messages.

See the details page for more information on using Redis.

Variables

Nchan makes several variables usabled in the config file:

$nchan_channel_id
The channel id extracted from a publisher or subscriber location request. For multiplexed locations, this is the first channel id in the list.
$nchan_channel_id1, $nchan_channel_id2, $nchan_channel_id3, $nchan_channel_id4
As above, but for the nth channel id in multiplexed channels.
$nchan_subscriber_type
For subscriber locations, this variable is set to the subscriber type (websocket, longpoll, etc.).
$nchan_publisher_type
For publisher locations, this variable is set to the subscriber type (http or websocket).
$nchan_prev_message_id, $nchan_message_id The current and previous (if applicable) message id for publisher request or subscriber response.
$nchan_channel_event For channel events, this is the event name. Useful when configuring nchan_channel_event_string.

Additionally, nchan_stub_status data is also exposed as variables. These are available only when nchan_stub_status is enabled on at least one location:

$nchan_stub_status_total_published_messages
$nchan_stub_status_stored_messages
$nchan_stub_status_shared_memory_used
$nchan_stub_status_channels
$nchan_stub_status_subscribers
$nchan_stub_status_redis_pending_commands
$nchan_stub_status_redis_connected_servers
$nchan_stub_status_total_ipc_alerts_received
$nchan_stub_status_ipc_queued_alerts
$nchan_stub_status_total_ipc_send_delay
$nchan_stub_status_total_ipc_receive_delay

Configuration Directives

nchan_channel_id
arguments: 1 - 7
default: (none)
context: server, location, if

Channel id for a publisher or subscriber location. Can have up to 4 values to subscribe to up to 4 channels.
more details
nchan_channel_id_split_delimiter
arguments: 1
default: (none)
context: server, location, if

Split the channel id into several ids for multiplexing using the delimiter string provided.
more details
nchan_eventsource_event
arguments: 1
default: (none)
context: server, location, if

Set the EventSource event: line to this value. When used in a publisher location, overrides the published message's X-EventSource-Event header and associates the message with the given value. When used in a subscriber location, overrides all messages' associated event: string with the given value.
nchan_longpoll_multipart_response [ off | on | raw ]
arguments: 1
default: off
context: server, location, if

when set to 'on', enable sending multiple messages in a single longpoll response, separated using the multipart/mixed content-type scheme. If there is only one available message in response to a long-poll request, it is sent unmodified. This is useful for high-latency long-polling connections as a way to minimize round-trips to the server. When set to 'raw', sends multiple messages using the http-raw-stream message separator.
nchan_publisher [ http | websocket ]
arguments: 0 - 2
default: http websocket
context: server, location, if
legacy name: push_publisher

Defines a server or location as a publisher endpoint. Requests to a publisher location are treated as messages to be sent to subscribers. See the protocol documentation for a detailed description.
more details
nchan_publisher_channel_id
arguments: 1 - 7
default: (none)
context: server, location, if

Channel id for publisher location.
nchan_publisher_upstream_request <url>
arguments: 1
context: server, location, if

Send POST request to internal location (which may proxy to an upstream server) with published message in the request body. Useful for bridging websocket publishers with HTTP applications, or for transforming message via upstream application before publishing to a channel.
The upstream response code determines how publishing will proceed. A 200 OK will publish the message from the upstream response's body. A 304 Not Modified will publish the message as it was received from the publisher. A 204 No Content will result in the message not being published.
more details
nchan_pubsub [ http | websocket | eventsource | longpoll | intervalpoll | chunked | multipart-mixed | http-raw-stream ]
arguments: 0 - 6
default: http websocket eventsource longpoll chunked multipart-mixed
context: server, location, if

Defines a server or location as a pubsub endpoint. For long-polling, GETs subscribe. and POSTs publish. For Websockets, publishing data on a connection does not yield a channel metadata response. Without additional configuration, this turns a location into an echo server.
more details
nchan_subscribe_request <url>
arguments: 1
context: server, location, if

Send GET request to internal location (which may proxy to an upstream server) after subscribing. Disabled for longpoll and interval-polling subscribers.
more details
nchan_subscriber [ websocket | eventsource | longpoll | intervalpoll | chunked | multipart-mixed | http-raw-stream ]
arguments: 0 - 5
default: websocket eventsource longpoll chunked multipart-mixed
context: server, location, if
legacy name: push_subscriber

Defines a server or location as a channel subscriber endpoint. This location represents a subscriber's interface to a channel's message queue. The queue is traversed automatically, starting at the position defined by the nchan_subscriber_first_message setting.
The value is a list of permitted subscriber types.
more details
nchan_subscriber_channel_id
arguments: 1 - 7
default: (none)
context: server, location, if

Channel id for subscriber location. Can have up to 4 values to subscribe to up to 4 channels.
nchan_subscriber_compound_etag_message_id
arguments: 1
default: off
context: server, location, if

Override the default behavior of using both Last-Modified and Etag headers for the message id.
Enabling this option packs the entire message id into the Etag header, and discards
Last-Modified and If-Modified-Since headers.
more details
nchan_subscriber_first_message [ oldest | newest | <number> ]
arguments: 1
default: oldest
context: server, location, if

Controls the first message received by a new subscriber. 'oldest' starts at the oldest available message in a channel's message queue, 'newest' waits until a message arrives. If a number n is specified, starts at nth message from the oldest. (-n starts at nth from now). 0 is equivalent to 'newest'.
nchan_subscriber_http_raw_stream_separator <string>
arguments: 1
default: \n
context: server, location, if

Message separator string for the http-raw-stream subscriber. Automatically terminated with a newline character.
nchan_subscriber_last_message_id
arguments: 1 - 5
default: $http_last_event_id $arg_last_event_id
context: server, location, if

If If-Modified-Since and If-None-Match headers are absent, set the message id to the first non-empty of these values. Used primarily as a workaround for the inability to set the first Last-Message-Id of a web browser's EventSource object.
nchan_subscriber_message_id_custom_etag_header
arguments: 1
default: (none)
context: server, location, if

Use a custom header instead of the Etag header for message ID in subscriber responses. This setting is a hack, useful when behind a caching proxy such as Cloudflare that under some conditions (like using gzip encoding) swallow the Etag header.
nchan_subscriber_timeout <number> (seconds)
arguments: 1
default: 0 (none)
context: http, server, location, if
legacy name: push_subscriber_timeout

Maximum time a subscriber may wait for a message before being disconnected. If you don't want a subscriber's connection to timeout, set this to 0. When possible, the subscriber will get a response with a 408 Request Timeout status; otherwise the subscriber will simply be disconnected.
nchan_unsubscribe_request <url>
arguments: 1
context: server, location, if

Send GET request to internal location (which may proxy to an upstream server) after unsubscribing. Disabled for longpoll and interval-polling subscribers.
more details
nchan_websocket_ping_interval <number> (seconds)
arguments: 1
default: 0 (none)
context: server, location, if

Interval for sending websocket ping frames. Disabled by default.
nchan_authorize_request <url>
arguments: 1
context: server, location, if

Send GET request to internal location (which may proxy to an upstream server) for authorization of a publisher or subscriber request. A 200 response authorizes the request, a 403 response forbids it.
more details
nchan_max_reserved_memory <size>
arguments: 1
default: 32M
context: http
legacy name: push_max_reserved_memory

The size of the shared memory chunk this module will use for message queuing and buffering.
more details
nchan_message_buffer_length [ <number> | <variable> ]
arguments: 1
default: 10
context: http, server, location
legacy names: push_max_message_buffer_length, push_message_buffer_length

Publisher configuration setting the maximum number of messages to store per channel. A channel's message buffer will retain a maximum of this many most recent messages. An Nginx variable can also be used to set the buffer length dynamically.
nchan_message_timeout [ <time> | <variable> ]
arguments: 1
default: 1h
context: http, server, location
legacy name: push_message_timeout

Publisher configuration setting the length of time a message may be queued before it is considered expired. If you do not want messages to expire, set this to 0. Note that messages always expire from oldest to newest, so an older message may prevent a newer one with a shorter timeout from expiring. An Nginx variable can also be used to set the timeout dynamically.
nchan_redis_idle_channel_cache_timeout <time>
arguments: 1
default: 30s
context: http, server, location

A Redis-stored channel and its messages are removed from memory (local cache) after this timeout, provided there are no local subscribers.
nchan_redis_namespace <string>
arguments: 1
context: http, server, upstream

Prefix all Redis keys with this string. All Nchan-related keys in redis will be of the form "nchan_redis_namespace:*" . Default is empty.
nchan_redis_pass
arguments: 1
context: http, server, location

Use an upstream config block for Redis servers.
more details
nchan_redis_ping_interval
arguments: 1
default: 4m
context: http, server, location

Send a keepalive command to redis to keep the Nchan redis clients from disconnecting. Set to 0 to disable.
nchan_redis_server
arguments: 1
context: upstream

Used in upstream { } blocks to set redis servers.
more details
nchan_redis_storage_mode [ distributed | backup ]
arguments: 1
default: distributed
context: http, server, upstream

The mode of operation of the Redis server. In distributed mode, messages are published directly to Redis, and retrieved in real-time. Any number of Nchan servers in distributed mode can share the Redis server (or cluster). Useful for horizontal scalability, but had the penalty of all message publishing going through Redis first.

In backup mode, messages are published locally first, then later forwarded to Redis, and are retrieved only upon chanel initialization. Only one Nchan server should use a Redis server (or cluster) in this mode. Useful for data persistence without sacrificing response times to the latency of a round-trip to Redis.
nchan_redis_url
arguments: 1
default: 127.0.0.1:6379
context: http, server, location

The path to a redis server, of the form 'redis://:password@hostname:6379/0'. Shorthand of the form 'host:port' or just 'host' is also accepted.
more details
nchan_store_messages [ on | off ]
arguments: 1
default: on
context: http, server, location, if
legacy name: push_store_messages

Publisher configuration. "off" is equivalent to setting nchan_message_buffer_length 0, which disables the buffering of old messages. Using this setting is not recommended when publishing very quickly, as it may result in missed messages.
nchan_use_redis [ on | off ]
arguments: 1
default: off
context: http, server, location

Use redis for message storage at this location.
more details
nchan_access_control_allow_origin <string>
arguments: 1
default: $http_origin
context: http, server, location

Set the Cross-Origin Resource Sharing (CORS) Access-Control-Allow-Origin header to this value. If the incoming request's Origin header does not match this value, respond with a 403 Forbidden.
nchan_channel_group <string>
arguments: 1
default: (none)
context: server, location, if
legacy name: push_channel_group

The accounting and security group a channel belongs to. Works like a prefix string to the channel id. Can be set with nginx variables.
nchan_channel_group_accounting
arguments: 1
default: off
context: server, location

Enable tracking channel, subscriber, and message information on a per-channel-group basis. Can be used to place upper limits on channel groups.
nchan_group_location [ get | set | delete | off ]
arguments: 0 - 3
default: get set delete
context: location

Group information and configuration location. GET request for group info, POST to set limits, DELETE to delete all channels in group.
nchan_group_max_channels <number>
arguments: 1
default: 0 (unlimited)
context: location

Maximum number of channels allowed in the group.
nchan_group_max_messages <number>
arguments: 1
default: 0 (unlimited)
context: location

Maximum number of messages allowed for all the channels in the group.
nchan_group_max_messages_disk <number>
arguments: 1
default: 0 (unlimited)
context: location

Maximum amount of disk space allowed for the messages of all the channels in the group.
nchan_group_max_messages_memory <number>
arguments: 1
default: 0 (unlimited)
context: location

Maximum amount of shared memory allowed for the messages of all the channels in the group.
nchan_group_max_subscribers <number>
arguments: 1
default: 0 (unlimited)
context: location

Maximum number of subscribers allowed for the messages of all the channels in the group.
nchan_subscribe_existing_channels_only [ on | off ]
arguments: 1
default: off
context: http, server, location
legacy name: push_authorized_channels_only

Whether or not a subscriber may create a channel by sending a request to a subscriber location. If set to on, a publisher must send a POST or PUT request before a subscriber can request messages on the channel. Otherwise, all subscriber requests to nonexistent channels will get a 403 Forbidden response.
nchan_channel_event_string <string>
arguments: 1
default: "$nchan_channel_event $nchan_channel_id"
context: server, location, if

Contents of channel event message
nchan_channel_events_channel_id
arguments: 1
context: server, location, if

Channel id where nchan_channel_id's events should be sent. Events like subscriber enqueue/dequeue, publishing messages, etc. Useful for application debugging. The channel event message is configurable via nchan_channel_event_string. The channel group for events is hardcoded to 'meta'.
more details
nchan_stub_status
arguments: 0
context: location

Similar to Nginx's stub_status directive, requests to an nchan_stub_status location get a response with some vital Nchan statistics. This data does not account for information from other Nchan instances, and monitors only local connections, published messages, etc.
more details
nchan_max_channel_id_length <number>
arguments: 1
default: 512
context: http, server, location
legacy name: push_max_channel_id_length

Maximum permissible channel id length (number of characters). Longer ids will be truncated.
nchan_max_channel_subscribers <number>
arguments: 1
default: 0 (unlimited)
context: http, server, location
legacy name: push_max_channel_subscribers

Maximum concurrent subscribers to the channel on this Nchan server. Does not include subscribers on other Nchan instances when using a shared Redis server.
nchan_channel_timeout
arguments: 1
context: http, server, location
legacy name: push_channel_timeout

Amount of time an empty channel hangs around. Don't mess with this setting unless you know what you are doing!
nchan_storage_engine [ memory | redis ]
arguments: 1
default: memory
context: http, server, location

Development directive to completely replace default storage engine. Don't use unless you are an Nchan developer.

Contribute

Please support this project with a donation to keep me warm through the winter. I accept bitcoin at 15dLBzRS4HLRwCCVjx4emYkxXcyAPmGxM3 . Other donation methods can be found at https://nchan.slact.net

Name		Name	Last commit message	Last commit date
Latest commit History 2,708 Commits
dev		dev
src		src
LICENCE		LICENCE
NchanSubscriber.js		NchanSubscriber.js
README.md		README.md
changelog.txt		changelog.txt
cloc-exclude.txt		cloc-exclude.txt
config		config
nchan_logo.png		nchan_logo.png

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