Liquidsoap svn : Interactions with the Harbor

Harbor as HTTP server

The harbor server can be used as a HTTP server. You can use the function harbor.http.register to register HTTP handlers. Its parameters are are follow:

harbor.http.register(port=8080,method="GET",uri,handler) where:

handler function has type:

(~protocol:string, ~data:string, 
 ~headers:[(string*string)], string)->string))->unit

where:

The handler function returns HTTP and HTML data to be sent to the client, for instance:

HTTP/1.1 200 OK\r\n\
Content-type: text/html\r\n\
Content-Length: 35\r\n\
\r\n\
<html><body>It works!</body></html>

(\r\n should always be used for line return in HTTP content)

For convenience, a http_response function is provided to create a HTTP response string. It has the following type:

(?protocol:string,?code:int,?headers:[(string*string)],
 ?data:string)->string

where:

Thess functions can be used to create your own HTTP interface. Some examples are:

Redirect Icecast's pages

Some source clients using the harbor may also request pages that are served by an icecast server, for instance listeners statistics. In this case, you can register the following handler:

# Redirect all files other
# than /admin.* to icecast,
# located at localhost:8000
def redirect_icecast(~protocol,~data,~headers,uri) =
   http_response(
     protocol=protocol,
     code=301,
     headers=[("Location","http://localhost:8000#{uri}")]
   )
end

# Register this handler at port 8005
# (provided harbor sources are also served
#  from this port).
harbor.http.register(port=8005,method="GET",
                     "^/(?!admin)",
                     redirect_icecast)
Grab the code!

Another alternative, less recommanded, is to directly fetch the page's content from the Icecast server:

# Serve all files other
# than /admin.* by fetching data
# from Icecast, located at localhost:8000
def proxy_icecast(~protocol,~data,~headers,uri) =
  def f(x) =
    # Replace Host
    if string.capitalize(fst(x)) == "HOST" then
      "Host: localhost:8000"
    else
      "#{fst(x)}: #{snd(x)}"
    end
  end
  headers = list.map(f,headers)
  headers = string.concat(separator="\r\n",headers)
  request = 
    "#{method} #{uri} #{protocol}\r\n\
     #{headers}\r\n\r\n"
  get_process_output("echo #{quote(request)} | \
                      nc localhost 8000")
end

# Register this handler at port 8005
# (provided harbor sources are also served
#  from this port).
harbor.http.register(port=8005,method="GET",
                     "^/(?!admin)",
                     proxy_icecast)
Grab the code!

This method is not recommenced because some servers may not close the socket after serving a request, causing nc and liquidsoap to hang.

Get metadata

You can use harbor to register HTTP services to fecth/set the metadata of a source. For instance, using the JSON export function json_of:

meta = ref []

# s = some source

# Update current metadata
# converted in UTF8
def update_meta(m) =
  m = metadata.export(m)
  recode = string.recode(out_enc="UTF-8")
  def f(x) =
    (recode(fst(x)),recode(snd(x)))
  end
  meta := list.map(f,m)
end

# Apply update_metadata
# every time we see a new
# metadata
s = on_metadata(update_meta,s)

# Return the json content
# of meta
def get_meta(~protocol,~data,~headers,uri) =
  m = !meta
  http_response(
    protocol=protocol,
    code=200,
    headers=[("Content-Type","application/json; charset=utf-8")],
    data=json_of(m)
  )
end

# Register get_meta at port 700
harbor.http.register(port=7000,method="GET","/getmeta",get_meta)
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Once the script is running, a GET/POST request for /getmeta at port 7000 returns the following:

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8

{
  "genre": "Soul",
  "album": "The Complete Stax-Volt Singles: 1959-1968 (Disc 8)",
  "artist": "Astors",
  "title": "Daddy Didn't Tell Me"
}

Which can be used with AJAX-based backends to fetch the current metadata of source s

Set metadata

Using insert_metadata, you can register a GET handler that updates the metadata of a given source. For instance:

# s = some source

# x is of type ((metadata)->unit)*source
# first part is a function used to update
# metadata and second part is the source 
# whose metadata are updated
x = insert_metadata(s)

# Get the function
insert = fst(x)

# Redefine s as the new source
s = snd(x)

# The handler
def set_meta(~protocol,~data,~headers,uri) =
  # Split uri of the form request?foo=bar&...
  # into (request,[("foo","bar"),..])
  x = url.split(uri)

  # Filter out unusual metadata
  meta = metadata.export(snd(x))
  
  # Grab the returned message
  ret =
    if meta != [] then
      insert(meta)
      "OK!"
    else
      "No metadata to add!"
  end

  # Return response
  http_response(
   protocol=protocol,
   code=200,
   headers=[("Content-Type","text/html")],
   data="<html><body><b>#{ret}</b></body></html>"
  )
end

# Register handler on port 700
harbor.http.register(port=7000,method="GET","/setmeta",set_meta)
Grab the code!

Now, a request of the form http://server:7000/setmeta?title=foo will update the metadata of source s with [("title","foo")]. You can use this handler, for instance, in a custom HTML form.

Limitations

When using harbor's HTTP server, please be warned that the server is not meant to be used under heavy load. Therefore, it should not be exposed to your users/listeners if you expect many of them. In this case, you should use it as a backend/middle-end and have some kind of caching between harbor and the final user. In particular, the harbor server is not meant to server big files because it loads their entire content in memory before sending them. However, the harbor HTTP server is fully equipped to serve any kind of CGI script.