R/mongoReply.r

In strongh/mongor: A driver for MongoDB

##' Revieve and parse a reply
##'
##' Uses lower-level mongoResp to read response from the socket connection.
##' Strips out the header and parses the document(s).
##'
##' @param conn a socket connection
##' @return list of objects from Mongo

mongoReply <-
  function(conn){
    msg <- mongoResp(conn)

    ## rest of header
    msg.length <- msg[1:4]
    msg = msg[-c(1:4)]
    
    request.id <- msg[1:4]
    msg <- msg[-c(1:4)]

    response.to <- msg[1:4]
    msg <- msg[-c(1:4)]
    
    op.code <- msg[1:4]
    msg <- msg[-c(1:4)]
    ## end header
    
    ## op_reply    
    response_flags <- msg[1:4]
    msg <- msg[-c(1:4)]

    cursor.id <- msg[1:8] # int64
    msg <- msg[-c(1:8)]
    
    starting.from <- msg[1:4]
    msg <- msg[-c(1:4)]
    
    num.returned <- msg[1:4]
    msg <- msg[-c(1:4)]


    out <- list()

    while(length(msg) > 4){ # a document is at least 5 bytes
      next.doc.len <- decode_int32(msg[1:4])
      if (next.doc.len == 1){# wtf, mongo
        msg <- msg[-c(1:4)]      
        next()
      }
      doc <- decode_document(msg[1:next.doc.len])
      msg <- msg[-c(1:next.doc.len)]
      if("_id" %in% names(doc))
        doc <- doc[-pmatch("_id", names(doc))]
      if (!is.null(unlist(doc))) # mongo sometimes returns empty docs?
        out <- append(out, list(doc))
      ## handle errors!
      if ("errmsg" %in% names(doc))
        stop("Mongo returned the following error : ", doc$errmsg)
    }
    flush(conn) #sometimes mongo sounds double replies... strange.

    ## apply attributes to out
    attr(out, "cursor.id") <- cursor.id
    class(out) <- c("mongoResult", "list")
    
    out
  }