1 {h2 "MQTT Demo"} 2 {#HTML
<p>Preparation: load Schelte Bronn's mqtt package</p>} 3 {package require mqtt} 4 {#HTML
<p>Define a callback function which is invoked on reception
of a subscription. The callback stores the received data
with a timestamp in an array indexed by the so called topic,
i.e. the item(s) the subscription refers to.</p>} 5 {proc callback {topic content retain} {
    set content [encoding convertfrom utf-8 $content]
    set now [clock seconds]
    set date [clock format $now -format "%Y-%m-%d"]
    set time [clock format $now -format "%H:%M:%S"]
    # cut "de.wsv/pegel/cm" prefix from topic
    set topic [join [lrange [split $topic /] 3 end] /]
    set ::DATA($topic) [list $date $time $content]
}} 6 {#HTML
<p>Create an MQTT client and connect it to the Mosquitto test server.</p>} 7 {set MQTT_CLIENT [mqtt new]
$MQTT_CLIENT connect test-client test.mosquitto.org 1883} 8 {#HTML
<p>Subscribe to topic(s), here we choose the river levels published by
the GWDS/WSV.</p>} 9 {$MQTT_CLIENT subscribe "de.wsv/pegel/cm/#" callback} 10 {#HTML
<p>From now on, periodic updates should be written into the DATA array.</p>} 11 {table {topic data} [array get DATA]} 12 {#HTML
<p>Refresh the table above each minute.</p>} 13 {proc refresh {} {
    after cancel refresh
    after 60000 refresh
    tsb::eval 11
}
refresh} 14 {tsb::save mqtt.tsb}

8 {#HTML
<p>Display the images from table [Categories].</p>} 4 {#HTML
<p>Let's retrieve the schema diagram of the Northwind database ...</p>} 10 {tsb::save northwind.tsb} 9 {foreach img [DB eval {select Picture from [Categories]}] {
    img_from_binary $img image/jpeg 0
}} 5 {img_from_binary [curl_get https://raw.githubusercontent.com/jpwhite3/northwind-SQLite3/master/Northwind_ERD.png] image/png 0} 1 {h2 "Northwind Sample With SQLite3"} 6 {#HTML
<p>Now we create an in-memory SQLite3 database,
fill it with the NorthWind data from SQL source,
and finally list data fromthe [Categories] table.</p>} 2 {#HTML
<p>Some helper code to fetch data from an URL ...</p>} 7 {package require sqlite3

sqlite3 DB :memory:

DB eval [encoding convertfrom iso8859-15 [curl_get https://raw.githubusercontent.com/jpwhite3/northwind-SQLite3/master/Northwind.Sqlite3.create.sql]]

table {CategoryID CategoryName Description} [DB eval {select CategoryID, CategoryName, Description from [Categories]}]} 3 {package require TclCurl

proc curl_get {url} {
    set h [curl::init]
    $h configure -url $url -bodyvar result
    catch {$h perform} e
    if {$e != 0} {
        return -code error [curl::easystrerror $e]
    }
    $h cleanup
    return $result
}}