'''`multipart/x-mixed-replace`''' is an [HTTP] header. Your server can use it to push dynamically updated content to the web browser. It works by telling the browser to keep the connection open and replace the web page or piece of media it is displaying with another when it receives a special token. The header is old and widely supported. It works in legacy browsers, even http://web.archive.org/web/19991008003359/http://www.abiglime.com/webmaster/articles/cgi/032498.htm%|%Netscape 1.1%|%. This page shows an implementation of a `multipart/x-mixed-replace` HTTP server in plain Tcl. ** Code ** ====== #! /usr/bin/env tclsh # An example of how to serve dynamic web content with # multipart/x-mixed-replace. # Copyright (c) 2021 D. Bohdan. License: MIT. package require Tcl 8.6-10 set image [join { data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACAAAAAgBAMAAACBVGfHAAAAMFBM VEXy9PH+/xb/ysn/ev8A+vmhk/+XmJYA6wCBgYD/R0UArQA1ZiodCuEAMQAAAXEFCARuxRLHAA AAg0lEQVR42r3OR1UFURAE0DuFAhz0eQZIGpCAOL4EsDAWMEB2MArI6Z3TK1Z/eztULW/YYXtk 9focAAURYPKEgATQHFQHHYDl6oYdBqm28QpxDADEQQcd5s1/e7zhHCsu9Y29wXL3bBu4xgWSYr STQ6NMCMQZIBSMX0kJ8CMJYwpRAMA7X8kSzYsnKHwAAAAASUVORK5CYII= } {}] proc main {} { set server [socket -server serve 8080] vwait ::done close $server } proc serve {conn clientAddr clientPort} { fconfigure $conn -buffering none -translation binary set boundary boundary-[expr rand()] send [mp-header $boundary] send --$boundary send "Content-type: text/plain\r\n" send {Hello, text } send --$boundary after 1000 send "Content-type: text/plain\r\n" send { plain world!} send --$boundary after 1000 send "Content-type: image/png\r\n" set imageBin [binary decode base64 [string range $::image 22 end]] send $imageBin false send --$boundary after 1000 set s {Hello, the wonderful world of HTML!} set len [llength $s] for {set i -1} {$i <= $len} {incr i} { send "Content-type: text/html\r\n" send "

[lrange $s 0 $i]

" send [expr { $i == $len ? "--$boundary--" : "--$boundary" }] after 300 } set ::done true } proc send {data {nl true}} { upvar 1 conn conn puts -nonewline $conn $data if {$nl} { puts -nonewline $conn \r\n } } proc mp-header boundary { append h "HTTP/1.1 200 OK\r\n" append h "Content-type:\ multipart/x-mixed-replace;boundary=\"$boundary\"\r\n" append h \r\n } main ====== ** See also ** * https://docstore.mik.ua/orelly/web2/xhtml/ch13_03.htm%|%“Server-Push Documents”%|% in ''HTML & XHTML: The Definitive Guide, 4th Edition''. <> Example | Web