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GNU Info (gawkinet.info)CGI LibA Simple CGI Library -------------------- HTTP is like being married: you have to be able to handle whatever you're given, while being very careful what you send back. Phil Smith III, `http://www.netfunny.com/rhf/jokes/99/Mar/http.html' In Note: A Web Service with Interaction, we saw the function `CGI_setup' as part of the web server "core logic" framework. The code presented there handles almost everything necessary for CGI requests. One thing it doesn't do is handle encoded characters in the requests. For example, an `&' is encoded as a percent sign followed by the hexadecimal value--`%26'. These encoded values should be decoded. Following is a simple library to perform these tasks. This code is used for all web server examples used throughout the rest of this Info file. If you want to use it for your own web server, store the source code into a file named `inetlib.awk'. Then you can include these functions into your code by placing the following statement into your program: @include inetlib.awk on the first line of your script. But beware, this mechanism is only possible if you invoke your web server script with `igawk' instead of the usual `awk' or `gawk'. Here is the code: # CGI Library and core of a web server # Global arrays # GETARG --- arguments to CGI GET command # MENU --- menu items (path names) # PARAM --- parameters of form x=y # Optional variable MyHost contains host address # Optional variable MyPort contains port number # Needs TopHeader, TopDoc, TopFooter # Sets MyPrefix, HttpService, Status, Reason BEGIN { if (MyHost == "") { "uname -n" | getline MyHost close("uname -n") } if (MyPort == 0) MyPort = 8080 HttpService = "/inet/tcp/" MyPort "/0/0" MyPrefix = "http://" MyHost ":" MyPort SetUpServer() while ("awk" != "complex") { # header lines are terminated this way RS = ORS = "\r\n" Status = 200 # this means OK Reason = "OK" Header = TopHeader Document = TopDoc Footer = TopFooter if (GETARG["Method"] == "GET") { HandleGET() } else if (GETARG["Method"] == "HEAD") { # not yet implemented } else if (GETARG["Method"] != "") { print "bad method", GETARG["Method"] } Prompt = Header Document Footer print "HTTP/1.0", Status, Reason |& HttpService print "Connection: Close" |& HttpService print "Pragma: no-cache" |& HttpService len = length(Prompt) + length(ORS) print "Content-length:", len |& HttpService print ORS Prompt |& HttpService # ignore all the header lines while ((HttpService |& getline) > 0) continue # stop talking to this client close(HttpService) # wait for new client request HttpService |& getline # do some logging print systime(), strftime(), $0 CGI_setup($1, $2, $3) } } function CGI_setup( method, uri, version, i) { delete GETARG delete MENU delete PARAM GETARG["Method"] = method GETARG["URI"] = uri GETARG["Version"] = version i = index(uri, "?") if (i > 0) { # is there a "?" indicating a CGI request? split(substr(uri, 1, i-1), MENU, "[/:]") split(substr(uri, i+1), PARAM, "&") for (i in PARAM) { PARAM[i] = _CGI_decode(PARAM[i]) j = index(PARAM[i], "=") GETARG[substr(PARAM[i], 1, j-1)] = \ substr(PARAM[i], j+1) } } else { # there is no "?", no need for splitting PARAMs split(uri, MENU, "[/:]") } for (i in MENU) # decode characters in path if (i > 4) # but not those in host name MENU[i] = _CGI_decode(MENU[i]) } This isolates details in a single function, `CGI_setup'. Decoding of encoded characters is pushed off to a helper function, `_CGI_decode'. The use of the leading underscore (`_') in the function name is intended to indicate that it is an "internal" function, although there is nothing to enforce this: function _CGI_decode(str, hexdigs, i, pre, code1, code2, val, result) { hexdigs = "123456789abcdef" i = index(str, "%") if (i == 0) # no work to do return str do { pre = substr(str, 1, i-1) # part before %xx code1 = substr(str, i+1, 1) # first hex digit code2 = substr(str, i+2, 1) # second hex digit str = substr(str, i+3) # rest of string code1 = tolower(code1) code2 = tolower(code2) val = index(hexdigs, code1) * 16 \ + index(hexdigs, code2) result = result pre sprintf("%c", val) i = index(str, "%") } while (i != 0) if (length(str) > 0) result = result str return result } This works by splitting the string apart around an encoded character. The two digits are converted to lowercase and looked up in a string of hex digits. Note that `0' is not in the string on purpose; `index' returns zero when it's not found, automatically giving the correct value! Once the hexadecimal value is converted from characters in a string into a numerical value, `sprintf' converts the value back into a real character. The following is a simple test harness for the above functions: BEGIN { CGI_setup("GET", "http://www.gnu.org/cgi-bin/foo?p1=stuff&p2=stuff%26junk" \ "&percent=a %25 sign", "1.0") for (i in MENU) printf "MENU[\"%s\"] = %s\n", i, MENU[i] for (i in PARAM) printf "PARAM[\"%s\"] = %s\n", i, PARAM[i] for (i in GETARG) printf "GETARG[\"%s\"] = %s\n", i, GETARG[i] } And this is the result when we run it: $ gawk -f testserv.awk -| MENU["4"] = www.gnu.org -| MENU["5"] = cgi-bin -| MENU["6"] = foo -| MENU["1"] = http -| MENU["2"] = -| MENU["3"] = -| PARAM["1"] = p1=stuff -| PARAM["2"] = p2=stuff&junk -| PARAM["3"] = percent=a % sign -| GETARG["p1"] = stuff -| GETARG["percent"] = a % sign -| GETARG["p2"] = stuff&junk -| GETARG["Method"] = GET -| GETARG["Version"] = 1.0 -| GETARG["URI"] = http://www.gnu.org/cgi-bin/foo?p1=stuff& p2=stuff%26junk&percent=a %25 sign automatically generated by info2www version 1.2.2.9 |