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+'\"
+'\" Copyright (c) 1995-1997 Sun Microsystems, Inc.
+'\"
+'\" See the file "license.terms" for information on usage and redistribution
+'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
+'\" 
+'\" SCCS: @(#) http.n 1.11 97/08/07 16:45:02
+'\" 
+.so man.macros
+.TH "Http" n 8.0 Tcl "Tcl Built-In Commands"
+.BS
+'\" Note:  do not modify the .SH NAME line immediately below!
+.SH NAME
+Http \- Client-side implementation of the HTTP/1.0 protocol.
+.SH SYNOPSIS
+\fBpackage require http ?2.0?\fP
+.sp
+\fB::http::config \fI?options?\fR
+.sp
+\fB::http::geturl \fIurl ?options?\fR
+.sp
+\fB::http::formatQuery \fIlist\fR
+.sp
+\fB::http::reset \fItoken\fR
+.sp
+\fB::http::wait \fItoken\fR
+.sp
+\fB::http::status \fItoken\fR
+.sp
+\fB::http::size \fItoken\fR
+.sp
+\fB::http::code \fItoken\fR
+.sp
+\fB::http::data \fItoken\fR
+.BE
+
+.SH DESCRIPTION
+.PP
+The \fBhttp\fR package provides the client side of the HTTP/1.0
+protocol.  The package implements the GET, POST, and HEAD operations
+of HTTP/1.0.  It allows configuration of a proxy host to get through
+firewalls.  The package is compatible with the \fBSafesock\fR security
+policy, so it can be used by untrusted applets to do URL fetching from
+a restricted set of hosts.
+.PP
+The \fB::http::geturl\fR procedure does a HTTP transaction.
+Its \fIoptions \fR determine whether a GET, POST, or HEAD transaction
+is performed.  
+The return value of \fB::http::geturl\fR is a token for the transaction.
+The value is also the name of an array in the ::http namespace
+ that contains state
+information about the transaction.  The elements of this array are
+described in the STATE ARRAY section.
+.PP
+If the \fB-command\fP option is specified, then
+the HTTP operation is done in the background.
+\fB::http::geturl\fR returns immediately after generating the
+HTTP request and the callback is invoked
+when the transaction completes.  For this to work, the Tcl event loop
+must be active.  In Tk applications this is always true.  For pure-Tcl
+applications, the caller can use \fB::http::wait\fR after calling
+\fB::http::geturl\fR to start the event loop.
+.SH COMMANDS
+.TP
+\fB::http::config\fP ?\fIoptions\fR?
+The \fB::http::config\fR command is used to set and query the name of the
+proxy server and port, and the User-Agent name used in the HTTP
+requests.  If no options are specified, then the current configuration
+is returned.  If a single argument is specified, then it should be one
+of the flags described below.  In this case the current value of
+that setting is returned.  Otherwise, the options should be a set of
+flags and values that define the configuration:
+.RS
+.TP
+\fB\-accept\fP \fImimetypes\fP
+The Accept header of the request.  The default is */*, which means that
+all types of documents are accepted.  Otherwise you can supply a 
+comma separated list of mime type patterns that you are
+willing to receive.  For example, "image/gif, image/jpeg, text/*".
+.TP
+\fB\-proxyhost\fP \fIhostname\fP
+The name of the proxy host, if any.  If this value is the
+empty string, the URL host is contacted directly.
+.TP
+\fB\-proxyport\fP \fInumber\fP
+The proxy port number.
+.TP
+\fB\-proxyfilter\fP \fIcommand\fP
+The command is a callback that is made during
+\fB::http::geturl\fR
+to determine if a proxy is required for a given host.  One argument, a
+host name, is added to \fIcommand\fR when it is invoked.  If a proxy
+is required, the callback should return a two element list containing
+the proxy server and proxy port.  Otherwise the filter should return
+an empty list.  The default filter returns the values of the
+\fB\-proxyhost\fR and \fB\-proxyport\fR settings if they are
+non-empty.
+.TP
+\fB\-useragent\fP \fIstring\fP
+The value of the User-Agent header in the HTTP request.  The default
+is \fB"Tcl http client package 2.0."\fR
+.RE
+.TP
+\fB::http::geturl\fP \fIurl\fP ?\fIoptions\fP? 
+The \fB::http::geturl \fR command is the main procedure in the package.
+The \fB\-query\fR option causes a POST operation and
+the \fB\-validate\fR option causes a HEAD operation;
+otherwise, a GET operation is performed.  The \fB::http::geturl\fR command
+returns a \fItoken\fR value that can be used to get
+information about the transaction.  See the STATE ARRAY section for
+details.  The \fB::http::geturl\fR command blocks until the operation
+completes, unless the \fB\-command\fR option specifies a callback
+that is invoked when the HTTP transaction completes.
+\fB::http::geturl\fR takes several options:
+.RS
+.TP
+\fB\-blocksize\fP \fIsize\fP
+The blocksize used when reading the URL.
+At most 
+\fIsize\fR
+bytes are read at once.  After each block, a call to the
+\fB\-progress\fR
+callback is made.
+.TP
+\fB\-channel\fP \fIname\fP
+Copy the URL contents to channel \fIname\fR instead of saving it in
+\fBstate(body)\fR.
+.TP
+\fB\-command\fP \fIcallback\fP
+Invoke \fIcallback\fP after the HTTP transaction completes.
+This option causes \fB::http::geturl\fP to return immediately.
+The \fIcallback\fP gets an additional argument that is the \fItoken\fR returned
+from \fB::http::geturl\fR. This token is the name of an array that is
+described in the STATE ARRAY section.  Here is a template for the
+callback:
+.RS
+.CS
+proc httpCallback {token} {
+    upvar #0 $token state
+    # Access state as a Tcl array
+}
+.CE
+.RE
+.TP
+\fB\-handler\fP \fIcallback\fP
+Invoke \fIcallback\fP whenever HTTP data is available; if present, nothing
+else will be done with the HTTP data.  This procedure gets two additional
+arguments: the socket for the HTTP data and the \fItoken\fR returned from
+\fB::http::geturl\fR.  The token is the name of a global array that is described
+in the STATE ARRAY section.  The procedure is expected to return the number
+of bytes read from the socket.  Here is a template for the callback:
+.RS
+.CS
+proc httpHandlerCallback {socket token} {
+    upvar #0 $token state
+    # Access socket, and state as a Tcl array
+    ...
+    (example: set data [read $socket 1000];set nbytes [string length $data])
+    ...
+    return nbytes
+}
+.CE
+.RE
+.TP
+\fB\-headers\fP \fIkeyvaluelist\fP
+This option is used to add extra headers to the HTTP request.  The
+\fIkeyvaluelist\fR argument must be a list with an even number of
+elements that alternate between keys and values.  The keys become
+header field names.  Newlines are stripped from the values so the
+header cannot be corrupted.  For example, if \fIkeyvaluelist\fR is
+\fBPragma no-cache\fR then the following header is included in the
+HTTP request:
+.CS
+Pragma: no-cache
+.CE
+.TP
+\fB\-progress\fP \fIcallback\fP
+The \fIcallback\fR is made after each transfer of data from the URL.
+The callback gets three additional arguments: the \fItoken\fR from
+\fB::http::geturl\fR, the expected total size of the contents from the
+\fBContent-Length\fR meta-data, and the current number of bytes
+transferred so far.  The expected total size may be unknown, in which
+case zero is passed to the callback.  Here is a template for the
+progress callback:
+.RS
+.CS
+proc httpProgress {token total current} {
+    upvar #0 $token state
+}
+.CE
+.RE
+.TP
+\fB\-query\fP \fIquery\fP
+This flag causes \fB::http::geturl\fR to do a POST request that passes the
+\fIquery\fR to the server. The \fIquery\fR must be a x-url-encoding
+formatted query.  The \fB::http::formatQuery\fR procedure can be used to
+do the formatting.
+.TP
+\fB\-timeout\fP \fImilliseconds\fP
+If \fImilliseconds\fR is non-zero, then \fB::http::geturl\fR sets up a timeout
+to occur after the specified number of milliseconds.
+A timeout results in a call to \fB::http::reset\fP and to
+the \fB-command\fP callback, if specified.
+The return value of \fB::http::status\fP is \fBtimeout\fP
+after a timeout has occurred.
+.TP
+\fB\-validate\fP \fIboolean\fP
+If \fIboolean\fR is non-zero, then \fB::http::geturl\fR does an HTTP HEAD
+request.  This request returns meta information about the URL, but the
+contents are not returned.  The meta information is available in the
+\fBstate(meta) \fR variable after the transaction.  See the STATE
+ARRAY section for details.
+.RE
+.TP
+\fB::http::formatQuery\fP \fIkey value\fP ?\fIkey value\fP ...?
+This procedure does x-url-encoding of query data.  It takes an even
+number of arguments that are the keys and values of the query.  It
+encodes the keys and values, and generates one string that has the
+proper & and = separators.  The result is suitable for the
+\fB\-query\fR value passed to \fB::http::geturl\fR.
+.TP
+\fB::http::reset\fP \fItoken\fP ?\fIwhy\fP?
+This command resets the HTTP transaction identified by \fItoken\fR, if
+any.  This sets the \fBstate(status)\fP value to \fIwhy\fP, which defaults to \fBreset\fR, and then calls the registered \fB\-command\fR callback.
+.TP
+\fB::http::wait\fP \fItoken\fP
+This is a convenience procedure that blocks and waits for the
+transaction to complete.  This only works in trusted code because it
+uses \fBvwait\fR.
+.TP
+\fB::http::data\fP \fItoken\fP
+This is a convenience procedure that returns the \fBbody\fP element
+(i.e., the URL data) of the state array.
+.TP
+\fB::http::status\fP \fItoken\fP
+This is a convenience procedure that returns the \fBstatus\fP element of
+the state array.
+.TP
+\fB::http::code\fP \fItoken\fP
+This is a convenience procedure that returns the \fBhttp\fP element of the
+state array.
+.TP
+\fB::http::size\fP \fItoken\fP
+This is a convenience procedure that returns the \fBcurrentsize\fP
+element of the state array.
+.SH "STATE ARRAY"
+The \fB::http::geturl\fR procedure returns a \fItoken\fR that can be used to
+get to the state of the HTTP transaction in the form of a Tcl array.
+Use this construct to create an easy-to-use array variable:
+.CS
+upvar #0 $token state
+.CE
+The following elements of the array are supported:
+.RS
+.TP
+\fBbody\fR
+The contents of the URL.  This will be empty if the \fB\-channel\fR
+option has been specified.  This value is returned by the \fB::http::data\fP command.
+.TP
+\fBcurrentsize\fR
+The current number of bytes fetched from the URL.
+This value is returned by the \fB::http::size\fP command.
+.TP
+\fBerror\fR
+If defined, this is the error string seen when the HTTP transaction
+was aborted.
+.TP
+\fBhttp\fR
+The HTTP status reply from the server.  This value
+is returned by the \fB::http::code\fP command.  The format of this value is:
+.RS
+.CS
+\fIcode string\fP
+.CE
+The \fIcode\fR is a three-digit number defined in the HTTP standard.
+A code of 200 is OK.  Codes beginning with 4 or 5 indicate errors.
+Codes beginning with 3 are redirection errors.  In this case the
+\fBLocation\fR meta-data specifies a new URL that contains the
+requested information.
+.RE
+.TP
+\fBmeta\fR
+The HTTP protocol returns meta-data that describes the URL contents.
+The \fBmeta\fR element of the state array is a list of the keys and
+values of the meta-data.  This is in a format useful for initializing
+an array that just contains the meta-data:
+.RS
+.CS
+array set meta $state(meta)
+.CE
+Some of the meta-data keys are listed below, but the HTTP standard defines
+more, and servers are free to add their own.
+.TP
+\fBContent-Type\fR
+The type of the URL contents.  Examples include \fBtext/html\fR,
+\fBimage/gif,\fR \fBapplication/postscript\fR and
+\fBapplication/x-tcl\fR.
+.TP
+\fBContent-Length\fR
+The advertised size of the contents.  The actual size obtained by
+\fB::http::geturl\fR is available as \fBstate(size)\fR.
+.TP
+\fBLocation\fR
+An alternate URL that contains the requested data.
+.RE
+.TP
+\fBstatus\fR
+Either \fBok\fR, for successful completion, \fBreset\fR for
+user-reset, or \fBerror\fR for an error condition.  During the
+transaction this value is the empty string.
+.TP
+\fBtotalsize\fR
+A copy of the \fBContent-Length\fR meta-data value.
+.TP
+\fBtype\fR
+A copy of the \fBContent-Type\fR meta-data value.
+.TP
+\fBurl\fR
+The requested URL.
+.RE
+.SH EXAMPLE
+.DS
+# Copy a URL to a file and print meta-data
+proc ::http::copy { url file {chunk 4096} } {
+    set out [open $file w]
+    set token [geturl $url -channel $out -progress ::http::Progress \\
+	-blocksize $chunk]
+    close $out
+    # This ends the line started by http::Progress
+    puts stderr ""
+    upvar #0 $token state
+    set max 0
+    foreach {name value} $state(meta) {
+	if {[string length $name] > $max} {
+	    set max [string length $name]
+	}
+	if {[regexp -nocase ^location$ $name]} {
+	    # Handle URL redirects
+	    puts stderr "Location:$value"
+	    return [copy [string trim $value] $file $chunk]
+	}
+    }
+    incr max
+    foreach {name value} $state(meta) {
+	puts [format "%-*s %s" $max $name: $value]
+    }
+
+    return $token
+}
+proc ::http::Progress {args} {
+    puts -nonewline stderr . ; flush stderr
+}
+
+.DE
+.SH "SEE ALSO"
+safe(n), socket(n), safesock(n)
+.SH KEYWORDS
+security policy, socket
+
+