freebsd-skq/contrib/tcl/doc/http.n

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'\" Copyright (c) 1995-1997 Sun Microsystems, Inc.
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'\" SCCS: @(#) http.n 1.10 97/06/24 17:15:09
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.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 ?1.0?\fP
.sp
\fBhttp_config \fI?options?\fR
.sp
\fBhttp_get \fIurl ?options?\fR
.sp
\fBhttp_formatQuery \fIlist\fR
.sp
\fBhttp_reset \fItoken\fR
.sp
\fBhttp_wait \fItoken\fR
.sp
\fBhttp_status \fItoken\fR
.sp
\fBhttp_size \fItoken\fR
.sp
\fBhttp_code \fItoken\fR
.sp
\fBhttp_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 \fBhttp_get\fR procedure does a HTTP transaction.
Its \fIoptions \fR determine whether a GET, POST, or HEAD transaction
is performed.  
The return value of \fBhttp_get\fR is a token for the transaction.
The value is also the name of a global array 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.
\fBhttp_get\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 \fBhttp_wait\fR after calling
\fBhttp_get\fR to start the event loop.
.SH COMMANDS
.TP
\fBhttp_config\fP ?\fIoptions\fR?
The \fBhttp_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
\fBhttp_get\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 1.0."\fR
.RE
.TP
\fBhttp_get\fP \fIurl\fP ?\fIoptions\fP? 
The \fBhttp_get \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 \fBhttp_get\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 \fBhttp_get\fR command blocks until the operation
completes, unless the \fB\-command\fR option specifies a callback
that is invoked when the HTTP transaction completes.
\fBhttp_get\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 \fBhttp_get\fP to return immediately.
The \fIcallback\fP gets an additional argument that is the \fItoken\fR returned
from \fBhttp_get\fR. This token is the name of a global 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
\fBhttp_get\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
\fBhttp_get\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 \fBhttp_get\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 \fBhttp_formatQuery\fR procedure can be used to
do the formatting.
.TP
\fB\-timeout\fP \fImilliseconds\fP
If \fImilliseconds\fR is non-zero, then \fBhttp_get\fR sets up a timeout
to occur after the specified number of milliseconds.
A timeout results in a call to \fBhttp_reset\fP and to
the \fB-command\fP callback, if specified.
The return value of \fBhttp_status\fP is \fBtimeout\fP
after a timeout has occurred.
.TP
\fB\-validate\fP \fIboolean\fP
If \fIboolean\fR is non-zero, then \fBhttp_get\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
\fBhttp_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 \fBhttp_get\fR.
.TP
\fBhttp_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
\fBhttp_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
\fBhttp_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
\fBhttp_status\fP \fItoken\fP
This is a convenience procedure that returns the \fBstatus\fP element of
the state array.
.TP
\fBhttp_code\fP \fItoken\fP
This is a convenience procedure that returns the \fBhttp\fP element of the
state array.
.TP
\fBhttp_size\fP \fItoken\fP
This is a convenience procedure that returns the \fBcurrentsize\fP
element of the state array.
.SH "STATE ARRAY"
The \fBhttp_get\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 \fBhttp_data\fP command.
.TP
\fBcurrentsize\fR
The current number of bytes fetched from the URL.
This value is returned by the \fBhttp_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 \fBhttp_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
\fBhttp_get\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 [http_get $url -channel $out -progress HttpProgress \\
	-blocksize $chunk]
    close $out
    # This ends the line started by HttpProgress
    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 [Http_Copy [string trim $value] $file $chunk]
	}
    }
    incr max
    foreach {name value} $state(meta) {
	puts [format "%-*s %s" $max $name: $value]
    }

    return $token
}
proc HttpProgress {args} {
    puts -nonewline stderr . ; flush stderr
}

.DE
.SH "SEE ALSO"
safe(n), socket(n), safesock(n)
.SH KEYWORDS
security policy, socket