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http(n) Tcl Bundled Packages http(n)

NAME

http - Client-side implementation of the HTTP/1.0 protocol.

SYNOPSIS

ppaacckkaaggee rreeqquuiirree hhttttpp ??22..55?? ::::hhttttpp::::ccoonnffiigg ?options? ::::hhttttpp::::ggeettuurrll url ?options? ::::hhttttpp::::ffoorrmmaattQQuueerryy key value ?key value ...? ::::hhttttpp::::rreesseett token ?why? ::::hhttttpp::::wwaaiitt token ::::hhttttpp::::ssttaattuuss token ::::hhttttpp::::ssiizzee token ::::hhttttpp::::ccooddee token ::::hhttttpp::::nnccooddee token ::::hhttttpp::::ddaattaa token ::::hhttttpp::::eerrrroorr token ::::hhttttpp::::cclleeaannuupp token ::::hhttttpp::::rreeggiisstteerr proto port command ::::hhttttpp::::uunnrreeggiisstteerr proto

DESCRIPTION

The hhttttpp 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 SSaaffeessoocckk security policy, so it can be used by untrusted applets to do URL fetching from a restricted set of

hosts. This package can be extended to support additional HTTP trans-

port protocols, such as HTTPS, by providing a custom ssoocckkeett command, via hhttttpp::::rreeggiisstteerr. The ::::hhttttpp::::ggeettuurrll procedure does a HTTP transaction. Its options determine whether a GET, POST, or HEAD transaction is performed. The return value of ::::hhttttpp::::ggeettuurrll is a token for the transaction. The

value is also the name of an array in the ::http namespace that con-

tains state information about the transaction. The elements of this array are described in the STATE ARRAY section.

If the -ccoommmmaanndd option is specified, then the HTTP operation is done in

the background. ::::hhttttpp::::ggeettuurrll returns immediately after generating

the HTTP request and the callback is invoked when the transaction com-

pletes. 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 ::::hhttttpp::::wwaaiitt after calling ::::hhttttpp::::ggeettuurrll to start the event loop. CCOOMMMMAANNDDSS ::::hhttttpp::::ccoonnffiigg ?options? The ::::hhttttpp::::ccoonnffiigg 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:

-aacccceepptt mimetypes

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 exam-

ple, "image/gif, image/jpeg, text/*".

-pprrooxxyyhhoosstt hostname

The name of the proxy host, if any. If this value is the empty string, the URL host is contacted directly.

-pprrooxxyyppoorrtt number

The proxy port number.

-pprrooxxyyffiilltteerr command

The command is a callback that is made during ::::hhttttpp::::ggeettuurrll to determine if a proxy is required for a

given host. One argument, a host name, is added to com-

mand 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 -pprrooxxyyhhoosstt and -pprrooxxyyppoorrtt settings if they

are non-empty.

-uurrlleennccooddiinngg encoding

The encoding used for creating the x-url-encoded URLs

with ::::hhttttpp::::ffoorrmmaattQQuueerryy. The default is uuttff-88, as spec-

ified by RFC 2718. Prior to http 2.5 this was unspeci-

fied, and that behavior can be returned by specifying the

empty string ({{}}), although iso8859-1 is recommended to

restore similar behavior but without the ::::hhttttpp::::ffoorrmmaatt-

QQuueerryy throwing an error processing non-latin-1 charac-

ters.

-uusseerraaggeenntt string

The value of the User-Agent header in the HTTP request.

The default is ""TTccll hhttttpp cclliieenntt ppaacckkaaggee 22..44.."" ::::hhttttpp::::ggeettuurrll url ?options? The ::::hhttttpp::::ggeettuurrll command is the main procedure in the package.

The -qquueerryy option causes a POST operation and the -vvaalliiddaattee

option causes a HEAD operation; otherwise, a GET operation is performed. The ::::hhttttpp::::ggeettuurrll command returns a token value that can be used to get information about the transaction. See

the STATE ARRAY and ERRORS section for details. The

::::hhttttpp::::ggeettuurrll command blocks until the operation completes,

unless the -ccoommmmaanndd option specifies a callback that is invoked

when the HTTP transaction completes. ::::hhttttpp::::ggeettuurrll takes sev-

eral options:

-bbiinnaarryy boolean

Specifies whether to force interpreting the url data as

binary. Normally this is auto-detected (anything not

beginning with a tteexxtt content type or whose content encoding is ggzziipp or ccoommpprreessss is considered binary data).

-bblloocckkssiizzee size

The blocksize used when reading the URL. At most size bytes are read at once. After each block, a call to the

-pprrooggrreessss callback is made (if that option is specified).

-cchhaannnneell name

Copy the URL contents to channel name instead of saving it in ssttaattee((bbooddyy)).

-ccoommmmaanndd callback

Invoke callback after the HTTP transaction completes. This option causes ::::hhttttpp::::ggeettuurrll to return immediately. The callback gets an additional argument that is the token returned from ::::hhttttpp::::ggeettuurrll. This token is the name of an array that is described in the STATE ARRAY section. Here is a template for the callback:

proc httpCallback {token} {

upvar #0 $token state

# Access state as a Tcl array

}

-hhaannddlleerr callback

Invoke callback 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 token returned from ::::hhttttpp::::ggeettuurrll. The token is the name of a global array

that is described in the STATE ARRAY section. The proce-

dure is expected to return the number of bytes read from the socket. Here is a template for the callback:

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 }

-hheeaaddeerrss keyvaluelist

This option is used to add extra headers to the HTTP request. The keyvaluelist argument must be a list with an even number of elements that alternate between keys

and values. The keys become header field names. New-

lines are stripped from the values so the header cannot

be corrupted. For example, if keyvaluelist is PPrraaggmmaa nnoo-

ccaacchhee then the following header is included in the HTTP request:

Pragma: no-cache

-pprrooggrreessss callback

The callback is made after each transfer of data from the URL. The callback gets three additional arguments: the token from ::::hhttttpp::::ggeettuurrll, the expected total size of the

contents from the CCoonntteenntt-LLeennggtthh meta-data, and the cur-

rent 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:

proc httpProgress {token total current} {

upvar #0 $token state

}

-qquueerryy query

This flag causes ::::hhttttpp::::ggeettuurrll to do a POST request that

passes the query to the server. The query must be a x-

url-encoding formatted query. The ::::hhttttpp::::ffoorrmmaattQQuueerryy

procedure can be used to do the formatting.

-qquueerryybblloocckkssiizzee size

The blocksize used when posting query data to the URL. At most size bytes are written at once. After each

block, a call to the -qquueerryypprrooggrreessss callback is made (if

that option is specified).

-qquueerryycchhaannnneell channelID

This flag causes ::::hhttttpp::::ggeettuurrll to do a POST request that passes the data contained in channelID to the server. The

data contained in channelID must be a x-url-encoding for-

matted query unless the -ttyyppee option below is used. If a

Content-Length header is not specified via the -hheeaaddeerrss

options, ::::hhttttpp::::ggeettuurrll attempts to determine the size of the post data in order to create that header. If it is unable to determine the size, it returns an error.

-qquueerryypprrooggrreessss callback

The callback is made after each transfer of data to the

URL (i.e. POST) and acts exactly like the -pprrooggrreessss

option (the callback format is the same).

-ttiimmeeoouutt milliseconds

If milliseconds is non-zero, then ::::hhttttpp::::ggeettuurrll sets up

a timeout to occur after the specified number of mil-

liseconds. A timeout results in a call to ::::hhttttpp::::rreesseett

and to the -ccoommmmaanndd callback, if specified. The return

value of ::::hhttttpp::::ssttaattuuss is ttiimmeeoouutt after a timeout has occurred.

-ttyyppee mime-type

Use mime-type as the CCoonntteenntt-TTyyppee value, instead of the

default value (aapppplliiccaattiioonn//xx-wwwwww-ffoorrmm-uurrlleennccooddeedd) during

a POST operation.

-vvaalliiddaattee boolean

If boolean is non-zero, then ::::hhttttpp::::ggeettuurrll 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 ssttaattee((mmeettaa)) vari-

able after the transaction. See the STATE ARRAY section for details. ::::hhttttpp::::ffoorrmmaattQQuueerryy key value ?key value ...?

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 -qquueerryy value passed to ::::hhttttpp::::ggeettuurrll.

::::hhttttpp::::rreesseett token ?why? This command resets the HTTP transaction identified by token, if any. This sets the ssttaattee((ssttaattuuss)) value to why, which defaults

to rreesseett, and then calls the registered -ccoommmmaanndd callback.

::::hhttttpp::::wwaaiitt token This is a convenience procedure that blocks and waits for the transaction to complete. This only works in trusted code because it uses vvwwaaiitt. Also, it's not useful for the case where

::::hhttttpp::::ggeettuurrll is called without the -ccoommmmaanndd option because in

this case the ::::hhttttpp::::ggeettuurrll call doesn't return until the HTTP transaction is complete, and thus there's nothing to wait for. ::::hhttttpp::::ddaattaa token This is a convenience procedure that returns the bbooddyy element (i.e., the URL data) of the state array. ::::hhttttpp::::eerrrroorr token This is a convenience procedure that returns the eerrrroorr element of the state array. ::::hhttttpp::::ssttaattuuss token This is a convenience procedure that returns the ssttaattuuss element of the state array. ::::hhttttpp::::ccooddee token This is a convenience procedure that returns the hhttttpp element of the state array. ::::hhttttpp::::nnccooddee token This is a convenience procedure that returns just the numeric return code (200, 404, etc.) from the hhttttpp element of the state array. ::::hhttttpp::::ssiizzee token This is a convenience procedure that returns the ccuurrrreennttssiizzee element of the state array, which represents the number of bytes received from the URL in the ::::hhttttpp::::ggeettuurrll call. ::::hhttttpp::::cclleeaannuupp token

This procedure cleans up the state associated with the connec-

tion identified by token. After this call, the procedures like

::::hhttttpp::::ddaattaa cannot be used to get information about the opera-

tion. It is strongly recommended that you call this function after you're done with a given HTTP request. Not doing so will result in memory not being freed, and if your app calls

::::hhttttpp::::ggeettuurrll enough times, the memory leak could cause a per-

formance hit...or worse. ::::hhttttpp::::rreeggiisstteerr proto port command This procedure allows one to provide custom HTTP transport types such as HTTPS, by registering a prefix, the default port, and the command to execute to create the Tcl cchhaannnneell. E.g.:

package require http

package require tls

http::register https 443 ::tls::socket

set token [http::geturl https://my.secure.site/]

::::hhttttpp::::uunnrreeggiisstteerr proto

This procedure unregisters a protocol handler that was previ-

ously registered via hhttttpp::::rreeggiisstteerr. EERRRROORRSS The hhttttpp::::ggeettuurrll procedure will raise errors in the following cases:

invalid command line options, an invalid URL, a URL on a non-existent

host, or a URL at a bad port on an existing host. These errors mean that it cannot even start the network transaction. It will also raise an error if it gets an I/O error while writing out the HTTP request

header. For synchronous ::::hhttttpp::::ggeettuurrll calls (where -ccoommmmaanndd is not

specified), it will raise an error if it gets an I/O error while read-

ing the HTTP reply headers or data. Because ::::hhttttpp::::ggeettuurrll doesn't return a token in these cases, it does all the required cleanup and there's no issue of your app having to call ::::hhttttpp::::cclleeaannuupp.

For asynchronous ::::hhttttpp::::ggeettuurrll calls, all of the above error situa-

tions apply, except that if there's any error while reading the HTTP reply headers or data, no exception is thrown. This is because after writing the HTTP headers, ::::hhttttpp::::ggeettuurrll returns, and the rest of the HTTP transaction occurs in the background. The command callback can check if any error occurred during the read by calling ::::hhttttpp::::ssttaattuuss to check the status and if its error, calling ::::hhttttpp::::eerrrroorr to get the error message. Alternatively, if the main program flow reaches a point where it needs to know the result of the asynchronous HTTP request, it can call ::::hhttttpp::::wwaaiitt and then check status and error, just as the callback does. In any case, you must still call hhttttpp::::cclleeaannuupp to delete the state array when you're done. There are other possible results of the HTTP transaction determined by examining the status from hhttttpp::::ssttaattuuss. These are described below. ok If the HTTP transaction completes entirely, then status will be ookk. However, you should still check the hhttttpp::::ccooddee value to get the HTTP status. The hhttttpp::::nnccooddee procedure provides just the

numeric error (e.g., 200, 404 or 500) while the hhttttpp::::ccooddee pro-

cedure returns a value like "HTTP 404 File not found". eof If the server closes the socket without replying, then no error is raised, but the status of the transaction will be eeooff. error The error message will also be stored in the eerrrroorr status array element, accessible via ::::hhttttpp::::eerrrroorr. Another error possibility is that hhttttpp::::ggeettuurrll is unable to write all the post query data to the server before the server responds and closes the socket. The error message is saved in the ppoosstteerrrroorr status array element and then hhttttpp::::ggeettuurrll attempts to complete the transaction. If it can read the server's response it will end up with an ookk status, otherwise it will have an eeooff status. SSTTAATTEE AARRRRAAYY The ::::hhttttpp::::ggeettuurrll procedure returns a token 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:

upvar #0 $token state

Once the data associated with the url is no longer needed, the state array should be unset to free up storage. The hhttttpp::::cclleeaannuupp procedure is provided for that purpose. The following elements of the array are supported: bbooddyy The contents of the URL. This will be empty if the

-cchhaannnneell option has been specified. This value is

returned by the ::::hhttttpp::::ddaattaa command. cchhaarrsseett

The value of the charset attribute from the CCoonntteenntt-TTyyppee

meta-data value. If none was specified, this defaults to

the RFC standard iissoo88885599-11, or the value of

$$::::hhttttpp::::ddeeffaauullttCChhaarrsseett. Incoming text data will be

automatically converted from this charset to utf-8.

ccooddiinngg A copy of the CCoonntteenntt-EEnnccooddiinngg meta-data value.

ccuurrrreennttssiizzee The current number of bytes fetched from the URL. This value is returned by the ::::hhttttpp::::ssiizzee command. eerrrroorr If defined, this is the error string seen when the HTTP transaction was aborted. hhttttpp The HTTP status reply from the server. This value is returned by the ::::hhttttpp::::ccooddee command. The format of this value is: HTTP/1.0 code string

The code 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 redi-

rection errors. In this case the LLooccaattiioonn meta-data

specifies a new URL that contains the requested informa-

tion.

mmeettaa The HTTP protocol returns meta-data that describes the

URL contents. The mmeettaa 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 con-

tains the meta-data:

array set meta $state(meta)

Some of the meta-data keys are listed below, but the HTTP

standard defines more, and servers are free to add their own.

CCoonntteenntt-TTyyppee

The type of the URL contents. Examples include tteexxtt//hhttmmll, iimmaaggee//ggiiff,, aapppplliiccaattiioonn//ppoossttssccrriipptt and

aapppplliiccaattiioonn//xx-ttccll.

CCoonntteenntt-LLeennggtthh

The advertised size of the contents. The actual size obtained by ::::hhttttpp::::ggeettuurrll is available as ssttaattee((ssiizzee)). LLooccaattiioonn An alternate URL that contains the requested data. ppoosstteerrrroorr The error, if any, that occurred while writing the post query data to the server.

ssttaattuuss Either ookk, for successful completion, rreesseett for user-

reset, ttiimmeeoouutt if a timeout occurred before the transac-

tion could complete, or eerrrroorr for an error condition. During the transaction this value is the empty string. ttoottaallssiizzee

A copy of the CCoonntteenntt-LLeennggtthh meta-data value.

ttyyppee A copy of the CCoonntteenntt-TTyyppee meta-data value.

uurrll The requested URL. EEXXAAMMPPLLEE

# 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

}