httpd - HTTP protocol implementation
The package httpd implements the server side of the HTTP protocol and as such can be used as the core of any Tcl based web server implementation. One such full-fledged web server is tclhttpd.
Note: This package does not provide the ability to register a callback when a request was received completely. It dispatches all collected requests to the package httpd::url instead. This package then provides an interface for the definition and usage of a database mapping from urls to implementations, i.e. Tcl commands handling them.
The API is divided into the following four categories, each described in its own section.
Operations to handle the server at large.
Initializes the internal data structures of the package. Has to be called before Httpd_Server or Httpd_SecureServer. Some of the others public commands of this package will call this command on their own if it had not been called before.
A convenience command. It calls Httpd_ServerShutdown, Httpd_SecureServerShutdown, and all callback commands registered with the package through Httpd_RegisterShutdown.
The registered callbacks are called before the two shutdown commands of this package. Any errors thrown by the callbacks are logged via the package httpd::log, but ignored otherwise.
The result of the command is a boolean value. false signals to the caller that at least one of the registered callbacks threw an error.
Registers cmd as a callback which will be called when the server is shutdown via Httpd_Shutdown. Errors thrown by cmd during its invocation are logged, but otherwise ignored. Any result returned by cmd is ignored]. The cmd is called without any argument.
Starts the server by listening for connections on the desired port. This may be re-run to re-start the server.
If no port was specified it defaults to 80. The caller can specify the qualified host name returned in the Host field of each server response. This defaults to the result of info hostname. A non-default interface address can be specified through ipaddr. Otherwise IP_ADDR_ANY is used so the server can accept connections from any interface.
Automatically calls Httpd_Init if it has not been done manually before.
The command returns the empty string.
Note: It is possible for the package to have the server listen on multiple ports, just call this command more than once. However note that the package remembers only the last port opened for listening. This means that a shutdown will stop only connections on the last port opened with this command, and nothing else.
This command closes the listening socket of the server. Existing HTTP connections are kept open, but no new connection will be possible.
Like Httpd_Server, except that additional setup for SSL is performed, requiring the package TLS, and that the port defaults to 443.
Like Httpd_ServerShutdown, except that listening socket for secure connections is closed.
If a sock is specified it is remembered globally as the current socket. Otherwise the globally remembered current socket is returned.
Defines a global email address for the webmaster. If no address was specified the last address set is returned.
Initialize a virtual server. The file is an alternate config file, (e.g., "tclhttpd.rc"). The pages for each virtual server are processed inside their own safe interpreter.
Like Httpd_VirtualHost except that the first argument is a list of host names. All of these share the same config file.
A global array variable containing global configuration information.
Chunk size for copies. For example POST data.
Exists and true after package was initialized by Httpd_Init.
Non-default ipaddr for the server (for multiple interfaces).
Path of the directory containing the Tcl scripts.
The port this server is serving.
The main listening socket id.
The server ID for the HTTP protocol.
A list of Tcl callbacks to run when the server shuts down.
Blocking mode value for sockets (normally this should be 0).
Time before the server closes a kept-alive socket (msecs).
Time before the server kills an in-progress transaction (msecs).
Time allowed to drain extra post data.
The version number.
Max number of transactions per socket (keep alive).
Management operations for connections.
The state of the open connection is stored in global variables, one per connection. These variables are arrays and have the prefix Httpd. Their distinguishing suffix is the handle of the channel (socket) they belong to. This means that any user code which has a connection handle can import the connection state into its current scope via a command like
upvar #0 Httpd$sock data
The elements of this array are documented here. URL implementations are free to hang additional state off the data array as long as they do not clobber the elements documented below. These keys in the state array are semi-public, or "well known". There are a few API's to access them, but URL implementations can rely on these:
A list of protocol (http or https), name, and port that capture the server-side of the socket address. Available through the Httpd_Protocol, Httpd_Name, and Httpd_Port API's.
The complete URL, including protocol, servername, and query.
Either http or https.
The URL after the server name and before the '?'. In other words, the url path.
The URL after the '?'.
The remote client's IP address.
Client certificate (The result of tls::status). This is only relevant to connections coming in over a secure port.
The host specified in the URL, if any (proxy case).
The port specified in the URL, if any.
HTTP header request lines (e.g., mime,content-type).
Content-Length.
List of Set-Cookie headers to stick into the response. Use Httpd_SetCookie to append to this.
Set by Url_Dispatch (in package httpd::url) to be the URL domain prefix.
Set by Url_Dispatch to be the URL domain suffix.
Set by the package httpd::auth to "Basic", etc.
Set by the package httpd::auth to the username from Basic authentication.
Set by the package httpd::auth to the "realm,$username" from Basic auth. You can overwrite this session ID with something more useful.
Fields used by this module.
The number of keep-alive connections allowed.
AfterID of event that will terminate the connection on timeout.
State of request processing.
1.0 or 1.1.
The current line of the HTTP request.
List indicating the order of MIME header lines.
Current header key.
State bit for Netscape SSL newline bug hack.
Command to invoke when request has completed.
Size of file returned by Httpd_ReturnFile.
Open file used by fcopy to return a file, or CGI pipe.
During the dispatch of a request the element HTTP_CHANNEL contains the channel handle of the connection for that request.
Danger: This is true only until the URL implementation enters the event loop on its own. After that this element can be overwritten by another request served in parallel. In other words this information is not reliable. A package using this variable is httpd::cookie, especially the command Cookie_Get.
It would have been better to provide a cookie retrieval command in this API here.
If no socket handle sock is provided the regular (non-secure) listening port is returned. Otherwise the port for the connection running over the specified socket is returned.
Returns the port number of the secure listening port, if a secure server was activated. An empty string will be returned if no secure server is running.
Returns the DNS name of the client connected to the server over the socket sock.
Returns the protocol for the connection. Either http or https. Used by Httpd_SelfUrl.
Return the server name for the connection sock. Used by Httpd_SelfUrl.
This command takes a server-relative url and returns the equivalent absolute url (containing server name, port, etc). The connection sock is required to be able to distinguish between regular and secure ports.
Register a procedure cmd to be called when an HTTP request is completed on the socket sock, either normally or forcibly closed. This gives a URL implementation a guaranteed callback to clean up or log requests.
The callback will be invoked with two additional arguments, sock and a string, in this order. The string can be empty. If the string is not empty it will contain an error message.
Note that completed here does not mean completion of getting all input for the request, but rather that the response to the request was completed and sent to the client as well.
"Closes" the connection sock. Note that the socket channel the connection runs over might actually remain open for a keep-alive connection. Calling this means a HTTP transaction is fully complete. The optional message defaults to Close. If the boolean flag closeit is set the socket for the connection is closed no matter what type the connection.
This cleans up all state associated with the connection, including after events for timeouts, the data array, and fileevents.
Detect if a request has been sent and completed. The holder of a socket might need to know if the URL request was completed with one of the return-data commands, or is still lingering open. The result is a boolean value. true signals that the last request was fully completed.
This command, and its counterpart Httpd_Resume can be used by the backend handling an url to temporarily disable and re-enable the reception of data from the connection sock. For example if there are long-lasting server-side operations to handle the request which block and then enter the event loop on their own.
If a timeout is set for the suspension the pending request will be forcibly aborted with an error reply when the time runs out.
An example user of this mechanism are the all commands reading posted data (see below). They suspend normal operation, take over the socket to read the posted data and when reactivate the normal processing.
See Httpd_Suspend above.
Connects the connection coming in over sock with the channel fd. Any data arriving on sock is copied over to fd and vice versa. If either channel is closed the other will be closed too.
This is the basic mechanism to redirect the internal processing of a request to an external application, i.e. for CGI processing, or to a a subordinate web server.
This command returns a dictionary containing the received HTTP protocol headers for the connection sock. The keys are header names without the trailing colon and mapped to lower case (e.g., content-type). The system adds two pseudo-headers: One that contains the original request URL; its name is "url". Another that contains the request protocol; its name is "method". There are no duplications in the header keys. If any headers were repeated, their values were combined by separating them with commas.
The commands listed here technically belong to the section Connection Management, but are important enough to warrant their own section. They deal with data which was POST'ed as part of a request (form data, uploaded files).
Returns the amount of post data available in bytes for the current request, i.e. sent over the connection associated with the socket sock.
Synchronously reads posted data from the socket sock and appends it to the buffer variable varName. If size is not specified Httpd(bufsize) bytes will be read.
The command returns the total number of bytes accumulated so far.
Activates the asynchronous reading of posted data from the socket sock, as it arrives. Whenever more posted data arrives on the socket sock the specified command prefix cmd will be called. This is a convenience command wrapped around Httpd_GetPostDataAsync (see below) setting things up so that arriving data is added to the query component of the status variable for the connection.
Activates the asynchronous reading of posted data from the socket sock, as it arrives. Whenever more posted data arrives on the socket sock the data is appended to the specified variable (varName) and specified command prefix cmd will be called. The data is read in blocksize chunks.
The specified command prefix cmd is called with three additional arguments, the sock, the varName, and an additional string, either empty or containing an error message, in this order.
An alternative to Httpd_GetPostDataAsync. Sets up the asynchronous copying of the data posted to the socket sock to the channel. The command prefix cmd is called when the copying completed, with two additional argument, sock and channel, in this order.
Returns the socket sock containing the posted data, as long as there is POST data to read for the connection over this socket. If no data is present (anymore) an error will be thrown. The number of bytes present is written into the variable sizeName.
The commands listed here technically belong to the section Connection Management, but are important enough to warrant their own section. They deal with the generation of replies in general, predefined and generic. The latter ones can to be used by the packages implementing the handling of urls
Add the encoded cookie to the reply for the current request on connection sock. This command has to be called before using either Httpd_ReturnFile or Httpd_ReturnData.
See http://wp.netscape.com/newsref/std/cookie_spec.html for the specification of what cookies are and how they work.
See package httpd::cookie for commands to help in the creation of cookies.
Remove previously set cookies from the reply for the current request on connection sock. Any cookies that match the glob pattern are removed. This is useful for expiring a cookie that was previously set.
Sends the contents of the file with name path and mime type type as the reply to the current request on the connection sock. If an offset is specified that number of bytes are skipped from the start of the file.
The request will be completed by the time this command returns. This implies that completion callback have been called and that sock has been closed.
Like Httpd_ReturnFile, except that the content is specified directly as an argument to the command. This command also allows the specification of an HTTP return code. If none is specified it will default to 200 (Data follows). Beyond that the caller can order the command to keep the connection sock open after the data was sent ("close == 1"). By default the connection would be closed, like it is done by Httpd_ReturnFile.
Like Httpd_ReturnData, except that a Last-Modified header is part of the reply so that proxy servers can cache it. The information for this header line is taken from date. In contrast to Httpd_ReturnData the connection is always closed. This is like for Httpd_ReturnFile.
Send the error message detail with HTTP response code, log it, and close the connection sock. This is the most basic error response the server can generate. Other packages may generate their own error responses. The package httpd::doc is an example of this.
This command generates a redirect to newurl reply (code 302) and then closes the connection sock. It assumes that newurl contains an absolute url.
A wrapper around Httpd_Redirect for a newurl which is on this server. In other words, this commands expects a server relative url, and not an absolute one.
Generate a redirect reply for the connection sock because the trailing slash is not present on a URL that corresponds to a directory.
This command generates a "Not modified" reply (code 304) and then closes the connection sock.
Generates a "Authorization required" reply (code 401) and then closes the connection sock. The type is usually basic. The data in realm is used by browsers to cache credentials.
http::log, httpd::config, httpd::cookie, httpd::counter, httpd::logstd, httpd::threadmgr, httpd::url, httpd::version
http, tclhttpd, web server
Copyright © 2003 Andreas Kupries <andreas_kupries@users.sourceforge.net>