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Man Pages


Manual Reference Pages  -  LIBDOMBEYEVENTS (8)

NAME

dombey - Generic SCGI Application Server Library

CONTENTS

Synopsis
Description
     Usage
     Scgi_init_func()
     Scgi_set_name()
     Scgi_set_periodic()
     Scgi_request_handler()
     Scgi_write_conn()
     Access To Request Data
     Access To Uploaded Files
     Scgi_encrypt_files()
     Scgi_read_encrypted()
     Convenience Functions
     Access To Configuration Variables
     Signals
     Resource Limits
     Configuration
     Command-line Options
Authors

SYNOPSIS

#include <dombeyevents.h> -I/usr/local/include -L/usr/local/lib -ldombeyevents -lcrypto

DESCRIPTION

The Libdombey package provides 3 generic SCGI application servers. The libraries handle network and concurrrency tasks. You supply code to service connections. Separate libraries provide multi-process, multi-threaded, and event-driven servers. All 3 libraries service TCP or UNIX-domain connections. This manual describes the event-driven library. The multi-process and multi-threaded libraries are described in the "libdombey" manual.

    USAGE

The library provides your server’s "main" function. You define 2 functions to match the following prototypes.
void scgi_init_func();
int scgi_request_handler( void *, int );

Do not define any other global symbol beginning with the five characters 'scgi_’ because the library reserves that namespace.

    SCGI_INIT_FUNC()

In scgi_init_func(), perform the initialization tasks your server needs to do once at server start-up.

The library calls scgi_init_func():

  • after changing to the directory specified by the -r command line option.
  • before attempting to change the server’s user and group to the values specified by the command line options. If the server starts as root, scgi_init_func() will execute as root.
  • before the server becomes a daemon and starts listening for connections. The standard streams are connected to the terminal from which the server was started. Error and informative messages should be sent to the terminal.

    SCGI_SET_NAME()

To set the server’s name, call scgi_set_name() inside scgi_init_func().
void scgi_set_name( char * );

If not set, the server’s name defaults to "dombey". The server’s name is used in two ways.

  • When a server is running, stderr is connected to /dev/null. Errors are reported with syslog(3). The library calls openlog() with the server’s name to ensure log entries are identified by the server’s name.
  • The server’s pidfile is written to /var/run/ if the server is started as root. The filename is the server’s name with ".pid" appended to it. This file is used by rc.d scripts to stop the server. A sample script is included in the dombey distribution.

    SCGI_SET_PERIODIC()

You can install a function for the library to invoke periodically with:
void scgi_set_periodic( void (*)(), int );

The function pointed to by first argument is called when the number of seconds specified by the second argument have elapsed and then again repeatedly when that number of seconds has elapsed since the last call.

    SCGI_REQUEST_HANDLER()

The library calls scgi_request_handler() (possibly multiple times) to service each connection.
int scgi_request_handler( void *, int );

The opaque pointer argument identifies the current connection. You pass the pointer to other library functions as necessary.

The second argument is set to 0 the first time the function is invoked for a connection. On successive invocations, the argument is set to the return value of scgi_request_handler() on its previous invocation.

Servers are blocked while scgi_request_handler() runs.

Queue response data for the client with scgi_write_conn().

  • To abort a response, return a value less than 0. Queued data is discarded, and the connection is closed.
  • To indicate that the complete response has been queued for the client, return 0.
  • To indicate that a partial response has been queued for the client, return 1. scgi_request_handler() is called again when the queued data has been sent to the client.
  • To indicate that you want to be notified when a descriptor becomes readable, return the descriptor. scgi_request_handler() is called when the descriptor is readable. The event is a oneshot event.

    SCGI_WRITE_CONN()

To queue response data for the client, pass a character pointer to scgi_write_conn().
int scgi_write_conn( void *conn, char *data );

The function’s first argument is the opaque pointer passed to scgi_request_handler(). The function’s second argument is a character pointer to the data, which must be zero-terminated. The library copies the data to an internal buffer.

scgi_write_conn() does not write the data but queues it for delivery. When the socket is writeable, the library will send up to one buffer of queued data to the client, in discrete writes, until the outgoing queue is consumed. Writes are multiplexed with events on other connections. To ensure smooth multiplexing, queue large data in chunks with separate calls to scgi_write_conn().

scgi_write_conn() returns:

  • -1 if the opaque pointer does not reference a connection.
  • -2 If the server cannot enlarge the queue.
  • 0 on success.

If the function returns -2, the server cannot allocate memory. There is no point continuing to service this connection. Perform any clean up operations necessary, and then return -1 from scgi_request_handler() to drop the connection.

    ACCESS TO REQUEST DATA

Dombey recognizes requests that use both GET and POST parameters in the same request. Inside scgi_request_handler(), use the following library functions to access the environment, the parameters, and cookies. The first argument to all of these functions is the opaque pointer passed to scgi_request_handler().

char *scgi_get_env( void *conn, char * );
char **scgi_get_envs( void *conn );

char *scgi_get_param( void *conn, char * ); char **scgi_get_params( void *conn );

char *scgi_get_cookie( void *conn, char * ); char **scgi_get_cookies( void *conn );

scgi_get_env() retrieves the value of one particular SCGI environment variable. Pass the name of the variable as argument, and the function returns that variable’s value or NULL if the variable is not defined.

scgi_get_envs() returns an array of character pointers listing all the SCGI environment variables and their values with each variable name followed by its value. The array is always terminated with a NULL pointer.

scgi_get_param() retrieves the decoded value of one particular SCGI parameter. Pass the name of the parameter as argument, and the function returns that parameter’s value or NULL if the parameter is not defined.

scgi_get_params() returns an array of character pointers listing all the SCGI parameters and their values with each parameter name followed by its value. The array is always terminated by a NULL pointer.

scgi_get_cookie() retrieves the value of one named cookie defined in the the HTTP_COOKIE environment variable. Pass the name of the desired cookie as argument, and the function returns that cookie’s value or NULL if the cookie is not set.

scgi_get_cookies() returns an array of character pointers listing all the cookies defined in HTTP_COOKIE with each cookie name followed by its value. The array is always terminated by a NULL pointer.

    ACCESS TO UPLOADED FILES

Inside scgi_request_handler(), use the following library functions to access files uploaded by the client.
char **scgi_get_file( void *conn, char * );
char **scgi_get_next_file( void *conn, char **, char * );
char **scgi_get_files( void *conn );

When processing a POSTed multipart/form-data document, elements of that document with a "filename" parameter are stored in files in the directory specified by the -r option. Files are created with mkstemp(). All files are unlink()ed by the library when scgi_request_handler() returns. If you want the files to persist, hard link new names to them.

scgi_get_file() retrieves the files array entries associated with a particular SCGI parameter. Pass the name of the parameter as argument, and the function returns a pointer to character pointer. Index the returned pointer with 0 to access the client filename. Index the pointer with 1 to access the local filename. Index the pointer with 2 to access the key used to encrypt the file. Index the pointer with 3 to access the iv used to encrypt the file. The last two values are NULL if the file is not encrypted.

If the user did not select a file to upload for a particular file input, the entry for that input is placed in the params array, and the parameter’s value is the empty string. If scgi_get_file() returns NULL for an expected form element, then call scgi_get_param(). If that function returns the empty string, the user did not select a file to upload. If that function returns NULL, the named input was not part of the originating form.

For file inputs that have the multiple attribute set, dombey creates more than one entry in the files array with the same name. Calling scgi_get_file() will only return the data for the first file. To access the next file, call scgi_get_next_file() with the address returned by scgi_get_file() and the name of the parameter. To access the remainder of the files, call scgi_get_next_file() with the address it returned on its previous invocation and the name of the parameter. When there are no more entries of the same name, the function returns NULL.

scgi_get_files() returns a NULL-terminated array of character pointers listing the parameters of all the files uploaded by the current request. The array consists of groups of 5 ajacent entries for each uploaded file. The first entry of each group is the "name" parameter (the name of the input in the form from which the file was posted). The second entry is the "filename" parameter (the filename on the client machine). The third entry is the filename on the local filesystem where the file has been stored. The fourth entry is the key used to encrypt the file or NULL if the file is not encrypted. The fifth entry is the initialization vector used to encrypt the file or NULL if the file is not encrypted.

    SCGI_ENCRYPT_FILES()

Dombey can encrypt uploaded files with the AES-256 cipher in CBC mode. A random key and initialization vector are generated for each encrypted file. Files are encrypted on the fly with no data reaching storage unencrypted. To enable encryption, call the following function with the argument set to a non-zero value. To disable encryption, set the argument to 0.
void scgi_encrypt_files( int on );

    SCGI_READ_ENCRYPTED()

Read encrypted files with the following function.
char *scgi_read_encrypted( void *conn, int fd, int *len, char *key, char *iv );

First, call the function with fd set to -2 to establish a cipher context. The len argument must point to an int to hold status codes. The key and iv arguments must point to the key and iv values for the file.

Next, open the filename with open(2), and call scgi_read_encrypted() with fd set to the open file descriptor. The function returns a pointer to a dynamically allocated array of character data. The length of the data is placed into len. Free the data when you are finished with it. Upon EOF, the function returns NULL with len set to 0. Upon failure, the function returns NULL with len set to -1. An error message is logged with syslog(3). The cipher context is automatically cleaned when an error occurs or when EOF is read.

The key and iv arguments can be NULL after the cipher context has been established.

If you do not read a file to EOF, call the function with fd set to -1 to clean the cipher context. Calling the function with fd set to -2 also cleans any previously established context.

DO MIX CALLS OF scgi_read_encrypted() TO DIFFERENT OPEN FILES BECAUSE IT MAINTAINS ONLY ONE CIPHER CONTEXT AT A TIME.

    CONVENIENCE FUNCTIONS

Use these convenience functions to encode a string in x-www-form-urlencoding and to escape <, >, and & with their HTML entities.
char *scgi_form_encode( char * );
char *scgi_html_escape( char * );

Both functions return dynamically allocated strings that must be freed by the caller. These functions will return NULL if memory cannot be allocated.

    ACCESS TO CONFIGURATION VARIABLES

You can examine the following configuration variables from your code, but you must not modify them. See the CONFIGURATION section for more information.
char *scgi_config_file;
char *scgi_root_dir;
char *scgi_interface;
char *scgi_port;
char *scgi_user;
char *scgi_group;

scgi_config_file
  points to the value passed to the -f option. Defaults to NULL.
scgi_root_dir points to the value passed to the -r option. Must be explicitly set.
scgi_interface points to the value passed to the -i option. Defaults to "".
scgi_port points to the value passed as argument to the -p option. Defaults to "4000".
scgi_user points to the value passed as argument to the -u option. Defaults to "nobody".
scgi_group points to the value passed as argument to the -g option. Defaults to "nobody".

    SIGNALS

Upon receipt of SIGBUS or SIGSEGV, the library restarts the server with a call to execv(3). If you want to do something else, install your own handler.

If your server starts as root and changes user and group, the library will be unable to restart if your server is not executable by the user or group.

The library will be unable to perform the operations that require root privileges after restart unless you turn on the setuid bit of the server (chmod u=+s).

    RESOURCE LIMITS

Dombey stores the information for 25 SCGI environment variables, 25 SCGI parameters and 25 cookies. More items provided in a client request are ignored.

    CONFIGURATION

Dombey writes its pidfile into /var/run/ if it is started as root. Stop the library with SIGTERM. Dombey does graceful stops. Servers with established connections exit after all established connections close. If you want to kill a server outright, send it a SIGKILL. A sample control script is provided in the dombey distribution. To use the script, replace all occurrences of "dombey" with the value you pass to scgi_set_name(). The script must be named as the value you passed to scgi_set_name() and installed in /usr/local/etc/rc.d.

Two variables must be added to /etc/rc.conf to use the script. Substitute your server’s name for "dombey":

dombey_enable="YES"
dombey_flags="-u www -g www -r /usr/local/dombey"

If the "enable" variable is set to "YES", the server is started at system start. Use the following rc commands.

/usr/local/etc/rc.d/dombey start
/usr/local/etc/rc.d/dombey stop
/usr/local/etc/rc.d/dombey restart
/usr/local/etc/rc.d/dombey status

If you do not want the server started on system start, then set

dombey_enable="NO"

and use the following commands:

/usr/local/etc/rc.d/dombey forcestart
/usr/local/etc/rc.d/dombey forcestop
/usr/local/etc/rc.d/dombey forcerestart
/usr/local/etc/rc.d/dombey forcestatus

    COMMAND-LINE OPTIONS

The following command-line options are recognized by dombey servers. The -r option is mandatory.
-r Use the -r option to specify the absolute path to the server root directory. Dombey chdir(2)s here.
-l By default, dombey listens on all TCP interfaces it can find capable of IPv4 or IPv6. The -l option instructs the library to listen on a UNIX-domain socket instead. Specify the path to the socket as argument. The server creates the socket when it starts, unlinking it first if it already exists in the filesystem. The owner and group of the socket are changed to the values of the -u and -g options. The permisssions of the socket are set to srwxrwx---.
-p The -p option specifies the port to listen on. This defaults to 4000. To bind to a port lower than 1024, the server must be started as root.
-i By default, dombey accepts connections on all interfaces it can find capable of IPv4 or IPv6. The -i option limits dombey to accepting connections from a specified interface. Pass the IP address of the desired interface as argument.
-q The -q option specifies the backlog of client connections queued by the OS kernel for the server to subsequently service. This value defaults to 1024. The kernel actually uses a queue of 1.5 times the size of the specified value. Connections arriving when the queue is full are dropped by the kernel. Libdombey does not le you set this value to less than 1024.
-u
-g
  The -u and the -g options specify the user and group of the server. Both values default to "nobody". To change user, the server must be started as root.

Dombey restarts servers on receipt of SIGSEGV or SIGBUS.

If your server starts as root and changes user and group, the library will be unable to restart if your server is not executable by the user or group.

The library will be unable to perform the operations that require root privileges after restart unless you turn on the setuid bit of the server (chmod +s).

-e The -e option specifies the maximum acceptable size in bytes of files uploaded in multipart/form-data POSTS. This value defaults to 2000000. Connections attempting to upload a file larger than this are dropped without explanation.
-b The -b option specifies a maximum acceptable data size in bytes. This value defaults to 10000. This limit prevents malicious clients from tricking the server into consuming arbitrary amounts of memory.

For GET requests this value is ignored.

For POST requests that are encoded with x-www-form-urlencoding, this value is the maximum size of request bodies. Connections are dropped without explanantion when CONTENT_LENGTH exceeds this value.

For POST requests that are multipart/form-data documents, this value specifies the maximum size of each non-file entity in the document. Connections with CONTENT_LENGTH set to a value greater than the maximum configured request body size are dropped without explanation.

-x The -x option prevents dombey from becoming a daemon or writing its pidfile to /var/run/. Stderr is connected to the terminal so that diagnostic output should be sent to the terminal.
-f The -f option specifies a filename as argument. Dombey assigns it to the global character pointer named scgi_config_file. This enables the code in scgi_init_func() and scgi_worker_init_func() to read a configuration file.

AUTHORS


.An James Bailie Aq jimmy@mammothcheese.ca
http://www.mammothcheese.ca
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