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Man Pages


Manual Reference Pages  -  LIBDOMBEY (8)

NAME

dombey - Generic SCGI Application Server Library

CONTENTS

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

SYNOPSIS

#include <dombey.h> (-pthread) -I/usr/local/include -L/usr/local/lib -ldombey(threads) -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-drivent servers. All 3 libraries service TCP or UNIX-domain connections. This manual describes the multi-process and multi-threaded libraries. The event-driven library is described in the "libdombeyevents" manual.

An example SCGI server is included in the dombey distribution, named test.c. It can be linked against the multi-process and multi-threaded libraries.

    USAGE

The libraries provide your server’s "main" function. You define 3 functions to match the following prototypes.
void scgi_init_func();
void scgi_worker_init_func();
void scgi_request_handler( FILE * );

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

    SCGI_REQUEST_HANDLER()

One master process/thread grows and shrinks a pool of workers to service connections. Workers call scgi_request_handler() once to service each connection that they accept. Workers close connections when scgi_request_handler() returns.

scgi_request_handler() is invoked with the FILE pointer of a write-only buffered stream that is connected to the client. You use the standard buffered IO functions to send data to the client. If you wish to use non-buffered IO, use the fileno() function to determine the descriptor that is associated with the FILE pointer. Do not close the FILE pointer or its underlying descriptor, or you will crash your server.

    SCGI_INIT_FUNC()

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

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()

in scgi_init_func(), you can install a function for the master 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_WORKER_INIT_FUNC()

In scgi_worker_init_func(), perform the initialization tasks each worker needs to perform independently of the master. For example, open unique database connections for each worker in scgi_worker_init_func().

scgi_worker_init_func() is called after:

  • the user and group of the server process have been changed to the values specified by the -u and -g command line options.
  • the standard streams are connected to /dev/null. Therefore errors must be reported with syslog(3).

    SIGNALS

Both libraries need to catch SIGTERM, so do not change the disposition of that signal.

The multi-threaded library additionally needs to catch SIGUSR1, so do not change the disposition of that signal in multi-threaded servers.

Upon receipt of SIGBUS or SIGSEGV, libdombey 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).

    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.
char *scgi_get_env( char * );
char **scgi_get_envs();

char *scgi_get_param( char * ); char **scgi_get_params();

char *scgi_get_cookie( char * ); char **scgi_get_cookies();

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( char * );
char **scgi_get_next_file( char **, char * );
char **scgi_get_files();

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( 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.

    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".

    RESOURCE LIMITS

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

    THREADED SERVERS

If your threaded server encounters an unrecoverable error call scgi_thread_exit() in the thread with the error. DO NOT call pthread_exit() directly.
void scgi_thread_exit();

To create and manage globally-visible data that is unique for each connection use the pthread thread-specific data functions. The following are the minimal set of functions that you need to understand. All are documented in manual pages.

pthread_key_create();
pthread_setspecific();
pthread_getspecific();

Each thread maps keys to its thread-specific storage space.

  • In scgi_init_func(), create your keys with pthread_key_create(). Pass a destructor function to pthread_key_create() to free the space workers associate with keys, or your server will leak memory on thread termination.
  • In scgi_worker_init_func(), malloc(3) the current thread’s thread-specific storage and install it with pthread_setspecific().
  • In scgi_request_handler(), retrieve your thread-specific storage with pthread_getspecific(). Put fresh data in your storage as you like in each invocation of scgi_request_handler().
  • Release any dynamically allocated storage that will not be freed by your keys’ destructors before returning from scgi_request_handler().

    CONFIGURATION

Dombey writes its pidfile into /var/run/ if it is started as root. Stop the library with SIGTERM. Dombey does graceful stops. Idle workers exit immediately. Workers 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. POSTed files are stored in this directory.
-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.
-n The -n options specifies the number of idle workers the master will attempt to keep ready. The value defaults to 5. The library actually allows the number of idle workers to reach half this value before it creates more.
-m The -m option specifies the maximum number of workers which can run at any time. The value defaults to 25. This value is the maximum number of simultaneous connections a server can accept. The value specified must be equal to or greater than the value specified for -n.
-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.
-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.

-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.
-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).

-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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