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NAME dombey -- Generic SCGI Application Server Library SYNOPSIS #include <dombey.h> (-pthread) -I/usr/local/include -L/usr/local/lib -ldombey(threads) -lcrypto DESCRIPTION Libdombey provides 3 generic SCGI application servers as libraries. The libraries handle network and concurrency 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 multi-process and multi-threaded libraries. The event-driven library is described in the "libdombeyevents" manual. An bare bones example SCGI server is included in the dombey distribu- tion, named test.c. The server can be linked against the multi-process and multi-threaded libraries. USAGE The libraries provide your server's "main" function. You define 4 functions to match the following prototypes. void scgi_init_func(); void scgi_exit_func(); void scgi_worker_init_func(); void scgi_request_handler( FILE * ); Do not define any other global symbol beginning with the five charac- ters 'scgi_' because dombey reserves that namespace. SCGI_REQUEST_HANDLER() One master process/thread grows and shrinks a pool of workers to ser- vice 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. Dombey 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 val- ues specified by the command line options. If the server starts as root, scgi_init_func() executes as root. • before the server becomes a daemon and starts listening for connec- tions. 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_STACK_SIZE() Threaded servers typically want small thread stacks. The system de- fault is 2M. Set the stack size for threaded servers with scgi_set_stack_size(). The function is only available in the threaded library and can only be called from inside scgi_init_func(). int scgi_set_stack_size( int ); The function returns 0 on success and 1 on error. On error, an error message is printed to stderr. You must ensure that the kernal tunable kern.threads.max_threads_per_proc is set to a value appropriate for your server. The default value is 1500. The variable can be set at system start by putting an assignment into /etc/sysctl.conf. SCGI_EXIT_FUNC() If you have exit handlers you would like to register to run before the server exits, do not invoke atexit() from scgi_init_func(). If you do so, your handlers are run when the server becomes a daemon. The server forks to create a new session. The dying parent process will call your handlers when it exits. Instead, call your cleanup code from scgi_exit_func(). If you need to invoke worker-specific cleanup code in a multi-process server, you can install your cleanup handlers with atexit() inside scgi_worker_init_func(). If you need to invoke worker-specific cleanup code in a multi-threaded server, you can call your cleanup code from the destructor functions of your thread-specific keys. 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). Dombey 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" ap- pended 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 in- voke periodically with: void scgi_set_periodic( void (*)(), int ); Dombey calls the function pointed to by first argument 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(). Dombey calls scgi_worker_init_func() 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, dombey will be unable to restart if your server is not executable by the user or group. Dombey will be unable to perform the operations that require root priv- ileges after restart unless you turn on the setuid bit of the server (chmod u=+s). ACCESS TO REQUEST DATA 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 pa- rameter. 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 direc- tory specified by the -r option. Files are created with mkstemp(), and filenames begin with the characters "dombey-" so that you may disguish dombey's working files from files your application uses. All files are unlink()ed by dombey 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 re- turned pointer with 0 to access the client filename. Index the pointer with 1 to access the local filename. Index the pointer with 2 to ac- cess the key used to encrypt the file. Index the pointer with 3 to ac- cess the iv used to encrypt the file. The last two values are NULL if the file is not encrypted. If these values are not NULL, the key is 32 bytes, and the iv is 16 bytes. Both values may contain zeros. If the user did not select a file to upload for a particular file in- put, 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. scgi_get_file() only returns 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 re- quest. The array consists of groups of 5 ajacent entries for each up- loaded 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 filesys- tem 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 GCM mode (see the -c option). A random key and initialization vector are gener- ated for each encrypted file. Files are encrypted on the fly with no data reaching storage unencrypted. To enable encryption, call the fol- lowing 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 con- text. 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 mes- sage 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. CONVENIENCE FUNCTIONS Use these convenience functions to encode a string in x-www-form-urlen- coding 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. De- faults 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. De- faults to "". scgi_port points to the value passed as argument to the -p op- tion. Defaults to "4000". scgi_user points to the value passed as argument to the -u op- tion. Defaults to "nobody". scgi_group points to the value passed as argument to the -g op- tion. Defaults to "nobody". LIMITS Dombey stores the information for 25 SCGI environment variables, 50 SCGI parameters (including uploaded files), and 25 cookies. More items provided in a client request are ignored. See the COMMAND-LINE OPTIONS for how to use the -a, -b, and -e options to limit the amount of data clients can submit. 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 con- nection 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 is not freed by your keys' destructors before returning from scgi_request_handler(). CONFIGURATION If it is started as root, dombey writes its pidfile into /var/run/. Stop dombey with SIGTERM. Dombey stops gracefully. Idle workers exit immediately. Workers with established connections exit after estab- lished connections close. To kill a server outright, send it a SIGKILL. A sample control script, dombey.rcfile, is provided in the dombey dis- tribution. To use the script, replace all occurrences of "dombey" with the value that you pass to scgi_set_name(). Rename the script to the same value. Install the script in /usr/local/etc/rc.d. Add the fol- lowing variables to /etc/rc.conf. 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 sys- tem start. Use the following control commands. service dombey start service dombey stop service dombey restart service dombey status If you do not want the server started on system start, then set dombey_enable="NO" Use the following control commands. service dombey onestart service dombey onestop service dombey onerestart service dombey onestatus DEBUGGING To debug a server, compile it with the -g and -O0 compiler options. With the debugger, invoke the server with dombey's -x option. This forces the server to run as a single-thread foreground process. You must use -x option regardless of the concurrency type of the server. If you suspect a library bug exists, compile the dombey source to ob- ject files with symbol information with "make debug". The object files can be included in your projects to allow you to trace the dombey func- tion calls. 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 interfaces it can find capable of IPv4 or IPv6. The -l option instructs dombey 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 ac- cepting connections from a specified interface. Pass the IP ad- dress of the desired interface as argument. -n The -n options specifies the number of idle workers the master at- tempts to keep ready. The value defaults to 5. Dombey 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. -a The -a option specifies the maximum number of parameters accepted in a multipart/form-data POST request. By default, dombey accepts up to 50 parameters in a GET or a POST request. More items are silently discarded. Use -a to lower this parameter for multi- part/form-data POSTs. You cannot set the parameter to a value greater than 50 or less than 1. -b The -b option specifies a maximum acceptable data size in bytes. This value defaults to 10000. • For GET requests this value is ignored. We rely on the web server to limit the length of request lines. • 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 in the POST. -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 assumed to be malicious and are dropped without explana- tion. Setting this parameter to 0 causes dombey to drop connec- tions that submit files in POSTS. -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, dombey will be unable to restart if your server is not executable by the user or group. Dombey 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). -c Previous versions of the library used CBC mode when encrypting files. If you want to continue to use CBC mode, add the -c option to your server's command line. -x This option is useful when debugging servers. The -x option pre- vents dombey from becoming a daemon and creating multiple workers. Servers run as single thread iterative servers. -f The -f option specifies a filename as argument. Dombey assigns it to the global character pointer named scgi_config_file. This en- ables the code in scgi_init_func() and scgi_worker_init_func() to read a configuration file. AUTHORS James Bailie <jimmy@mammothcheese.ca> http://www.mammothcheese.ca Tue Apr 21, 2020 dombey(3)
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