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NAME dombey -- Generic SCGI Application Server Library SYNOPSIS #include <dombeyevents.h> -I/usr/local/include -L/usr/local/lib -ldombeyevents -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 event-driven li- brary. The multi-process and multi-threaded libraries are described in the "libdombey" manual. USAGE Dombey provides your server's "main" function. You define 3 functions to match the following prototypes. void scgi_init_func(); void scgi_exit_func(); int scgi_request_handler( void *, int ); Do not define any other global symbol beginning with the five charac- ters 'scgi_' because dombey reserves that namespace. SCGI_INIT_FUNC() In scgi_init_func(), perform the initialization tasks your server needs to do once at server start-up. 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_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() Install a function for dombey to invoke 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_REQUEST_HANDLER() Dombey calls scgi_request_handler() (possibly multiple times) to ser- vice 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. Queue response data for the client with scgi_write_conn(). • To abort a response, return a value less than -1. Queued data is discarded, and the connection is closed. • To service the connection in stages without queuing data, return -1 after each stage that does not queue data. scgi_request_handler() is called again when the connection is writeable. This is a oneshot event. • 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. Dombey calls scgi_request_handler() 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. Dombey calls scgi_request_han- dler() when the descriptor is readable. The event is a oneshot event. SCGI_GET_USER_DATA() The library provides space where you can store a generic pointer or a float for every connection. A pointer to the storage space is returned by scgi_get_user_data(). union scgi_user_data { void *ptr; float num; }; union scgi_user_data *scgi_get_user_data( void * ); The function accepts the opaque pointer that identifies a connection. 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_re- quest_handler(). The function's second argument is a character pointer to the data, which must be zero-terminated. Dombey 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, dombey sends 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 Inside scgi_request_handler(), use the following library functions to access the environment, the parameters, and cookies. The first argu- ment to all of these functions is the opaque pointer passed to scgi_re- quest_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 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( 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 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( void *conn, 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. DO NOT MIX CALLS OF scgi_read_encrypted() TO DIFFERENT OPEN FILES BE- CAUSE IT MAINTAINS ONLY ONE CIPHER CONTEXT AT A TIME. 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. These functions return NULL if memory cannot be allo- cated. 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". SIGNALS Upon receipt of SIGBUS or SIGSEGV, dombey 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). 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. 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. -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. -m By default, dombey maintains no more than 16384 simultaneous con- nections. The -m option changes this value. -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, 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). -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. -x This option is useful when debugging servers. The -x option pre- vents dombey from becoming a daemon. -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. -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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