dombey(8) FreeBSD System Manager's Manual dombey(8)
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 library. 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 characters
'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():
o after changing to the directory specified by the -r command line
option.
o 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() executes as root.
o 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_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.
o 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.
o 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()
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 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.
Queue response data for the client with scgi_write_conn().
o To abort a response, return a value less than -1. Queued data is
discarded, and the connection is closed.
o 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.
o To indicate that the complete response has been queued for the
client, return 0.
o 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.
o To indicate that you want to be notified when a descriptor becomes
readable, return the descriptor. Dombey calls scgi_request_handler()
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_request_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:
o -1 if the opaque pointer does not reference a connection.
o -2 If the server cannot enlarge the queue.
o 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 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(), 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
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 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 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. 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 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 NOT 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 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, 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
privileges 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 established
connections close. To kill a server outright, send it a SIGKILL.
A sample control script, dombey.rcfile, is provided in the dombey
distribution. 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
following 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 system
start. Use the following control 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"
Use the following control 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
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 object
files with symbol information with "make debug". The object files can be
included in your projects to allow you to trace the dombey function
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 TCP 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 accepting
connections from a specified interface. Pass the IP address of the
desired interface as argument.
-m By default, dombey maintains no more than 16384 simultaneous
connections. 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 multipart/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.
o For GET requests this value is ignored. We rely on the web
server to limit the length of request lines.
o 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.
o 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 explanation.
Setting this parameter to 0 causes dombey to drop connections that
submit files in POSTS.
-x This option is useful when debugging servers. The -x option prevents
dombey from becoming a daemon, creating multiple workers, and writing
its pidfile to /var/run/. 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 enables
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
Thu Jan 04, 2018