libdap  Updated for version 3.20.6
libdap4 is an implementation of OPeNDAP's DAP protocol.
libdap::DODSFilter Class Reference

Common functions for DODS server filter programs. More...

#include <DODSFilter.h>

Public Types

enum  Response {
  Unknown_Response, DAS_Response, DDS_Response, DataDDS_Response,
  DDX_Response, DataDDX_Response, BLOB_Response, Version_Response
}
 

Public Member Functions

virtual void dataset_constraint (DDS &dds, ConstraintEvaluator &eval, ostream &out, bool ce_eval=true) const
 
virtual void dataset_constraint (DDS &dds, ConstraintEvaluator &eval, FILE *out, bool ce_eval=true) const
 
virtual void dataset_constraint_ddx (DDS &dds, ConstraintEvaluator &eval, ostream &out, const string &boundary, const string &start, bool ce_eval=true) const
 
 DODSFilter ()
 
 DODSFilter (int argc, char *argv[]) throw (Error)
 DODSFilter constructor. More...
 
virtual void establish_timeout (ostream &stream) const
 
virtual void establish_timeout (FILE *stream) const
 
virtual void functional_constraint (BaseType &var, DDS &dds, ConstraintEvaluator &eval, ostream &out) const
 
virtual void functional_constraint (BaseType &var, DDS &dds, ConstraintEvaluator &eval, FILE *out) const
 
virtual string get_action () const
 
virtual string get_cache_dir () const
 Get the cache directory. More...
 
virtual string get_ce () const
 Get the constraint expression. More...
 
virtual string get_cgi_version () const
 
virtual time_t get_das_last_modified_time (const string &anc_location="") const
 
virtual time_t get_data_last_modified_time (const string &anc_location="") const
 
virtual time_t get_dataset_last_modified_time () const
 
virtual string get_dataset_name () const
 Get the dataset name. More...
 
virtual string get_dataset_version () const
 Get the version information for the dataset. More...
 
virtual time_t get_dds_last_modified_time (const string &anc_location="") const
 
virtual time_t get_request_if_modified_since () const
 
virtual Response get_response () const
 
int get_timeout () const
 
virtual string get_URL () const
 
virtual bool is_conditional () const
 Is this request conditional? More...
 
virtual void print_usage () const
 Print usage information for a filter program. More...
 
virtual void send_das (DAS &das, const string &anc_location="", bool with_mime_headers=true) const
 
virtual void send_das (ostream &out, DAS &das, const string &anc_location="", bool with_mime_headers=true) const
 Transmit a DAS. More...
 
virtual void send_das (FILE *out, DAS &das, const string &anc_location="", bool with_mime_headers=true) const
 Transmit a DAS. More...
 
virtual void send_data (DDS &dds, ConstraintEvaluator &eval, ostream &data_stream, const string &anc_location="", bool with_mime_headers=true) const
 Transmit data. More...
 
virtual void send_data (DDS &dds, ConstraintEvaluator &eval, FILE *data_stream, const string &anc_location="", bool with_mime_headers=true) const
 Transmit data. More...
 
virtual void send_data_ddx (DDS &dds, ConstraintEvaluator &eval, ostream &data_stream, const string &start, const string &boundary, const string &anc_location="", bool with_mime_headers=true) const
 Transmit data. More...
 
virtual void send_dds (DDS &dds, ConstraintEvaluator &eval, bool constrained=false, const string &anc_location="", bool with_mime_headers=true) const
 
virtual void send_dds (ostream &out, DDS &dds, ConstraintEvaluator &eval, bool constrained=false, const string &anc_location="", bool with_mime_headers=true) const
 Transmit a DDS. More...
 
virtual void send_dds (FILE *out, DDS &dds, ConstraintEvaluator &eval, bool constrained=false, const string &anc_location="", bool with_mime_headers=true) const
 Transmit a DDS. More...
 
virtual void send_ddx (DDS &dds, ConstraintEvaluator &eval, ostream &out, bool with_mime_headers=true) const
 
virtual void send_ddx (DDS &dds, ConstraintEvaluator &eval, FILE *out, bool with_mime_headers=true) const
 
virtual void send_version_info () const
 Send version information back to the client program. More...
 
virtual void set_ce (string _ce)
 
virtual void set_cgi_version (string version)
 
virtual void set_dataset_name (const string _dataset)
 
virtual void set_response (const string &r)
 
void set_timeout (int timeout=0)
 
virtual void set_URL (const string &url)
 

Protected Member Functions

void initialize ()
 
void initialize (int argc, char *argv[])
 
virtual int process_options (int argc, char *argv[])
 

Protected Attributes

string d_action
 
time_t d_anc_das_lmt
 
time_t d_anc_dds_lmt
 
string d_anc_dir
 
string d_anc_file
 
bool d_bad_options
 
string d_cache_dir
 
string d_cgi_ver
 
bool d_comp
 
bool d_conditional_request
 
string d_dap2ce
 
string d_dataset
 
time_t d_if_modified_since
 
string d_program_name
 
Response d_response
 
int d_timeout
 
string d_url
 

Detailed Description

Common functions for DODS server filter programs.

When a DODS server receives a request from a DODS client, the server CGI script dispatches the request to one of several ``filter'' programs. Each filter is responsible for returning a different aspect of the dataset information: one is for data, one is for the dataset DDS, one is for the dataset DAS, and a fourth is for a usage message describing the server itself. Some installations may have additional optional filters.

The filter program receives a data request from the dispatch script. It receives its operating parameters from the command line, like any UNIX command, and it returns its output to standard output, which the httpd server packages up into a reply to the client.

This class contains some common functions for the filter programs used to make up the DODS data servers. The filter programs do not have to be called by a CGI program, but that is the normal mechanism by which they are invoked.

Todo:

Add a test to make sure that the required arguments are given.

We need to rethink the ancillary file/directory stuff. I don't think it's ever been used...

Author
jhrg 8/26/97

Definition at line 78 of file DODSFilter.h.

Member Enumeration Documentation

◆ Response

Types of responses DODSFilter know about.

Definition at line 82 of file DODSFilter.h.

Constructor & Destructor Documentation

◆ DODSFilter() [1/2]

libdap::DODSFilter::DODSFilter ( )
inline

Make an empty instance. Use the set_*() methods to load with needed values. You must call at least set_dataset_name() or be requesting version information.

Todo:
Add methods to provide a way to set all of the parameters this class contains. They can currently only be set using the argc/argv command line parameters.

Definition at line 129 of file DODSFilter.h.

◆ DODSFilter() [2/2]

libdap::DODSFilter::DODSFilter ( int  argc,
char *  argv[] 
)
throw (Error
)

DODSFilter constructor.

Create an instance of DODSFilter using the command line arguments passed by the CGI (or other) program. The default constructor is private; this and the copy constructor (which is just the default copy constructor) are the only way to create an instance of DODSFilter.

These are the valid options:

filename

The name of the file on which the filter is to operate. Usually this would be the file whose data has been requested. In fact, this class can be specialized and any meaning can be associated to this string. It could be the name of a database, for example.

-o response

Specifies the type of response desired. The response is a string and must be one of DAS, DDS, DataDDS or Version. Note that Version returns version information in the body of the response and is useful for debugging, et cetera. Each response returns version information in an HTTP header for internal use by a client.

-c

Send compressed data. Data are compressed using the deflate program.

-e expression

This option specifies a non-blank constraint expression used to subsample a dataset.

-v cgi-version

Set the CGI/Server version to cgi-version. This is a way for the caller to set version information passed back to the client either as the response to a version request of in the response headers.

-d ancdir

Specifies that ancillary data be sought in the ancdir directory. ancdir must end in '/'.

-f ancfile

Specifies that ancillary data may be found in a file called ancfile.

-r cache directory

Specify a directory to use if/when files are to be cached. Not all handlers support caching and each uses its own rules tailored to a specific file or data type.

-t timeout

Specifies a a timeout value in seconds. If the server runs longer than timeout seconds, an Error is returned to the client explaining that the request has timed out.

-l time

Indicates that the request is a conditional request; send a complete response if and only if the data has changed since time. If it has not changed since time, then send a 304 (Not Modified) response. The time parameter is the Last-Modified time from an If-Modified-Since condition GET request. It is given in seconds since the start of the Unix epoch (Midnight, 1 Jan 1970).

Definition at line 170 of file DODSFilter.cc.

Member Function Documentation

◆ establish_timeout()

void libdap::DODSFilter::establish_timeout ( FILE *  stream) const
virtual

Use values of this instance to establish a timeout alarm for the server. If the timeout value is zero, do nothing.

Todo:
When the alarm handler is called, two CRLF pairs are dumped to the stream and then an Error object is sent. No attempt is made to write the 'correct' MIME headers for an Error object. Instead, a savvy client will know that when an exception is thrown during a deserialize operation, it should scan ahead in the input stream for an Error object. Add this, or a sensible variant once libdap++ supports reliable error delivery. Dumb clients will never get the Error object...

Definition at line 628 of file DODSFilter.cc.

◆ get_action()

string libdap::DODSFilter::get_action ( ) const
virtual

Get the string name of the response to be returned.

Definition at line 458 of file DODSFilter.cc.

◆ get_cache_dir()

string libdap::DODSFilter::get_cache_dir ( ) const
virtual

Get the cache directory.

The cache_dir is used to hold the cached .dds and .das files. By default, this returns an empty string (store cache files in current directory.

Returns
A string object that contains the cache file directory.

Definition at line 594 of file DODSFilter.cc.

◆ get_ce()

string libdap::DODSFilter::get_ce ( ) const
virtual

Get the constraint expression.

Return the entire constraint expression in a string. This includes both the projection and selection clauses, but not the question mark.

Returns
A string object that contains the constraint expression.

Definition at line 350 of file DODSFilter.cc.

◆ get_cgi_version()

string libdap::DODSFilter::get_cgi_version ( ) const
virtual

Return the version information passed to the instance when it was created. This string is passed to the DODSFilter ctor using the -v option.

Returns
The version string supplied at initialization.

Definition at line 338 of file DODSFilter.cc.

◆ get_das_last_modified_time()

time_t libdap::DODSFilter::get_das_last_modified_time ( const string &  anc_location = "") const
virtual

Get the last modified time for the dataset's DAS. This time, given in seconds since the epoch (1 Jan 1970 00:00:00 GMT), is the greater of the datasets's and any ancillary DAS' last modified time.

Parameters
anc_locationA directory to search for ancillary files (in addition to the CWD).
Returns
Time of last modification of the DAS.
See also
get_dataset_last_modified_time()
get_dds_last_modified_time()

Definition at line 499 of file DODSFilter.cc.

◆ get_data_last_modified_time()

time_t libdap::DODSFilter::get_data_last_modified_time ( const string &  anc_location = "") const
virtual

Get the last modified time to be used for a particular data request. This method should look at both the constraint expression and any ancillary files for this dataset. The implementation provided here returns the latest time returned by the get_dataset...(), get_das...() and get_dds...() methods and does not currently check the CE.

Parameters
anc_locationA directory to search for ancillary files (in addition to the CWD).
Returns
Time of last modification of the data.
See also
get_dataset_last_modified_time()
get_das_last_modified_time()
get_dds_last_modified_time()

Definition at line 551 of file DODSFilter.cc.

◆ get_dataset_last_modified_time()

time_t libdap::DODSFilter::get_dataset_last_modified_time ( ) const
virtual

Get the dataset's last modified time. This returns the time at which the dataset was last modified as defined by UNIX's notion of modification. This does not take into account the modification of an ancillary DAS or DDS. Time is given in seconds since the epoch (1 Jan 1970 00:00:00 GMT).

This method perform a simple check on the file named by the dataset given when the DODSFilter instance was created. If the dataset is not a filter, this method returns the current time. Servers which provide access to non-file-based data should subclass DODSFilter and supply a more suitable version of this method.

From the stat(2) man page: ``Traditionally, st_mtime is changed by mknod(2), utime(2), and write(2). The st_mtime is not changed for changes in owner, group, hard link count, or mode.''

Returns
Time of the last modification in seconds since the epoch.
See also
get_das_last_modified_time()
get_dds_last_modified_time()

Definition at line 484 of file DODSFilter.cc.

◆ get_dataset_name()

string libdap::DODSFilter::get_dataset_name ( ) const
virtual

Get the dataset name.

The ``dataset name'' is the filename or other string that the filter program will use to access the data. In some cases this will indicate a disk file containing the data. In others, it may represent a database query or some other exotic data access method.

Returns
A string object that contains the name of the dataset.

Definition at line 370 of file DODSFilter.cc.

◆ get_dataset_version()

string libdap::DODSFilter::get_dataset_version ( ) const
virtual

Get the version information for the dataset.

To read version information that is specific to a certain dataset, override this method with an implementation that does what you want. By default, this returns an empty string.

Returns
A string object that contains the dataset version information.

Definition at line 409 of file DODSFilter.cc.

◆ get_dds_last_modified_time()

time_t libdap::DODSFilter::get_dds_last_modified_time ( const string &  anc_location = "") const
virtual

Get the last modified time for the dataset's DDS. This time, given in seconds since the epoch (1 Jan 1970 00:00:00 GMT), is the greater of the datasets's and any ancillary DDS' last modified time.

Returns
Time of last modification of the DDS.
See also
get_dataset_last_modified_time()
get_dds_last_modified_time()

Definition at line 522 of file DODSFilter.cc.

◆ get_request_if_modified_since()

time_t libdap::DODSFilter::get_request_if_modified_since ( ) const
virtual

Get the value of a conditional request's If-Modified-Since header. This value is used to determine if the request should get a full response or a Not Modified (304) response. The time is given in seconds since the Unix epoch (midnight, 1 Jan 1970). If no time was given with the request, this methods returns -1.

Returns
If-Modified-Since time from a condition GET request.

Definition at line 582 of file DODSFilter.cc.

◆ get_response()

DODSFilter::Response libdap::DODSFilter::get_response ( ) const
virtual

Get the enum name of the response to be returned.

Definition at line 452 of file DODSFilter.cc.

◆ get_timeout()

int libdap::DODSFilter::get_timeout ( ) const

Get the server's timeout value.

Definition at line 611 of file DODSFilter.cc.

◆ get_URL()

string libdap::DODSFilter::get_URL ( ) const
virtual

Get the URL. This returns the URL, minus the constraint originally sent to the server.

Returns
The URL.

Definition at line 385 of file DODSFilter.cc.

◆ initialize() [1/2]

void libdap::DODSFilter::initialize ( )
protected

Called when initializing a DODSFilter that's not going to be passed a command line arguments.

Definition at line 194 of file DODSFilter.cc.

◆ initialize() [2/2]

void libdap::DODSFilter::initialize ( int  argc,
char *  argv[] 
)
protected

Initialize. Specializations can call this once an empty DODSFilter has been created using the default constructor. Using a method such as this provides a way to specialize the process_options() method and then have that specialization called by the subclass' constructor.

This class and any class that specializes it should call this method in its constructor. Note that when this method is called, the object is not fully constructed.

Parameters
argcThe argument count
argvThe vector of char * argument strings.

Definition at line 235 of file DODSFilter.cc.

◆ is_conditional()

bool libdap::DODSFilter::is_conditional ( ) const
virtual

Is this request conditional?

Returns
True if the request is conditional.
See also
get_request_if_modified_since().

Definition at line 308 of file DODSFilter.cc.

◆ print_usage()

void libdap::DODSFilter::print_usage ( ) const
virtual

Print usage information for a filter program.

This message is printed when the filter program is incorrectly invoked by the dispatch CGI. This is an error in the server installation or the CGI implementation, so the error message is written to stderr instead of stdout. A server's stderr messages show up in the httpd log file. In addition, an error object is sent back to the client program telling them that the server is broken.

Definition at line 665 of file DODSFilter.cc.

◆ process_options()

int libdap::DODSFilter::process_options ( int  argc,
char *  argv[] 
)
protectedvirtual

Processing the command line options passed to the filter is handled by this method so that specializations can change the options easily.

Parameters
argcThe argument count
argvThe vector of char * argument strings.
Returns
The index of the next, unprocessed, argument. This must be the identifier passed to the filter program that identifies the data source. It's often a file name.

Definition at line 264 of file DODSFilter.cc.

◆ send_das() [1/2]

void libdap::DODSFilter::send_das ( ostream &  out,
DAS das,
const string &  anc_location = "",
bool  with_mime_headers = true 
) const
virtual

Transmit a DAS.

This function formats and prints an ASCII representation of a DAS on stdout. This has the effect of sending the DAS object back to the client program.

Parameters
outThe output stream to which the DAS is to be sent.
dasThe DAS object to be sent.
anc_locationThe directory in which the external DAS file resides.
with_mime_headersIf true (the default) send MIME headers.
Returns
void
See also
DAS

Definition at line 716 of file DODSFilter.cc.

◆ send_das() [2/2]

void libdap::DODSFilter::send_das ( FILE *  out,
DAS das,
const string &  anc_location = "",
bool  with_mime_headers = true 
) const
virtual

Transmit a DAS.

This function formats and prints an ASCII representation of a DAS on stdout. This has the effect of sending the DAS object back to the client program.

Parameters
outThe output FILE to which the DAS is to be sent.
dasThe DAS object to be sent.
anc_locationThe directory in which the external DAS file resides.
with_mime_headersIf true (the default) send MIME headers.
Returns
void
See also
DAS

Definition at line 696 of file DODSFilter.cc.

◆ send_data() [1/2]

void libdap::DODSFilter::send_data ( DDS dds,
ConstraintEvaluator eval,
ostream &  data_stream,
const string &  anc_location = "",
bool  with_mime_headers = true 
) const
virtual

Transmit data.

Send the data in the DDS object back to the client program. The data is encoded using a Marshaller, and enclosed in a MIME document which is all sent to data_stream. If this is being called from a CGI, data_stream is probably stdout and writing to it has the effect of sending the response back to the client.

Parameters
ddsA DDS object containing the data to be sent.
evalA reference to the ConstraintEvaluator to use.
data_streamWrite the response to this stream.
anc_locationA directory to search for ancillary files (in addition to the CWD). This is used in a call to get_data_last_modified_time().
with_mime_headersIf true, include the MIME headers in the response. Defaults to true.
Returns
void

Definition at line 976 of file DODSFilter.cc.

◆ send_data() [2/2]

void libdap::DODSFilter::send_data ( DDS dds,
ConstraintEvaluator eval,
FILE *  data_stream,
const string &  anc_location = "",
bool  with_mime_headers = true 
) const
virtual

Transmit data.

Send the data in the DDS object back to the client program. The data is encoded using a Marshaller, and enclosed in a MIME document which is all sent to data_stream. If this is being called from a CGI, data_stream is probably stdout and writing to it has the effect of sending the response back to the client.

Parameters
ddsA DDS object containing the data to be sent.
evalA reference to the ConstraintEvaluator to use.
data_streamWrite the response to this FILE.
anc_locationA directory to search for ancillary files (in addition to the CWD). This is used in a call to get_data_last_modified_time().
with_mime_headersIf true, include the MIME headers in the response. Defaults to true.
Returns
void

Definition at line 950 of file DODSFilter.cc.

◆ send_data_ddx()

void libdap::DODSFilter::send_data_ddx ( DDS dds,
ConstraintEvaluator eval,
ostream &  data_stream,
const string &  start,
const string &  boundary,
const string &  anc_location = "",
bool  with_mime_headers = true 
) const
virtual

Transmit data.

Send the data in the DDS object back to the client program. The data is encoded using a Marshaller, and enclosed in a MIME document which is all sent to data_stream. If this is being called from a CGI, data_stream is probably stdout and writing to it has the effect of sending the response back to the client.

Parameters
ddsA DDS object containing the data to be sent.
evalA reference to the ConstraintEvaluator to use.
data_streamWrite the response to this stream.
start
boundary
anc_locationA directory to search for ancillary files (in addition to the CWD). This is used in a call to get_data_last_modified_time().
with_mime_headersIf true, include the MIME headers in the response. Defaults to true.
Returns
void

Definition at line 1118 of file DODSFilter.cc.

◆ send_dds() [1/2]

void libdap::DODSFilter::send_dds ( ostream &  out,
DDS dds,
ConstraintEvaluator eval,
bool  constrained = false,
const string &  anc_location = "",
bool  with_mime_headers = true 
) const
virtual

Transmit a DDS.

This function formats and prints an ASCII representation of a DDS on stdout. When called by a CGI program, this has the effect of sending a DDS object back to the client program. Either an entire DDS or a constrained DDS may be sent.

Parameters
outThe output stream to which the DAS is to be sent.
ddsThe DDS to send back to a client.
evalA reference to the ConstraintEvaluator to use.
constrainedIf this argument is true, evaluate the current constraint expression and send the `constrained DDS' back to the client.
anc_locationThe directory in which the external DAS file resides.
with_mime_headersIf true (the default) send MIME headers.
Returns
void
See also
DDS

Definition at line 784 of file DODSFilter.cc.

◆ send_dds() [2/2]

void libdap::DODSFilter::send_dds ( FILE *  out,
DDS dds,
ConstraintEvaluator eval,
bool  constrained = false,
const string &  anc_location = "",
bool  with_mime_headers = true 
) const
virtual

Transmit a DDS.

This function formats and prints an ASCII representation of a DDS on stdout. When called by a CGI program, this has the effect of sending a DDS object back to the client program. Either an entire DDS or a constrained DDS may be sent.

Parameters
outThe output FILE to which the DAS is to be sent.
ddsThe DDS to send back to a client.
evalA reference to the ConstraintEvaluator to use.
constrainedIf this argument is true, evaluate the current constraint expression and send the `constrained DDS' back to the client.
anc_locationThe directory in which the external DAS file resides.
with_mime_headersIf true (the default) send MIME headers.
Returns
void
See also
DDS

Definition at line 757 of file DODSFilter.cc.

◆ send_ddx() [1/2]

void libdap::DODSFilter::send_ddx ( DDS dds,
ConstraintEvaluator eval,
ostream &  out,
bool  with_mime_headers = true 
) const
virtual

Send the DDX response. The DDX never contains data, instead it holds a reference to a Blob response which is used to get the data values. The DDS and DAS objects are built using code that already exists in the servers.

Parameters
ddsThe dataset's DDS with attributes in the variables.
evalA reference to the ConstraintEvaluator to use.
outDestination
with_mime_headersIf true, include the MIME headers in the response. Defaults to true.

Definition at line 1070 of file DODSFilter.cc.

◆ send_ddx() [2/2]

void libdap::DODSFilter::send_ddx ( DDS dds,
ConstraintEvaluator eval,
FILE *  out,
bool  with_mime_headers = true 
) const
virtual

Send the DDX response. The DDX never contains data, instead it holds a reference to a Blob response which is used to get the data values. The DDS and DAS objects are built using code that already exists in the servers.

Parameters
ddsThe dataset's DDS with attributes in the variables.
evalA reference to the ConstraintEvaluator to use.
outDestination
with_mime_headersIf true, include the MIME headers in the response. Defaults to true.

Definition at line 1051 of file DODSFilter.cc.

◆ send_version_info()

void libdap::DODSFilter::send_version_info ( ) const
virtual

Send version information back to the client program.

This function formats and sends to stdout version information from the httpd server, the server dispatch scripts, the DODS core software, and (optionally) the dataset.

Definition at line 679 of file DODSFilter.cc.

◆ set_cgi_version()

void libdap::DODSFilter::set_cgi_version ( string  version)
virtual

Set the CGI/Server version number. Servers use this when answering requests for version information. The version `number' should include both the name of the server (e.g., ff_dods) as well as the version number. Since this information is typically divined by configure, it's up to the executable to poke the correct value in using this method.

Note that the -v switch that this class understands is deprecated since it is usually called by Perl code. It makes more sense to have the actual C++ software set the version string.

Parameters
versionA version string for this server.

Definition at line 327 of file DODSFilter.cc.

◆ set_response()

void libdap::DODSFilter::set_response ( const string &  r)
virtual

Set the response to be returned. Valid response names are "DAS", "DDS", "DataDDS, "Version".

Parameters
rThe name of the object.
Exceptions
InternalErrThrown if the response is not one of the valid names.

Definition at line 420 of file DODSFilter.cc.

◆ set_timeout()

void libdap::DODSFilter::set_timeout ( int  t = 0)

Set the server's timeout value. A value of zero (the default) means no timeout.

Parameters
tServer timeout in seconds. Default is zero (no timeout).

Definition at line 604 of file DODSFilter.cc.

◆ set_URL()

void libdap::DODSFilter::set_URL ( const string &  url)
virtual

Set the URL. Set the URL sent to the server.

Parameters
urlThe URL, minus the constraint.

Definition at line 393 of file DODSFilter.cc.


The documentation for this class was generated from the following files: