libdap  3.20.11
About: OPeNDAP is a client/server system for making local data accessible to remote locations without regard to the local or remote storage format, architecture, or environment (see also ODC = The OPeNDAP Data Connector).
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Please find the libdap4 API documentation here:

##Updated for version 3.20.11

  • Fixed bug in computation of request_size_kb()
  • Fixed type issue in (#192)

##Updated for version 3.20.10 DOI

  • Support for RHEL8
  • Fix for bugs in the ce parser around inverted indices.
  • Fix for libdap4 github issue 147: Grid::get_map_iter() was off by one
  • Improvements to DAP4 api.
  • Fixed various memory leaks.
  • Replaced instances of &vector[0] with (RHEL8)

Updated for version 3.20.9 DOI

  • Started migrating from (deprecated) auto_ptr to C++11 unique_ptr
  • Migrated use of regex functions from outdfated GNU implementation to C++11 implementation (uses compile time swicth)

Updated for version 3.20.8 DOI

  • Modified Error so that it is more in line with C++11.
  • Added (shallow) unit64_t request size computations and max_request_size state.
  • Changed the internal representation of max response size to uint64_t and confined the overflow to just the (deprecated) functions.

Updated for version 3.20.7 DOI

  • Added code coverage (using gcov) to the CI processes.
  • Dropped support for CentOS-6 (whew!)
  • Improved Int64 support.
  • Corrected byte order issue with DAP4 data transmission.
  • Improved error reporting.

Updated for version 3.20.6 DOI

  • Stopped CE parse errors from returning user supplied strings in error messages.
  • README is now called

Updated for version 3.20.5 DOI

  • Memory leaks. Minor bug fixes. Lots of work on CI.

Updated for version 3.20.4 DOI

  • Updated for version 3.20.4
  • Memory leak fixes and C++11 features

Updated for version 3.20.3 DOI

  • Fixes and Debian packaging via Travis CI

Updated for version 3.20.2 DOI

  • Added libdap::Array::rename_dim()

Updated for version 3.20.1

  • Added Continuous Delivery for CentOS 6 and 7

Updated for version 3.20.0

  • We now have a Debian package for libdap.
  • Bug fixes; See the ChangeLog and NEWS files.

Updated for version 3.19.1

  • Bug fixes; See the ChangeLog and NEWS files.

Updated for version 3.18.3

  • Bug fixes; See the ChangeLog and NEWS files.

Updated for version 3.18.2

  • Added support for DAP4 filter operations.
  • For other information, see NEWS and ChangeLog

Updated for 3.16.0

libdap now supports parallel I/O for certain data write operations, mostly those involving larger amounts of data - Marshaller::put_vector and put_vector_part. The behavior can be 'turned off' by #undef the symbol USE_POSIX_THREADS in the XDSStreamMarshaller classes.

Added to libdap is the ability to send DAP2 responses in parts, so that code that builds large responses from multiple reads can write a part that is complete and then return to work on the next part. This is especially beneficial for aggregations that cross many granules. The new method is Marshaller::put_vector_part().

Added to libdap is a virtual void BaseType::clear_local_data() method that can be used to free the memory used by a BaseType to hold data values. This provides a way for the object to persist in memory without holding onto all of its data (which can be a substantial part of the object's total size).

Updated for 3.14.0

Bison 3 is required to build this code.

Updated for 3.13.3

Bug fix release

Updated for 3.13.2

Bug fix release

Updated for 3.13.1

A test baseline was updated to use both the DAP2 and DAP4 version of the XDAP/X-DAP header. This change was likely over doing things on our part, but it's important to have the source releases pass all their tests.

Updated 3.13.0

Support for clang: Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn) added.

Updated for version 3.12.1

Note that the documented behavior of BaseType::read() is now correctly implemented.

Updated for version 3.12.0

The server functions have been moved out of libdap and into their own BES module. Currently this modules is part of the BES, but that will change in the future. This version of libdap supports building very large arrays made up of constant value (e.g., to be used as masks in server functions you write).

For information on the way to make these functions, see: Note that this version of libdap requires bison 2.4. This is a change so the parsers can use C++ I/O streams and we can eventually drop the FILE* interfaces.

Updated for version 3.11.7

Minor tweak for the server function caching code: turn on or off the cache by adding or removing the directory /tmp/dap_functions_cache. If the directory is not present no caching of server function calls is done. All the other behaviors are otherwise identical.

Updated for version 3.11.6

There is a new cache for some kinds of response objects. It's size and location are currently fixed to 20GB bytes and "/tmp/dap_functions_cache/" but these will be made BES parameters in a future release.

Updated for version 3.11.5

A memory leak in XDRStreamMarshaller was fixed.

A bug in DDS::add_var_nocopy() was fixed.

Updated for version 3.11.2

Bug fixes and improvements in the implementations of some methods.

Updated for version 3.11.1

Bug fixes only.

Updated for version 3.11.0

Now constraint expressions can have multiple function calls that return data.

I've bumped up the DAP version from 3.3 to 3.4 to reflect this change.

Updated for Version 3.10.2

BaseType::transfer_attributes() and related methods provide a way for handlers to customize how attributes from a DAS object are merged into a DDS.

In the past we supported a kind of client-side system that could augment the attributes call the 'AIS' (Ancillary Information System). This has been removed - our server now supports the NcML language to do much the same thing but in a way that can be set on the server once for all users. It's also an emerging convention that's gaining wide support within the community.

Updated for Version 3.10.0

DAP 3.3 is now supported; see

This version of libdap contains many changes that are needed for both DAP 4 and the NcML handler. This version of the library is required for the Hyrax 1.6 handlers.

The 'deflate' program is no longer part of this library package since we are no longer supporting the old data server system (based on WWW's CGI specification).

Updated for version 3.9.2

Now libdap supports DAP 3.2. You can read about the evolving DAP 3.x protocol at If your client sends the XDAP-Accept header with a value of 3.2 the DDX is different (it includes protocol information and also an xmlbase element).

Behavior change for the DAS: In the past the format handlers added double quotes to the values of string attributes when they added those values to the AttrTable object. This meant that the value of the attribute in the C++ object was actually not correct since it contained quotes not found in the original attribute value. I modified libdap so that if an attribute value in the C++ AttrTable object does not have quotes then those quotes are added when the value is output in a DAS response (but not a DDX since there's no need to quote the value in that response). This ensures that the text in the DAS wire representation will parse whether a handler has added quotes or not (paving the way for fixed handlers). At the same time I fixed all of our handlers so that they no longer add the erroneous quotes. This fixes a problem with the DDX where the quotes were showing up as part of the attribute value. The change to libdap is such that a broken handler will not be any more broken but a fixed handler will work for both DAS and DDX generation.

If you have a handler and it's not adding quotes to the String attribute values - good, don't change that! If your handler does add quotes, please modify it so the DDX will be correct.

Our handler's old, broken, behavior can be resurrected by removing the ATTR_STRING_QUOTE FIX define in the appropriate files.

Updated for version 3.8.2 (23 June 2008)

HTTP Cache and win32 installer fixes (the latter are actually in the 3.8.1 installer for winXP). API change: The functions used to merge ancillary data have been moved to their own class (Ancillary).

Updated for version 3.8.1 (10 June 2008)

The syntax for PROXY_SERVER in the .dodsrc file was relaxed. See the .dodsrc file for more information.

Updated for Version 3.8.0 (29 February 2008)

The libdap classes and code are now inside of the libdap namespace. In order to access any of the classes, for example, you will need to do one of the following. After including the libdap headers you can:

  1. add a using statement for the entire libdap namespace:

using namespace libdap ;

  1. add a using statement for the classes that you will be using:

using libdap::DAS ;

  1. inside your code scope the use of libdap classes.

libdap::DAS *das = code_to_get_das() ;

Added method to HTTPCache to return not only the FILE pointer of a cached response but also the name of the file in the cache, to allow for this file name to be passed to data handlers in the BES to be read.

See NEWS for more information about changes for this version and ChangeLog for the gory details.

Updated for Version 3.7.10 (28 November 2007)

A bug fix release. See NEWS.

Updated for Version 3.7.9 (13 November 2007)

This release is a bug fix and refactoring release. Old classes which were no longer used have been removed, the FILE* output methods are slated to be replaced with ones which will use iostream and will support a chucked transfer 'Marshaller,' and the transfer_data() methods have been made a formal part of the library, implemented for all classes, fixed and renamed to intern_data(). Many bugs in the library were also fixed.

Updated for version 3.7.8 (26 June 2007)

The major fixes in this version are memory errors found and fixed in the Regex class and HTTP header processing software. This version also supports pkg-config on hosts that have that installed.

See NEWS for more information about changes for this version and ChangeLog for the gory details.

Notes for version 3.7.7 (2 May 2007)

The major fix here is to the source build. We've fixed the issue where source builds failed to make the dapserver and dapclient libraries.

Notes for version 3.7.6 (12 March 2007)

Two bug fixes, both minor. Problems in the linear_scale() constraint expression function and a bad/missing #include in GNURegex.h were fixed.

There was an error in the INSTALL file sent out in the previous release. It said this library implemented DAP version 3.2, but in fact it implements version 3.1. The version 3.2 release will be along soon (RSN).

Notes for version 3.7.5 (7 Feb 2007)

This version includes many fixes from the first Server4 beta release plus fixes for the server-side functions. It also includes a smoother Win32 build.

Notes for version 3.7.4 (2 Jan 2007)

Release for the Server4 beta release.

Notes for version 3.7.3 (24 Nov 2006)

This version of libdap contains a beta release of the server-side functions geogrid(), geoarray(), linear_scale() and version(). These can be used to select parts of Grids and Arrays using latitude and longitude values instead of array position indexes. The linear_scale() function can be used to scale variables (including those return by other function) using 'y = mx + b'. The version() function can be used to find out which versions of the functions are installed.


To get version information use the 'version()' function. Currently, version() can only be called when asking for data, and you must give the name of a data source, although in the default version of version() the data source is not used. The version function takes one optional argument which may be the strings 'help' or 'xml'. Use 'help' to get help on using the function; use 'xml' to get version information encoded using XML instead of plain text:

[jimg@zoe libdap]$ url= [jimg@zoe libdap]$ ./getdap -D "$url?version()" The data: String version = "Function set: version 1.0, grid 1.0, geogrid 1.0b2, geoarray 0.9b1, linear_scale 1.0b1";

[jimg@zoe libdap]$ ./getdap -D "$url?version(help)" The data: String version = "Usage: version() returns plain text information about ...

[jimg@zoe libdap]$ ./getdap -D "$url?version(xml)" The data: String version = " <function name="version" version="1.0"/> <function name="grid" version="1.0"/> <function name="geogrid" version="1.0"/> <function name="geoarray" version="1.0"/> <function name="linear_scale" version="1.0"/> ";

The geogrid function can only be used with variables that are Grids:

[jimg@zoe libdap]$ getdap -d "$url" Dataset { Float64 COADSX[COADSX = 180]; Float64 COADSY[COADSY = 90]; Float64 TIME[TIME = 12]; Grid { Array: Float32 SST[TIME = 12][COADSY = 90][COADSX = 180]; Maps: Float64 TIME[TIME = 12]; Float64 COADSY[COADSY = 90]; Float64 COADSX[COADSX = 180]; } SST; Grid { . . .

Pass the name of the Grid variable and the upper-left and lower-right corners of the lat/lon rectangle to geogrid. Optionally, pass one or more relational expressions to select parts of dimensions that are not lat/lon.

Note: in libdap 3.7.3 calling geogrid with a constraint on each dimension may return incorrect values that indicate missing data even though data should have been returned.

[jimg@zoe libdap]$ getdap -D "$url?geogrid(SST,30,-60,20,-60,\"TIME=366\")" The data: Grid { Array: Float32 SST[TIME = 1][COADSY = 7][COADSX = 2]; Maps: Float64 TIME[TIME = 1]; Float64 COADSY[COADSY = 7]; Float64 COADSX[COADSX = 2]; } SST = { Array: {{{24.4364, 25.0923},{23.7465, 24.4146},{19.843, 23.6033}, {16.8464, 17.7756},{16.65, 16.818},{-1e+34, 15.3656},{18.7214, 13.1286}}} Maps: {366}, {19, 21, 23, 25, 27, 29, 31}, {-61, -59} };

The geoarray() function works like geogrid() except that it's used to select from an Array variable and not a Grid. In addition to the four lat/lon values for selection rectangle, the caller must supply the data's corner points. A subsequent release of libdap will include a version that reads the data extent from the data source when possible so caller's won't normally have to know the data's extent ahead of time.

The linear_scale() function take either one or three arguments. The first (only) argument is the name of a variable or the return from another function. This variable will be scaled using the 'y = mx + b' equation where 'x' is the value(s) of the input variable and 'm' and 'b' are read from the data source using the values of attributes name 'scale_factor' and 'add_offset.' If these are not present, or to over ride their values, m and b can be supplied using the second and third arguments.

Note that there are still some problems with linear_scale() in this release.

See NEWS and ChangeLog for information about other changes

Notes for version 3.7.2

This version of libdap is required for the 9/15/06 alpha release of Server4. The library now contains software which enables Server4 to build the ASCII data response for all types of variables, including Sequence and nested Sequence variables. These features are additions to the API, so older code will work just fine with the new library. See NEWS for more specific info about bug fixes.

Notes for version 3.7.1

This is a bug fix release (mostly) made for users of the netcdf client library who need a fix for a problem dealing with attributes from the HDF4 server.

NOTES for version 3.7.0

This version includes new features and an implementation change.

This version of libdap now returns the DAP protocol version number, 3.1, in an HTTP response header. Use this to determine which protocol version the library implements. The inclusion of a protocol version number is the sole official new feature of DAP 3.1. Use Connect::get_protocol() to get the version number. Clients can use this to determine the features supported by a server. The Connect::get_version() method can still be used to get our server's implementation version. The distinction is that as more groups provide their own implementations of the DAP, the protocol version will provide a way for clients to determine capabilities independently of implementation.

The libdap library now contains an implementation of the DDX object/response, although this is an alpha implementation and it's actually been part of the library for some time now. The implementation contained in this version of the library is close enough to the version we intend for DAP4 that developers can start to use it. Most of the server handlers will return DDXs when asked.

The DDX combines the information previously held by the DDS and DAS objects, making it much easier to associate attributes to variables. As the name suggests, the DDX uses XML rather than curly-braces. You can drop the DDX into your favorite XML parser and get a DOM tree; no need to use our parsers. However, libdap contains a nice SAX parser that will build the libdap objects directly from the XML DDX object/response. Also included in libdap are methods to build a DDX using a DDS and DAS, so there's an easy migration path for both servers and clients.

Finally, the library contains two structural changes. First, the library named 'libdap' now holds the DAP implementation while two new libraries, 'libdapclient' and 'libdapserver', now hold the client and server helper classes which are not strictly part of the DAP. Secondly, the DDS/DDX object now takes the constraint evaluator as a parameter. The class ConstraintEvaluator holds our default evaluator, but it's now possible to use your own evaluator .

NOTES for version 3.6.1

Version 3.6.1 is bug fix release.

NOTES for version 3.6.0

This version of the library may not work older source code. Many of the deprecated methods have been removed.

Added are headers which send information about the version of the DAP protocol that the library implements (in contrast to the implementation of the library itself). A new header named XOPeNDAP-Server is used to send information about the implementation of servers.

The libtool interface version has been incremented from 3 to 4 (these versions do no track the software's release version since several releases might present compatible binary interfaces).

NOTES for version 3.5.3

This version of libdap++ cannot be used to build the 3.4.x and previous clients and/or servers. However, client and servers built using this code will work with the older clients and servers.


This directory contains the OPeNDAP C++ implementation of the Data Access Protocol version 2 (DAP2) with some extensions that will be part of DAP3. Documentation for this software can be found on the OPeNDAP home page at The NASA/ESE RFC which describes DAP2, implemented by the library, can be found at

The DAP2 is used to provide a uniform way of accessing a variety of different types of data across the Internet. It was originally part of the DODS and then NVODS projects. The focus of those projects was access to Earth-Science data, so much of the software developed using the DAP2 to date has centered on that discipline. However, the DAP2 data model is very general (and similar to a modern structured programming language) so it can be applied to a wide variety of fields.

The DAP2 is implemented as a set of C++ classes that can be used to build data servers and clients. The classes may be specialized to mimic the behavior of other data access APIs, such as netCDF. In this way, programs originally meant to work with local data in those formats can be re-linked and equipped to work with data stored remotely in many different formats. The classes can also by specialized to build standalone client programs.

The DAP2 is contained in a single library: libdap++.a. Also included in the library are classes and utility functions which simplify building clients and servers.


The file README.dodsrc describes the client-side behavior which can be controlled using the .dodsrc file. This includes client-side caching, proxy servers, et c., and is described in a separate file so it's easy to include in your clients.

The file README.AIS describes the prototype Ancillary Information Service (AIS) included in this version of the library. The AIS is (currently) a client-side capability which provides a way to augment DAP attributes. This is a very useful feature because it can be used to add missing metadata to a data source. The AIS is accessed by using the AISConnect class in place of Connect in your client.

This directory also contains test programs for the DAP2, a sample specialization of the classes, getdap (a useful command-line web client created with DAP2) and dap-config (a utility script to simplify linking with libdap.a). Also included as of version 3.5.2 is libdap.m4, an autoconf macro which developers can use along with autoconf to test for libdap. This macro will be installed in ${prefix}/share/aclocal and can be by any package which uses autoconf for its builds. See the file for more information.

We also have Java and C versions of the DAP2 library which inter-operate with software which uses this library. In other words, client programs built with the Java DAP2 implementation can communicate with servers built with this (C++) implementation of the DAP2. The C DAP2 library, called the Ocapi, only implements the client-side part of the protocol. Clients written using the Ocapi are interoperable with both the Java and C++ DAP2 libraries. Note that the Ocapi is in early beta and available only from CVS at this time (5 May 2005).


We don't need to do this since the STL is also not thread safe. Users of libdap have to be sure that multiple threads never make simultaneous and/or overlapping calls to a single copy of libdap. If several threads are part of a program and each will make calls to libdap, either those threads must synchronize their calls or arrange to each use their own copy of libdap. Some aspects of the library are thread-safe: the singleton classes are all protected as is the HTTP cache (which uses the local file system).


See the file INSTALL in this directory for information on building the library and the geturl client.


The OPeNDAP DAP library is copyrighted using the GNU Lesser GPL. See the file COPYING or contact the Free Software Foundation, Inc., at 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA. Older versions of the DAP were copyrighted by the University of Rhode Island and Massachusetts Institute of Technology; see the file COPYRIGHT_URI. The file deflate.c is also covered by COPYRIGHT_W3C.