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iRODS Library Examples

The goal of this repository is to provide simple examples demonstrating how to use the new libraries available in iRODS.

Table of Contents

iRODS Query Iterator

Available Since: v4.2.5

Demonstrates how to use irods::query to query the catalog.

#include <irods/irods_query.hpp>

#include <string>
#include <iostream>

void print_all_resource_names(rcComm_t& _conn)
{
    // Print all resource names known to iRODS.
    for (auto&& row : irods::query<rcComm_t>{&_conn, "select RESC_NAME"}) {
        std::cout << row[0] << '\n';
    }
}

iRODS Query Builder

Available Since: v4.2.7

Demonstrates how to construct query iterators via the query builder.

#include <irods/query_builder.hpp>

#include <vector>

void make_query()
{
    auto conn = // Our iRODS connection.

    // Construct the builder.
    // Builders can be copied and moved.
    irods::experimental::query_builder builder; 

    // Set the arguments for how the query should be constructed.
    // A reference to the builder object is always returned after setting an argument.
    //
    // Here, we are setting the type of query to construct as well as the zone
    // for which the query applies.
    //
    // The type always defaults to "general".
    builder.type(irods::experimental::query_type::general)
           .zone_hint("other_zone");

    // To construct the query, call build and pass the C type of
    // the connection and the SQL-like query statement.
    //
    // If the query string is empty, an exception will be thrown.
    auto general_query = builder.build<rcComm_t>(conn, "select COLL_NAME");

    // Use the query object as you normally would.
    for (auto&& row : general_query) {
        // Process results ...
    }

    // We can create more query objects using the same builder.
    // Let's try a specific query!

    // For specific queries, it is important to remember that the argument vector
    // is not copied into the query object. This means the argument vector must live
    // longer than the query object constructed by the builder.
    std::vector<std::string> args{"/other_zone/home/rods"};

    // All that is left is to update the builder options.
    // The zone is already set from a previous call.
    // So just bind the arguments and change the query type.
    auto specific_query = builder.type(irods::experimental::query_type::specific)
                                 .bind_arguments(args)
                                 .build<rcComm_t>(conn, "ShowCollAcls");

    for (auto&& row : specific_query) {
        // Process results ...
    }

    // Builders can also be reset to their original state by calling clear.
    builder.clear();
}

iRODS Connection Pool

Available Since: v4.2.5

Demonstrates how to use irods::connection_pool.

#include <irods/rodsClient.h>
#include <irods/connection_pool.hpp>

void init_connection_pool()
{
    rodsEnv env;

    if (getRodsEnv(&env) < 0) {
        // Handle error.
    }

    const int connection_pool_size = 4;
    const int refresh_time_in_secs = 600;

    // Creates a connection pool that manages 4 rcComm_t connections
    // and refreshes each connection every 600 seconds.
    irods::connection_pool pool{connection_pool_size,
                                env.rodsHost,
                                env.rodsPort,
                                env.rodsUserName,
                                env.rodsZone,
                                refresh_time_in_secs};

    // As an alternative to the steps above, you can use the following free
    // function to construct a connection pool. This function simply automates
    // all of the steps preceding this line. The primary difference is that the
    // pool is allocated on the heap and is returned via a shared pointer.
    //
    //     auto pool = irods::make_connection_pool(4);

    // Get a connection from the pool.
    // "conn" is returned to the pool when it goes out of scope.
    // The type returned from the pool is moveable, but it cannot be copied.
    auto conn = pool.get_connection();

    // The object returned from the pool is a proxy for an rcComm_t and
    // can be implicitly cast to a reference to rcComm_t.
    rcComm_t& reference = conn;

    // Here is an example of casting to a pointer.
    // Use this for C APIs.
    auto* pointer = static_cast<rcComm_t*>(conn);

    // You can also take ownership of connections created by the connection pool.
    // Taking ownership means the connection is no longer managed by the connection pool
    // and you are responsible for cleaning up any resources allocated by the connection.
    // Once the connection is released, the connection pool will create a new connection
    // in its place.
    auto* released_conn = conn.release();

    // Because connections can be released from the pool, it makes sense to provide an
    // operation for checking if the connection proxy still manages a valid connection.
    // Connection objects are now convertible to bool.
    if (conn) {
        // Do something with the connection ...
    }
}

iRODS Thread pool

Available Since: v4.2.5

Demonstrates how to use irods::thread_pool.

#include <irods/thread_pool.hpp>

void schedule_task_on_thread_pool()
{
    // Creates a thread pool with 4 threads.
    // iRODS thread pool will never launch more than "std::thread::hardware_concurrency()" threads.
    irods::thread_pool pool{4};

    // This is one way to schedule a task for execution
    // "irods::thread_pool::defer" schedules the task on the thread pool. If the current thread
    // belongs to the thread pool, then the task is scheduled after the current thread returns and
    // control is returned back to the thread pool. The task is never run inside of the "defer" call.
    irods::thread_pool::defer(pool, [] {
        // Do science later!
    });

    // This is a function object.
    struct scientific_task
    {
        void operator()()
        {
            // Do science!
        }
    };

    scientific_task task;

    // This is just like "defer" except the task is scheduled immediately. The task is never
    // executed inside of the "post" call.
    irods::thread_pool::post(pool, task);

    // This is just like "post" except, if the current thread belongs to the thread pool, then
    // the task is executed directly inside of the call to "dispatch".
    irods::thread_pool::dispatch(pool, [] {
        // Do science!
    });

    // Wait until ALL tasks have completed.
    // If this is not called, then on destruction of the thread pool, all tasks that have not
    // been executed are cancelled. Tasks that are still executing are allowed to finish.
    pool.join();
}

iRODS Filesystem

Available Since: v4.2.6

Demonstrates how to iterate over collections as well as other functionality. Because it implements the ISO C++17 Standard Filesystem library, you may use the documentation at cppreference.

Here are some helpful links:

// If you are writing server-side code and wish to enable the server-side API, you must
// define the following macro before including the library.
//
//    IRODS_FILESYSTEM_ENABLE_SERVER_SIDE_API
//
#include <irods/filesystem.hpp>

void iterating_over_collections()
{
    // IMPORTANT!!!
    // ~~~~~~~~~~~~
    // Notice that this library exists under the "experimental" namespace.
    // This is important if you're considering using this library. It means that any
    // library under this namespace could change in the future. Changes are likely
    // to only occur based on feedback from the community.
    namespace fs = irods::experimental::filesystem;

    // iRODS Filesystem has two namespaces, client and server.
    // Not all classes and functions require the use of these namespaces.

    try {
        auto conn = // Our iRODS connection.

        // Here's an example of how to iterate over a collection on the client-side.
        // Notice how the "client" namespace follows the "fs" namespace alias.
        // This is required by some functions and classes to control which implementation
        // should be used. If you wanted to do this on the server-side, you would replace
        // "client" with "server". This does not recurse into subcollections.
        for (auto&& e : fs::client::collection_iterator{conn, "/path/to/collection"}) {
            // Do something with the collection entry.
        }

        // To recursively iterate over a collection and all of its children, use a
        // recursive iterator.
        for (auto&& e : fs::client::recursive_collection_iterator{conn, "/path/to/collection"}) {
            // Do something with the collection entry.
        }

        // These iterators support shallow copying. This means, if you copy an iterator,
        // subsequent operations on the copy, such as iterating to the next entry, will
        // be visible to the original iterator.

        //
        // Let's try something new.
        //
        
        // How about getting the size of a data object.
        auto size = fs::client::data_object_size(conn, "/path/to/data_object");

        // Or checking if an object exists.
        if (fs::client::exists(conn, path)) {
            // Do something with it.
        }
    }
    catch (const fs::filesystem_error& e) {
        // Handle error.
    }
}

iRODS IOStreams

Available Since: v4.2.6

Demonstrates how to use dstream and default_transport to read and write data objects.

// Defines 3 classes:
// - idstream: Input-only stream for reading data objects.
// - odstream: Output-only stream for writing data objects.
// - dstream : Bidirectional stream for reading and writing data objects.
#include <irods/dstream.hpp>

// Defines the default transport mechanism for transporting bytes via the iRODS protocol.
//
// If you are writing server-side code and wish to enable the server-side API, you must
// define the following macro before including the transport library following this comment.
//
//     IRODS_IO_TRANSPORT_ENABLE_SERVER_SIDE_API
//
#include <irods/transport/default_transport.hpp>

void write_to_data_object()
{
    // IMPORTANT!!!
    // ~~~~~~~~~~~~
    // Notice that this library exists under the "experimental" namespace.
    // This is important if you're considering using this library. It means that any
    // library under this namespace could change in the future. Changes are likely
    // to only occur based on feedback from the community.
    namespace io = irods::experimental::io;

    auto conn = // Our iRODS connection.

    // Instantiates a new transport object which uses the iRODS protocol to read and
    // write bytes into a data object. Transport objects are designed to be used by IOStreams
    // objects such as dstream. "default_transport" is a wrapper around the iRODS C API for
    // reading and writing data objects.
    //
    // You can add support for more transport protocols by implementing the following interface:
    //
    //     https://github.com/irods/irods/blob/master/lib/core/include/transport/transport.hpp
    //
    io::client::default_transport xport{conn};

    // Here, we are creating a new output stream for writing. If the data object exists, then
    // the existing data object is opened, else a new data object is created.
    // We could have also used "dstream" itself, but then we'd need to pass in openmode flags
    // to instruct iRODS on how to open the data object.
    io::odstream out{xport, "/path/to/data_object"};

    if (!out) {
        // Handle error.
    }

    std::array<char, 4_Mb> buffer{}; // Buffer full of data.

    // This is the fastest way to write data into iRODS via the new stream API.
    // Bytes written this way are stored directly in the buffer as is.
    out.write(buffer.data(), buffer.size());

    // This will also write data into the data object. This is slower than the previous method
    // because stream operators format data.
    out << "Here is some more data ...\n";
}

void read_from_data_object()
{
    namespace io = irods::experimental::io;

    auto conn = // Our iRODS connection.

    // See function above for information about this type.
    io::client::default_transport xport{conn};

    // Here, we are creating a new input stream for reading. 
    io::idstream in{xport, "/path/to/data_object"};

    if (!in) {
        // Handle error.
    }

    std::array<char, 4_Mb> buffer{}; // Buffer to hold data.

    // This is the fastest way to write data into iRODS via the new stream API.
    // Bytes read this way are stored directly in the buffer as is.
    in.read(buffer.data(), buffer.size());

    // Read a single character sequence into "word".
    // This assumes the input stream contains a sequence of printable characters.
    std::string word;
    in >> word;

    std::string line;
    while (std::getline(in, line)) {
        // Read every line of the input stream until eof.
    }
}

iRODS Query Processor

Available Since: v4.2.6

Demonstrates how to use irods::query_processor.

#include <irods/query_processor.hpp>

#include <iostream>
#include <vector>
#include <mutex>

void process_all_query_results()
{
    // This will hold all data object absolute paths found by the query processor.
    std::vector<std::string> paths;

    // Protects the paths vector from simultaneous updates.
    std::mutex mtx;

    using query_processor = irods::query_processor<rcComm_t>;

    // This is where we create our query processor. As you can see, we pass it
    // the query string as well as the handler. The handler will process each row
    // (i.e. std::vector<std::string>) asynchronously. This means that it is your
    // responsibility to protect shared data if necessary.
    //
    // In the following example, the handler creates a path from "_row" and stores
    // it in the referenced "paths" container. Notice how a mutex is acquired before
    // adding the path to the container.
    query_processor qproc{"select COLL_NAME, DATA_NAME", [&paths](const auto& _row) {
        std::lock_guard lk{mtx};
        paths.push_back(_row[0] + '/' + _row[1]);
    }};

    auto thread_pool = // Our iRODS thread pool.
    auto conn = // Our iRODS connection.

    // This is how we run the query. Notice how the execute call accepts a thread
    // pool and connection. This allows developers to run queries on different
    // thread pools.
    //
    // The object returned is a handle to a std::future containing error information.
    // By doing this, the execution of the query and handling of its results are done
    // asynchronously, therefore the application is not blocked from doing other work.
    auto errors = qproc.execute(thread_pool, conn);

    // Because the errors are returned via a std::future, calling ".get()" will cause
    // the application to wait until all query results have been processed by the
    // handler provided on construction.
    for (auto&& error : errors.get()) {
        // Handle errors.
    }

    // Print all the results.
    for (auto&& path : paths) {
        std::cout << "path: " << path << '\n';
    }
}

iRODS With Durability

Available Since: v4.2.8

Demonstrates how to use irods::with_durability.

#include <irods/with_durability.hpp>

#include <irods/connection_pool.hpp>

void get_collection_status_over_unreliabile_network()
{
    namespace ix = irods::experimental;
    namespace fs = irods::experimental::filesystem;

    // Holds the status of the collection.
    fs::status s;

    // This is where we define our rules for how durable we want a particular set of
    // operations should be. Notice how we've set the number of retries and the delay
    // multiplier. These options are completely optional. The last result will be
    // returned to the call site. All intermediate results will be lost.
    //
    // The most important thing to understand about this function is the function-like
    // object that will be invoked. It is up to the developer to instruct "with_durability"
    // of when the set of operations have succeeded or failed, etc.
    //
    // See the following for more details:
    //
    //     https://github.com/irods/irods/blob/master/lib/core/include/with_durability.hpp
    //
    auto exec_result = ix::with_durability(ix::retries{5}, ix::delay_multiplier{2.f}, [&] {
        try {
            auto conn_pool = irods::make_connection_pool();
            s = fs::client::status(conn_pool->get_connection(), "/tempZone/home/rods");
            return ix::execution_result::success;
        }
        catch (const fs::filesystem_error&) {
            return ix::execution_result::failure;
        }

        // Any exception that escapes the function-like object will be caught by the
        // "with_durability" function.
    });

    // Here, we check the result of the operations and decide what should happen next. 
    if (ix::execution_result::success != exec_result) {
        // Handle failure.
    }

    // Print whether the collection exists.
    std::cout << "Status of collection: " << fs::client::exists(s) << '\n';
}

iRODS Key Value Proxy

Available Since: v4.2.8

Demonstrates how to use irods::key_value_proxy.

#include <irods/key_value_proxy.hpp>

#include <irods/dataObjOpen.h>
#include <irods/stringOpr.h>

#include <string>

void manipulating_keyValuePair_t()
{
    // Let's open a replica for writing using the iRODS C API.
    dataObjInp_t input{};
    input.createMode = 0600;
    input.openFlags = O_WRONLY;
    rstrcpy(input.objPath, "/tempZone/home/rods/foo", MAX_NAME_LEN);

    // Now, we need to set the options that target a specific replica.
    // Normally we'd use the "keyValuePair_t" family of functions to add/remove
    // options. Instead, we'll use the "key_value_proxy" class.
    irods::experimental::key_value_proxy kvp{input.condInput};

    // This proxy object does not own the underlying keyValuePair_t. It simply provides
    // a map-like interface to manipulate and inspect it.

    // Let's target a specific replica of this data object.
    // This adds the "REPL_NUM_KW" key to the underlying keyValuePair_t and sets its
    // value to the string "2". The string is copied into the object.
    kvp[REPL_NUM_KW] = "2";

    // This proxy type also supports checking if the kevValuePair_t contains a specific key.
    if (kvp.contains(RESC_NAME_KW)) {
        // Do something ...
    }

    // Extracting a value is easy too.
    const std::string value = kvp[RESC_HIER_STR_KW];
}

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