[jira] [Created] (HDFS-14478) Add libhdfs APIs for readFully and openFile

["Sahil Takiar (JIRA)" <ji...@apache.org>]

Sahil Takiar created HDFS-14478:
-----------------------------------

             Summary: Add libhdfs APIs for readFully and openFile
                 Key: HDFS-14478
                 URL: https://issues.apache.org/jira/browse/HDFS-14478
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: hdfs-client, libhdfs, native
            Reporter: Sahil Takiar
            Assignee: Sahil Takiar


HADOOP-15229 added a "FileSystem builder-based openFile() API" that allows specifying configuration values for opening files (similar to HADOOP-14365).

The {{PositionedReadable#readFully}} APIs have always existed.

Both of these APIs should be exposed by libhdfs.

Adding support for {{readFully}} should be straight-forward (a new libhdfs API called {{hdfsPreadFully}} whose implementation is similar to {{hdfsPread}}).

Support for {{openFile}} will be a little tricker as it is asynchronous and {{FutureDataInputStreamBuilder#build}} returns a {{CompletableFuture}}.

At a high level, the API for {{openFile}} could look something like this:
{code:java}
    LIBHDFS_EXTERNAL
    struct hdfsOpenFileBuilder *hdfsOpenFileBuilderAlloc(hdfsFS fs,
            const char *path, int flags);

    LIBHDFS_EXTERNAL
    void hdfsOpenFileBuilderFree(struct hdfsOpenFileBuilder *bld);

    LIBHDFS_EXTERNAL
    struct hdfsOpenFileBuilder *hdfsOpenFileBuilderMust(hdfsFS fs,
            const char *key, const char *value);

    LIBHDFS_EXTERNAL
    struct hdfsOpenFileBuilder *hdfsOpenFileBuilderOpt(hdfsFS fs,
            const char *key, const char *value);

    LIBHDFS_EXTERNAL
    hdfsFileFuture *hdfsOpenFileBuilderBuild(struct hdfsOpenFileBuilder *bld);

    LIBHDFS_EXTERNAL
    void hdfsOpenFileFutureFree(struct hdfsFileFuture *future);

    LIBHDFS_EXTERNAL
    hdfsFile hdfsOpenFileFutureGet(struct hdfsFileFuture *future);

    LIBHDFS_EXTERNAL
    hdfsFile hdfsOpenFileFutureGet(struct hdfsFileFuture *future, int64_t
            timeout, const char* timeUnit);

    LIBHDFS_EXTERNAL
    void hdfsOpenFileFutureCancel(struct hdfsFileFuture *future,
            bool mayInterruptIfRunning);
{code}
Instead of exposing all the functionality of {{CompleteableFuture}} libhdfs would just expose the functionality of {{Future}}.



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