HDFS-7838. Expose truncate API for libhdfs. (yliu)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -364,6 +364,8 @@ Release 2.7.0 - UNRELEASED
 
     HDFS-6488. Support HDFS superuser in NFS gateway. (brandonli)
 
+    HDFS-7838. Expose truncate API for libhdfs. (yliu)
+
   IMPROVEMENTS
 
     HDFS-7752. Improve description for

hadoop-hdfs-project/hadoop-hdfs/src/contrib/libwebhdfs/src/hdfs_web.c

@@ -1124,6 +1124,12 @@ done:
     return file;
 }
 
+int hdfsTruncateFile(hdfsFS fs, const char* path, tOffset newlength)
+{
+    errno = ENOTSUP;
+    return -1;
+}
+
 tSize hdfsWrite(hdfsFS fs, hdfsFile file, const void* buffer, tSize length)
 {
     if (length == 0) {

hadoop-hdfs-project/hadoop-hdfs/src/main/native/libhdfs/hdfs.c

@@ -1037,6 +1037,43 @@ done:
     return file;
 }
 
+int hdfsTruncateFile(hdfsFS fs, const char* path, tOffset newlength)
+{
+    jobject jFS = (jobject)fs;
+    jthrowable jthr;
+    jvalue jVal;
+    jobject jPath = NULL;
+
+    JNIEnv *env = getJNIEnv();
+
+    if (!env) {
+        errno = EINTERNAL;
+        return -1;
+    }
+
+    /* Create an object of org.apache.hadoop.fs.Path */
+    jthr = constructNewObjectOfPath(env, path, &jPath);
+    if (jthr) {
+        errno = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+            "hdfsTruncateFile(%s): constructNewObjectOfPath", path);
+        return -1;
+    }
+
+    jthr = invokeMethod(env, &jVal, INSTANCE, jFS, HADOOP_FS,
+                        "truncate", JMETHOD2(JPARAM(HADOOP_PATH), "J", "Z"),
+                        jPath, newlength);
+    destroyLocalReference(env, jPath);
+    if (jthr) {
+        errno = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+            "hdfsTruncateFile(%s): FileSystem#truncate", path);
+        return -1;
+    }
+    if (jVal.z == JNI_TRUE) {
+        return 1;
+    }
+    return 0;
+}
+
 int hdfsUnbufferFile(hdfsFile file)
 {
     int ret;

hadoop-hdfs-project/hadoop-hdfs/src/main/native/libhdfs/hdfs.h

@@ -395,6 +395,21 @@ extern  "C" {
     hdfsFile hdfsOpenFile(hdfsFS fs, const char* path, int flags,
                           int bufferSize, short replication, tSize blocksize);
 
+    /**
+     * hdfsTruncateFile - Truncate a hdfs file to given lenght.
+     * @param fs The configured filesystem handle.
+     * @param path The full path to the file.
+     * @param newlength The size the file is to be truncated to
+     * @return 1 if the file has been truncated to the desired newlength 
+     *         and is immediately available to be reused for write operations 
+     *         such as append.
+     *         0 if a background process of adjusting the length of the last 
+     *         block has been started, and clients should wait for it to
+     *         complete before proceeding with further file updates.
+     *         -1 on error.
+     */
+    int hdfsTruncateFile(hdfsFS fs, const char* path, tOffset newlength);
+
     /**
      * hdfsUnbufferFile - Reduce the buffering done on a file.
      *