Sahil Takiar created HDFS-14285:
-----------------------------------
Summary: libhdfs hdfsRead copies entire array even if its only
partially filled
Key: HDFS-14285
URL: https://issues.apache.org/jira/browse/HDFS-14285
Project: Hadoop HDFS
Issue Type: Bug
Components: hdfs-client, libhdfs, native
Reporter: Sahil Takiar
There is a bug in libhdfs {{hdfsRead}}
{code:java}
jthr = invokeMethod(env, &jVal, INSTANCE, jInputStream, HADOOP_ISTRM,
"read", "([B)I", jbRarray);
if (jthr) {
destroyLocalReference(env, jbRarray);
errno = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
"hdfsRead: FSDataInputStream#read");
return -1;
}
if (jVal.i < 0) {
// EOF
destroyLocalReference(env, jbRarray);
return 0;
} else if (jVal.i == 0) {
destroyLocalReference(env, jbRarray);
errno = EINTR;
return -1;
}
(*env)->GetByteArrayRegion(env, jbRarray, 0, noReadBytes, buffer);
{code}
The method makes a call to {{FSInputStream#read(byte[])}} to fill in the Java
byte array, however, {{#read(byte[])}} is not guaranteed to fill up the entire
array, instead it returns the number of bytes written to the array (which could
be less than the size of the array). Yet `{{GetByteArrayRegion}} decides to
copy the entire contents of the {{jbArray}} into the buffer ({{noReadBytes}} is
initialized to the length of the buffer and is never updated). So if
{{FSInputStream#read(byte[])}} decides to read less data than the size of the
byte array, the call to {{GetByteArrayRegion}} will essentially copy more bytes
than necessary.
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