Better error reporting when MemoryError reading a file

[jamshid]

s4cmd 2.1.0 outputs an inscrutable error and stack trace when it gets a MemoryError trying to read a file in read_file_chunk().

The debug verbose output does not say anything about the MemoryError, I only see it below because I added a bunch of print statements (starting with !) and a try/except handler in read_file_chunk().

Btw I was running in a container with only 200MB free, trying to write a 1GB file to an S3-compatible system. Hopefully s4cmd is not trying to load the entire file into memory?

# s4cmd --debug --verbose --endpoint-url http://backup66:8085 put 1G s3://mybucket/1G
  (D)s4cmd.py:662  read S3 keys from $HOME/.s3cfg file
  (D)s4cmd.py:128  >> put_handler(<s4cmd.CommandHandler object at 0x7f1d30cd9bd0>, ['put', '1G', 's3://mybucket/1G'])
!!!calling func
  (D)s4cmd.py:128  >> validate(<s4cmd.CommandHandler object at 0x7f1d30cd9bd0>, 'cmd|local|s3', ['put', '1G', 's3://mybucket/1G'])
!!!calling func
!!!back from func
  (D)s4cmd.py:132  << validate(<s4cmd.CommandHandler object at 0x7f1d30cd9bd0>, 'cmd|local|s3', ['put', '1G', 's3://mybucket/1G']): None
  (D)s4cmd.py:128  >> put_files(<s4cmd.S3Handler object at 0x7f1d3390f6d0>, ['1G'], 's3://mybucket/1G')
!!!calling func
  (D)s4cmd.py:128  >> put_single_file(<s4cmd.S3Handler object at 0x7f1d3390f6d0>, <s4cmd.ThreadPool object at 0x7f1d2ce9e2d0>, '1G', 's3://mybucket/1G')
!!!calling func
!!!back from func
  (D)s4cmd.py:132  << put_single_file(<s4cmd.S3Handler object at 0x7f1d3390f6d0>, <s4cmd.ThreadPool object at 0x7f1d2ce9e2d0>, '1G', 's3://mybucket/1G'): None
  (D)s4cmd.py:128  >> upload(<ThreadUtil(Thread-1, started daemon 139763283113728)>, '1G', 's3://mybucket/1G')
!!!calling func
  (D)s4cmd.py:128  >> lookup(<ThreadUtil(Thread-1, started daemon 139763283113728)>, <s4cmd.S3URL instance at 0x7f1d2436f6c8>)
!!!calling func
  (D)s4cmd.py:404  >> S3APICALL head_object(Bucket='mybucket', Key='1G')
!!!getattr () {'Bucket': 'mybucket', 'Key': '1G'}
!!!back from func
  (D)s4cmd.py:132  << lookup(<ThreadUtil(Thread-1, started daemon 139763283113728)>, <s4cmd.S3URL instance at 0x7f1d2436f6c8>): None
  (D)s4cmd.py:128  >> read_file_chunk(<ThreadUtil(Thread-1, started daemon 139763283113728)>, '1G', 0, 1073741824)
!!!calling func
!read_file_chunk 1G
!read_file_chunk 1G pos 0
!EXCEPTION: read_file_chunk 1G pos 0: <type 'exceptions.MemoryError'>
!!!fail: [Runtime Failure]  Unable to read data from source: 1G
  (E)s4cmd.py:185  [Runtime Failure] Unable to read data from source: 1G
Exception in thread Thread-1:ad(s)]
Traceback (most recent call last):
  File "/usr/lib64/python2.7/threading.py", line 812, in __bootstrap_inner
    self.run()
  File "/usr/bin/s4cmd.py", line 530, in run
    fail('[Runtime Failure] ', exc_info=e)
  File "/usr/bin/s4cmd.py", line 192, in fail
    raise RuntimeError(status)
RuntimeError: 1

!!!fail: [Thread Failure]  Unable to read data from source: 1G
  (E)s4cmd.py:185  [Thread Failure] Unable to read data from source: 1G
!!!fail: [Runtime Exception]  1
  (E)s4cmd.py:185  [Runtime Exception] 1
  (E)s4cmd.py:187  Traceback (most recent call last):
  File "/usr/bin/s4cmd.py", line 1939, in main
    CommandHandler(opt).run(args)
  File "/usr/bin/s4cmd.py", line 1568, in run
    CommandHandler.__dict__[cmd + '_handler'](self, args)
  File "/usr/bin/s4cmd.py", line 130, in wrapper
    ret = func(*args, **kargs)
  File "/usr/bin/s4cmd.py", line 1666, in put_handler
    self.s3handler().put_files(source, target)
  File "/usr/bin/s4cmd.py", line 130, in wrapper
    ret = func(*args, **kargs)
  File "/usr/bin/s4cmd.py", line 825, in put_files
    pool.join()
  File "/usr/bin/s4cmd.py", line 598, in join
    self.tasks.join()
  File "/usr/bin/s4cmd.py", line 473, in join
    fail('[Thread Failure] ', exc_info=self.exc_info)
  File "/usr/bin/s4cmd.py", line 192, in fail
    raise RuntimeError(status)
RuntimeError: 1