WebAgg Saving JPEG Raises Error

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To reproduce, run the following script (in master, on Python 2.7):

import matplotlib
matplotlib.use('webagg')
import matplotlib.pyplot as plt
plt.plot([1,2,3])
plt.show()

ERROR:tornado.application:Uncaught exception GET /1/download.jpeg (127.0.0.1)
HTTPServerRequest(protocol='http', host='127.0.0.1:8988', method='GET', uri='/1/download.jpeg', version='HTTP/1.1', remote_ip='127.0.0.1', headers={'Connection': 'keep-alive', 'Accept-Language': 'en-US,en;q=0.5', 'Accept-Encoding': 'gzip, deflate', 'Referer': 'http://127.0.0.1:8988/', 'Host': '127.0.0.1:8988', 'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8', 'User-Agent': 'Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:33.0) Gecko/20100101 Firefox/33.0'})
Traceback (most recent call last):
  File "/home/afrl/anaconda/lib/python2.7/site-packages/tornado/web.py", line 1332, in _execute
    result = method(*self.path_args, **self.path_kwargs)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backends/backend_webagg.py", line 201, in get
    manager.canvas.print_figure(buff, format=fmt)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backend_bases.py", line 2216, in print_figure
    **kwargs)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backends/backend_agg.py", line 581, in print_jpg
    return image.save(filename_or_obj, format='jpeg', **options)
  File "/home/afrl/anaconda/lib/python2.7/site-packages/PIL/Image.py", line 1439, in save
    save_handler(self, fp, filename)
  File "/home/afrl/anaconda/lib/python2.7/site-packages/PIL/JpegImagePlugin.py", line 471, in _save
    ImageFile._save(im, fp, [("jpeg", (0,0)+im.size, 0, rawmode)])
  File "/home/afrl/anaconda/lib/python2.7/site-packages/PIL/ImageFile.py", line 476, in _save
    fh = fp.fileno()
UnsupportedOperation: fileno
ERROR:tornado.access:500 GET /1/download.jpeg (127.0.0.1) 27.78ms

It looks like PIL is looking for a fileno attribute on the object but the io.BytesIO obj passed by backend_webagg has no fileno.

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PIL is checking for an AttributeError, but this is raising the rather odd UnsupportedOperation error.

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Other filetype problems:

PGF:

ERROR:tornado.application:Uncaught exception GET /1/download.pgf (127.0.0.1)
HTTPServerRequest(protocol='http', host='127.0.0.1:8988', method='GET', uri='/1/download.pgf', version='HTTP/1.1', remote_ip='127.0.0.1', headers={'Connection': 'keep-alive', 'Accept-Language': 'en-US,en;q=0.5', 'Accept-Encoding': 'gzip, deflate', 'Referer': 'http://127.0.0.1:8988/', 'Host': '127.0.0.1:8988', 'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8', 'User-Agent': 'Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:33.0) Gecko/20100101 Firefox/33.0'})
Traceback (most recent call last):
  File "/home/afrl/anaconda/lib/python2.7/site-packages/tornado/web.py", line 1332, in _execute
    result = method(*self.path_args, **self.path_kwargs)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backends/backend_webagg.py", line 201, in get
    manager.canvas.print_figure(buff, format=fmt)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backend_bases.py", line 2216, in print_figure
    **kwargs)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backends/backend_pgf.py", line 838, in print_pgf
    if not os.path.exists(fname_or_fh.name):
AttributeError: '_io.BytesIO' object has no attribute 'name'

TIF (similar to JPEG problem):

ERROR:tornado.application:Uncaught exception GET /1/download.tif (127.0.0.1)
HTTPServerRequest(protocol='http', host='127.0.0.1:8988', method='GET', uri='/1/download.tif', version='HTTP/1.1', remote_ip='127.0.0.1', headers={'Connection': 'keep-alive', 'Accept-Language': 'en-US,en;q=0.5', 'Accept-Encoding': 'gzip, deflate', 'Referer': 'http://127.0.0.1:8988/', 'Host': '127.0.0.1:8988', 'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8', 'User-Agent': 'Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:33.0) Gecko/20100101 Firefox/33.0'})
Traceback (most recent call last):
  File "/home/afrl/anaconda/lib/python2.7/site-packages/tornado/web.py", line 1332, in _execute
    result = method(*self.path_args, **self.path_kwargs)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backends/backend_webagg.py", line 201, in get
    manager.canvas.print_figure(buff, format=fmt)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backend_bases.py", line 2216, in print_figure
    **kwargs)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backends/backend_agg.py", line 592, in print_tif
    dpi=dpi)
  File "/home/afrl/anaconda/lib/python2.7/site-packages/PIL/Image.py", line 1439, in save
    save_handler(self, fp, filename)
  File "/home/afrl/anaconda/lib/python2.7/site-packages/PIL/TiffImagePlugin.py", line 841, in _save
    ("raw", (0,0)+im.size, offset, (rawmode, stride, 1))
  File "/home/afrl/anaconda/lib/python2.7/site-packages/PIL/ImageFile.py", line 476, in _save
    fh = fp.fileno()
UnsupportedOperation: fileno
ERROR:tornado.access:500 GET /1/download.tif (127.0.0.1) 39.17ms

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The following fixes the BytesIO problems:

diff --git a/lib/matplotlib/backends/backend_webagg.py b/lib/matplotlib/backends/backend_webagg.py
index 9583906..16ef87b 100644
--- a/lib/matplotlib/backends/backend_webagg.py
+++ b/lib/matplotlib/backends/backend_webagg.py
@@ -197,7 +197,13 @@ class WebAggApplication(tornado.web.Application):

             self.set_header('Content-Type', mimetypes.get(fmt, 'binary'))

-            buff = io.BytesIO()
+            # override fileno to raise AttributeError so PIL doesn't error
+            class BytesIO(io.BytesIO):
+                @property
+                def fileno(self):
+                    raise AttributeError
+
+            buff = BytesIO()
             manager.canvas.print_figure(buff, format=fmt)
             self.write(buff.getvalue())

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I tried working around the pgf error, but then got this error:

ERROR:tornado.application:Uncaught exception GET /1/download.pgf (127.0.0.1)
HTTPServerRequest(protocol='http', host='127.0.0.1:8988', method='GET', uri='/1/download.pgf', version='HTTP/1.1', remote_ip='127.0.0.1', headers={'Connection': 'keep-alive', 'Accept-Language': 'en-US,en;q=0.5', 'Accept-Encoding': 'gzip, deflate', 'Referer': 'http://127.0.0.1:8988/', 'Host': '127.0.0.1:8988', 'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8', 'User-Agent': 'Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:33.0) Gecko/20100101 Firefox/33.0'})
Traceback (most recent call last):
  File "/home/afrl/anaconda/lib/python2.7/site-packages/tornado/web.py", line 1332, in _execute
    result = method(*self.path_args, **self.path_kwargs)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backends/backend_webagg.py", line 207, in get
    manager.canvas.print_figure(buff, format=fmt)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backend_bases.py", line 2216, in print_figure
    **kwargs)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backends/backend_pgf.py", line 843, in print_pgf
    self._print_pgf_to_fh(fname_or_fh, *args, **kwargs)
  File "/home/afrl/workspace/matplotlib/lib/matplotlib/backends/backend_pgf.py", line 805, in _print_pgf_to_fh
    fh.write(header_text)
TypeError: 'unicode' does not have the buffer interface