Process PDF->RGB in groups of 50 pages

PDFtoPPM was producing RGB files faster than they were getting consumed.
Since the RGB files were only getting removed after they were sent, this
was leading to /tmp in the server getting clogged.

This solution consists in processing and sending images in chunks of 50
pages. This solution is slightly inefficient since it can't process and
send data simultaneously. That will be solved in a future commit.

Fixes #574

dangerzone/conversion/common.py

@@ -10,12 +10,14 @@ import subprocess
 import sys
 import time
 from abc import abstractmethod
-from typing import Callable, Dict, List, Optional, Tuple, Union
+from typing import Callable, Dict, Generator, List, Optional, Tuple, Union
 
 TIMEOUT_PER_PAGE: float = 30  # (seconds)
 TIMEOUT_PER_MB: float = 30  # (seconds)
 TIMEOUT_MIN: float = 60  # (seconds)
 
+PAGE_BATCH_SIZE = 50  # number of pages to be processed simulatenously
+
 
 def running_on_qubes() -> bool:
     # https://www.qubes-os.org/faq/#what-is-the-canonical-way-to-detect-qubes-vm
@@ -44,6 +46,16 @@ def calculate_timeout(size: float, pages: Optional[float] = None) -> float:
     return timeout
 
 
+def batch_iterator(num_pages: int) -> Generator[Tuple[int, int], None, None]:
+    """Iterates over batches of PAGE_BATCH_SIZE pages"""
+    for first_page in range(1, num_pages + 1, PAGE_BATCH_SIZE):
+        if first_page + PAGE_BATCH_SIZE >= num_pages:  # Last batch
+            last_page = num_pages
+        else:
+            last_page = first_page + PAGE_BATCH_SIZE - 1
+        yield (first_page, last_page)
+
+
 class DangerzoneConverter:
     def __init__(self, progress_callback: Optional[Callable] = None) -> None:
         self.percentage: float = 0.0

dangerzone/conversion/doc_to_pixels.py

@@ -19,7 +19,14 @@ from typing import Dict, List, Optional
 import magic
 
 from . import errors
-from .common import DangerzoneConverter, running_on_qubes
+from .common import (
+    PAGE_BATCH_SIZE,
+    DangerzoneConverter,
+    batch_iterator,
+    running_on_qubes,
+)
+
+PAGE_BASE = "/tmp/page"
 
 
 class DocumentToPixels(DangerzoneConverter):
@@ -276,39 +283,70 @@ class DocumentToPixels(DangerzoneConverter):
         # Get a more precise timeout, based on the number of pages
         timeout = self.calculate_timeout(size, num_pages)
 
-        async def pdftoppm_progress_callback(line: bytes) -> None:
-            """Function called for every line the 'pdftoppm' command outputs
+        if timeout is None:
+            timeout_per_batch = None
+        else:
+            timeout_per_batch = timeout / (int(num_pages / PAGE_BATCH_SIZE) + 1)
+        for first_page, last_page in batch_iterator(num_pages):
+            await self.pdf_to_rgb(first_page, last_page, pdf_filename, timeout_per_batch)
+            await self.send_rgb_files(first_page, last_page, num_pages)
 
-            Sample pdftoppm output:
+        final_files = (
+            glob.glob("/tmp/page-*.rgb")
+            + glob.glob("/tmp/page-*.width")
+            + glob.glob("/tmp/page-*.height")
+        )
 
-                $ pdftoppm sample.pdf  /tmp/safe -progress
-                1 4 /tmp/safe-1.ppm
-                2 4 /tmp/safe-2.ppm
-                3 4 /tmp/safe-3.ppm
-                4 4 /tmp/safe-4.ppm
+        # XXX: Sanity check to avoid situations like #560.
+        if not running_on_qubes() and len(final_files) != 3 * num_pages:
+            raise errors.PageCountMismatch()
 
-            Each successful line is in the format "{page} {page_num} {ppm_filename}"
-            """
-            try:
-                (page_str, num_pages_str, _) = line.decode().split()
-                num_pages = int(num_pages_str)
-                page = int(page_str)
-            except ValueError as e:
-                # Ignore all non-progress related output, since pdftoppm sends
-                # everything to stderr and thus, errors can't be distinguished
-                # easily. We rely instead on the exit code.
-                return
+        # Move converted files into /tmp/dangerzone
+        for filename in final_files:
+            shutil.move(filename, "/tmp/dangerzone")
 
+        self.update_progress("Converted document to pixels")
+
+    async def pdf_to_rgb(
+        self,
+        first_page: int,
+        last_page: int,
+        pdf_filename: str,
+        timeout: Optional[float],
+    ) -> None:
+        await self.run_command(
+            [
+                "pdftoppm",
+                pdf_filename,
+                PAGE_BASE,
+                "-progress",
+                "-f",
+                str(first_page),
+                "-l",
+                str(last_page),
+            ],
+            error_message="Conversion from PDF to PPM failed",
+            timeout_message=(
+                f"Error converting from PDF to PPM, pdftoppm timed out after {timeout}"
+                " seconds"
+            ),
+            timeout=timeout,
+        )
+
+    async def send_rgb_files(
+        self, first_page: int, last_page: int, num_pages: int
+    ) -> None:
+        for page in range(first_page, last_page + 1):
             percentage_per_page = 45.0 / num_pages
             self.percentage += percentage_per_page
-            self.update_progress(f"Converting page {page}/{num_pages} to pixels")
+            self.update_progress(f"Converting pages {page}/{num_pages} to pixels")
 
-            zero_padding = "0" * (len(num_pages_str) - len(page_str))
-            ppm_filename = f"{page_base}-{zero_padding}{page}.ppm"
-            rgb_filename = f"{page_base}-{page}.rgb"
-            width_filename = f"{page_base}-{page}.width"
-            height_filename = f"{page_base}-{page}.height"
-            filename_base = f"{page_base}-{page}"
+            zero_padding = "0" * (len(str(num_pages)) - len(str(page)))
+            ppm_filename = f"{PAGE_BASE}-{zero_padding}{page}.ppm"
+            rgb_filename = f"{PAGE_BASE}-{page}.rgb"
+            width_filename = f"{PAGE_BASE}-{page}.width"
+            height_filename = f"{PAGE_BASE}-{page}.height"
+            filename_base = f"{PAGE_BASE}-{page}"
 
             with open(ppm_filename, "rb") as f:
                 # NOTE: PPM files have multiple ways of writing headers.
@@ -339,40 +377,6 @@ class DocumentToPixels(DangerzoneConverter):
             # Delete the ppm file
             os.remove(ppm_filename)
 
-        page_base = "/tmp/page"
-
-        await self.run_command(
-            [
-                "pdftoppm",
-                pdf_filename,
-                page_base,
-                "-progress",
-            ],
-            error_message="Conversion from PDF to PPM failed",
-            timeout_message=(
-                f"Error converting from PDF to PPM, pdftoppm timed out after {timeout}"
-                " seconds"
-            ),
-            stderr_callback=pdftoppm_progress_callback,
-            timeout=timeout,
-        )
-
-        final_files = (
-            glob.glob("/tmp/page-*.rgb")
-            + glob.glob("/tmp/page-*.width")
-            + glob.glob("/tmp/page-*.height")
-        )
-
-        # XXX: Sanity check to avoid situations like #560.
-        if not running_on_qubes() and len(final_files) != 3 * num_pages:
-            raise errors.PageCountMismatch()
-
-        # Move converted files into /tmp/dangerzone
-        for filename in final_files:
-            shutil.move(filename, "/tmp/dangerzone")
-
-        self.update_progress("Converted document to pixels")
-
     async def install_libreoffice_ext(self, libreoffice_ext: str) -> None:
         self.update_progress(f"Installing LibreOffice extension '{libreoffice_ext}'")
         unzip_args = [