feat(server, html2pdf): implement better error reporting when Chrome is not found

**WHAT:**

This change improves the error message when the StrictDoc web server
cannot find a Chrome installation on the system it is running on.

**WHY:**

Before this change, the error message was a simple Internal Server Error
without an explicit indication that the Chrome could not be found. A
user would have to dig through the server logs to understand the issue.

**HOW:**

This integrates the upstream html2pdf4doc work where the error reporting
was improved in the main.py driver program.

In particular, the driver now exits with a specific exit code
`COULD_NOT_FIND_CHROME = 5` that we can rely on in StrictDoc to identify
the missing Chrome issue.

strictdoc-project/html2pdf4doc_python#58
strictdoc-project/html2pdf4doc_python#70

Author: stanislaw

pyproject.toml

@@ -95,7 +95,7 @@ dependencies = [
     "WebSockets",
 
     # HTML2PDF dependencies
-    "html2pdf4doc >= 0.0.23",
+    "html2pdf4doc >= 0.0.24",
 
     # Robot Framework dependencies
     "robotframework >= 4.0.0",

strictdoc/export/html2pdf/pdf_print_driver.py

@@ -3,13 +3,53 @@
 """
 
 import os.path
-from subprocess import CompletedProcess, TimeoutExpired, run
+from subprocess import CalledProcessError, CompletedProcess, TimeoutExpired, run
 from typing import List, Tuple
 
+from html2pdf4doc.main import HPDExitCode
+
 from strictdoc.core.project_config import ProjectConfig
 from strictdoc.helpers.timing import measure_performance
 
 
+class PDFPrintDriverException(Exception):
+    def __init__(self, exception: Exception):
+        super().__init__()
+        self.exception: Exception = exception
+
+    def get_server_user_message(self) -> str:
+        """
+        Provide a user-friendly message that describes the underlying exception/error.
+        """
+
+        if self.is_could_not_detect_chrome():
+            return "HTML2PDF could not detect an existing Chrome installation."
+
+        if self.is_timeout_error():
+            return "HTML2PDF timeout error."
+
+        if self.is_js_success_timeout():
+            return "HTML2PDF.js success timeout error."
+
+        return "HTML2PDF internal error."
+
+    def is_timeout_error(self) -> bool:
+        return isinstance(self.exception, TimeoutExpired)
+
+    def is_could_not_detect_chrome(self) -> bool:
+        return (
+            isinstance(self.exception, CalledProcessError)
+            and self.exception.returncode == HPDExitCode.COULD_NOT_FIND_CHROME
+        )
+
+    def is_js_success_timeout(self) -> bool:
+        return (
+            isinstance(self.exception, CalledProcessError)
+            and self.exception.returncode
+            == HPDExitCode.DID_NOT_RECEIVE_SUCCESS_STATUS_FROM_HTML2PDF4DOC_JS
+        )
+
+
 class PDFPrintDriver:
     @staticmethod
     def get_pdf_from_html(
@@ -52,7 +92,7 @@ def get_pdf_from_html(
                 _: CompletedProcess[bytes] = run(
                     cmd,
                     capture_output=False,
-                    check=False,
+                    check=True,
                 )
-            except TimeoutExpired:
-                raise TimeoutError from None
+            except Exception as e_:
+                raise PDFPrintDriverException(e_) from e_

strictdoc/server/routers/main_router.py

@@ -113,7 +113,10 @@
 from strictdoc.export.html.html_templates import HTMLTemplates, JinjaEnvironment
 from strictdoc.export.html.renderers.link_renderer import LinkRenderer
 from strictdoc.export.html.renderers.markup_renderer import MarkupRenderer
-from strictdoc.export.html2pdf.pdf_print_driver import PDFPrintDriver
+from strictdoc.export.html2pdf.pdf_print_driver import (
+    PDFPrintDriver,
+    PDFPrintDriverException,
+)
 from strictdoc.export.json.json_generator import JSONGenerator
 from strictdoc.helpers.cast import assert_cast
 from strictdoc.helpers.file_modification_time import (
@@ -134,7 +137,7 @@
 
 HTTP_STATUS_BAD_REQUEST = 400
 HTTP_STATUS_PRECONDITION_FAILED = 412
-HTTP_STATUS_GATEWAY_TIMEOUT = 504
+HTTP_STATUS_INTERNAL_SERVER_ERROR = 500
 
 AUTOCOMPLETE_LIMIT = 50
 
@@ -2148,6 +2151,9 @@ def get_export_html2pdf(document_mid: str) -> Response:  # noqa: ARG001
         path_to_output_pdf = os.path.join(
             project_config.export_output_html_root, "html", "_temp.pdf"
         )
+
+        # FIXME: Add this print driver to a service bus object to make it
+        #        unit-testable.
         pdf_print_driver = PDFPrintDriver()
         with open(path_to_output_html, mode="w", encoding="utf8") as temp_file_:
             temp_file_.write(document_content)
@@ -2158,10 +2164,10 @@ def get_export_html2pdf(document_mid: str) -> Response:  # noqa: ARG001
                     project_config,
                     [(path_to_output_html, path_to_output_pdf)],
                 )
-            except TimeoutError:  # pragma: no cover
+            except PDFPrintDriverException as e_:  # pragma: no cover
                 return Response(
-                    content="HTML2PDF timeout error.",
-                    status_code=HTTP_STATUS_GATEWAY_TIMEOUT,
+                    content=e_.get_server_user_message(),
+                    status_code=HTTP_STATUS_INTERNAL_SERVER_ERROR,
                 )
 
             return FileResponse(