Validation of resource content against cacheid

Added a test that checks that the static resources returned by the
server have content that matches their cacheid. This test currently
fails because some binary resources (e.g. png images) are garbled by the
dos2unix conversion.

test/server.cpp

@@ -359,6 +359,57 @@ R"EXPECTEDRESULT(    <link type="text/css" href="/ROOT%23%3F/skin/search_results
   }
 }
 
+std::string getCacheIdFromUrl(const std::string& url)
+{
+  const std::string q("?cacheid=");
+  const auto i = url.find(q);
+  return i == std::string::npos ? "" : url.substr(i + q.size());
+}
+
+std::string runExternalCmdAndGetItsOutput(const std::string& cmd)
+{
+  std::string cmdOutput;
+
+#ifdef _WIN32
+#define popen _popen
+#define pclose _pclose
+#endif
+
+  if (FILE* pPipe = popen(cmd.c_str(), "r"))
+  {
+    char buf[128];
+    while (fgets(buf, 128, pPipe)) {
+        cmdOutput += std::string(buf, buf+128);
+    }
+
+    pclose(pPipe);
+  }
+
+  return cmdOutput;
+}
+
+std::string getSha1OfResponseData(const std::string& url)
+{
+  const std::string pythonScript =
+    "import urllib.request as req; "
+    "import hashlib; "
+    "print(hashlib.sha1(req.urlopen('" + url + "').read()).hexdigest())";
+  const std::string cmd = "python3 -c \"" + pythonScript + "\"";
+  return runExternalCmdAndGetItsOutput(cmd);
+}
+
+TEST_F(ServerTest, CacheIdsOfStaticResourcesMatchTheSha1HashOfResourceContent)
+{
+  for ( const Resource& res : all200Resources() ) {
+    if ( res.kind == STATIC_CONTENT ) {
+      const TestContext ctx{ {"url", res.url} };
+      const std::string fullUrl = "http://localhost:" + std::to_string(SERVER_PORT) + res.url;
+      const std::string sha1 = getSha1OfResponseData(fullUrl);
+      ASSERT_EQ(sha1.substr(0, 8), getCacheIdFromUrl(res.url)) << ctx;
+    }
+  }
+}
+
 const char* urls400[] = {
   "/ROOT%23%3F/search",
   "/ROOT%23%3F/search?content=zimfile",