site: better error messages

this includes deduplicating some code, and attempts at error messages
for files which could not be parsed as json but aren't actually valid
age-encrypted files (there doesn't seem to be some easy way to validate
that these files are valid age files without knowing the key).

1 files changed, 27 insertions, 14 deletions

diff --git a/site/index.html b/site/index.html
index 6dc12fa..ced3af8 100644
--- a/site/index.html
+++ b/site/index.html
@@ -169,7 +169,7 @@
                      console.log(response.text())
                      window.location.href = "thanks.html";
                  }
-                 errormsg.innerText = "POST request returned error code: "
+                 errormsg.innerText = "POST request returned error code:\n"
                                     + response.status + ": " + response.statusText;
                  errormsg.hidden = false;
              }).catch(error => {
@@ -225,11 +225,22 @@
          };
      }
 
+     function mkReadError (msg) {
+         appendChildren(root, [
+             mkElement("h1", "Error"),
+             mkElement("p", msg),
+             appendChildren(
+                 mkElement("p","attempted path: "),
+                 [mkElement("tt", surveyUrl)]
+             )
+         ]);
+     }
+
      async function main () {
          // initialise the web assembly parts of this
          await init();
          const Http = new XMLHttpRequest();
-         const url=  surveyUrl;
+         const url = surveyUrl;
          Http.open("GET", url);
          Http.responseType = "arraybuffer";
          Http.send();
@@ -243,31 +254,33 @@
                      try {
                          survey = JSON.parse(string);
                      } catch (e) {
-                         console.log ("survey appears to be encrypted");
-                         askPassphrase(bytearray);
+                         if (string.lastIndexOf("age-encryption.org/v1") === 0) {
+                             console.log ("survey appears to be encrypted");
+                             askPassphrase(bytearray);
+                         } else {
+                             mkReadError ("Could not load this survey; it appears to be in a wrong or unknown format.");
+                         }
                      }
                      /// if the survey was unencrypted, start it here. If it
                      /// was encrypted, we need to wait for user action via
-                     /// a js callback (handled in askPassphrase).
+                     /// a js callback (handled in askPassphrase). This is
+                     /// out here only to avoid catching errors from within mkSurvey.
                      if (survey !== null) {
                          mkSurvey(survey);
                      }
                  // couldn't load survey json, show error message
                  } else {
-                     appendChildren(root, [
-                         mkElement("h1", "Error"),
-                         mkElement("p", "Could not load this survey; are you sure that it exists?"),
-                         appendChildren(
-                             mkElement("p","attempted path: "),
-                             [mkElement("tt", surveyUrl)]
-                         )
-                     ]);
+                     mkReadError ("Could not load this survey; are you sure that it exists?");
                  }
              }
          }
      }
 
+     if (surveyUrl === "") {
+         mkReadError ("There's nothing here. Maybe try appending something after the url?\n\nAlternatively, check to see if you copied the whole url.");
+     } else {
+         main ()
+     }
 
-     main ()
     </script>
 </html>