Implement report parsing for Tarpaulin

The generated Tarpaulin HTML report does not have stats to parse via the
DOM - the data is injected via a script tag, which only has line-by-line
coverage, though it includes statistics for each file. The total coverage is
counted by summing the covered/coverable stats reported for each file.

Also, the bad version for express is fixed, and messages are
included for errors that occur for the POST endpoint.

1 files changed, 24 insertions, 2 deletions

diff --git a/src/formats.ts b/src/formats.ts
index 34f97df..5d389b4 100644
--- a/src/formats.ts
+++ b/src/formats.ts
@@ -33,8 +33,30 @@ const FormatsObj: FormatObj = {
   formats: {
     tarpaulin: {
       parse_coverage: (file: Document) => {
-        //TODO parse coverage from file (example?)
-        return 0.0;
+        const scripts = file.getElementsByTagName("script");
+        if (scripts.length == 0) {
+          throw new Error("Invalid report document");
+        }
+        const data = scripts[0].text;
+        const accumFunc = (regex: RegExp) => {
+          let acc: number = 0;
+          while (true) {
+            const match = regex.exec(data);
+            if (match === null) break;
+            acc += Number(match[1]);
+          }
+
+          return acc;
+        };
+
+        const covered = accumFunc(/"covered":(\d*)/g);
+        const coverable = accumFunc(/"coverable":(\d*)/g);
+
+        // do not error if LOC is 0
+        if (coverable === 0) {
+          return 0.0;
+        }
+        return (100 * covered) / coverable;
       },
       match_color: default_color_matches
     }