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.

2 files changed, 32 insertions, 5 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
     }
diff --git a/src/index.ts b/src/index.ts
index 4fe80a9..d592405 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -36,12 +36,12 @@ app.post("/v1/:org/:repo/:branch/:commit.html", (req, res) => {
   const { token, format } = req.query;
   //TODO @Metadata token should come from metadata
   if (token != TOKEN) {
-    return res.status(401).send();
+    return res.status(401).send("Invalid token");
   }
 
   const reporter = format || "tarpaulin";
   if (!formats.list_formats().includes(reporter)) {
-    return res.status(406).send();
+    return res.status(406).send("Report format unknown");
   }
 
   //TODO acquire file, verify file size/content type (HTML)
@@ -51,7 +51,12 @@ app.post("/v1/:org/:repo/:branch/:commit.html", (req, res) => {
 
   const doc = new DOMParser().parseFromString(contents, "text/html");
   const formatter = formats.get_format(reporter);
-  const coverage = formatter.parse_coverage(doc);
+  let coverage: number;
+  try {
+    coverage = formatter.parse_coverage(doc);
+  } catch {
+    return res.status(400).send("Invalid report document");
+  }
 
   const badge = badgen({
     label: "coverage",