feat: URL encode dataset (#242)

## Which problem is this PR solving?

When sending data, the dataset name forms part of the URL path and
should be URL encoded so restricted characters are preserved. This is
particularly important if the dataset name included a forward slash `/`
which results in an invalid URL path and the Honeycomb API rejecting the
request.

## Short description of the changes
- URL encode the dataset before sending data
- Add tests to verify dataset is encoded correctly for use in the
request path

transmission/transmission.go

@@ -422,7 +422,7 @@ func (b *batchAgg) fireBatch(events []*Event) {
 	}
 
 	// build the HTTP request
-	url.Path = path.Join(url.Path, "/1/batch", dataset)
+	url.Path = buildReqestPath(url.Path, dataset)
 
 	// One retry allowed for connection timeouts.
 	var resp *http.Response
@@ -742,3 +742,7 @@ func buildReqReader(jsonEncoded []byte, compress bool) (io.Reader, bool) {
 type nower interface {
 	Now() time.Time
 }
+
+func buildReqestPath(existingPath, dataset string) string {
+	return path.Join(existingPath, "/1/batch", url.PathEscape(dataset))
+}

transmission/transmission_test.go

@@ -1358,3 +1358,44 @@ func TestFireBatchWithUnauthorizedResponse(t *testing.T) {
 		testEquals(t, l.logs[0], "APIKey 'written' was rejected. Please verify APIKey is correct.")
 	})
 }
+
+func TestBuildRequestPath(t *testing.T) {
+	testCases := []struct {
+		datasetName  string
+		expectedPath string
+	}{
+		{
+			datasetName:  "foobar",
+			expectedPath: "/1/batch/foobar",
+		},
+		{
+			datasetName:  "foo.bar",
+			expectedPath: "/1/batch/foo.bar",
+		},
+		{
+			datasetName:  "foo-bar",
+			expectedPath: "/1/batch/foo-bar",
+		},
+		{
+			datasetName:  "foo/bar",
+			expectedPath: "/1/batch/foo%2Fbar",
+		},
+		{
+			datasetName:  "foo(bar)",
+			expectedPath: "/1/batch/foo%28bar%29",
+		},
+		{
+			datasetName:  "foo[bar]",
+			expectedPath: "/1/batch/foo%5Bbar%5D",
+		},
+		{
+			datasetName:  "foo{bar}",
+			expectedPath: "/1/batch/foo%7Bbar%7D",
+		},
+	}
+
+	for _, tc := range testCases {
+		path := buildReqestPath("", tc.datasetName)
+		assert.Equal(t, tc.expectedPath, path)
+	}
+}