Add timing function to build data module (#595)

* Add timing function to builddata module

lib/build-data.sh

@@ -17,6 +17,16 @@ bd_set() {
   kv_set "$BUILD_DATA_FILE" "$1" "$2"
 }
 
+# similar to mtime from stdlib
+bd_time() {
+  local key="$1"
+  local start="$2"
+  local end="${3:-$(nowms)}"
+  local time
+  time="$(echo "${start}" "${end}" | awk '{ printf "%.3f", ($2 - $1)/1000 }')"
+  kv_set "$BUILD_DATA_FILE" "$key" "$time"
+}
+
 log_build_data() {
   # print all values on one line in logfmt format
   # https://brandur.org/logfmt

test/unit

@@ -166,6 +166,18 @@ testBuildData() {
   # this isn't required, and this test serves as documentation
   bd_set "a" "this should come first"
   assertEquals "a=\"this should come first\" foo=\"value with spaces\" test=different-foo" "$(log_build_data)"
+
+  # dates generated by running `nowms; sleep 10; nowms`
+  bd_time "time" "1545178120033" "1545178130043"
+  assertEquals "10.010" "$(bd_get time)"
+
+  # dates generated by running `nowms; sleep 1; nowms`
+  bd_time "time" "1545178503025" "1545178504027"
+  assertEquals "1.002" "$(bd_get time)"
+
+  # dates generated by running `nowms; sleep 30; nowms`
+  bd_time "time" "1545178521204" "1545178551206"
+  assertEquals "30.002" "$(bd_get time)"
 }
 
 testWebConcurrencyProfileScript() {