Simplify bin/report implementation

bin/compile

@@ -15,13 +15,13 @@ ENV_DIR=$3
 source "${BP_DIR}/lib/util.sh"
 source "${BP_DIR}/lib/common.sh"
 source "${BP_DIR}/lib/maven.sh"
-source "${BP_DIR}/lib/metadata.sh"
+source "${BP_DIR}/lib/metrics.sh"
 
 # Initialise the buildpack metadata store.
 # This is used to track state across builds (for cache invalidation and messaging when build
 # configuration changes) and also so that `bin/report` can generate the build report.
-meta_init "${CACHE_DIR}" "java"
-meta_setup
+metrics::init "${CACHE_DIR}" "java"
+metrics::setup
 
 export_env_dir "${ENV_DIR}" "." "JAVA_OPTS|JAVA_TOOL_OPTIONS"
 

bin/report

@@ -33,52 +33,7 @@ if [[ -f "${EXPORT_FILE}" ]]; then
 	source "${EXPORT_FILE}"
 fi
 
-source "${BUILDPACK_DIR}/lib/metadata.sh"
-meta_init "${CACHE_DIR}" "java"
+source "${BUILDPACK_DIR}/lib/metrics.sh"
 
-# Emit the key / value pair unquoted to stdout. Skips if the value is empty.
-# Based on: https://github.com/heroku/heroku-buildpack-nodejs/blob/main/bin/report
-kv_pair() {
-	local key="${1}"
-	local value="${2}"
-	if [[ -n "${value}" ]]; then
-		echo "${key}: ${value}"
-	fi
-}
-
-# Emit the key / value pair to stdout, safely quoting the string. Skips if the value is empty.
-# Based on: https://github.com/heroku/heroku-buildpack-nodejs/blob/main/bin/report
-# (Though instead uses single quotes instead of double to avoid escaping issues.)
-kv_pair_string() {
-	local key="${1}"
-	local value="${2}"
-	if [[ -n "${value}" ]]; then
-		# Escape any existing single quotes, which for YAML means replacing `'` with `''`.
-		value="${value//\'/\'\'}"
-		echo "${key}: '${value}'"
-	fi
-}
-
-STRING_FIELDS=(
-	# Fields coming from jvm-common
-	openjdk_version
-	openjdk_distribution
-	openjdk_version_selector
-)
-
-# We don't want to quote numeric or boolean fields.
-ALL_OTHER_FIELDS=(
-	# Fields coming from jvm-common
-	openjdk_install_duration
-	app_has_jdk_overlay
-)
-
-for field in "${STRING_FIELDS[@]}"; do
-	# shellcheck disable=SC2312 # TODO: Invoke this command separately to avoid masking its return value.
-	kv_pair_string "${field}" "$(meta_get "${field}")"
-done
-
-for field in "${ALL_OTHER_FIELDS[@]}"; do
-	# shellcheck disable=SC2312 # TODO: Invoke this command separately to avoid masking its return value.
-	kv_pair "${field}" "$(meta_get "${field}")"
-done
+metrics::init "${CACHE_DIR}" "java"
+metrics::print_bin_report_yaml

lib/metrics.sh

@@ -0,0 +1,116 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+
+# This buildpack cannot currently run with `set -u`! This needs to be fixed.
+# set -euo pipefail
+set -eo pipefail
+
+BUILDPACK_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && cd .. && pwd)"
+
+source "${BUILDPACK_DIR}/lib/util.sh"
+
+# Variables shared by this whole module
+METRICS_DATA_FILE=""
+PREVIOUS_METRICS_DATA_FILE=""
+
+# Initializes the environment required for metrics collection.
+# Must be called before you can use any other functions from this file!
+#
+# Usage:
+# ```
+# metrics::init "${CACHE_DIR}" "scala"
+# ```
+metrics::init() {
+	local cache_dir="${1}"
+	local buildpack_name="${2}"
+
+	METRICS_DATA_FILE="${cache_dir}/metrics-data/${buildpack_name}"
+	PREVIOUS_METRICS_DATA_FILE="${cache_dir}/metrics-data/${buildpack_name}-prev"
+}
+
+# Initializes the metrics collection environment by setting up data files.
+#
+# WARNING: This function prunes existing metrics should there be any.
+#
+# Usage:
+# ```
+# metrics::init "${CACHE_DIR}" "scala"
+# metrics::setup
+# ```
+metrics::setup() {
+	if [[ -f "${METRICS_DATA_FILE}" ]]; then
+		cp "${METRICS_DATA_FILE}" "${PREVIOUS_METRICS_DATA_FILE}"
+	fi
+
+	mkdir -p "$(dirname "${METRICS_DATA_FILE}")"
+	echo "{}" >"${METRICS_DATA_FILE}"
+}
+
+# Sets a metric value as raw JSON data.
+# The value parameter must be valid JSON value (number, boolean, string, etc.).
+#
+# NOTE: Strings must be wrapped in double quotes (use `metrics::set_string` for convenience).
+#
+# Usage:
+# ```
+# metrics::set_raw "build_duration" "42.5"
+# metrics::set_raw "success" "true"
+# metrics::set_raw "message" '"Hello World"'
+# ```
+metrics::set_raw() {
+	local key="${1}"
+	local value="${2}"
+
+	local new_data_file_contents
+	new_data_file_contents=$(jq <"${METRICS_DATA_FILE}" --arg key "${key}" --argjson value "${value}" '. + { ($key): ($value) }')
+
+	echo "${new_data_file_contents}" >"${METRICS_DATA_FILE}"
+}
+
+# Sets a metric value as a string.
+# The value will be automatically wrapped in double quotes and escaped for JSON.
+#
+# Usage:
+# ```
+# metrics::set_string "buildpack_version" "1.2.3"
+# metrics::set_string "jvm_distribution" "Heroku"
+# ```
+metrics::set_string() {
+	local key="${1}"
+	local value="${2}"
+
+	# This works because jq's `--arg` always results in a string value
+	metrics::set_raw "${key}" "$(jq -n --arg value "${value}" '$value')"
+}
+
+# Sets a metric for elapsed time between two timestamps.
+# If end timestamp is not provided, current time is used.
+# Time is calculated in seconds with millisecond precision.
+#
+# Usage:
+# ```
+# start_time=$(util::nowms)
+# # ... some operation ...
+# metrics::set_duration "compile_duration" "${start_time}"
+# ```
+metrics::set_duration() {
+	local key="${1}"
+	local start="${2}"
+	local end="${3:-$(util::nowms)}"
+	local time
+	time="$(echo "${start}" "${end}" | awk '{ printf "%.3f", ($2 - $1)/1000 }')"
+	metrics::set_raw "${key}" "${time}"
+}
+
+# Prints all metrics data in YAML format suitable for `bin/report`.
+# Each metric key-value pair is output as a separate YAML line.
+#
+# Usage:
+# ```
+# metrics::print_bin_report_yaml
+# ```
+metrics::print_bin_report_yaml() {
+	jq -r 'keys[] as $key | (.[$key] | tojson) as $value | "\($key): \($value)"' <"${METRICS_DATA_FILE}"
+}