Allow caching some API responses that change rarely

api/api_common.inc

@@ -24,3 +24,25 @@ function get_flag_value(array $query_params, string $flagname)
         return $bool;
     }
 }
+
+/**
+ * Send headers telling the client it's OK to cache the page
+ */
+function send_cache_header(int $cache_time, ?string $cache_type = "private", bool $immutable = true): void
+{
+    if ($cache_type && !in_array($cache_type, ["public", "private"])) {
+        throw new ValueError("Invalid value for 'cache_type'");
+    }
+
+    $cache_settings = ["max-age=$cache_time"];
+
+    if ($cache_type) {
+        $cache_settings[] = $cache_type;
+    }
+
+    if ($immutable) {
+        $cache_settings[] = "immutable";
+    }
+
+    header("Cache-Control: " . join(", ", $cache_settings));
+}

api/v1_docs.inc

@@ -1,5 +1,6 @@
 <?php
 include_once($relPath.'faq.inc');
+include_once("api_common.inc");
 
 /** @param array<string, string|string[]> $query_params */
 function api_v1_documents(string $method, array $data, array $query_params): array
@@ -14,10 +15,12 @@ function api_v1_documents(string $method, array $data, array $query_params): arr
                 $docs_with_lang[] = $doc;
             }
         }
-        return $docs_with_lang;
+        $docs = $docs_with_lang;
     } else {
-        return array_keys($external_faq_overrides);
+        $docs = array_keys($external_faq_overrides);
     }
+    send_cache_header(60 * 60 * 24, "public");
+    return $docs;
 }
 
 /** @param array<string, string|string[]> $query_params */
@@ -29,6 +32,7 @@ function api_v1_document(string $method, array $data, array $query_params): stri
     if ("" === $faq_url) {
         throw new NotFoundError("$document is not available in language code '$lang_code'");
     }
+    send_cache_header(60 * 60 * 24, "public");
     return $faq_url;
 }
 
@@ -37,5 +41,6 @@ function api_v1_dictionaries(string $method, array $data, array $query_params):
 {
     $dict_list = get_languages_with_dictionaries();
     asort($dict_list);
+    send_cache_header(60 * 60 * 24, "public");
     return $dict_list;
 }

api/v1_projects.inc

@@ -887,6 +887,7 @@ function api_v1_project_wordcheck(string $method, array $data, array $query_para
 function api_v1_project_pickersets(string $method, array $data, array $query_params): array
 {
     $project = $data[":projectid"];
+    send_cache_header(60 * 60, "public");
     return $project->get_verbose_pickersets();
 }