mod_log_config: Add log_formatter support and a JSON log_formatter

changes-entries/mod_log_config.txt

@@ -0,0 +1 @@
+  *) mod_log_config: Add support for output log in JSON format [Thomas Meyer]

docs/manual/mod/mod_log_config.xml

@@ -454,6 +454,7 @@
 <description>Sets filename and format of log file</description>
 <syntax>CustomLog  <var>file</var>|<var>pipe</var>|<var>provider</var>
 <var>format</var>|<var>nickname</var>
+[formatter=json[,short]]
 [env=[!]<var>environment-variable</var>|
 expr=<var>expression</var>]</syntax>
 <contextlist><context>server config</context><context>virtual host</context>
@@ -525,7 +526,18 @@ CustomLog "logs/access_log" common
 CustomLog "logs/access_log" "%h %l %u %t \"%r\" %&gt;s %b"
     </highlight>
 
-    <p>The third argument is optional and controls whether or
+    <p>The third argument is optional and controls whether to use a special
+    formatter to create the log records. Currently only the formatter "json" is
+    supported which will create all log records according to RFC8259 and
+    each printed log record will be a JSON object.
+    The optional formatter option "short" make the json formatter output short
+    JSON key names. The JSON key names in short format are directly derived
+    from the format string, i.e. "%s" will result in a JSON of {"s":"304"}.
+    If the "short" option is not specified long JSON key names will be used for
+    better readability in JSON object, e.g. {"statusCode":"304"}
+    </p>
+
+    <p>The last argument is optional and controls whether or
     not to log a particular request. The condition can be the
     presence or absence (in the case of a '<code>env=!<var>name</var></code>'
     clause) of a particular variable in the server

include/httpd.h

@@ -1968,6 +1968,38 @@ AP_DECLARE(char *) ap_escape_html2(apr_pool_t *p, const char *s, int toasc)
 AP_DECLARE(char *) ap_escape_logitem(apr_pool_t *p, const char *str)
                    AP_FN_ATTR_NONNULL((1));
 
+/**
+ * Apply JSON escaping to a UTF string. Invalid UTF8 character sequences
+ * are replaced by the U+FFFD replacement character.
+ * @param dest The destination buffer, can be NULL
+ * @param src The original buffer
+ * @param srclen The length of the original buffer. Pass APR_ESCAPE_STRING
+ * for a NUL terminated string.
+ * @param quote If non zero, surround the string with quotes, and if the
+ * string is NULL, return the string "NULL".
+ * @param len If present, returns the length of the string
+ * @return APR_SUCCESS, or APR_NOTFOUND if the string resulted in no
+ * modification, APR_EINVAL if bad UTF8 is detected. In all cases valid
+ * UTF8 is returned.
+ */
+APR_DECLARE(apr_status_t) ap_escape_json(char *dest, const char *src,
+        apr_ssize_t srclen, int quote, apr_size_t *len);
+
+/**
+ * Apply JSON escaping to a UTF string. Invalid UTF8 character sequences
+ * are replaced by the U+FFFD replacement character.
+ * @param p Pool to allocate from
+ * @param src The original buffer
+ * @param srclen The length of the original buffer. Pass APR_ESCAPE_STRING
+ * for a NUL terminated string.
+ * @param quote If non zero, surround the string with quotes, and if the
+ * string is NULL, return the string "NULL".
+ * @return A zero padded buffer allocated from the pool on success, or
+ * NULL if src was NULL.
+ */
+APR_DECLARE(const char *) ap_pescape_json(apr_pool_t *p, const char *src,
+        apr_ssize_t srclen, int quote);
+
 /**
  * Escape a string for logging into the error log (without a pool)
  * @param dest The buffer to write to