Var: $request_id variable.

This variable contains a string that is formed using random data and
can be used as a unique request identifier.

This closes #714 issue on GitHub.

3 files changed, 59 insertions, 0 deletions

diff --git a/docs/changes.xml b/docs/changes.xml
index 74cd5db7..2c01a1e0 100644
--- a/docs/changes.xml
+++ b/docs/changes.xml
@@ -26,6 +26,13 @@ NGINX Unit updated to 1.32.0.
 </para>
 </change>
 
+<change type="feature">
+<para>
+$request_id variable contains a string that is formed using random data and
+can be used as a unique request identifier.
+</para>
+</change>
+
 </changes>
 
 
diff --git a/src/nxt_http_variables.c b/src/nxt_http_variables.c
index 46594a6b..ec744317 100644
--- a/src/nxt_http_variables.c
+++ b/src/nxt_http_variables.c
@@ -28,6 +28,8 @@ static u_char *nxt_http_log_date(u_char *buf, nxt_realtime_t *now,
     struct tm *tm, size_t size, const char *format);
 static nxt_int_t nxt_http_var_request_line(nxt_task_t *task, nxt_str_t *str,
     void *ctx, void *data);
+static nxt_int_t nxt_http_var_request_id(nxt_task_t *task, nxt_str_t *str,
+    void *ctx, void *data);
 static nxt_int_t nxt_http_var_status(nxt_task_t *task, nxt_str_t *str,
     void *ctx, void *data);
 static nxt_int_t nxt_http_var_body_bytes_sent(nxt_task_t *task, nxt_str_t *str,
@@ -90,6 +92,10 @@ static nxt_var_decl_t  nxt_http_vars[] = {
         .handler = nxt_http_var_request_line,
         .cacheable = 1,
     }, {
+        .name = nxt_string("request_id"),
+        .handler = nxt_http_var_request_id,
+        .cacheable = 1,
+    }, {
         .name = nxt_string("status"),
         .handler = nxt_http_var_status,
         .cacheable = 1,
@@ -396,6 +402,32 @@ nxt_http_var_request_line(nxt_task_t *task, nxt_str_t *str, void *ctx,
 
 
 static nxt_int_t
+nxt_http_var_request_id(nxt_task_t *task, nxt_str_t *str, void *ctx,
+    void *data)
+{
+    nxt_random_t        *rand;
+    nxt_http_request_t  *r;
+
+    r = ctx;
+
+    str->start = nxt_mp_nget(r->mem_pool, 32);
+    if (nxt_slow_path(str->start == NULL)) {
+        return NXT_ERROR;
+    }
+
+    str->length = 32;
+
+    rand = &task->thread->random;
+
+    (void) nxt_sprintf(str->start, str->start + 32, "%08xD%08xD%08xD%08xD",
+                       nxt_random(rand), nxt_random(rand),
+                       nxt_random(rand), nxt_random(rand));
+
+    return NXT_OK;
+}
+
+
+static nxt_int_t
 nxt_http_var_body_bytes_sent(nxt_task_t *task, nxt_str_t *str, void *ctx,
     void *data)
 {
diff --git a/test/test_variables.py b/test/test_variables.py
index c9b173fa..813bd8c6 100644
--- a/test/test_variables.py
+++ b/test/test_variables.py
@@ -211,6 +211,26 @@ def test_variables_request_line(search_in_file, wait_for_record):
     assert wait_for_record(reg, 'access.log') is not None
 
 
+def test_variables_request_id(search_in_file, wait_for_record, findall):
+    set_format('$uri $request_id $request_id')
+
+    assert search_in_file(r'/request_id', 'access.log') is None
+    assert client.get(url='/request_id_1')['status'] == 200
+    assert client.get(url='/request_id_2')['status'] == 200
+    assert wait_for_record(r'/request_id_2', 'access.log') is not None
+
+    id1 = findall(
+        r'^\/request_id_1 ([0-9a-f]{32}) ([0-9a-f]{32})$', 'access.log'
+    )[0]
+    id2 = findall(
+        r'^\/request_id_2 ([0-9a-f]{32}) ([0-9a-f]{32})$', 'access.log'
+    )[0]
+
+    assert id1[0] == id1[1], 'same ids first'
+    assert id2[0] == id2[1], 'same ids second'
+    assert id1[0] != id2[0], 'first id != second id'
+
+
 def test_variables_status(search_in_file, wait_for_record):
     set_format('$status')