From 23f529476634f34379b7830ba92a797d563971d4 Mon Sep 17 00:00:00 2001
From: Alan Richards <alarobric@gmail.com>
Date: Tue, 26 Sep 2023 21:04:04 +0000
Subject: [PATCH] out_loki: add ability to add arbitrary http headers and
 adjust the URI path

Following pattern from prometheus_remote_write, this adds the option to add
arbitrary http headers.
It also adds the ability to manually set the URI path. Previously it was hardcoded as
`/loki/api/v1/push`. Existing behaviour is maintained and this is an optional override.

Tested against a Loki endpoint and logging reverse proxy.

Signed-off-by: Alan Richards <alarobric@gmail.com>
---
 plugins/out_loki/loki.c | 36 +++++++++++++++++++++++++++++++++++-
 plugins/out_loki/loki.h |  4 ++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/plugins/out_loki/loki.c b/plugins/out_loki/loki.c
index d93a3f9aad6..ab9c4aae8a9 100644
--- a/plugins/out_loki/loki.c
+++ b/plugins/out_loki/loki.c
@@ -1515,6 +1515,11 @@ static void cb_loki_flush(struct flb_event_chunk *event_chunk,
     struct flb_connection *u_conn;
     struct flb_http_client *c;
     struct flb_loki_dynamic_tenant_id_entry *dynamic_tenant_id;
+    struct mk_list *head;
+    struct flb_config_map_val *mv;
+    struct flb_slist_entry *key = NULL;
+    struct flb_slist_entry *val = NULL;
+    char * uri;
 
     dynamic_tenant_id = FLB_TLS_GET(thread_local_tenant_id);
 
@@ -1577,8 +1582,15 @@ static void cb_loki_flush(struct flb_event_chunk *event_chunk,
         FLB_OUTPUT_RETURN(FLB_RETRY);
     }
 
+    /* Optional URI to replace default */
+    if (ctx->uri) {
+        uri = ctx->uri;
+    } else {
+        uri = FLB_LOKI_URI;
+    }
+
     /* Create HTTP client context */
-    c = flb_http_client(u_conn, FLB_HTTP_POST, FLB_LOKI_URI,
+    c = flb_http_client(u_conn, FLB_HTTP_POST, uri,
                         out_buf, out_size,
                         ctx->tcp_host, ctx->tcp_port,
                         NULL, 0);
@@ -1604,6 +1616,16 @@ static void cb_loki_flush(struct flb_event_chunk *event_chunk,
         flb_http_bearer_auth(c, ctx->bearer_token);
     }
 
+    /* Arbitrary additional headers */
+    flb_config_map_foreach(head, mv, ctx->headers) {
+        key = mk_list_entry_first(mv->val.list, struct flb_slist_entry, _head);
+        val = mk_list_entry_last(mv->val.list, struct flb_slist_entry, _head);
+
+        flb_http_add_header(c,
+                            key->str, flb_sds_len(key->str),
+                            val->str, flb_sds_len(val->str));
+    }
+
     /* Add Content-Type header */
     flb_http_add_header(c,
                         FLB_LOKI_CT, sizeof(FLB_LOKI_CT) - 1,
@@ -1805,6 +1827,18 @@ static struct flb_config_map config_map[] = {
      "Set bearer token auth"
     },
 
+    {
+     FLB_CONFIG_MAP_SLIST_1, "header", NULL,
+     FLB_CONFIG_MAP_MULT, FLB_TRUE, offsetof(struct flb_loki, headers),
+     "Add a HTTP header key/value pair. Multiple headers can be set"
+    },
+
+    {
+     FLB_CONFIG_MAP_STR, "uri", NULL,
+     0, FLB_TRUE, offsetof(struct flb_loki, uri),
+     "Specify an optional HTTP URI for the target web server, e.g: /something"
+    },
+
     {
      FLB_CONFIG_MAP_STR, "compress", NULL,
      0, FLB_FALSE, 0,
diff --git a/plugins/out_loki/loki.h b/plugins/out_loki/loki.h
index 2011cee3ded..58008da33b0 100644
--- a/plugins/out_loki/loki.h
+++ b/plugins/out_loki/loki.h
@@ -77,6 +77,7 @@ struct flb_loki {
     /* Private */
     int tcp_port;
     char *tcp_host;
+    char *uri;
     int out_line_format;
     int ra_used;                        /* number of record accessor label keys */
     struct flb_record_accessor *ra_k8s; /* kubernetes record accessor */
@@ -93,6 +94,9 @@ struct flb_loki {
 
     /* Plugin instance */
     struct flb_output_instance *ins;
+
+    /* Arbitrary HTTP headers */
+    struct mk_list *headers;
 };
 
 #endif