From f2eda44fccf888643e438a4c0cfb1720e22a2f84 Mon Sep 17 00:00:00 2001
From: Eduardo Silva <eduardo@chronosphere.io>
Date: Tue, 6 Jan 2026 13:01:58 -0600
Subject: [PATCH] out_opentelemetry: on HTTP/2, read and process gRPC status
 code

Signed-off-by: Eduardo Silva <eduardo@chronosphere.io>
---
 plugins/out_opentelemetry/opentelemetry.c | 134 +++++++++++++++++++++-
 1 file changed, 133 insertions(+), 1 deletion(-)

diff --git a/plugins/out_opentelemetry/opentelemetry.c b/plugins/out_opentelemetry/opentelemetry.c
index aac8e48af59..47cd6d12623 100644
--- a/plugins/out_opentelemetry/opentelemetry.c
+++ b/plugins/out_opentelemetry/opentelemetry.c
@@ -30,9 +30,11 @@
 #include <cfl/cfl.h>
 #include <fluent-otel-proto/fluent-otel.h>
 
-#include <cmetrics/cmetrics.h>
 #include <fluent-bit/flb_gzip.h>
 #include <fluent-bit/flb_zstd.h>
+#include <fluent-bit/flb_hash_table.h>
+
+#include <cmetrics/cmetrics.h>
 #include <cmetrics/cmt_encode_opentelemetry.h>
 
 #include <ctraces/ctraces.h>
@@ -75,6 +77,115 @@ static int is_http_status_code_retrayable(int http_code)
     return FLB_FALSE;
 }
 
+static int opentelemetry_is_grpc_status_retryable(int status_code)
+{
+    if (status_code == 1  || /* CANCELLED */
+        status_code == 4  || /* DEADLINE_EXCEEDED */
+        status_code == 8  || /* RESOURCE_EXHAUSTED */
+        status_code == 10 || /* ABORTED */
+        status_code == 13 || /* INTERNAL */
+        status_code == 14) { /* UNAVAILABLE */
+        return FLB_TRUE;
+    }
+
+    return FLB_FALSE;
+}
+
+static int opentelemetry_lookup_header_value(struct flb_hash_table *table,
+                                             const char *name,
+                                             cfl_sds_t *out_value)
+{
+    void   *value;
+    size_t  value_length;
+    int     result;
+
+    if (table == NULL) {
+        return FLB_FALSE;
+    }
+
+    result = flb_hash_table_get(table,
+                                name,
+                                strlen(name),
+                                &value,
+                                &value_length);
+
+    if (result == -1) {
+        return FLB_FALSE;
+    }
+
+    *out_value = cfl_sds_create_len((const char *) value, value_length);
+
+    if (*out_value == NULL) {
+        return FLB_FALSE;
+    }
+
+    return FLB_TRUE;
+}
+
+static int opentelemetry_check_grpc_status(struct opentelemetry_context *ctx,
+                                           struct flb_http_response *response)
+{
+    cfl_sds_t grpc_message;
+    cfl_sds_t grpc_status_text;
+    int      grpc_status;
+    int       result;
+
+    grpc_message = NULL;
+    grpc_status_text = NULL;
+    grpc_status = 0;
+    result = FLB_OK;
+
+    /* ref: https://grpc.io/docs/guides/status-codes/ */
+    if (opentelemetry_lookup_header_value(response->trailer_headers,
+                                          "grpc-status",
+                                          &grpc_status_text) == FLB_FALSE &&
+        opentelemetry_lookup_header_value(response->headers,
+                                          "grpc-status",
+                                          &grpc_status_text) == FLB_FALSE) {
+
+        return FLB_OK;
+    }
+
+    grpc_status = strtol(grpc_status_text, NULL, 10);
+
+    if (opentelemetry_lookup_header_value(response->trailer_headers,
+                                          "grpc-message",
+                                          &grpc_message) == FLB_FALSE) {
+        opentelemetry_lookup_header_value(response->headers,
+                                          "grpc-message",
+                                          &grpc_message);
+    }
+
+    if (grpc_status != 0) {
+        if (grpc_message != NULL) {
+            flb_plg_error(ctx->ins,
+                          "grpc-status=%d, grpc-message=%s",
+                          grpc_status,
+                          grpc_message);
+        }
+        else {
+            flb_plg_error(ctx->ins, "grpc-status=%d", grpc_status);
+        }
+
+        if (opentelemetry_is_grpc_status_retryable(grpc_status)) {
+            result = FLB_RETRY;
+        }
+        else {
+            result = FLB_ERROR;
+        }
+    }
+
+    if (grpc_message != NULL) {
+        cfl_sds_destroy(grpc_message);
+    }
+
+    if (grpc_status_text != NULL) {
+        cfl_sds_destroy(grpc_status_text);
+    }
+
+    return result;
+}
+
 int opentelemetry_legacy_post(struct opentelemetry_context *ctx,
                               const void *body, size_t body_len,
                               const char *tag, int tag_len,
@@ -342,6 +453,20 @@ int opentelemetry_post(struct opentelemetry_context *ctx,
 
     if (request->protocol_version == HTTP_PROTOCOL_VERSION_20 &&
         ctx->enable_grpc_flag) {
+        /* nghttp2 does not automatically add the TE header because it is not
+         * tied to the gRPC semantics, so we must set the required
+         * "te: trailers" header explicitly for gRPC-over-HTTP/2.
+         */
+        result = flb_http_request_set_header(request,
+                                             "te", 2,
+                                             "trailers", 8);
+
+        if (result != 0) {
+            flb_plg_error(ctx->ins, "failed to set gRPC TE header");
+            flb_http_client_request_destroy(request, FLB_TRUE);
+
+            return FLB_RETRY;
+        }
 
         grpc_body = cfl_sds_create_size(body_len + 5);
 
@@ -521,6 +646,13 @@ int opentelemetry_post(struct opentelemetry_context *ctx,
         out_ret = FLB_OK;
     }
 
+    if (ctx->enable_grpc_flag && request->protocol_version == HTTP_PROTOCOL_VERSION_20 && out_ret == FLB_OK) {
+        result = opentelemetry_check_grpc_status(ctx, response);
+        if (result != FLB_OK) {
+            out_ret = result;
+        }
+    }
+
     flb_http_client_request_destroy(request, FLB_TRUE);
 
     return out_ret;