out_opentelemetry: add support for zstd compression

This patch adds a new compression mechanism called 'zstd', this is
available through the 'compress' configuration property, in the configuration file
it can be enabled with:

  pipeline:
     outputs:
      - name: opentelemetry
        match: '*'
        compress: zstd

Signed-off-by: Eduardo Silva <eduardo@chronosphere.io>

plugins/out_opentelemetry/opentelemetry.c

@@ -325,6 +325,9 @@ int opentelemetry_post(struct opentelemetry_context *ctx,
         if (ctx->compress_gzip == FLB_TRUE) {
             compression_algorithm = "gzip";
         }
+        else if (ctx->compress_zstd == FLB_TRUE) {
+            compression_algorithm = "zstd";
+        }
 
         result = flb_http_request_set_parameters(request,
                         FLB_HTTP_CLIENT_ARGUMENT_URI(http_uri),
@@ -407,7 +410,7 @@ int opentelemetry_post(struct opentelemetry_context *ctx,
         if (ctx->log_response_payload &&
             response->body != NULL &&
             cfl_sds_len(response->body) > 0) {
-            flb_plg_info(ctx->ins, "%s:%i, HTTP status=%i\n%s",
+            flb_plg_info(ctx->ins, "%s:%i, HTTP status=%i%s",
                             ctx->host, ctx->port,
                             response->status, response->body);
         }
@@ -840,7 +843,7 @@ static struct flb_config_map config_map[] = {
     {
      FLB_CONFIG_MAP_STR, "compress", NULL,
      0, FLB_FALSE, 0,
-     "Set payload compression mechanism. Option available is 'gzip'"
+     "Set payload compression mechanism. Options available are 'gzip' and 'zstd'."
     },
     /*
      * Logs Properties

plugins/out_opentelemetry/opentelemetry.h

@@ -156,9 +156,12 @@ struct opentelemetry_context {
     /* instance context */
     struct flb_output_instance *ins;
 
-    /* Compression mode (gzip) */
+    /* compression: gzip */
     int compress_gzip;
 
+    /* compression: zstd */
+    int compress_zstd;
+
     /* FLB/OTLP Record accessor patterns */
     struct flb_record_accessor *ra_meta_schema;
     struct flb_record_accessor *ra_meta_resource_id;

plugins/out_opentelemetry/opentelemetry_conf.c

@@ -404,6 +404,13 @@ struct opentelemetry_context *flb_opentelemetry_context_create(struct flb_output
         if (strcasecmp(tmp, "gzip") == 0) {
             ctx->compress_gzip = FLB_TRUE;
         }
+        else if (strcasecmp(tmp, "zstd") == 0) {
+            ctx->compress_zstd = FLB_TRUE;
+        }
+        else {
+            flb_plg_error(ctx->ins, "Unknown compression method %s", tmp);
+            return NULL;
+        }
     }
 
     ctx->ra_observed_timestamp_metadata = flb_ra_create((char*)ctx->logs_observed_timestamp_metadata_key,