add metrics for compressed/uncompressed payload size

examples/openresty/nginx.conf

@@ -7,7 +7,8 @@ init_worker_by_lua_block {
     local attr = require("opentelemetry.attribute")
 
     -- create exporter
-    local exporter = otlp_exporter_new(exporter_client_new("otel-collector:4317", 3))
+    local use_gzip = true
+    local exporter = otlp_exporter_new(exporter_client_new("otel-collector:4317", 3), 10000, use_gzip)
     -- create span processor
     local batch_span_processor = batch_span_processor_new(exporter)
     -- create tracer provider

lib/opentelemetry/trace/exporter/http_client.lua

@@ -1,5 +1,9 @@
 local http = require("resty.http")
 local zlib = require("zlib")
+local otel_global = require("opentelemetry.global")
+local exporter_request_compressed_payload_size = "otel.otlp_exporter.request_compressed_payload_size"
+local exporter_request_uncompressed_payload_size = "otel.otlp_exporter.request_uncompressed_payload_size"
+
 local _M = {
 }
 
@@ -47,8 +51,17 @@ function _M.do_request(self, body, encode_gzip)
         -- https://github.com/brimworks/lua-zlib/issues/4#issuecomment-26383801
         self.headers["Content-Encoding"] = "gzip"
         local deflate_stream = zlib.deflate(zlib.BEST_COMPRESSION, 15+16)
-        local compressed_body = deflate_stream(body, "finish")
+        local compressed_body, _, bytes_in, bytes_out = deflate_stream(body, "finish")
+
+        otel_global.metrics_reporter:record_value(
+            exporter_request_uncompressed_payload_size, bytes_in)
+        otel_global.metrics_reporter:record_value(
+            exporter_request_compressed_payload_size, bytes_out)
+
         body = compressed_body
+    else
+        otel_global.metrics_reporter:record_value(
+            exporter_request_uncompressed_payload_size, string.len(body))
     end
 
     local res, err = self.httpc:request_uri(self.uri, {

lib/opentelemetry/trace/exporter/otlp.lua

@@ -14,14 +14,16 @@ local mt = {
     __index = _M
 }
 
-function _M.new(http_client, timeout_ms, circuit_reset_timeout_ms, circuit_open_threshold)
+function _M.new(http_client, timeout_ms, use_gzip, circuit_reset_timeout_ms, circuit_open_threshold)
+    use_gzip = use_gzip or false
     local self = {
         client = http_client,
         timeout_ms = timeout_ms or DEFAULT_TIMEOUT_MS,
+        use_gzip = use_gzip,
         circuit = circuit.new({
             reset_timeout_ms = circuit_reset_timeout_ms,
             failure_threshold = circuit_open_threshold
-        })
+        }),
     }
     return setmetatable(self, mt)
 end
@@ -55,7 +57,7 @@ local function call_collector(exporter, pb_encoded_body)
         end
 
         -- Make request
-        res, res_error = exporter.client:do_request(pb_encoded_body, true)
+        res, res_error = exporter.client:do_request(pb_encoded_body, exporter.use_gzip)
         local after_time = util.gettimeofday_ms()
         otel_global.metrics_reporter:record_value(
             exporter_request_duration_metric, after_time - current_time)

spec/trace/exporter/otlp_spec.lua

@@ -17,7 +17,22 @@ describe("export_spans", function()
         stub(ngx, "log")
         cb:export_spans({ span })
         ngx.log:revert()
-        assert.spy(c.do_request).was_called_with(c, match.is_string(), match.is_all_of(match.is_boolean(), match.is_equal(true)))
+        assert.spy(c.do_request).was_called_with(c, match.is_string(), match.is_equal(false))
+    end)
+
+    it("invokes do_request with gzip compression when configured to do so", function()
+        local span
+        local ctx = context.new()
+        ctx, span = tracer:start(ctx, "test span")
+        span:finish()
+        local c = client.new("http://localhost:8080", 10)
+        spy.on(c, "do_request")
+        local cb = exporter.new(c, 10000, true) -- use_gzip = true
+        -- Supress log message, since we expect it
+        stub(ngx, "log")
+        cb:export_spans({ span })
+        ngx.log:revert()
+        assert.spy(c.do_request).was_called_with(c, match.is_string(), match.is_equal(true))
     end)
 
     it("doesn't invoke protected_call when failures is equal to retry limit", function()