fix(asm): fix another body read blocking problem on Flask (#4446) (#4480)

Signed-off-by: Juanjo Alvarez <[email protected]>

Signed-off-by: Juanjo Alvarez <[email protected]>
(cherry picked from commit 4008a0f)

Co-authored-by: Juanjo Alvarez Martinez <[email protected]>

Author: mergify[bot]

ddtrace/contrib/flask/patch.py

@@ -359,13 +359,15 @@ def traced_wsgi_app(pin, wrapped, instance, args, kwargs):
             wsgi_input = environ.get("wsgi.input", "")
 
             # Copy wsgi input if not seekable
-            try:
-                seekable = wsgi_input.seekable()
-            except AttributeError:
-                seekable = False
-            if not seekable:
-                body = wsgi_input.read()
-                environ["wsgi.input"] = BytesIO(body)
+            if wsgi_input:
+                try:
+                    seekable = wsgi_input.seekable()
+                except AttributeError:
+                    seekable = False
+                if not seekable:
+                    content_length = int(environ.get("CONTENT_LENGTH", 0))
+                    body = wsgi_input.read(content_length) if content_length else wsgi_input.read()
+                    environ["wsgi.input"] = BytesIO(body)
 
             try:
                 if content_type == "application/json":
@@ -387,10 +389,11 @@ def traced_wsgi_app(pin, wrapped, instance, args, kwargs):
                 log.warning("Failed to parse werkzeug request body", exc_info=True)
             finally:
                 # Reset wsgi input to the beginning
-                if seekable:
-                    wsgi_input.seek(0)
-                else:
-                    environ["wsgi.input"] = BytesIO(body)
+                if wsgi_input:
+                    if seekable:
+                        wsgi_input.seek(0)
+                    else:
+                        environ["wsgi.input"] = BytesIO(body)
 
         trace_utils.set_http_meta(
             span,

releasenotes/notes/fix-another-flask-body-blocking-acd533aa3c1bd46e.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    ASM: fix a body read problem on some corner case where don't passing the content length makes wsgi.input.read() blocks.