HTTP/[23]: continue upload when state.drain is set

- as reported in #10433, HTTP/2 uploads may stall when a response is
  received before the upload is done. This happens when the
  data->state.drain is set for such a transfer, as the special handling
  in transfer.c from then on only cared about downloads.
- add continuation of uploads, if applicable, in this case.
- add pytest case test_07_12_upload_seq_large to reproduce this scenario
  (although, current nghttp2 implementation is using drain less often)

Reported-by: Lucas Pardue

Fixes #10433
Closes #10443

tests/tests-httpd/testenv/env.py

@@ -82,14 +82,14 @@ class EnvConfig:
                         lib.lower() for lib in m.group('libs').split(' ')
                     ]
                     self.curl_props['libs'] = [
-                        re.sub(r'/.*', '',lib) for lib in self.curl_props['lib_versions']
+                        re.sub(r'/.*', '', lib) for lib in self.curl_props['lib_versions']
                     ]
             if l.startswith('Features: '):
                 self.curl_props['features'] = [
                     feat.lower() for feat in l[10:].split(' ')
                 ]
             if l.startswith('Protocols: '):
-                self.curl_props['protocols'] =  [
+                self.curl_props['protocols'] = [
                     prot.lower() for prot in l[11:].split(' ')
                 ]
         self.nghttpx_with_h3 = re.match(r'.* nghttp3/.*', p.stdout.strip())
@@ -222,11 +222,11 @@ class Env:
         return 'unknown'
 
     @staticmethod
-    def curl_os() -> bool:
+    def curl_os() -> str:
         return Env.CONFIG.curl_props['os']
 
     @staticmethod
-    def curl_version() -> bool:
+    def curl_version() -> str:
         return Env.CONFIG.curl_props['version']
 
     @staticmethod
@@ -336,3 +336,17 @@ class Env:
         if alpn_proto in ['h3']:
             return f'{domain}:{self.h3_port}'
         return f'{domain}:{self.http_port}'
+
+    def make_data_file(self, indir: str, fname: str, fsize: int) -> str:
+        fpath = os.path.join(indir, fname)
+        s10 = "0123456789"
+        s = (101 * s10) + s10[0:3]
+        with open(fpath, 'w') as fd:
+            for i in range(int(fsize / 1024)):
+                fd.write(f"{i:09d}-{s}\n")
+            remain = int(fsize % 1024)
+            if remain != 0:
+                i = int(fsize / 1024) + 1
+                s = f"{i:09d}-{s}\n"
+                fd.write(s[0:remain])
+        return fpath