[PATCH 37/43] www: update internal docs

[Eric Wong <e@yhbt.net>]

We no longer favor getline+close for streaming PSGI responses
when using public-inbox-httpd.  We still support it for other
PSGI servers, though.
---
 Documentation/technical/ds.txt   |  4 ++--
 lib/PublicInbox/GetlineBody.pm   |  4 +---
 lib/PublicInbox/GzipFilter.pm    | 17 +++++++++++++----
 lib/PublicInbox/HTTPD.pm         |  5 ++---
 lib/PublicInbox/Mbox.pm          |  8 ++------
 lib/PublicInbox/View.pm          |  2 +-
 lib/PublicInbox/WwwAtomStream.pm |  6 ++----
 lib/PublicInbox/WwwStream.pm     |  7 +++----
 8 files changed, 26 insertions(+), 27 deletions(-)

diff --git a/Documentation/technical/ds.txt b/Documentation/technical/ds.txt
index cbd06cfb4..a0793ca23 100644
--- a/Documentation/technical/ds.txt
+++ b/Documentation/technical/ds.txt
@@ -64,8 +64,8 @@ Augmented features:
 * ->requeue support.  An optimization of the AddTimer(0, ...) idiom
   for immediately dispatching code at the next event loop iteration.
   public-inbox uses this for fairly generating large responses
-  iteratively (see PublicInbox::NNTP::long_response or the use of
-  ->getline callbacks for generating gigantic gzipped mboxes).
+  iteratively (see PublicInbox::NNTP::long_response or git_async_cat
+  for blob retrievals).
 
 New features
 
diff --git a/lib/PublicInbox/GetlineBody.pm b/lib/PublicInbox/GetlineBody.pm
index 6becaaf5f..988bc63f4 100644
--- a/lib/PublicInbox/GetlineBody.pm
+++ b/lib/PublicInbox/GetlineBody.pm
@@ -5,9 +5,7 @@
 # end callback when the object goes out-of-scope.
 # This depends on rpipe being _blocking_ on getline.
 #
-# public-inbox-httpd favors "getline" response bodies to take a
-# "pull"-based approach to feeding slow clients (as opposed to a
-# more common "push" model)
+# This is only used by generic PSGI servers and not public-inbox-httpd
 package PublicInbox::GetlineBody;
 use strict;
 use warnings;
diff --git a/lib/PublicInbox/GzipFilter.pm b/lib/PublicInbox/GzipFilter.pm
index 6380f50e9..d72ad3c88 100644
--- a/lib/PublicInbox/GzipFilter.pm
+++ b/lib/PublicInbox/GzipFilter.pm
@@ -1,7 +1,16 @@
 # Copyright (C) 2020 all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
-
-# Qspawn filter
+#
+# In public-inbox <=1.5.0, public-inbox-httpd favored "getline"
+# response bodies to take a "pull"-based approach to feeding
+# slow clients (as opposed to a more common "push" model).
+#
+# In newer versions, public-inbox-httpd supports a backpressure-aware
+# pull/push model which also accounts for slow git blob storage.
+# {async_next} callbacks only run when the DS {wbuf} is drained
+# {async_eml} callbacks only run when a blob arrives from git.
+#
+# We continue to support getline+close for generic PSGI servers.
 package PublicInbox::GzipFilter;
 use strict;
 use parent qw(Exporter);
@@ -14,12 +23,12 @@ our @EXPORT_OK = qw(gzf_maybe);
 my %OPT = (-WindowBits => 15 + 16, -AppendOutput => 1);
 my @GZIP_HDRS = qw(Vary Accept-Encoding Content-Encoding gzip);
 
-sub new { bless {}, shift }
+sub new { bless {}, shift } # qspawn filter
 
 # for Qspawn if using $env->{'pi-httpd.async'}
 sub attach {
 	my ($self, $http_out) = @_;
-	$self->{http_out} = $http_out;
+	$self->{http_out} = $http_out; # PublicInbox::HTTP::{Chunked,Identity}
 	$self
 }
 
diff --git a/lib/PublicInbox/HTTPD.pm b/lib/PublicInbox/HTTPD.pm
index 331939699..a9f55ff61 100644
--- a/lib/PublicInbox/HTTPD.pm
+++ b/lib/PublicInbox/HTTPD.pm
@@ -36,9 +36,8 @@ sub new {
 
 		# XXX unstable API!, only GitHTTPBackend needs
 		# this to limit git-http-backend(1) parallelism.
-		# The rest of our PSGI code is generic, relying
-		# on "pull" model using "getline" to prevent
-		# over-buffering.
+		# We also check for the truthiness of this to
+		# detect when to use git_async_cat for slow blobs
 		'pi-httpd.async' => \&pi_httpd_async
 	);
 	bless {
diff --git a/lib/PublicInbox/Mbox.pm b/lib/PublicInbox/Mbox.pm
index abdf43c93..8726b9f64 100644
--- a/lib/PublicInbox/Mbox.pm
+++ b/lib/PublicInbox/Mbox.pm
@@ -1,12 +1,8 @@
 # Copyright (C) 2015-2020 all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 
-# Streaming (via getline) interface for formatting messages as an mboxrd.
-# Used by the PSGI web interface.
-#
-# public-inbox-httpd favors "getline" response bodies to take a
-# "pull"-based approach to feeding slow clients (as opposed to a
-# more common "push" model)
+# Streaming interface for mboxrd HTTP responses
+# See PublicInbox::GzipFilter for details.
 package PublicInbox::Mbox;
 use strict;
 use parent 'PublicInbox::GzipFilter';
diff --git a/lib/PublicInbox/View.pm b/lib/PublicInbox/View.pm
index 895e4f278..60dad6bac 100644
--- a/lib/PublicInbox/View.pm
+++ b/lib/PublicInbox/View.pm
@@ -415,7 +415,7 @@ sub stream_thread ($$) {
 	PublicInbox::WwwStream::aresponse($ctx, 200, \&stream_thread_i);
 }
 
-# /$INBOX/$MESSAGE_ID/t/
+# /$INBOX/$MSGID/t/ and /$INBOX/$MSGID/T/
 sub thread_html {
 	my ($ctx) = @_;
 	my $mid = $ctx->{mid};
diff --git a/lib/PublicInbox/WwwAtomStream.pm b/lib/PublicInbox/WwwAtomStream.pm
index 073df1dfa..3b5b133a5 100644
--- a/lib/PublicInbox/WwwAtomStream.pm
+++ b/lib/PublicInbox/WwwAtomStream.pm
@@ -1,10 +1,8 @@
 # Copyright (C) 2016-2020 all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 #
-# Atom body stream for which yields getline+close methods
-# public-inbox-httpd favors "getline" response bodies to take a
-# "pull"-based approach to feeding slow clients (as opposed to a
-# more common "push" model)
+# Atom body stream for HTTP responses
+# See PublicInbox::GzipFilter for details.
 package PublicInbox::WwwAtomStream;
 use strict;
 use parent 'PublicInbox::GzipFilter';
diff --git a/lib/PublicInbox/WwwStream.pm b/lib/PublicInbox/WwwStream.pm
index 7d257a191..23b03f0e8 100644
--- a/lib/PublicInbox/WwwStream.pm
+++ b/lib/PublicInbox/WwwStream.pm
@@ -1,11 +1,10 @@
 # Copyright (C) 2016-2020 all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 #
-# HTML body stream for which yields getline+close methods
+# HTML body stream for which yields getline+close methods for
+# generic PSGI servers and callbacks for public-inbox-httpd.
 #
-# public-inbox-httpd favors "getline" response bodies to take a
-# "pull"-based approach to feeding slow clients (as opposed to a
-# more common "push" model)
+# See PublicInbox::GzipFilter parent class for more info.
 package PublicInbox::WwwStream;
 use strict;
 use parent qw(Exporter PublicInbox::GzipFilter);