oauth: Add unit tests for multiplexer handling

To better record the internal behaviors of oauth-curl.c, add a unit test
suite for the socket and timer handling code. This is all based on TAP
and driven by our existing Test::More infrastructure.

This commit is a replay of 1443b6c, which was reverted due to
buildfarm failures. Compared with that, this version protects the build
targets in the Makefile with a with_libcurl conditional, and it tweaks
the code style in 001_oauth.pl.

Reviewed-by: Dagfinn Ilmari Mannsåker <[email protected]>
Reviewed-by: Andrew Dunstan <[email protected]>
Discussion: https://postgr.es/m/CAOYmi+nDZxJHaWj9_jRSyf8uMToCADAmOfJEggsKW-kY7aUwHA@mail.gmail.com
Discussion: https://postgr.es/m/CAOYmi+m=xY0P_uAzAP_884uF-GhQ3wrineGwc9AEnb6fYxVqVQ@mail.gmail.com

Author: jchampio

src/interfaces/libpq-oauth/Makefile

@@ -54,10 +54,6 @@ SHLIB_EXPORTS = exports.txt
 # Disable -bundle_loader on macOS.
 BE_DLLLIBS =
 
-# By default, a library without an SONAME doesn't get a static library, so we
-# add it to the build explicitly.
-all: all-lib all-static-lib
-
 # Shared library stuff
 include $(top_srcdir)/src/Makefile.shlib
 
@@ -66,6 +62,28 @@ include $(top_srcdir)/src/Makefile.shlib
 %_shlib.o: %.c %.o
 	$(CC) $(CFLAGS) $(CFLAGS_SL) $(CPPFLAGS) $(CPPFLAGS_SHLIB) -c $< -o $@
 
+.PHONY: all-tests
+all-tests: oauth_tests$(X)
+
+oauth_tests$(X): test-oauth-curl.o oauth-utils.o $(WIN32RES) | submake-libpgport submake-libpq
+	$(CC) $(CFLAGS) $^ $(LDFLAGS) $(LDFLAGS_EX) $(SHLIB_LINK) -o $@
+
+#
+# Top-Level Targets
+#
+# The existence of a t/ folder induces the buildfarm to run Make directly on
+# this subdirectory, bypassing the recursion skip in src/interfaces/Makefile.
+# Wrap the standard build targets in a with_libcurl conditional to avoid
+# building OAuth code on platforms that haven't requested it. (The "clean"-style
+# targets remain available.)
+#
+
+ifeq ($(with_libcurl), yes)
+
+# By default, a library without an SONAME doesn't get a static library, so we
+# add it to the build explicitly.
+all: all-lib all-static-lib
+
 # Ignore the standard rules for SONAME-less installation; we want both the
 # static and shared libraries to go into libdir.
 install: all installdirs $(stlib) $(shlib)
@@ -75,9 +93,19 @@ install: all installdirs $(stlib) $(shlib)
 installdirs:
 	$(MKDIR_P) '$(DESTDIR)$(libdir)'
 
+check: all-tests
+	$(prove_check)
+
+installcheck: all-tests
+	$(prove_installcheck)
+
+endif # with_libcurl
+
 uninstall:
 	rm -f '$(DESTDIR)$(libdir)/$(stlib)'
 	rm -f '$(DESTDIR)$(libdir)/$(shlib)'
 
 clean distclean: clean-lib
 	rm -f $(OBJS) $(OBJS_STATIC) $(OBJS_SHLIB)
+	rm -f test-oauth-curl.o oauth_tests$(X)
+	rm -rf tmp_check

src/interfaces/libpq-oauth/meson.build

@@ -47,3 +47,38 @@ libpq_oauth_so = shared_module(libpq_oauth_name,
   link_args: export_fmt.format(export_file.full_path()),
   kwargs: default_lib_args,
 )
+
+libpq_oauth_test_deps = []
+
+oauth_test_sources = files('test-oauth-curl.c') + libpq_oauth_so_sources
+
+if host_system == 'windows'
+  oauth_test_sources += rc_bin_gen.process(win32ver_rc, extra_args: [
+    '--NAME', 'oauth_tests',
+    '--FILEDESC', 'OAuth unit test program',])
+endif
+
+libpq_oauth_test_deps += executable('oauth_tests',
+  oauth_test_sources,
+  dependencies: [frontend_shlib_code, libpq, libpq_oauth_deps],
+  kwargs: default_bin_args + {
+    'c_args': default_bin_args.get('c_args', []) + libpq_oauth_so_c_args,
+    'c_pch': pch_postgres_fe_h,
+    'include_directories': [libpq_inc, postgres_inc],
+    'install': false,
+  }
+)
+
+testprep_targets += libpq_oauth_test_deps
+
+tests += {
+  'name': 'libpq-oauth',
+  'sd': meson.current_source_dir(),
+  'bd': meson.current_build_dir(),
+  'tap': {
+    'tests': [
+      't/001_oauth.pl',
+    ],
+    'deps': libpq_oauth_test_deps,
+  },
+}

src/interfaces/libpq-oauth/t/001_oauth.pl

@@ -0,0 +1,24 @@
+# Copyright (c) 2025, PostgreSQL Global Development Group
+use strict;
+use warnings FATAL => 'all';
+
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Defer entirely to the oauth_tests executable. stdout/err is routed through
+# Test::More so that our logging infrastructure can handle it correctly. Using
+# IPC::Run::new_chunker seems to help interleave the two streams a little better
+# than without.
+#
+# TODO: prove can also deal with native executables itself, which we could
+# probably make use of via PROVE_TESTS on the Makefile side. But the Meson setup
+# calls Perl directly, which would require more code to work around... and
+# there's still the matter of logging.
+my $builder = Test::More->builder;
+my $out = $builder->output;
+my $err = $builder->failure_output;
+
+IPC::Run::run ['oauth_tests'],
+  '>' => (IPC::Run::new_chunker, sub { $out->print($_[0]) }),
+  '2>' => (IPC::Run::new_chunker, sub { $err->print($_[0]) })
+  or die "oauth_tests returned $?";