test-lib-functions: introduce the 'test_set_port' helper function

Several test scripts run daemons like 'git-daemon' or Apache, and
communicate with them through TCP sockets.  To have unique ports where
these daemons are accessible, the ports are usually the number of the
corresponding test scripts, unless the user overrides them via
environment variables, and thus all those tests and test libs contain
more or less the same bit of one-liner boilerplate code to find out
the port.  The last patch in this series will make this a bit more
complicated.

Factor out finding the port for a daemon into the common helper
function 'test_set_port' to avoid repeating ourselves.

Take special care of test scripts with "low" numbers:

  - Test numbers below 1024 would result in a port that's only usable
    as root, so set their port to '10000 + test-nr' to make sure it
    doesn't interfere with other tests in the test suite.  This makes
    the hardcoded port number in 't0410-partial-clone.sh' unnecessary,
    remove it.

  - The shell's arithmetic evaluation interprets numbers with leading
    zeros as octal values, which means that test number below 1000 and
    containing the digits 8 or 9 will trigger an error.  Remove all
    leading zeros from the test numbers to prevent this.

Note that the 'git p4' tests are unlike the other tests involving
daemons in that:

  - 'lib-git-p4.sh' doesn't use the test's number for unique port as
    is, but does a bit of additional arithmetic on top [1].

  - The port is not overridable via an environment variable.

With this patch even 'git p4' tests will use the test's number as
default port, and it will be overridable via the P4DPORT environment
variable.

[1] Commit fc00233071 (git-p4 tests: refactor and cleanup, 2011-08-22)
    introduced that "unusual" unique port computation without
    explaining why it was necessary (as opposed to simply using the
    test number as is).  It seems to be just unnecessary complication,
    and in any case that commit came way before the "test nr as unique
    port" got "standardized" for other daemons in commits c44132fcf3
    (tests: auto-set git-daemon port, 2014-02-10), 3bb486e439 (tests:
    auto-set LIB_HTTPD_PORT from test name, 2014-02-10), and
    bf9d7df950 (t/lib-git-svn.sh: improve svnserve tests with parallel
    make test, 2017-12-01).

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-git-daemon.sh

@@ -28,7 +28,7 @@ then
 	test_skip_or_die $GIT_TEST_GIT_DAEMON "file system does not support FIFOs"
 fi
 
-LIB_GIT_DAEMON_PORT=${LIB_GIT_DAEMON_PORT-${this_test#t}}
+test_set_port LIB_GIT_DAEMON_PORT
 
 GIT_DAEMON_PID=
 GIT_DAEMON_DOCUMENT_ROOT_PATH="$PWD"/repo

t/lib-git-p4.sh

@@ -53,14 +53,7 @@ time_in_seconds () {
 	(cd / && "$PYTHON_PATH" -c 'import time; print(int(time.time()))')
 }
 
-# Try to pick a unique port: guess a large number, then hope
-# no more than one of each test is running.
-#
-# This does not handle the case where somebody else is running the
-# same tests and has chosen the same ports.
-testid=${this_test#t}
-git_p4_test_start=9800
-P4DPORT=$((10669 + ($testid - $git_p4_test_start)))
+test_set_port P4DPORT
 
 P4PORT=localhost:$P4DPORT
 P4CLIENT=client

t/lib-git-svn.sh

@@ -13,6 +13,7 @@ fi
 GIT_DIR=$PWD/.git
 GIT_SVN_DIR=$GIT_DIR/svn/refs/remotes/git-svn
 SVN_TREE=$GIT_SVN_DIR/svn-tree
+test_set_port SVNSERVE_PORT
 
 svn >/dev/null 2>&1
 if test $? -ne 1
@@ -119,7 +120,6 @@ require_svnserve () {
 }
 
 start_svnserve () {
-	SVNSERVE_PORT=${SVNSERVE_PORT-${this_test#t}}
 	svnserve --listen-port $SVNSERVE_PORT \
 		 --root "$rawsvnrepo" \
 		 --listen-once \

t/lib-httpd.sh

@@ -82,7 +82,7 @@ case $(uname) in
 esac
 
 LIB_HTTPD_PATH=${LIB_HTTPD_PATH-"$DEFAULT_HTTPD_PATH"}
-LIB_HTTPD_PORT=${LIB_HTTPD_PORT-${this_test#t}}
+test_set_port LIB_HTTPD_PORT
 
 TEST_PATH="$TEST_DIRECTORY"/lib-httpd
 HTTPD_ROOT_PATH="$PWD"/httpd

t/t0410-partial-clone.sh

@@ -480,7 +480,6 @@ test_expect_success 'gc stops traversal when a missing but promised object is re
 	! grep "$TREE_HASH" out
 '
 
-LIB_HTTPD_PORT=12345  # default port, 410, cannot be used as non-root
 . "$TEST_DIRECTORY"/lib-httpd.sh
 start_httpd
 

t/t5512-ls-remote.sh

@@ -260,7 +260,7 @@ test_lazy_prereq GIT_DAEMON '
 # This test spawns a daemon, so run it only if the user would be OK with
 # testing with git-daemon.
 test_expect_success PIPE,JGIT,GIT_DAEMON 'indicate no refs in standards-compliant empty remote' '
-	JGIT_DAEMON_PORT=${JGIT_DAEMON_PORT-${this_test#t}} &&
+	test_set_port JGIT_DAEMON_PORT &&
 	JGIT_DAEMON_PID= &&
 	git init --bare empty.git &&
 	>empty.git/git-daemon-export-ok &&

t/test-lib-functions.sh

@@ -1263,3 +1263,39 @@ test_oid () {
 	fi &&
 	eval "printf '%s' \"\${$var}\""
 }
+
+# Choose a port number based on the test script's number and store it in
+# the given variable name, unless that variable already contains a number.
+test_set_port () {
+	local var=$1 port
+
+	if test $# -ne 1 || test -z "$var"
+	then
+		BUG "test_set_port requires a variable name"
+	fi
+
+	eval port=\$$var
+	case "$port" in
+	"")
+		# No port is set in the given env var, use the test
+		# number as port number instead.
+		# Remove not only the leading 't', but all leading zeros
+		# as well, so the arithmetic below won't (mis)interpret
+		# a test number like '0123' as an octal value.
+		port=${this_test#${this_test%%[1-9]*}}
+		if test "${port:-0}" -lt 1024
+		then
+			# root-only port, use a larger one instead.
+			port=$(($port + 10000))
+		fi
+
+		eval $var=$port
+		;;
+	*[^0-9]*|0*)
+		error >&7 "invalid port number: $port"
+		;;
+	*)
+		# The user has specified the port.
+		;;
+	esac
+}