Move various files that don't need to be in basic/ to shared/

This doesn't have much effect on the final build, because we link libbasic.a
into libsystemd-shared.so, so in the end, all the object built from basic/
end up in libsystemd-shared. And when the static library is linked into binaries,
any objects that are included in it but are not used are trimmed. Hence, the
size of output artifacts doesn't change:

$ du -sb /var/tmp/inst*
54181861	/var/tmp/inst1    (old)
54207441	/var/tmp/inst1s   (old split-usr)
54182477	/var/tmp/inst2    (new)
54208041	/var/tmp/inst2s   (new split-usr)

(The negligible change in size is because libsystemd-shared.so is bigger
by a few hundred bytes. I guess it's because symbols are named differently
or something like that.)

The effect is on the build process, in particular partial builds. This change
effectively moves the requirements on some build steps toward the leaves of the
dependency tree. Two effects:
- when building items that do not depend on libsystemd-shared, we
  build less stuff for libbasic.a (which wouldn't be used anyway,
  so it's a net win).
- when building items that do depend on libshared, we reduce libbasic.a as a
  synchronization point, possibly allowing better parallelism.

Method:
1. copy list of .h files from src/basic/meson.build to /tmp/basic
2. $ for i in $(grep '.h$' /tmp/basic); do echo $i; git --no-pager grep "include \"$i\"" src/basic/ 'src/lib*' 'src/nss-*' 'src/journal/sd-journal.c' |grep -v "${i%.h}.c";echo ;done | less

1 files changed, 59 insertions, 0 deletions

diff --git a/src/shared/web-util.c b/src/shared/web-util.c
new file mode 100644
index 0000000000..82221af194
--- /dev/null
+++ b/src/shared/web-util.c
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <stdbool.h>
+
+#include "string-util.h"
+#include "utf8.h"
+#include "web-util.h"
+
+bool http_etag_is_valid(const char *etag) {
+        if (isempty(etag))
+                return false;
+
+        if (!endswith(etag, "\""))
+                return false;
+
+        if (!startswith(etag, "\"") && !startswith(etag, "W/\""))
+                return false;
+
+        return true;
+}
+
+bool http_url_is_valid(const char *url) {
+        const char *p;
+
+        if (isempty(url))
+                return false;
+
+        p = startswith(url, "http://");
+        if (!p)
+                p = startswith(url, "https://");
+        if (!p)
+                return false;
+
+        if (isempty(p))
+                return false;
+
+        return ascii_is_valid(p);
+}
+
+bool documentation_url_is_valid(const char *url) {
+        const char *p;
+
+        if (isempty(url))
+                return false;
+
+        if (http_url_is_valid(url))
+                return true;
+
+        p = startswith(url, "file:/");
+        if (!p)
+                p = startswith(url, "info:");
+        if (!p)
+                p = startswith(url, "man:");
+
+        if (isempty(p))
+                return false;
+
+        return ascii_is_valid(p);
+}