add a CacheServer entry in pacman configuration snippet...pacman-v6.1.0

... comment the regular server entry and update the documentation in
README file.

The server error limit was introduced in pacman 6.0.0, which caused some
trouble with pacredir: Returning 404 (not found) is common case and no
fatal error.

This should be fixed with pacman 7.0.0, that will understand CacheServer
in configuration. Hopefully.

Add the required bits in include file for pacman.

4 files changed, 24 insertions, 473 deletions

diff --git a/README.md b/README.md
index 69a278c..4a20c63 100644
--- a/README.md
+++ b/README.md
@@ -54,7 +54,17 @@ definitions in `pacman.conf`:
 
 > Include = /etc/pacman.d/pacredir
 
-Do not worry if `pacman` reports:
+To get a better idea what happens in the background have a look at
+[the request flow chart](FLOW.md).
+
+### Databases from cache server
+
+By default databases are not fetched from cache servers. To make that
+happen just add the server twice, additionally as regular server. This
+is prepared in `/etc/pacman.d/pacredir`, just uncomment the corresponding
+line.
+
+Do not worry if `pacman` reports the following after the change:
 
 > error: failed retrieving file 'core.db' from 127.0.0.1:7077 : The
 > requested URL returned error: 404 Not Found
@@ -66,74 +76,19 @@ Please note that `pacredir` redirects to the most recent database file
 found on the local network if it is not too old (currently 24 hours). To
 make sure you really do have the latest files run `pacman -Syu` *twice*.
 
-To get a better idea what happens in the background have a look at
-[the request flow chart](FLOW.md).
-
 Current caveat
 --------------
 
-With its latest release `pacman` now supports a *server error limit*: Three
-download errors from a server results in the server being skipped for the
-remainder of this transaction.
+With `pacman`'s latest major release `6.x` it now supports a
+*server error limit*: Three download errors from a server results in the
+server being skipped for the remainder of this transaction.
 However `pacredir` sends a "*404 - not found*" response if the file is not
 available in local network - and is skipped after just three misses.
 
-This new feature is not configurable at runtime, so rebuilding `pacman` with
-one of the following patches is the way to make things work with `pacredir`.
-
-### Disable server error limit
-
-This is the simplest workaround - just disable the server error limit.
-
-    --- a/lib/libalpm/dload.c
-    +++ b/lib/libalpm/dload.c
-    @@ -60,7 +60,7 @@ static int curl_gethost(const char *url, char *buffer, size_t buf_len);
-     
-     /* number of "soft" errors required to blacklist a server, set to 0 to disable
-      * server blacklisting */
-    -const unsigned int server_error_limit = 3;
-    +const unsigned int server_error_limit = 0;
-     
-     struct server_error_count {
-     	char server[HOSTNAME_SIZE];
-
-We can agree this is not to be desired - in general the feature is reasonable.
-
-### Support http header to indicate a soft failure
-
-This solution is simple, yet powerful:
-[Support http header 'Cache-Control: no-cache' for soft failure](patches/0001-support-http-header-Cache-Control-no-cache-for-soft-failure.patch)
-
-By setting the HTTP header `Cache-Control: no-cache` when returning with
-the status code `404` (not found) the server can indicate that this is a
-soft failure. No error message is shown, and server's error count is
-not increased.
-
-Sadly upstream denied, again.
-
-Anyway, pushed this as merge request to Gitlab, which was closed without
-merging. 😢
-
-~~[support http header 'Cache-Control: no-cache' for soft failure](https://gitlab.archlinux.org/pacman/pacman/-/merge_requests/76)~~
-
-### Implement CacheServer
-
-A more complex solution that breaks current API is:
-[Implement CacheServer](patches/0001-implement-CacheServer.patch)
-
-This implements a new configuration option `CacheServer`. Adding a cache
-server makes it ignore the server error limit.
-
-Handling for soft failures is demanded in a long standing upstream bug, and
-the given patch could solve it:
-[FS#23407 - Allow soft failures on Server URLs](https://bugs.archlinux.org/task/23407)
-
-Pushed this as merge request to Gitlab:
-[implement CacheServer](https://gitlab.archlinux.org/pacman/pacman/-/merge_requests/74)
-
-Looks like this is going to be closed as well, but Andrew opened a merge
-request with his own implementation:
+Currently there is a merge request to 
 [add cache server support](https://gitlab.archlinux.org/pacman/pacman/-/merge_requests/98)
+to `pacman`. That would resolve the situation, so let's hope that will be
+merged soon and is available with `pacman` version `7.x`.
 
 Security
 --------
diff --git a/pacman/pacredir b/pacman/pacredir
index 0a1e1fc..8c049f7 100644
--- a/pacman/pacredir
+++ b/pacman/pacredir
@@ -1,2 +1,8 @@
 # Make sure local service pacredir is running!
-Server = http://127.0.0.1:7077/
+
+# Add pacredir as a cache server. This makes pacman request package files.
+CacheServer = http://127.0.0.1:7077/
+
+# Uncomment this to add pacredir as a regular server as well. This makes
+# pacman request database files from pacredir.
+#Server = http://127.0.0.1:7077/
diff --git a/patches/0001-implement-CacheServer.patch b/patches/0001-implement-CacheServer.patch
deleted file mode 100644
index 061d123..0000000
--- a/patches/0001-implement-CacheServer.patch
+++ /dev/null
@@ -1,341 +0,0 @@
-From a5239c9b76a515598afdb3e698dc82263341b1ad Mon Sep 17 00:00:00 2001
-From: Christian Hesse <mail@eworm.de>
-Date: Fri, 21 Jan 2022 16:11:02 +0100
-Subject: [PATCH] implement CacheServer
-
-This implements a new configuration option 'CacheServer'. Adding a cache
-server makes it ignore the server error limit.
-
-We have a struct that stores the server errors. Extend (and rename) this
-struct to store if this is a cache server. The errors are not increased
-for cache servers, thus they are never ignored.
-
-Signed-off-by: Christian Hesse <mail@eworm.de>
----
- doc/pacman.conf.5.asciidoc |  5 ++++
- lib/libalpm/alpm.h         |  7 +++--
- lib/libalpm/db.c           | 22 ++++++++++++----
- lib/libalpm/db.h           |  1 +
- lib/libalpm/dload.c        | 52 +++++++++++++++++++++++++++++++-------
- lib/libalpm/dload.h        |  2 ++
- src/pacman/conf.c          | 16 +++++++++---
- src/pacman/conf.h          |  1 +
- src/pacman/pacman-conf.c   |  1 +
- 9 files changed, 88 insertions(+), 19 deletions(-)
-
-diff --git a/doc/pacman.conf.5.asciidoc b/doc/pacman.conf.5.asciidoc
-index 41f3ea03..a25e35eb 100644
---- a/doc/pacman.conf.5.asciidoc
-+++ b/doc/pacman.conf.5.asciidoc
-@@ -243,6 +243,11 @@ number.
- *Server =* url::
- 	A full URL to a location where the database, packages, and signatures (if
- 	available) for this repository can be found.
-+
-+*CacheServer =* url::
-+	A full URL to a location where packages, and signatures (if available)
-+	for this repository can be found. There's no server error limit, log
-+	messages are not shown for server side errors (http code >= 400).
- +
- During parsing, pacman will define the `$repo` variable to the name of the
- current section. This is often utilized in files specified using the 'Include'
-diff --git a/lib/libalpm/alpm.h b/lib/libalpm/alpm.h
-index cdf71fdc..14889b9c 100644
---- a/lib/libalpm/alpm.h
-+++ b/lib/libalpm/alpm.h
-@@ -1322,16 +1322,19 @@ alpm_list_t *alpm_db_get_servers(const alpm_db_t *db);
- /** Sets the list of servers for the database to use.
-  * @param db the database to set the servers. The list will be duped and
-  * the original will still need to be freed by the caller.
-+ * @param cacheservers a char* list of cacheservers.
-  * @param servers a char* list of servers.
-  */
--int alpm_db_set_servers(alpm_db_t *db, alpm_list_t *servers);
-+int alpm_db_set_servers(alpm_db_t *db, alpm_list_t *cacheservers,
-+		alpm_list_t *servers);
- 
- /** Add a download server to a database.
-  * @param db database pointer
-  * @param url url of the server
-+ * @param cache 0 for regular server, 1 for cacheserver
-  * @return 0 on success, -1 on error (pm_errno is set accordingly)
-  */
--int alpm_db_add_server(alpm_db_t *db, const char *url);
-+int alpm_db_add_server(alpm_db_t *db, const char *url, const int cache);
- 
- /** Remove a download server from a database.
-  * @param db database pointer
-diff --git a/lib/libalpm/db.c b/lib/libalpm/db.c
-index ece8eae6..e9bca9c8 100644
---- a/lib/libalpm/db.c
-+++ b/lib/libalpm/db.c
-@@ -36,6 +36,7 @@
- #include "alpm.h"
- #include "package.h"
- #include "group.h"
-+#include "dload.h"
- 
- alpm_db_t SYMEXPORT *alpm_register_syncdb(alpm_handle_t *handle,
- 		const char *treename, int siglevel)
-@@ -137,14 +138,22 @@ alpm_list_t SYMEXPORT *alpm_db_get_servers(const alpm_db_t *db)
- 	return db->servers;
- }
- 
--int SYMEXPORT alpm_db_set_servers(alpm_db_t *db, alpm_list_t *servers)
-+int SYMEXPORT alpm_db_set_servers(alpm_db_t *db, alpm_list_t *cacheservers,
-+		alpm_list_t *servers)
- {
- 	alpm_list_t *i;
- 	ASSERT(db != NULL, return -1);
-+	FREELIST(db->cacheservers);
- 	FREELIST(db->servers);
-+	for(i = cacheservers; i; i = i->next) {
-+		char *url = i->data;
-+		if(alpm_db_add_server(db, url, 1) != 0) {
-+			return -1;
-+		}
-+	}
- 	for(i = servers; i; i = i->next) {
- 		char *url = i->data;
--		if(alpm_db_add_server(db, url) != 0) {
-+		if(alpm_db_add_server(db, url, 0) != 0) {
- 			return -1;
- 		}
- 	}
-@@ -164,7 +173,7 @@ static char *sanitize_url(const char *url)
- 	return newurl;
- }
- 
--int SYMEXPORT alpm_db_add_server(alpm_db_t *db, const char *url)
-+int SYMEXPORT alpm_db_add_server(alpm_db_t *db, const char *url, const int cache)
- {
- 	char *newurl;
- 
-@@ -178,8 +187,11 @@ int SYMEXPORT alpm_db_add_server(alpm_db_t *db, const char *url)
- 		return -1;
- 	}
- 	db->servers = alpm_list_add(db->servers, newurl);
--	_alpm_log(db->handle, ALPM_LOG_DEBUG, "adding new server URL to database '%s': %s\n",
--			db->treename, newurl);
-+	if(cache) {
-+		server_make_cache(db->handle, newurl);
-+	}
-+	_alpm_log(db->handle, ALPM_LOG_DEBUG, "adding new %sserver URL to database '%s': %s\n",
-+			cache ? "cache " : "", db->treename, newurl);
- 
- 	return 0;
- }
-diff --git a/lib/libalpm/db.h b/lib/libalpm/db.h
-index c9400365..50812e28 100644
---- a/lib/libalpm/db.h
-+++ b/lib/libalpm/db.h
-@@ -69,6 +69,7 @@ struct _alpm_db_t {
- 	char *_path;
- 	alpm_pkghash_t *pkgcache;
- 	alpm_list_t *grpcache;
-+	alpm_list_t *cacheservers;
- 	alpm_list_t *servers;
- 	const struct db_operations *ops;
- 
-diff --git a/lib/libalpm/dload.c b/lib/libalpm/dload.c
-index 7c27c3ea..3b3e5dc4 100644
---- a/lib/libalpm/dload.c
-+++ b/lib/libalpm/dload.c
-@@ -62,15 +62,16 @@ static int curl_gethost(const char *url, char *buffer, size_t buf_len);
-  * server blacklisting */
- const unsigned int server_error_limit = 3;
- 
--struct server_error_count {
-+struct server_opts {
- 	char server[HOSTNAME_SIZE];
-+	unsigned int cache;
- 	unsigned int errors;
- };
- 
--static struct server_error_count *find_server_errors(alpm_handle_t *handle, const char *server)
-+static struct server_opts *find_server_errors(alpm_handle_t *handle, const char *server)
- {
- 	alpm_list_t *i;
--	struct server_error_count *h;
-+	struct server_opts *h;
- 	char hostname[HOSTNAME_SIZE];
- 	/* key off the hostname because a host may serve multiple repos under
- 	 * different url's and errors are likely to be host-wide */
-@@ -83,7 +84,7 @@ static struct server_error_count *find_server_errors(alpm_handle_t *handle, cons
- 			return h;
- 		}
- 	}
--	if((h = calloc(sizeof(struct server_error_count), 1))
-+	if((h = calloc(sizeof(struct server_opts), 1))
- 			&& alpm_list_append(&handle->server_errors, h)) {
- 		strcpy(h->server, hostname);
- 		h->errors = 0;
-@@ -94,9 +95,38 @@ static struct server_error_count *find_server_errors(alpm_handle_t *handle, cons
- 	}
- }
- 
-+static int is_cache_server(alpm_handle_t *handle, const char *server)
-+{
-+	struct server_opts *h;
-+	if((h = find_server_errors(handle, server))) {
-+		return h->cache;
-+	}
-+	return 0;
-+}
-+
-+static int should_skip_cacheserver(alpm_handle_t *handle, const char *server, const char *filepath)
-+{
-+	if(!is_cache_server(handle, server)) {
-+		return 0;
-+	}
-+	if(filepath) {
-+		int len = strlen(filepath);
-+		return (len > 3 && strncmp(filepath + len - 3, ".db", 3) == 0) ? 1 : 0;
-+	}
-+	return 0;
-+}
-+
-+void server_make_cache(alpm_handle_t *handle, const char *server)
-+{
-+	struct server_opts *h;
-+	if((h = find_server_errors(handle, server))) {
-+		h->cache = 1;
-+	}
-+}
-+
- static int should_skip_server(alpm_handle_t *handle, const char *server)
- {
--	struct server_error_count *h;
-+	struct server_opts *h;
- 	if(server_error_limit && (h = find_server_errors(handle, server)) ) {
- 		return h->errors >= server_error_limit;
- 	}
-@@ -105,9 +135,10 @@ static int should_skip_server(alpm_handle_t *handle, const char *server)
- 
- static void server_increment_error(alpm_handle_t *handle, const char *server, int count)
- {
--	struct server_error_count *h;
-+	struct server_opts *h;
- 	if(server_error_limit
- 			&& (h = find_server_errors(handle, server))
-+			&& !is_cache_server(handle, server)
- 			&& !should_skip_server(handle, server) ) {
- 		h->errors += count;
- 
-@@ -414,7 +445,8 @@ static int curl_retry_next_server(CURLM *curlm, CURL *curl, struct dload_payload
- 	struct stat st;
- 	alpm_handle_t *handle = payload->handle;
- 
--	while(payload->servers && should_skip_server(handle, payload->servers->data)) {
-+	while(payload->servers && (should_skip_server(handle, payload->servers->data)
-+				|| should_skip_cacheserver(handle, payload->servers->data, payload->filepath))) {
- 		payload->servers = payload->servers->next;
- 	}
- 	if(!payload->servers) {
-@@ -511,7 +543,7 @@ static int curl_check_finished_download(CURLM *curlm, CURLMsg *msg,
- 					/* non-translated message is same as libcurl */
- 					snprintf(payload->error_buffer, sizeof(payload->error_buffer),
- 							"The requested URL returned error: %ld", payload->respcode);
--					_alpm_log(handle, ALPM_LOG_ERROR,
-+					_alpm_log(handle, is_cache_server(handle, payload->fileurl) ? ALPM_LOG_DEBUG : ALPM_LOG_ERROR,
- 							_("failed retrieving file '%s' from %s : %s\n"),
- 							payload->remote_name, hostname, payload->error_buffer);
- 					server_soft_error(handle, payload->fileurl);
-@@ -769,7 +801,9 @@ static int curl_add_payload(alpm_handle_t *handle, CURLM *curlm,
- 		ASSERT(!payload->filepath, GOTO_ERR(handle, ALPM_ERR_WRONG_ARGS, cleanup));
- 	} else {
- 		const char *server;
--		while(payload->servers && should_skip_server(handle, payload->servers->data)) {
-+
-+		while(payload->servers && (should_skip_server(handle, payload->servers->data)
-+					|| should_skip_cacheserver(handle, payload->servers->data, payload->filepath))) {
- 			payload->servers = payload->servers->next;
- 		}
- 
-diff --git a/lib/libalpm/dload.h b/lib/libalpm/dload.h
-index 9438e04a..d117244d 100644
---- a/lib/libalpm/dload.h
-+++ b/lib/libalpm/dload.h
-@@ -58,6 +58,8 @@ struct dload_payload {
- #endif
- };
- 
-+void server_make_cache(alpm_handle_t *handle, const char *server);
-+
- void _alpm_dload_payload_reset(struct dload_payload *payload);
- 
- int _alpm_download(alpm_handle_t *handle,
-diff --git a/src/pacman/conf.c b/src/pacman/conf.c
-index f9edf75b..04bb478b 100644
---- a/src/pacman/conf.c
-+++ b/src/pacman/conf.c
-@@ -172,6 +172,7 @@ void config_repo_free(config_repo_t *repo)
- 		return;
- 	}
- 	free(repo->name);
-+	FREELIST(repo->cacheservers);
- 	FREELIST(repo->servers);
- 	free(repo);
- }
-@@ -781,9 +782,9 @@ static char *replace_server_vars(config_t *c, config_repo_t *r, const char *s)
- 	}
- }
- 
--static int _add_mirror(alpm_db_t *db, char *value)
-+static int _add_mirror(alpm_db_t *db, char *value, const int cache)
- {
--	if(alpm_db_add_server(db, value) != 0) {
-+	if(alpm_db_add_server(db, value, cache) != 0) {
- 		/* pm_errno is set by alpm_db_setserver */
- 		pm_printf(ALPM_LOG_ERROR, _("could not add server URL to database '%s': %s (%s)\n"),
- 				alpm_db_get_name(db), value, alpm_strerror(alpm_errno(config->handle)));
-@@ -809,8 +810,14 @@ static int register_repo(config_repo_t *repo)
- 			repo->usage, repo->name);
- 	alpm_db_set_usage(db, repo->usage);
- 
-+	for(i = repo->cacheservers; i; i = alpm_list_next(i)) {
-+		if(_add_mirror(db, i->data, 1) != 0) {
-+			return 1;
-+		}
-+	}
-+
- 	for(i = repo->servers; i; i = alpm_list_next(i)) {
--		if(_add_mirror(db, i->data) != 0) {
-+		if(_add_mirror(db, i->data, 0) != 0) {
- 			return 1;
- 		}
- 	}
-@@ -993,6 +1000,9 @@ static int _parse_repo(const char *key, char *value, const char *file,
- 	if(strcmp(key, "Server") == 0) {
- 		CHECK_VALUE(value);
- 		repo->servers = alpm_list_add(repo->servers, strdup(value));
-+	} else if(strcmp(key, "CacheServer") == 0) {
-+		CHECK_VALUE(value);
-+		repo->cacheservers = alpm_list_add(repo->cacheservers, strdup(value));
- 	} else if(strcmp(key, "SigLevel") == 0) {
- 		CHECK_VALUE(value);
- 		alpm_list_t *values = NULL;
-diff --git a/src/pacman/conf.h b/src/pacman/conf.h
-index f7916ca9..f242f522 100644
---- a/src/pacman/conf.h
-+++ b/src/pacman/conf.h
-@@ -37,6 +37,7 @@ typedef struct __colstr_t {
- 
- typedef struct __config_repo_t {
- 	char *name;
-+	alpm_list_t *cacheservers;
- 	alpm_list_t *servers;
- 	int usage;
- 	int siglevel;
-diff --git a/src/pacman/pacman-conf.c b/src/pacman/pacman-conf.c
-index a9d1f52b..db648d4c 100644
---- a/src/pacman/pacman-conf.c
-+++ b/src/pacman/pacman-conf.c
-@@ -236,6 +236,7 @@ static void dump_repo(config_repo_t *repo)
- {
- 	show_usage("Usage", repo->usage);
- 	show_siglevel("SigLevel", repo->siglevel, 0);
-+	show_list_str("CacheServer", repo->cacheservers);
- 	show_list_str("Server", repo->servers);
- }
- 
diff --git a/patches/0001-support-http-header-Cache-Control-no-cache-for-soft-failure.patch b/patches/0001-support-http-header-Cache-Control-no-cache-for-soft-failure.patch
deleted file mode 100644
index 17154a9..0000000
--- a/patches/0001-support-http-header-Cache-Control-no-cache-for-soft-failure.patch
+++ /dev/null
@@ -1,69 +0,0 @@
-From b2d83e4d7e17d2a6d1fe8efa19e74d4f1eb1d64c Mon Sep 17 00:00:00 2001
-From: Christian Hesse <mail@eworm.de>
-Date: Fri, 21 May 2021 09:52:34 +0200
-Subject: [PATCH 1/1] support http header 'Cache-Control: no-cache' for soft
- failure
-
-The idea has been borrowed from cloud providers' reverse proxies and
-load balancers. These accept http headers to control caching behaviour,
-even to control 'negative caching' when error codes are returned.
-
-By setting the http header 'Cache-Control: no-cache' when returning with
-the status code 404 (not found) the server can indicate that this is a
-soft failure. No error message is shown, and server's error count is
-not increased.
-
-This can be used by servers that are not expected to be complete, for
-example when serving a local cache [0]. In nginx this can be achived by
-acting on error_page and sending the extra header by adding a directive:
-
-    server {
-        listen 8080 default_server;
-        root /var/cache/pacman/pkg;
-        error_page 404 = @no-cache;
-        location @no-cache {
-            add_header Cache-Control "no-cache" always;
-        }
-    }
-
-Also this is a perfect match for pacredir [1].
-
-[0] https://wiki.archlinux.org/title/Pacman/Tips_and_tricks#Network_shared_pacman_cache
-[1] https://git.eworm.de/cgit/pacredir/about/
-
-Signed-off-by: Christian Hesse <mail@eworm.de>
----
- lib/libalpm/dload.c | 11 +++++++++++
- 1 file changed, 11 insertions(+)
-
-diff --git a/lib/libalpm/dload.c b/lib/libalpm/dload.c
-index 4fa17b35..74462bba 100644
---- a/lib/libalpm/dload.c
-+++ b/lib/libalpm/dload.c
-@@ -274,8 +274,10 @@ static size_t dload_parseheader_cb(void *ptr, size_t size, size_t nmemb, void *u
- {
- 	size_t realsize = size * nmemb;
- 	const char *fptr, *endptr = NULL;
-+	const char * const cc_header = "Cache-Control:";
- 	const char * const cd_header = "Content-Disposition:";
- 	const char * const fn_key = "filename=";
-+	const char * const nc_key = "no-cache";
- 	struct dload_payload *payload = (struct dload_payload *)user;
- 	long respcode;
- 
-@@ -302,6 +304,15 @@ static size_t dload_parseheader_cb(void *ptr, size_t size, size_t nmemb, void *u
- 		}
- 	}
- 
-+	/* By setting the http header 'Cache-Control: no-cache' the server can indicate
-+	   that this is a soft failure which should not be cached. No error message is
-+	   shown, and server's error count is not increased. */
-+	if(_alpm_raw_ncmp(cc_header, ptr, strlen(cc_header)) == 0) {
-+		if(strstr(ptr, nc_key)) {
-+			payload->errors_ok = 1;
-+		}
-+	}
-+
- 	curl_easy_getinfo(payload->curl, CURLINFO_RESPONSE_CODE, &respcode);
- 	if(payload->respcode != respcode) {
- 		payload->respcode = respcode;