MEDIUM: pattern: Add support for virtual and optional files for patterns

Before this patch, it was not possible to use a list of patterns, map or a
list of acls, without an existing file.  However, it could be handy to just
use an ID, with no file on the disk. It is pretty useful for everyone
managing dynamically these lists. It could also be handy to try to load a
list from a file if it exists without failing if not. This way, it could be
possible to make a cold start without any file (instead of empty file),
dynamically add and del patterns, dump the list to the file periodically to
reuse it on reload (via an external process).

In this patch, we uses some prefixes to be able to use virtual or optional
files.

The default case remains unchanged. regular files are used. A filename, with
no prefix, is used as reference, and it must exist on the disk. With the
prefix "file@", the same is performed. Internally this prefix is
skipped. Thus the same file, with ou without "file@" prefix, references the
same list of patterns.

To use a virtual map, "virt@" prefix must be used. No file is read, even if
the following name looks like a file. It is just an ID. The prefix is part
of ID and must always be used.

To use a optional file, ie a file that may or may not exist on a disk at
startup, "opt@" prefix must be used. If the file exists, its content is
loaded. But HAProxy doesn't complain if not. The prefix is not part of
ID. For a given file, optional files and regular files reference the same
list of patterns.

This patch should fix the issue #2202.

include/haproxy/pattern-t.h

@@ -92,9 +92,11 @@ enum {
 	PAT_MATCH_NUM
 };
 
-#define PAT_REF_MAP 0x1 /* Set if the reference is used by at least one map. */
-#define PAT_REF_ACL 0x2 /* Set if the reference is used by at least one acl. */
-#define PAT_REF_SMP 0x4 /* Flag used if the reference contains a sample. */
+#define PAT_REF_MAP  0x01 /* Set if the reference is used by at least one map. */
+#define PAT_REF_ACL  0x02 /* Set if the reference is used by at least one acl. */
+#define PAT_REF_SMP  0x04 /* Flag used if the reference contains a sample. */
+#define PAT_REF_FILE 0x08 /* Set if the reference was loaded from a file */
+#define PAT_REF_ID   0x10 /* Set if the reference is only an ID (not loaded from a file) */
 
 /* This struct contain a list of reference strings for dunamically
  * updatable patterns.

src/pattern.c

@@ -1547,6 +1547,10 @@ struct pat_ref *pat_ref_lookup(const char *reference)
 {
 	struct pat_ref *ref;
 
+	/* Skip file@ prefix, it is the default case. Can be mixed with ref omitting the prefix */
+	if (strlen(reference) > 5 && strncmp(reference, "file@", 5) == 0)
+		reference += 5;
+
 	list_for_each_entry(ref, &pattern_reference, list)
 		if (ref->reference && strcmp(reference, ref->reference) == 0)
 			return ref;
@@ -1818,6 +1822,22 @@ struct pat_ref *pat_ref_new(const char *reference, const char *display, unsigned
 		}
 	}
 
+
+	if (strlen(reference) > 5 && strncmp(reference, "virt@", 5) == 0)
+		flags |= PAT_REF_ID;
+	else if (strlen(reference) > 4 && strncmp(reference, "opt@", 4) == 0) {
+		flags |= (PAT_REF_ID|PAT_REF_FILE); // Will be decided later
+		reference += 4;
+	}
+	else {
+		/* A file by default */
+		flags |= PAT_REF_FILE;
+		/* Skip file@ prefix to be mixed with ref omitting the prefix */
+		if (strlen(reference) > 5 && strncmp(reference, "file@", 5) == 0)
+			reference += 5;
+	}
+
+
 	ref->reference = strdup(reference);
 	if (!ref->reference) {
 		free(ref->display);
@@ -2236,9 +2256,15 @@ int pat_ref_read_from_file_smp(struct pat_ref *ref, char **err)
 
 	file = fopen(ref->reference, "r");
 	if (!file) {
+		if (ref->flags & PAT_REF_ID) {
+			/* file not found for an optional file, switch it to a virtual list of patterns */
+			ref->flags &= ~PAT_REF_FILE;
+			return 1;
+		}
 		memprintf(err, "failed to open pattern file <%s>", ref->reference);
 		return 0;
 	}
+	ref->flags |= PAT_REF_FILE;
 
 	/* now parse all patterns. The file may contain only one pattern
 	 * followed by one value per line. The start spaces, separator spaces
@@ -2318,6 +2344,11 @@ int pat_ref_read_from_file(struct pat_ref *ref, char **err)
 
 	file = fopen(ref->reference, "r");
 	if (!file) {
+		if (ref->flags & PAT_REF_ID) {
+			/* file not found for an optional file, switch it to a virtual list of patterns */
+			ref->flags &= ~PAT_REF_FILE;
+			return 1;
+		}
 		memprintf(err, "failed to open pattern file <%s>", ref->reference);
 		return 0;
 	}
@@ -2391,14 +2422,16 @@ int pattern_read_from_file(struct pattern_head *head, unsigned int refflags,
 			return 0;
 		}
 
-		if (load_smp) {
-			ref->flags |= PAT_REF_SMP;
-			if (!pat_ref_read_from_file_smp(ref, err))
-				return 0;
-		}
-		else {
-			if (!pat_ref_read_from_file(ref, err))
-				return 0;
+		if (ref->flags & PAT_REF_FILE) {
+			if (load_smp) {
+				ref->flags |= PAT_REF_SMP;
+				if (!pat_ref_read_from_file_smp(ref, err))
+					return 0;
+			}
+			else {
+				if (!pat_ref_read_from_file(ref, err))
+					return 0;
+			}
 		}
 	}
 	else {