Do not change the referenced matched tag data (from gettag()).

Fixes a regression introduced in the refactor in commit
e43b7a48b08a6bbcb4e730e80395b3257681b33e

Now copy the data by value. This structure is small and no performance
regression has been seen.

This was because the tag ID was modified which made subsequent parsed tags of
this type behave strangely:

	ctx.tag->id = RSSTagGuidPermalinkTrue;

Input data to reproduce:

<rss>
<channel>

<item>
<guid isPermaLink="false">https://def/</guid>
</item>

<item>
<guid>https://abc/</guid>
</item>

</channel>
</rss>

1 files changed, 46 insertions, 39 deletions

diff --git a/sfeed.c b/sfeed.c
index 7eab8ab..b765852 100644
--- a/sfeed.c
+++ b/sfeed.c
@@ -90,7 +90,7 @@ enum {
 typedef struct feedcontext {
 	String          *field;        /* current FeedItem field String */
 	FeedField        fields[FeedFieldLast]; /* data for current item */
-	FeedTag          *tag;         /* unique current parsed tag */
+	FeedTag          tag;          /* unique current parsed tag */
 	int              iscontent;    /* in content data */
 	int              iscontenttag; /* in content tag */
 	enum ContentType contenttype;  /* content-type for item */
@@ -206,7 +206,7 @@ static const int FieldSeparator = '\t';
 static const char *FieldMultiSeparator = "|";
 static const char *baseurl = "";
 
-static FeedContext ctx = { .tag = &notag };
+static FeedContext ctx;
 static XMLParser parser; /* XML parser state */
 static String tmpstr;
 static enum ContentType tmpcontenttype; /* content-type for item */
@@ -687,7 +687,7 @@ xmlattr(XMLParser *p, const char *t, size_t tl, const char *n, size_t nl,
 		return;
 	}
 
-	if (!ctx.tag->id)
+	if (!ctx.tag.id)
 		return;
 
 	/* content-type may be: Atom: text, xhtml, html or mime-type.
@@ -709,36 +709,36 @@ xmlattr(XMLParser *p, const char *t, size_t tl, const char *n, size_t nl,
 	}
 
 	if (ctx.feedtype == FeedTypeRSS) {
-		if (ctx.tag->id == RSSTagEnclosure &&
+		if (ctx.tag.id == RSSTagEnclosure &&
 		    isattr(n, nl, STRP("url"))) {
 			string_append(&tmpstr, v, vl);
-		} else if ((ctx.tag->id == RSSTagGuid ||
-		            ctx.tag->id == RSSTagGuidPermalinkFalse ||
-			    ctx.tag->id == RSSTagGuidPermalinkTrue) &&
+		} else if ((ctx.tag.id == RSSTagGuid ||
+		            ctx.tag.id == RSSTagGuidPermalinkFalse ||
+			    ctx.tag.id == RSSTagGuidPermalinkTrue) &&
 		           isattr(n, nl, STRP("ispermalink"))) {
 			if (isattr(v, vl, STRP("true")))
-				ctx.tag->id = RSSTagGuidPermalinkTrue;
+				ctx.tag.id = RSSTagGuidPermalinkTrue;
 			else
-				ctx.tag->id = RSSTagGuidPermalinkFalse;
+				ctx.tag.id = RSSTagGuidPermalinkFalse;
 		}
 	} else if (ctx.feedtype == FeedTypeAtom) {
-		if (ctx.tag->id == AtomTagLink ||
-		    ctx.tag->id == AtomTagLinkAlternate ||
-		    ctx.tag->id == AtomTagLinkEnclosure) {
+		if (ctx.tag.id == AtomTagLink ||
+		    ctx.tag.id == AtomTagLinkAlternate ||
+		    ctx.tag.id == AtomTagLinkEnclosure) {
 			if (isattr(n, nl, STRP("rel"))) {
 				/* empty or "alternate": other types could be
 				   "enclosure", "related", "self" or "via" */
 				if (!vl || isattr(v, vl, STRP("alternate")))
-					ctx.tag->id = AtomTagLinkAlternate;
+					ctx.tag.id = AtomTagLinkAlternate;
 				else if (isattr(v, vl, STRP("enclosure")))
-					ctx.tag->id = AtomTagLinkEnclosure;
+					ctx.tag.id = AtomTagLinkEnclosure;
 				else
-					ctx.tag->id = AtomTagLink; /* unknown */
-			} else if (ctx.tag->id != AtomTagLink &&
+					ctx.tag.id = AtomTagLink; /* unknown */
+			} else if (ctx.tag.id != AtomTagLink &&
 			           isattr(n, nl, STRP("href"))) {
 				string_append(&tmpstr, v, vl);
 			}
-		} else if (ctx.tag->id == AtomTagCategory &&
+		} else if (ctx.tag.id == AtomTagCategory &&
 			   isattr(n, nl, STRP("term"))) {
 			string_append(&tmpstr, v, vl);
 		}
@@ -759,7 +759,7 @@ xmlattrentity(XMLParser *p, const char *t, size_t tl, const char *n, size_t nl,
 		return;
 	}
 
-	if (!ctx.tag->id)
+	if (!ctx.tag.id)
 		return;
 
 	/* try to translate entity, else just pass as data to
@@ -807,7 +807,7 @@ xmldata(XMLParser *p, const char *s, size_t len)
 	if (!ctx.field)
 		return;
 
-	if (ISFEEDFIELDMULTI(fieldmap[ctx.tag->id]))
+	if (ISFEEDFIELDMULTI(fieldmap[ctx.tag.id]))
 		string_append(&tmpstr, s, len);
 	else
 		string_append(ctx.field, s, len);
@@ -833,6 +833,8 @@ xmldataentity(XMLParser *p, const char *data, size_t datalen)
 static void
 xmltagstart(XMLParser *p, const char *t, size_t tl)
 {
+	FeedTag *f;
+
 	if (ISINCONTENT(ctx)) {
 		if (ctx.contenttype == ContentTypeHTML) {
 			ctx.attrcount = 0;
@@ -852,28 +854,31 @@ xmltagstart(XMLParser *p, const char *t, size_t tl)
 	}
 
 	/* field tagid already set or nested tags. */
-	if (ctx.tag->id) {
+	if (ctx.tag.id) {
 		/* nested <author><name> for Atom */
-		if (ctx.tag->id == AtomTagAuthor &&
+		if (ctx.tag.id == AtomTagAuthor &&
 		    istag(t, tl, STRP("name"))) {
-			ctx.tag = &atomtagauthorname;
+			memcpy(&(ctx.tag), &atomtagauthorname, sizeof(ctx.tag));
 		} else {
 			return; /* other nested tags are not allowed: return */
 		}
 	}
 
 	/* in item */
-	if (ctx.tag->id == TagUnknown && !(ctx.tag = gettag(ctx.feedtype, t, tl)))
-		ctx.tag = &notag;
+	if (ctx.tag.id == TagUnknown) {
+		if (!(f = gettag(ctx.feedtype, t, tl)))
+			f = &notag;
+		memcpy(&(ctx.tag), f, sizeof(ctx.tag));
+	}
 
-	switch (ctx.tag->id) {
+	switch (ctx.tag.id) {
 	case AtomTagLink:
 		/* without a rel attribute the default link type is "alternate" */
-		ctx.tag->id = AtomTagLinkAlternate;
+		ctx.tag.id = AtomTagLinkAlternate;
 		break;
 	case RSSTagGuid:
 		/* without a ispermalink attribute the default value is "true" */
-		ctx.tag->id = RSSTagGuidPermalinkTrue;
+		ctx.tag.id = RSSTagGuidPermalinkTrue;
 		break;
 	case RSSTagContentEncoded:
 	case RSSTagDescription:
@@ -907,7 +912,7 @@ xmltagstartparsed(XMLParser *p, const char *t, size_t tl, int isshort)
 		return;
 	}
 
-	tagid = ctx.tag->id;
+	tagid = ctx.tag.id;
 
 	/* map tag type to field: unknown or lesser priority is ignored,
 	   when tags of the same type are repeated only the first is used. */
@@ -928,7 +933,7 @@ xmltagstartparsed(XMLParser *p, const char *t, size_t tl, int isshort)
 
 	/* clear field if it is overwritten (with a priority order) for the new
 	   value, if the field can have multiple values then do not clear it. */
-	if (!ISFEEDFIELDMULTI(fieldmap[ctx.tag->id]))
+	if (!ISFEEDFIELDMULTI(fieldmap[ctx.tag.id]))
 		string_clear(ctx.field);
 }
 
@@ -942,7 +947,7 @@ xmltagend(XMLParser *p, const char *t, size_t tl, int isshort)
 
 	if (ISINCONTENT(ctx)) {
 		/* not close content field */
-		if (!istag(ctx.tag->name, ctx.tag->len, t, tl)) {
+		if (!istag(ctx.tag.name, ctx.tag.len, t, tl)) {
 			if (!isshort && ctx.contenttype == ContentTypeHTML) {
 				xmldata(p, "</", 2);
 				xmldata(p, t, tl);
@@ -950,18 +955,18 @@ xmltagend(XMLParser *p, const char *t, size_t tl, int isshort)
 			}
 			return;
 		}
-	} else if (ctx.tag->id && istag(ctx.tag->name, ctx.tag->len, t, tl)) {
+	} else if (ctx.tag.id && istag(ctx.tag.name, ctx.tag.len, t, tl)) {
 		/* matched tag end: close it */
 		/* copy also to the link field if the attribute isPermaLink="true"
 		    and it is not set by a tag with higher prio. */
-		if (ctx.tag->id == RSSTagGuidPermalinkTrue && ctx.field &&
-		    ctx.tag->id > ctx.fields[FeedFieldLink].tagid) {
+		if (ctx.tag.id == RSSTagGuidPermalinkTrue && ctx.field &&
+		    ctx.tag.id > ctx.fields[FeedFieldLink].tagid) {
 			string_clear(&ctx.fields[FeedFieldLink].str);
 			string_append(&ctx.fields[FeedFieldLink].str,
 			              ctx.field->data, ctx.field->len);
-			ctx.fields[FeedFieldLink].tagid = ctx.tag->id;
+			ctx.fields[FeedFieldLink].tagid = ctx.tag.id;
 		}
-	} else if (!ctx.tag->id && ((ctx.feedtype == FeedTypeAtom &&
+	} else if (!ctx.tag.id && ((ctx.feedtype == FeedTypeAtom &&
 	   istag(t, tl, STRP("entry"))) || /* Atom */
 	   (ctx.feedtype == FeedTypeRSS &&
 	   istag(t, tl, STRP("item"))))) /* RSS */
@@ -985,7 +990,7 @@ xmltagend(XMLParser *p, const char *t, size_t tl, int isshort)
 	   directly and need more context, for example by it's tag
 	   attributes, like the Atom link rel="alternate|enclosure". */
 	if (tmpstr.len && ctx.field) {
-		if (ISFEEDFIELDMULTI(fieldmap[ctx.tag->id])) {
+		if (ISFEEDFIELDMULTI(fieldmap[ctx.tag.id])) {
 			if (ctx.field->len)
 				string_append(ctx.field, FieldMultiSeparator, 1);
 			string_append(ctx.field, tmpstr.data, tmpstr.len);
@@ -998,10 +1003,10 @@ xmltagend(XMLParser *p, const char *t, size_t tl, int isshort)
 	/* close field */
 	string_clear(&tmpstr); /* reuse and clear temporary string */
 
-	if (ctx.tag->id == AtomTagAuthorName)
-		ctx.tag = &atomtagauthor; /* outer tag */
+	if (ctx.tag.id == AtomTagAuthorName)
+		memcpy(&(ctx.tag), &atomtagauthor, sizeof(ctx.tag)); /* outer tag */
 	else
-		ctx.tag = &notag;
+		memcpy(&(ctx.tag), &notag, sizeof(ctx.tag));
 
 	ctx.iscontent = 0;
 	ctx.field = NULL;
@@ -1016,6 +1021,8 @@ main(int argc, char *argv[])
 	if (argc > 1)
 		baseurl = argv[1];
 
+	memcpy(&(ctx.tag), &notag, sizeof(ctx.tag));
+
 	parser.xmlattr = xmlattr;
 	parser.xmlattrentity = xmlattrentity;
 	parser.xmlattrend = xmlattrend;