4 files changed, 108 insertions, 6 deletions
diff --git a/source/html.c b/source/html.c
index d1e28f8..d13ac5b 100644
--- a/source/html.c
+++ b/source/html.c
@@ -258,6 +258,85 @@ ssize_t html_ntxt(const char *txt, size_t len)
 	return left;
 }
 
+/*
+ * git ends a line only at a line feed. A browser also starts one at a carriage
+ * return with no line feed after it, since the HTML parser turns that into a
+ * line feed, and may at the other characters Unicode makes mandatory breaks.
+ * Escaping those keeps one line on the page for every line git counts, so the
+ * numbers beside the text stay in step with it.
+ */
+const char *html_line_break_escape(const char *p, const char *end, size_t *width)
+{
+	const char *esc;
+
+	switch ((unsigned char)*p) {
+	case '\r':
+		// The parser reads CR LF as the single line feed git ends the
+		// line with.
+		if (p + 1 < end && p[1] == '\n')
+			return NULL;
+		*width = 1;
+		return "\\r";
+	case '\v':
+		*width = 1;
+		return "\\v";
+	case '\f':
+		*width = 1;
+		return "\\f";
+	case 0xc2:
+		if (end - p < 2 || memcmp(p, "\xc2\x85", 2))
+			return NULL;
+		*width = 2;
+		return "\\u0085";
+	case 0xe2:
+		if (end - p >= 3 && !memcmp(p, "\xe2\x80\xa8", 3))
+			esc = "\\u2028";
+		else if (end - p >= 3 && !memcmp(p, "\xe2\x80\xa9", 3))
+			esc = "\\u2029";
+		else
+			return NULL;
+		*width = 3;
+		return esc;
+	default:
+		return NULL;
+	}
+}
+
+void html_blob_txt(const char *txt, size_t len)
+{
+	const char *end = txt + len;
+	const char *p;
+
+	for (p = txt; p < end; p++) {
+		const char *entity = NULL, *esc = NULL;
+		size_t width = 1;
+
+		if (*p == '<')
+			entity = "&lt;";
+		else if (*p == '>')
+			entity = "&gt;";
+		else if (*p == '&')
+			entity = "&amp;";
+		else
+			esc = html_line_break_escape(p, end, &width);
+		if (!entity && !esc)
+			continue;
+		html_raw(txt, p - txt);
+		if (entity) {
+			html(entity);
+		} else {
+			// The span lets a stylesheet tell the escape from the
+			// same characters typed into the file.
+			html("<span class='escape'>");
+			html(esc);
+			html("</span>");
+		}
+		p += width - 1;
+		txt = p + 1;
+	}
+	html_raw(txt, end - txt);
+}
+
 void html_attrf(const char *format, ...)
 {
 	va_list args;
diff --git a/source/html.h b/source/html.h
index c6c0e19..9cad3a6 100644
--- a/source/html.h
+++ b/source/html.h
@@ -61,6 +61,19 @@ extern void html_txt(const char *txt);
  */
 extern ssize_t html_ntxt(const char *txt, size_t len);
 
+/*
+ * The escape sequence a blob's text shows for the character at p when a
+ * browser would start a new line at it though git does not, or NULL for any
+ * other character. The character's length in bytes is stored in width.
+ */
+extern const char *html_line_break_escape(const char *p, const char *end, size_t *width);
+
+/*
+ * Escape the text of a blob for the page beside its line numbers, writing
+ * each character html_line_break_escape names as its escape sequence.
+ */
+extern void html_blob_txt(const char *txt, size_t len);
+
 extern void html_attr(const char *txt);
 extern void html_url_path(const char *txt);
 
diff --git a/source/ui-blame.c b/source/ui-blame.c
index 8fd6c83..f60020c 100644
--- a/source/ui-blame.c
+++ b/source/ui-blame.c
@@ -211,6 +211,15 @@ static size_t line_width(struct blame_scoreboard *sb, int line)
 	size_t width = 0;
 
 	while (pos < end) {
+		size_t len;
+		const char *esc = html_line_break_escape(pos, end, &len);
+
+		// An escaped character takes the room of its escape sequence.
+		if (esc) {
+			width += strlen(esc);
+			pos += len;
+			continue;
+		}
 		width++;
 		if (*pos++ == '\t')
 			width = (width + TAB_WIDTH - 1) & ~(TAB_WIDTH - 1);
@@ -297,9 +306,10 @@ static void print_blame_page(const struct object_id *oid, const char *path,
 	cgit_tree_link("tree", NULL, NULL, ctx.qry.head, rev, path);
 	html(")</div>\n");
 
-	// A NUL past the window buffer_is_binary sniffs would end html_txt
-	// early while the hash and line number columns still cover the whole
-	// file, so a blob holding one anywhere is treated as binary too.
+	// A NUL past the window buffer_is_binary sniffs would end a Lua
+	// filter's output early while the hash and line number columns still
+	// cover the whole file, so a blob holding one anywhere is treated as
+	// binary too.
 	if (buffer_is_binary(buf, size) || memchr(buf, 0, size)) {
 		struct blame_entry *ent = sb.ent, *next;
 
@@ -334,7 +344,7 @@ static void print_blame_page(const struct object_id *oid, const char *path,
 		cgit_close_filter(ctx.repo->source_filter);
 		free(filter_arg);
 	} else {
-		html_txt(buf);
+		html_blob_txt(buf, size);
 	}
 	html("</code></pre>");
 
diff --git a/source/ui-tree.c b/source/ui-tree.c
index 13a9787..1d8bb3d 100644
--- a/source/ui-tree.c
+++ b/source/ui-tree.c
@@ -113,7 +113,7 @@ static void print_text_buffer(const char *filename, char *buf, size_t size)
 	}
 
 	html("<td class='lines'><pre><code>");
-	html_txt(buf);
+	html_blob_txt(buf, size);
 	html("</code></pre></td></tr></table>\n");
 }
 
@@ -188,7 +188,7 @@ static bool print_object(const struct object_id *oid, const char *path,
 		return false;
 	}
 	// buffer_is_binary only sniffs the front of the blob, and a NUL past
-	// that window would end the escaped text render early while the line
+	// that window would end a Lua filter's output early while the line
 	// number column still counts the whole file, so check the rest too.
 	is_binary = buffer_is_binary(buf, size) || memchr(buf, 0, size);