Add libString.
diff --git a/src/libString/s_rdinstack.c b/src/libString/s_rdinstack.c
new file mode 100644
index 0000000..de12d21
--- /dev/null
+++ b/src/libString/s_rdinstack.c
@@ -0,0 +1,141 @@
+
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+#include "libString.h"
+
+struct Sinstack{
+ int depth;
+ Biobuf *fp[32]; /* hard limit to avoid infinite recursion */
+};
+
+/* initialize */
+extern Sinstack *
+s_allocinstack(char *file)
+{
+ Sinstack *sp;
+ Biobuf *fp;
+
+ fp = Bopen(file, OREAD);
+ if(fp == nil)
+ return nil;
+
+ sp = malloc(sizeof *sp);
+ sp->depth = 0;
+ sp->fp[0] = fp;
+ return sp;
+}
+
+extern void
+s_freeinstack(Sinstack *sp)
+{
+ while(sp->depth >= 0)
+ Bterm(sp->fp[sp->depth--]);
+ free(sp);
+}
+
+/* Append an input line to a String.
+ *
+ * Empty lines and leading whitespace are removed.
+ */
+static char *
+rdline(Biobuf *fp, String *to)
+{
+ int c;
+ int len = 0;
+
+ c = Bgetc(fp);
+
+ /* eat leading white */
+ while(c==' ' || c=='\t' || c=='\n' || c=='\r')
+ c = Bgetc(fp);
+
+ if(c < 0)
+ return 0;
+
+ for(;;){
+ switch(c) {
+ case -1:
+ goto out;
+ case '\\':
+ c = Bgetc(fp);
+ if (c != '\n') {
+ s_putc(to, '\\');
+ s_putc(to, c);
+ len += 2;
+ }
+ break;
+ case '\r':
+ break;
+ case '\n':
+ if(len != 0)
+ goto out;
+ break;
+ default:
+ s_putc(to, c);
+ len++;
+ break;
+ }
+ c = Bgetc(fp);
+ }
+out:
+ s_terminate(to);
+ return to->ptr - len;
+}
+
+/* Append an input line to a String.
+ *
+ * Returns a pointer to the character string (or 0).
+ * Leading whitespace and newlines are removed.
+ * Lines starting with #include cause us to descend into the new file.
+ * Empty lines and other lines starting with '#' are ignored.
+ */
+extern char *
+s_rdinstack(Sinstack *sp, String *to)
+{
+ char *p;
+ Biobuf *fp, *nfp;
+
+ s_terminate(to);
+ fp = sp->fp[sp->depth];
+
+ for(;;){
+ p = rdline(fp, to);
+ if(p == nil){
+ if(sp->depth == 0)
+ break;
+ Bterm(fp);
+ sp->depth--;
+ return s_rdinstack(sp, to);
+ }
+
+ if(strncmp(p, "#include", 8) == 0 && (p[8] == ' ' || p[8] == '\t')){
+ to->ptr = p;
+ p += 8;
+
+ /* sanity (and looping) */
+ if(sp->depth >= nelem(sp->fp))
+ sysfatal("s_recgetline: includes too deep");
+
+ /* skip white */
+ while(*p == ' ' || *p == '\t')
+ p++;
+
+ nfp = Bopen(p, OREAD);
+ if(nfp == nil)
+ continue;
+ sp->depth++;
+ sp->fp[sp->depth] = nfp;
+ return s_rdinstack(sp, to);
+ }
+
+ /* got milk? */
+ if(*p != '#')
+ break;
+
+ /* take care of comments */
+ to->ptr = p;
+ s_terminate(to);
+ }
+ return p;
+}
