awk: more efficient -f FILE, document what "some trick in next_token" is

function                                             old     new   delta
awk_main                                             890     898      +8

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 24 insertions, 9 deletions

diff --git a/editors/awk.c b/editors/awk.c
index 5f1d670a4..1b23c17d2 100644
--- a/editors/awk.c
+++ b/editors/awk.c
@@ -1217,6 +1217,8 @@ static uint32_t next_token(uint32_t expected)
                         if (!isalnum_(*p))
                                 syntax_error(EMSG_UNEXP_TOKEN); /* no */
                         /* yes */
+/* "move name one char back" trick: we need a byte for NUL terminator */
+/* NB: this results in argv[i][-1] being used (!!!) in e.g. "awk -e 'NAME'" case */
                         t_string = --p;
                         while (isalnum_(*++p)) {
                                 p[-1] = *p;
@@ -3345,7 +3347,7 @@ int awk_main(int argc UNUSED_PARAM, char **argv)
 #if ENABLE_FEATURE_AWK_GNU_EXTENSIONS
         llist_t *list_e = NULL;
 #endif
-        int i, j;
+        int i;
         var *v;
         var tv;
         char **envp;
@@ -3417,30 +3419,43 @@ int awk_main(int argc UNUSED_PARAM, char **argv)
                         bb_show_usage();
         }
         while (list_f) {
-                char *s = NULL;
-                FILE *from_file;
+                int fd;
+                char *s;
 
                 g_progname = llist_pop(&list_f);
-                from_file = xfopen_stdin(g_progname);
-                /* one byte is reserved for some trick in next_token */
-                for (i = j = 1; j > 0; i += j) {
-                        s = xrealloc(s, i + 4096);
-                        j = fread(s + i, 1, 4094, from_file);
+                fd = xopen_stdin(g_progname);
+                /* 1st byte is reserved for "move name one char back" trick in next_token */
+                i = 1;
+                s = NULL;
+                for (;;) {
+                        int sz;
+                        s = xrealloc(s, i + 1000);
+                        sz = safe_read(fd, s + i, 1000);
+                        if (sz <= 0)
+                                break;
+                        i += sz;
                 }
+                s = xrealloc(s, i + 1); /* trim unused 999 bytes */
                 s[i] = '\0';
-                fclose(from_file);
+                close(fd);
                 parse_program(s + 1);
                 free(s);
         }
         g_progname = "cmd. line";
 #if ENABLE_FEATURE_AWK_GNU_EXTENSIONS
         while (list_e) {
+                /* NB: "move name one char back" trick in next_token
+                 * can use argv[i][-1] here.
+                 */
                 parse_program(llist_pop(&list_e));
         }
 #endif
         if (!(opt & (OPT_f | OPT_e))) {
                 if (!*argv)
                         bb_show_usage();
+                /* NB: "move name one char back" trick in next_token
+                 * can use argv[i][-1] here.
+                 */
                 parse_program(*argv++);
         }