wiretap: Add a file_gets variant that returns a pointer to the NUL terminator

When using file_gets it's very difficult to determine how many characters
were read, because you can't distinguish between an embedded NUL and
a short line (note that the last line in a file may not have an LF at the
end). While it's still possible to do it via prefilling the buffer with
non-zero values, doing that is cumbersome, inefficient and error-prone.
This new function makes the task much easier.

The "p" in the name is meant to be reminiscent of the "p" in stpcpy.

Change-Id: I468d5ee71e3b6289925860651ba61b369301b3c9
Reviewed-on: https://code.wireshark.org/review/27333
Petri-Dish: Stig Bjørlykke <stig@bjorlykke.org>
Tested-by: Petri Dish Buildbot
Reviewed-by: Stig Bjørlykke <stig@bjorlykke.org>

2 files changed, 13 insertions, 3 deletions

diff --git a/wiretap/file_wrappers.c b/wiretap/file_wrappers.c
index cae0cfc491..daf0798ce7 100644
--- a/wiretap/file_wrappers.c
+++ b/wiretap/file_wrappers.c
@@ -1398,8 +1398,9 @@ file_getc(FILE_T file)
     return ret < 1 ? -1 : buf[0];
 }
 
+/* Like file_gets, but returns a pointer to the terminating NUL. */
 char *
-file_gets(char *buf, int len, FILE_T file)
+file_getsp(char *buf, int len, FILE_T file)
 {
     guint left, n;
     char *str;
@@ -1461,9 +1462,17 @@ file_gets(char *buf, int len, FILE_T file)
             buf += n;
         } while (left && eol == NULL);
 
-    /* found end-of-line or out of space -- terminate string and return it */
+    /* found end-of-line or out of space -- add a terminator and return
+       a pointer to it */
     buf[0] = 0;
-    return str;
+    return buf;
+}
+
+char *
+file_gets(char *buf, int len, FILE_T file)
+{
+    if (!file_getsp(buf, len, file)) return NULL;
+    return buf;
 }
 
 int
diff --git a/wiretap/file_wrappers.h b/wiretap/file_wrappers.h
index 64e0b6b166..40fe9c9788 100644
--- a/wiretap/file_wrappers.h
+++ b/wiretap/file_wrappers.h
@@ -26,6 +26,7 @@ WS_DLL_PUBLIC int file_read(void *buf, unsigned int count, FILE_T file);
 WS_DLL_PUBLIC int file_peekc(FILE_T stream);
 WS_DLL_PUBLIC int file_getc(FILE_T stream);
 WS_DLL_PUBLIC char *file_gets(char *buf, int len, FILE_T stream);
+WS_DLL_PUBLIC char *file_getsp(char *buf, int len, FILE_T stream);
 WS_DLL_PUBLIC int file_eof(FILE_T stream);
 WS_DLL_PUBLIC int file_error(FILE_T fh, gchar **err_info);
 extern void file_clearerr(FILE_T stream);