resource: Move sr_file_get_size() to resource.c

[libsigrok.git] / src / resource.c

diff --git a/src/resource.c b/src/resource.c
index b29be60863b0eb83584d04bfe777f75b6a666d46..bcb7a19146b59ef7ca6ea70372ae7a377d04d076 100644 (file)
--- a/src/resource.c
+++ b/src/resource.c
@@ -35,6 +35,47 @@
  * Access to resource files.
  */
 
+/** Retrieve the size of the open stream @a file.
+ *
+ * This function only works on seekable streams. However, the set of seekable
+ * streams is generally congruent with the set of streams that have a size.
+ * Code that needs to work with any type of stream (including pipes) should
+ * require neither seekability nor advance knowledge of the size.
+ * On failure, the return value is negative and errno is set.
+ *
+ * @param file An I/O stream opened in binary mode.
+ * @return The size of @a file in bytes, or a negative value on failure.
+ *
+ * @private
+ */
+SR_PRIV int64_t sr_file_get_size(FILE *file)
+{
+       off_t filepos, filesize;
+
+       /* ftello() and fseeko() are not standard C, but part of POSIX.1-2001.
+        * Thus, if these functions are available at all, they can reasonably
+        * be expected to also conform to POSIX semantics. In particular, this
+        * means that ftello() after fseeko(..., SEEK_END) has a defined result
+        * and can be used to get the size of a seekable stream.
+        * On Windows, the result is fully defined only for binary streams.
+        */
+       filepos = ftello(file);
+       if (filepos < 0)
+               return -1;
+
+       if (fseeko(file, 0, SEEK_END) < 0)
+               return -1;
+
+       filesize = ftello(file);
+       if (filesize < 0)
+               return -1;
+
+       if (fseeko(file, filepos, SEEK_SET) < 0)
+               return -1;
+
+       return filesize;
+}
+
 static FILE *try_open_file(const char *datadir, const char *subdir,
                const char *name)
 {