input: pass larger buffer to auto format detection

The previous implementation already was inconsistent (used to allocate
255 bytes and claimed that 128 bytes were sufficient). While existing
formats already required more than a few bytes of input (regular VCD
files' header sections exceed 255 bytes length).

Increase the buffer size that gets passed to input modules' match
method. Use 4MiB for consistency with other locations. Do not enforce a
minimum size, as there are valid input files which are shorter than 128
bytes. Auto-detection failed on those.

This addresses part of bug #1200.

diff --git a/src/input/input.c b/src/input/input.c
index 48660d379b9b6e69fde4546cbe8f91a7a67669b9..ee19d66169ece22b67254fdf4c330afbcccb62c7 100644 (file)
--- a/src/input/input.c
+++ b/src/input/input.c
@@ -29,6 +29,8 @@
 #define LOG_PREFIX "input"
 /** @endcond */
 
+#define CHUNK_SIZE     (4 * 1024 * 1024)
+
 /**
  * @file
  *
@@ -338,8 +340,10 @@ static gboolean check_required_metadata(const uint8_t *metadata, uint8_t *avail)
  * Try to find an input module that can parse the given buffer.
  *
  * The buffer must contain enough of the beginning of the file for
- * the input modules to find a match. This is format-dependent, but
- * 128 bytes is normally enough.
+ * the input modules to find a match. This is format-dependent. When
+ * magic strings get checked, 128 bytes normally could be enough. Note
+ * that some formats try to parse larger header sections, and benefit
+ * from seeing a larger scope.
  *
  * If an input module is found, an instance is created into *in.
  * Otherwise, *in contains NULL. When multiple input moduless claim
@@ -462,11 +466,9 @@ SR_API int sr_input_scan_file(const char *filename, const struct sr_input **in)
                fclose(stream);
                return SR_ERR;
        }
-       /* This actually allocates 256 bytes to allow for NUL termination. */
-       header = g_string_sized_new(255);
+       header = g_string_sized_new(CHUNK_SIZE);
        count = fread(header->str, 1, header->allocated_len - 1, stream);
-
-       if (count != header->allocated_len - 1 && ferror(stream)) {
+       if (count < 1 || ferror(stream)) {
                sr_err("Failed to read %s: %s", filename, g_strerror(errno));
                fclose(stream);
                g_string_free(header, TRUE);