expose compression type (tf_ctype_t) via tf_read_file_header

Previously, decoding any header with a non-zero compression type would result in a `TF_EINVALID_COMPRESSION_TYPE` error. Since none
of the compression logic applies to the header itself, this limitation was removed. `tf_read_file_header` will only return a
(repurposed) `TF_EINVALID_COMPRESSION_TYPE` error when the compression type is not mapped within the library.

Currently 3 values (as described in the fseq file spec) are supported:

TF_COMPRESSION_NONE // 0
TF_COMPRESSION_ZSTD // 1
TF_COMPRESSION_ZLIB // 2
 # Please enter the
commit message for your changes. Lines starting # with '#' will be ignored, and an empty message aborts the commit.

Author: Cryptkeeper

tinyfseq.c

@@ -35,7 +35,7 @@ const char *tf_err_str(enum tf_err_t err) {
         case TF_EINVALID_MAGIC:
             return "TF_EINVALID_MAGIC (invalid magic file signature)";
         case TF_EINVALID_COMPRESSION_TYPE:
-            return "TF_EINVALID_COMPRESSION_TYPE (compressed files are not supported)";
+            return "TF_EINVALID_COMPRESSION_TYPE (unknown compression format/unmapped `tf_ctype_t` value)";
         case TF_EINVALID_VAR_HEADER_SIZE:
             return "TF_EINVALID_VAR_HEADER_SIZE (undersized `tf_var_header_t` data decoding buffer)";
         case TF_EINVALID_VAR_VALUE_SIZE:
@@ -50,6 +50,17 @@ const char *tf_err_str(enum tf_err_t err) {
 #endif
 }
 
+static inline int tf_is_known_ctype(uint8_t b) {
+    switch (b) {
+        case TF_COMPRESSION_NONE:
+        case TF_COMPRESSION_ZSTD:
+        case TF_COMPRESSION_ZLIB:
+            return 1;
+        default:
+            return 0;
+    }
+}
+
 enum tf_err_t tf_read_file_header(const uint8_t *bd, int bs, struct tf_file_header_t *header, uint8_t **ep) {
     // header structure is a fixed 32 byte size according to schema
     // https://github.com/Cryptkeeper/fseq-file-format#header
@@ -70,11 +81,15 @@ enum tf_err_t tf_read_file_header(const uint8_t *bd, int bs, struct tf_file_head
 
     // upper 4 bits contain additional compression block count data that is ignored by tinyfseq
     // mask to lower 4 bits to filter only the compression type field
-    if ((bd[20] & 0xF) != 0) {
+    const uint8_t compressionType = bd[20] & 0xF;
+    if (!tf_is_known_ctype(compressionType)) {
         return TF_EINVALID_COMPRESSION_TYPE;
     }
 
-    memcpy((unsigned char *) &header->channelRangeCount, &bd[22], 1);
+    header->compressionType = (enum tf_ctype_t) compressionType;
+
+    header->channelRangeCount = bd[22];
+
     memcpy((unsigned char *) &header->sequenceUid, &bd[24], 8);
 
     if (ep != NULL) {

tinyfseq.h

@@ -48,16 +48,23 @@ enum tf_err_t {
  */
 const char *tf_err_str(enum tf_err_t err);
 
+enum tf_ctype_t {
+    TF_COMPRESSION_NONE,
+    TF_COMPRESSION_ZSTD,
+    TF_COMPRESSION_ZLIB,
+};
+
 struct tf_file_header_t {
-    uint16_t channelDataOffset;
-    uint8_t  minorVersion;
-    uint8_t  majorVersion;
-    uint16_t variableDataOffset;
-    uint32_t channelCount;
-    uint32_t frameCount;
-    uint8_t  frameStepTimeMillis;
-    uint8_t  channelRangeCount;
-    uint64_t sequenceUid;
+    uint16_t        channelDataOffset;
+    uint8_t         minorVersion;
+    uint8_t         majorVersion;
+    uint16_t        variableDataOffset;
+    uint32_t        channelCount;
+    uint32_t        frameCount;
+    uint8_t         frameStepTimeMillis;
+    enum tf_ctype_t compressionType;
+    uint8_t         channelRangeCount;
+    uint64_t        sequenceUid;
 } __attribute__((packed));
 
 /**