allow LZW CRINEX, use magic number for loader

src/georinex/rio.py

@@ -32,28 +32,41 @@ def opener(fn: T.TextIO | Path, header: bool = False) -> T.Iterator[T.TextIO]:
         if finf.st_size > 100e6:
             logging.info(f"opening {finf.st_size/1e6} MByte {fn.name}")
 
+        # %% get magic number
+        """https://en.wikipedia.org/wiki/List_of_file_signatures"""
+        with fn.open("rb") as fid:
+            magic = fid.read(4)
+
         suffix = fn.suffix.lower()
 
-        if suffix == ".gz":
+        if suffix == ".gz" or magic.startswith(b"\x1f\x8b"):
             with gzip.open(fn, "rt") as f:
                 _, is_crinex = rinex_version(first_nonblank_line(f))
                 f.seek(0)
 
                 if is_crinex and not header:
-                    # Conversion to string is necessary because of a quirk where gzip.open()
-                    # even with 'rt' doesn't decompress until read.
+                    """
+                    gzip compressed CRINEX
+                    Conversion to string is necessary because of a quirk where gzip.open()
+                    even with 'rt' doesn't decompress until read.
+                    """
                     f = io.StringIO(crx2rnx(f.read()))
                 yield f
-        elif suffix == ".bz2":
-            # this is for plain bzip2 files, NOT tar.bz2, which requires f.seek(512)
+        elif suffix == ".bz2" or magic.startswith(b"\x42\x5a\x68"):
+            """
+            plain bzip2 files, NOT tar.bz2, which requires f.seek(512)
+            """
             with bz2.open(fn, "rt") as f:
                 _, is_crinex = rinex_version(first_nonblank_line(f))
                 f.seek(0)
 
                 if is_crinex and not header:
+                    """
+                    bzip2 compressed CRINEX
+                    """
                     f = io.StringIO(crx2rnx(f.read()))
                 yield f
-        elif suffix == ".zip":
+        elif suffix == ".zip" or magic.startswith(b"\x50\x4b"):
             with zipfile.ZipFile(fn, "r") as z:
                 flist = z.namelist()
                 for rinexfn in flist:
@@ -62,9 +75,17 @@ def opener(fn: T.TextIO | Path, header: bool = False) -> T.Iterator[T.TextIO]:
                             io.TextIOWrapper(bf, encoding="ascii", errors="ignore").read()  # type: ignore
                         )
                         yield f
-        elif suffix == ".z":
+        elif suffix == ".z" or magic.startswith(b"\x1f\x9d"):
             with fn.open("rb") as zu:
                 with io.StringIO(unlzw(zu.read()).decode("ascii")) as f:
+                    _, is_crinex = rinex_version(first_nonblank_line(f))
+                    f.seek(0)
+
+                    if is_crinex and not header:
+                        """
+                        LZW compressed CRINEX
+                        """
+                        f = io.StringIO(crx2rnx(f.read()))
                     yield f
         else:  # assume not compressed (or Hatanaka)
             with fn.open("r", encoding="ascii", errors="ignore") as f: