Use resfo for parsing headers in UNRST file

Using resdata to ask for headers implies reading the entire file which
requires excessive memory.

Porting more of res2df to use resfo is postponed to a future issue.

Before this commit, obtaining the RST information for one particular
date in a 118GB UNRST file was not possible (requires at least more than
118GB of available memory). With this commit, the same operation can be
done in arund 6 GB of used memory.

mypy.ini

@@ -3,6 +3,9 @@
 [mypy-resdata.*]
 ignore_missing_imports = True
 
+[mypy-resfo.*]
+ignore_missing_imports = True
+
 [mypy-opm.*]
 ignore_missing_imports = True
 

res2df/grid.py

@@ -23,6 +23,7 @@
 import pandas as pd
 import pyarrow
 import pyarrow.feather
+import resfo
 from resdata.resfile import ResdataFile
 
 from .__version__ import __version__
@@ -199,11 +200,12 @@ def rst2df(
     # for all active cells:
     activecells = resdatafiles.get_egrid().getNumActive()
     rstvectors = []
-    for vec in resdatafiles.get_rstfile().headers:
-        if vec[1] == activecells and any(
-            fnmatch.fnmatch(vec[0], key) for key in vectors
+    for vec in resfo.lazy_read(resdatafiles.get_rstfilename()):
+        keyword_name = vec.read_keyword().strip()
+        if vec.read_length() == activecells and any(
+            fnmatch.fnmatch(keyword_name, key) for key in vectors
         ):
-            rstvectors.append(vec[0])
+            rstvectors.append(keyword_name)
     rstvectors = list(set(rstvectors))  # Make unique list
     # Note that all of these might not exist at all timesteps.
 

setup.py

@@ -17,6 +17,7 @@
 SETUP_REQUIREMENTS = ["setuptools>=28", "setuptools_scm"]
 REQUIREMENTS = [
     "resdata>=5.0.0-b0",
+    "resfo",
     "numpy",
     "opm>=2020.10.2",
     "pandas",