Export and clean up net downloading script

This patch moves out the net downloading script to an external script
file. Also the script is moderately rewritten for better readability
and speed.

* Use wget preferentially over curl, as curl is known to have
  small overheads.
* Use command insetad of hash to check if command exists. Reportedly,
  hash always returns zero in some POSIX shells even when the command
  fails.
* Command existence checks (wget/curl, sha256sum) are done only once at
  the beginning.
* Each of common patterns is grouped in a function. (get_nnue_filename,
  validate_network)
* Print out error/warning messages to stderr.

No functional change

scripts/net.sh

@@ -0,0 +1,75 @@
+#!/bin/sh
+
+wget_or_curl=$( (command -v wget > /dev/null 2>&1 && echo "wget -q") || \
+                (command -v curl > /dev/null 2>&1 && echo "curl -L -s -k"))
+
+if [ -z "$wget_or_curl" ]; then
+  >&2 printf "%s\n" "Neither wget or curl is installed." \
+	         "Install one of these tools to download NNUE files automatically."
+  exit 1
+fi
+
+sha256sum=$( (command -v shasum > /dev/null 2>&1 && echo "shasum -a 256") || \
+             (command -v sha256sum > /dev/null 2>&1 && echo "sha256sum"))
+
+if [ -z "$sha256sum" ]; then
+  >&2 echo "sha256sum not found, NNUE files will be assumed valid."
+fi
+
+get_nnue_filename() {
+  grep "$1" evaluate.h | grep "#define" | sed "s/.*\(nn-[a-z0-9]\{12\}.nnue\).*/\1/"
+}
+
+validate_network() {
+  # If no sha256sum command is available, assume the file is always valid.
+  if [ -n "$sha256sum" ] && [ -f "$1" ]; then
+    if [ "$1" != "nn-$($sha256sum "$1" | cut -c 1-12).nnue" ]; then
+      rm -f "$1"
+      return 1
+    fi
+  fi
+}
+
+fetch_network() {
+  _filename="$(get_nnue_filename "$1")"
+
+  if [ -z "$_filename" ]; then
+    >&2 echo "NNUE file name not found for: $1"
+    return 1
+  fi
+
+  if [ -f "$_filename" ]; then
+    if validate_network "$_filename"; then
+      echo "Existing $_filename validated, skipping download"
+      return
+    else
+      echo "Removing invalid NNUE file: $_filename"
+    fi
+  fi
+
+  for url in \
+    "https://tests.stockfishchess.org/api/nn/$_filename" \
+    "https://github.com/official-stockfish/networks/raw/master/$_filename"; do
+    echo "Downloading from $url ..."
+    if $wget_or_curl "$url"; then
+      if validate_network "$_filename"; then
+        echo "Successfully validated $_filename"
+      else
+        echo "Downloaded $_filename is invalid"
+        continue
+      fi
+    else
+      echo "Failed to download from $url"
+    fi
+    if [ -f "$_filename" ]; then
+      return
+    fi
+  done
+
+  # Download was not successful in the loop, return false.
+  >&2 echo "Failed to download $_filename"
+  return 1
+}
+
+fetch_network EvalFileDefaultNameBig && \
+fetch_network EvalFileDefaultNameSmall

src/Makefile

@@ -917,59 +917,9 @@ profileclean:
 	@rm -f stockfish.res
 	@rm -f ./-lstdc++.res
 
-define fetch_network
-	@echo "Default net: $(nnuenet)"
-	@if [ "x$(curl_or_wget)" = "x" ]; then \
-		echo "Neither curl nor wget is installed. Install one of these tools unless the net has been downloaded manually"; \
-	fi
-	@if [ "x$(shasum_command)" = "x" ]; then \
-		echo "shasum / sha256sum not found, skipping net validation"; \
-	elif test -f "$(nnuenet)"; then \
-		if [ "$(nnuenet)" != "nn-"`$(shasum_command) $(nnuenet) | cut -c1-12`".nnue" ]; then \
-			echo "Removing invalid network"; rm -f $(nnuenet); \
-		fi; \
-	fi;
-	@for nnuedownloadurl in "$(nnuedownloadurl1)" "$(nnuedownloadurl2)"; do \
-		if test -f "$(nnuenet)"; then \
-			echo "$(nnuenet) available : OK"; break; \
-		else \
-			if [ "x$(curl_or_wget)" != "x" ]; then \
-				echo "Downloading $${nnuedownloadurl}"; $(curl_or_wget) $${nnuedownloadurl} > $(nnuenet);\
-			else \
-				echo "No net found and download not possible"; exit 1;\
-			fi; \
-		fi; \
-		if [ "x$(shasum_command)" != "x" ]; then \
-			if [ "$(nnuenet)" != "nn-"`$(shasum_command) $(nnuenet) | cut -c1-12`".nnue" ]; then \
-				echo "Removing failed download"; rm -f $(nnuenet); \
-			fi; \
-		fi; \
-	done
-	@if ! test -f "$(nnuenet)"; then \
-		echo "Failed to download $(nnuenet)."; \
-	fi;
-	@if [ "x$(shasum_command)" != "x" ]; then \
-		if [ "$(nnuenet)" = "nn-"`$(shasum_command) $(nnuenet) | cut -c1-12`".nnue" ]; then \
-			echo "Network validated"; break; \
-		fi; \
-	fi;
-endef
-
-# set up shell variables for the net stuff
-define netvariables
-$(eval nnuenet := $(shell grep $(1) evaluate.h | grep define | sed 's/.*\(nn-[a-z0-9]\{12\}.nnue\).*/\1/'))
-$(eval nnuedownloadurl1 := https://tests.stockfishchess.org/api/nn/$(nnuenet))
-$(eval nnuedownloadurl2 := https://github.com/official-stockfish/networks/raw/master/$(nnuenet))
-$(eval curl_or_wget := $(shell if hash curl 2>/dev/null; then echo "curl -skL"; elif hash wget 2>/dev/null; then echo "wget -qO-"; fi))
-$(eval shasum_command := $(shell if hash shasum 2>/dev/null; then echo "shasum -a 256 "; elif hash sha256sum 2>/dev/null; then echo "sha256sum "; fi))
-endef
-
 # evaluation network (nnue)
 net:
-	$(call netvariables, EvalFileDefaultNameBig)
-	$(call fetch_network)
-	$(call netvariables, EvalFileDefaultNameSmall)
-	$(call fetch_network)
+	@$(SHELL) ../scripts/net.sh
 
 format:
 	$(CLANG-FORMAT) -i $(SRCS) $(HEADERS) -style=file