Add make-c-wrapper.sh for creating binary executable wrappers

pkgs/build-support/setup-hooks/make-c-wrapper.sh

@@ -0,0 +1,73 @@
+#!/bin/bash
+# make-c-wrapper.sh EXECUTABLE ARGS
+#
+# ARGS:
+# --argv0       NAME    : set name of executed process to NAME
+#                         (defaults to EXECUTABLE)
+# --set         VAR VAL : add VAR with value VAL to the executable’s
+#                         environment
+# --set-default VAR VAL : like --set, but only adds VAR if not already set in
+#                         the environment
+# --unset       VAR     : remove VAR from the environment
+#
+# To debug a binary wrapper after you compiled it, use the `strings` command
+
+escape_string_literal() {
+    # We need to make sure that special characters are escaped 
+    # before trying to create C string literals
+    result=${1//$'\\'/$'\\\\'}
+    result=${result//\"/'\"'}
+    result=${result//$'\n'/"\n"}
+    result=${result//$'\r'/"\r"}
+}
+
+escape_string_literal "$1"
+executable="${result}"
+args=("$@")
+
+printf "%s\n" "#include <unistd.h>"
+printf "%s\n" "#include <stdlib.h>"
+printf "\n%s\n" "int main(int argc, char **argv) {"
+for ((n = 1; n < ${#args[*]}; n += 1)); do
+    p="${args[$n]}"
+    if [[ "$p" == "--set" ]]; then
+        escape_string_literal "${args[$((n + 1))]}"
+        key="${result}"
+        escape_string_literal "${args[$((n + 2))]}"
+        value="${result}"
+        n=$((n + 2))
+        printf "%s\n" "    putenv(\"${key}=${value}\");"
+        docs="${docs:+$docs$'\n'}putenv(\"${key}=${value}\");"
+    elif [[ "$p" == "--set-default" ]]; then
+        escape_string_literal "${args[$((n + 1))]}"
+        key="${result}"
+        escape_string_literal "${args[$((n + 2))]}"
+        value="${result}"
+        n=$((n + 2))
+        printf "%s\n" "    setenv(\"${key}\", \"${value}\", 0);"
+        docs="${docs:+$docs$'\n'}setenv(\"${key}=${value}\", 0);"
+    elif [[ "$p" == "--unset" ]]; then
+        escape_string_literal "${args[$((n + 1))]}"
+        key="${result}"
+        printf "%s\n" "    unsetenv(\"$key\");"
+        docs="${docs:+$docs$'\n'}unsetenv(\"${key}=${value}\", 0);"
+        n=$((n + 1))
+    elif [[ "$p" == "--argv0" ]]; then
+        escape_string_literal "${args[$((n + 1))]}"
+        argv0="${result}"
+        n=$((n + 1))
+    else
+        # Using an error macro, we will make sure the compiler gives an understandable error message
+        printf "%s\n" "    #error make-c-wrapper.sh did not understand argument ${p}"
+    fi
+done
+printf "%s\n" "    argv[0] = \"${argv0:-${executable}}\";"
+printf "%s\n" "    return execv(\"${executable}\", argv);"
+printf "%s\n" "}"
+
+docs="${docs:+$docs$'\n'}argv[0] = \"${argv0:-${executable}}\";"
+docs="${docs:+$docs$'\n'}execv(\"${executable}\", argv);"
+docs="----------"$'\n'"This binary wrapper (created from generated C-code) is configured with the following settings:${docs:+$'\n'$docs}"
+escape_string_literal "$docs"
+docs=$result
+printf "\n%s\n" "const char* DOCS = \"$docs\";"