FIX: reading from virtual /proc files on Linux using read/part

resolves: Oldes/Rebol-issues#2303

src/core/p-file.c

@@ -405,7 +405,11 @@ REBINT Mode_Syms[] = {
 		len += cnt;
 		SET_FLAG(file->modes, RFM_RESEEK);
 	}
-	if (cnt > len) return (REBCNT)len;
+	// Originaly, when the requested part was larger then the reported file's size,
+	// then the reported file size was used instead. But on Posix there are virtual files,
+	// where the size is reported as 0. In this case we keep the user's requested length.
+	// See: https://github.com/Oldes/Rebol-issues/issues/2303
+	if (cnt > len && len > 0) return (REBCNT)len;
 	return (REBCNT)cnt;
 }
 

src/tests/units/port-test.r3

@@ -524,6 +524,27 @@ if system/platform = 'Windows [
 		--assert all [error? e: try [append/only p "aa"]  e/id = 'bad-refines]
 		try [delete %issue-1894]
 
+if exists? %/proc/cpuinfo [
+	--test-- "Reading from /proc files on Linux"
+	;@@ https://github.com/Oldes/Rebol-issues/issues/2303
+		--assert all [
+			not error? info: try [read/string %/proc/cpuinfo]
+			empty? info ;; empty, because to read this type of file, the size must be specified!
+		]
+		--assert all [
+			not error? info: try [read/string/part %/proc/cpuinfo 10000]
+			print info
+			0 < length? info
+		]
+]
+	--test-- "Reading an empty file"
+		--assert all [
+			file? write %empty ""
+			0 = length? read %empty
+			0 = length? read/part %empty 1000
+			port? delete %empty
+		]
+
 ===end-group===
 
 if system/platform = 'Windows [