Improvements to the libUseful RaiseError system

Errors.c

@@ -27,6 +27,33 @@ ListNode *ErrorsGet()
 }
 
 
+static bool ErrorOutputWanted(int flags)
+{
+bool result=TRUE;
+
+//if stderr isn't a tty then don't print, unless ERRFLAG_NOTTY is set
+//(this is used to disable this check when we consider syslog debugging too)
+if ( 
+		(! (flags & ERRFLAG_NOTTY)) && 
+		(! isatty(2))
+	) 
+{
+	if (! LibUsefulGetBool("Error:notty")) result=FALSE;
+}
+
+//if this error is a debug error, then don't print unless either LIBUSEFUL_DEBUG environment variable is set
+//or the libUseful:Debug internal value is set
+if (flags & ERRFLAG_DEBUG) 
+{
+	result=FALSE;
+	if (StrValid(getenv("LIBUSEFUL_DEBUG"))) result=TRUE;
+	if (LibUsefulGetValue("libUseful:Debug")) result=TRUE;
+}
+
+return(result);
+}
+
+
 void InternalRaiseError(int flags, const char *where, const char *file, int line, const char *FmtStr, ...)
 {
     char *Tempstr=NULL;
@@ -47,28 +74,23 @@ void InternalRaiseError(int flags, const char *where, const char *file, int line
     if (! Errors) Errors=ListCreate();
     if (flags & ERRFLAG_ERRNO) ptr=strerror(errno_save);
 
-    if (flags & ERRFLAG_DEBUG)
-    {
-        ptr=getenv("LIBUSEFUL_DEBUG");
-        if (StrEnd(ptr))
-        {
-            if (LibUsefulGetBool("libUseful:Debug")) ptr="y";
-        }
-
-        if (StrValid(ptr))
-        {
-            if (! LibUsefulGetBool("Error:Silent")) fprintf(stderr,"DEBUG: %s %s:%d %s. %s\n", where, file, line, Tempstr, ptr);
-            if (LibUsefulGetBool("Error:Syslog")) syslog(LOG_ERR,"DEBUG: %s %s:%d %s. %s", where, file, line, Tempstr, ptr);
-        }
-    }
-    else
+		//first consider if we want to print out a message on stderr
+		if (ErrorOutputWanted(flags))
+		{
+       if (! LibUsefulGetBool("Error:Silent")) fprintf(stderr,"DEBUG: %s %s:%d %s. %s\n", where, file, line, Tempstr, ptr);
+		}
+
+		//now consider if we want to syslog an error message. Pass ERRFLAG_NOTTY as it doesn't matter if stderr is not a
+		//tty for this case
+		if (ErrorOutputWanted(flags | ERRFLAG_NOTTY))
+		{
+       if (LibUsefulGetBool("Error:Syslog")) syslog(LOG_ERR,"DEBUG: %s %s:%d %s. %s", where, file, line, Tempstr, ptr);
+		}
+
+		//if this Error is just debugging, then never add it to the list of errors
+    if (! (flags & ERRFLAG_DEBUG))
     {
         Now=GetTime(TIME_MILLISECS);
-
-        if (! LibUsefulGetBool("Error:Silent")) fprintf(stderr,"ERROR: %s %s:%d %s. %s\n", where, file, line, Tempstr, ptr);
-        if (LibUsefulGetBool("Error:Syslog")) syslog(LOG_ERR,"ERROR: %s %s:%d %s. %s", where, file, line, Tempstr, ptr);
-
-
         Err=(TError *) calloc(1,sizeof(TError));
         Err->errval=errno_save;
         Err->when=Now;

Errors.h

@@ -12,6 +12,7 @@ Copyright (c) 2015 Colum Paget <[email protected]>
 #define ERRFLAG_ERRNO 1
 #define ERRFLAG_DEBUG 2
 #define ERRFLAG_CLEAR 4
+#define ERRFLAG_NOTTY 8
 
 
 /*
@@ -41,14 +42,34 @@ Errors are injected into the list with RaiseError like this:
 	the system when RaiseError was called. Also, if RaiseError prints out an error, then the string description of
   errno, as obtained from strerror will be appended to the output message.
 
-	If the flag ERRFLAG_DEBUG is set then RaiseError won't print anything out unless the environment variable
-	'LIBUSEFUL_DEBUG' is set (to any value) or the libUseful internal value 'Error:Debug' has been set to 'true' (or
-  'y' or 'yes') with LibUsefulSetValue. If ERRFLAG_DEBUG is passed then nothing is EVER added to the ErrorList.
+	Bye default RaiseError will not print out to stderr if stderr is not a tty, in order to prevent sending errors
+	up pipes and sockets to applications that aren't expecting them. If you want raise error to print even when
+	stderr is not a tty then either pass the ERRFLAG_NOTTY value, like this
+
+	RaiseError(ERRFLAG_ERRNO|ERRFLAG_NOTTY, "ServiceConnect", "host=%s port=%d",Host, Port);
+
+	or, if you don't want to have to do this every time you call RaiseError, then you can achieve the same by
+	setting the libUseful internal boolean value 'Error:notty', like this:
+
+	ListUsefulSetValue("Error:notty","Y")
+
+	If the flag ERRFLAG_DEBUG is set then RaiseError won't print anything out by default. So this line:
+
+	RaiseError(ERRFLAG_DEBUG, "ServiceConnect", "host=%s port=%d",Host, Port);
+
+	Wouldn't produce any output normally.  This allows you to have debugging lines that can be switched on as 
+	needed. There's two ways to activate debugging. Firstly there's the environment variable 'LIBUSEFUL_DEBUG'. 
+	When this environment variable exists and is non-empty  then RaiseError calls will print out, even if they're
+	passed ERRFLAG_DEBUG. Secondly there's the libuseful internal value 'Error:Debug'. When this has been set to 
+	'true' (or 'y' or 'yes') with LibUsefulSetValue, then again all debugging lines will print out.
+
+	If ERRFLAG_DEBUG is passed then nothing is EVER added to the ErrorList, the 'error' is just a debugging line
+	and it's assumed that the program continues normally.
 
 	If the libUseful internal value 'Error:Silent' is set true/yes/y with ListUsefulSetValue then RaiseError never
-  prints errors to stderr. If  the value 'Error:Syslog' is set true/yes/y then error and debug messages are sent
-  to the system logger via syslog
+  prints errors to stderr, regardless of any other config.
 
+	If  the value 'Error:Syslog' is set true/yes/y then error and debug messages are sent to the system logger via syslog
 */