This patch logs raw socket data, to assist debugging when discriminating
between server and fetchmail bugs.

Apply it to socket.c (works as of 6.3.20) and set the environment
variable FETCHMAIL_RAW_LOGFILE to a log file writable by fetchmail. If
it's not there, it gets created with mode 0600 (which requires directory
write permission).

The file gets appended to, so you can log into named pipes, character
(stream) devices and to the console if you're so inclined.

Note 1: any logging failures cause fetchmail to abort() forcefully.

Note 2: raw control characters persist in the log and are not filtered
out. In doubt use a pager that filters control characters, or use tools
such as a binary-capable text edtior, vim's xxd, or hexdump, or od, to
view the raw log message.

-- Matthias Andree, June 2011

diff --git a/socket.c b/socket.c
index daa291d..dab91ba 100644
--- a/socket.c
+++ b/socket.c
@@ -333,6 +333,49 @@ static	SSL *_ssl_context[FD_SETSIZE];
 static SSL	*SSLGetContext( int );
 #endif /* SSL_ENABLE */
 
+#include <fcntl.h>
+
+static const char *rawlogfile;
+static FILE *rlogstream;
+
+static int SockLog(void) {
+    static int haveinit;
+    static int wantlog;
+    static int logfd = -1;
+
+    if (!haveinit) {
+	haveinit = 1;
+	if ((rawlogfile = getenv("FETCHMAIL_RAW_LOGFILE"))) {
+	    if ((logfd = open(rawlogfile, O_WRONLY|O_APPEND|O_CREAT, 0600)) == -1) {
+		report(stderr, GT_("FETCHMAIL_RAW_LOGFILE is set, but opening \"%s\" for appending write failed: %s\n"), rawlogfile, strerror(errno));
+		abort();
+	    }
+	    if (!(rlogstream = fdopen(logfd, "a"))) {
+		report(stderr, GT_("FETCHMAIL_RAW_LOGFILE is set, but fdopen(%d) failed: %s\n"), logfd, strerror(errno));
+		abort();
+	    }
+	    setvbuf(rlogstream, NULL, _IOLBF, 0);
+	    wantlog = 1;
+	}
+    }
+    return wantlog;
+}
+
+static void LogPrintf(const char *fmt, ...) {
+    va_list va;
+    const char *locsav;
+    va_start(va, fmt);
+    if (!SockLog()) return;
+    locsav = setlocale(LC_ALL, NULL);
+    (void)setlocale(LC_ALL, "C");
+    if (EOF == vfprintf(rlogstream, fmt, va) || EOF == fflush(rlogstream)) {
+	report(stderr, GT_("FETCHMAIL_RAW_LOGFILE is set, but logging failed: %s\n"), strerror(errno));
+	abort();
+    }
+    (void)setlocale(LC_ALL, locsav);
+    va_end(va);
+}
+
 int SockWrite(int sock, const char *buf, int len)
 {
     int n, wrlen = 0;
@@ -340,6 +383,8 @@ int SockWrite(int sock, const char *buf, int len)
     SSL *ssl;
 #endif
 
+    LogPrintf("[>%d-%s count=%04d] %.*s%s", sock, SSLGetContext(sock) ? "crypt" : "plain", len, len, buf, (len < 1 || buf[len - 1] != '\n') ? "\n" : "");
+
     while (len)
     {
 #ifdef SSL_ENABLE
@@ -442,6 +487,8 @@ int SockRead(int sock, char *buf, int len)
 	    (!newline && len);
     *bp = '\0';
 
+    LogPrintf("[<%d-%s count=%04d] %.*s%s", sock, SSLGetContext(sock) ? "crypt" : "plain", bp - buf, bp - buf, buf, newline ? "" : "\n");
+
     return bp - buf;
 }