ADDED   file-tail.scm
Index: file-tail.scm
==================================================================
--- /dev/null
+++ file-tail.scm
@@ -0,0 +1,76 @@
+
+(use (prefix sqlite3 sqlite3:) posix typed-records) 
+
+(define (open-tail-db )
+  (let* ((basedir   (create-directory (conc "/tmp/" (current-user-name))))
+	 (dbpath    (conc basedir "/megatest_logs.db"))
+	 (dbexists  (file-exists? dbpath))
+	 (db        (sqlite3:open-database dbpath))
+	 (handler   (sqlite3:make-busy-timeout 136000)))
+    (sqlite3:set-busy-handler! db handler)
+    (sqlite3:execute db "PRAGMA synchronous = 0;")
+    (if (not dbexists)
+	(begin
+	  (sqlite3:execute db "CREATE TABLE IF NOT EXISTS log_files (id INTEGER PRIMARY KEY,filename TEXT,event_time TIMESTAMP DEFAULT (strftime('%s','now')));")
+	  (sqlite3:execute db "CREATE TABLE IF NOT EXISTS log_data  (id INTEGER PRIMARY KEY,fid INTEGER,line TEXT,event_time TIMESTAMP DEFAULT (strftime('%s','now')));")
+	  ))
+    db))
+
+(define (tail-write db fid lines)
+  (sqlite3:with-transaction
+   db
+   (lambda ()
+     (for-each
+      (lambda (line)
+	(sqlite3:execute db "INSERT INTO log_data (fid,line) VALUES (?,?);" fid line))
+      lines))))
+
+(define (tail-get-fid db fname)
+  (let ((fid   (handle-exceptions
+		   exn
+		   #f
+		 (sqlite3:first-result db "SELECT id FROM log_files WHERE filename=?;" fname))))
+    (if fid
+	fid
+	(begin
+	  (sqlite3:execute db "INSERT INTO log_files (filename) VALUES (?);" fname)
+	  (tail-get-fid db fname)))))
+
+(define (file-tail fname #!key (db-in #f))
+  (let* ((inp (open-input-file fname))
+	 (db  (or db-in (open-tail-db)))
+	 (fid (tail-get-fid db fname)))
+    (let loop ((inl    (read-line inp))
+	       (lines '())
+	       (lastwr (current-seconds)))
+      (if (eof-object? inl)
+	  (let ((timed-out (> (- (current-seconds) lastwr) 60)))
+	    (if timed-out (tail-write db fid (reverse lines)))
+	    (sleep 1)
+	    (if timed-out
+		(loop (read-line inp) '() (current-seconds))
+		(loop (read-line inp) lines lastwr)))
+	  (let* ((savelines (> (length lines) 19)))
+	    ;; (print inl)
+	    (if savelines (tail-write db fid (reverse lines)))
+	    (loop (read-line inp)
+		  (if savelines
+		      '()
+		      (cons inl lines))
+		  (if savelines
+		      (current-seconds)
+		      lastwr)))))))
+
+;; offset -20 means get last 20 lines
+;;
+(define (tail-get-lines db fid offset count)
+  (if (> offset 0)
+      (map-row (lambda (id line)
+		 (vector id line))
+	       db
+	       "SELECT id,line FROM log_data WHERE fid=? OFFSET ? LIMIT ?;" fid offset count)
+      (reverse ;; get N from the end
+       (map-row (lambda (id line)
+		  (vector id line))
+		db
+		"SELECT id,line FROM log_data WHERE fid=? ORDER BY id DESC LIMIT ?;" fid (abs offset)))))